User:Abyssal/Aquatic behavior in ceratopsians

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Paleoenvironmental associations and taphonomy[edit]

David Eberth published a review of the stratigraphic, paleoenvironmental, and taphonomic information known about ceratopsians.[1] He complained that such information "lacks detail" and cited a need for research focused on that topic, especially for recent Asian discoveries.[1] Eberth intended for his review to provide a "preliminary assesment of the paleoenvironmental associations of ceratopsians ... using stratigraphic assignments, inferred paleoclimatic and depositional settings, and unusual geologic features."[1] He also reviewed the taphonomy of some taxa.[1]

Eberth concludes that that ceratopsians "retained a long term preferential association with wetland paleoenvironments."[1] These environments included the areas surrounding lakes, as well as "alluvial and coastal plains."[1] However, by the Late Cretaceous, basal[disambiguation needed] forms began exploiting drier areas including habitats that were semi- to fully arid or with weather patterns divided into wet and dry seasons.[1] Such exploitation of drier environments seems to have occurred in both Asia and North America.[1] During the Campanian, neoceratopsians in Canada and Alaska "fluorished," experiencing an increase in taxonomic diversity.[1] At this time, favorable "warm temperate to subtropical" climatic conditions characterized the wetlands of the coastal plains lining the western shore of the Interior Seaway.[1]

Eberth bemoaned the "patch[iness]" of ceratopsian taphonomic data and noted that most of what had been done focused on bone beds usually dominated by a single taxon.[1] This focus on bonebed taphonomy was especially ture for centrosaurines.[1] He noted however, that "high-quality and exquisite three-dimensional preservation of basal neoceratopsians" was acting as a "catalyst" for taphonomic study of Asian ceratopsians.[1] Eberth stated that additional taphonomic research would be useful for reaching answers on issues of contention among paleontologists.[1] Examples of issues Eberth thought could have light shed on them included whether Psittacosaurus lived a terrestrial or semi-aquatic lifestyle, whether or not Protoceratops was nocturnal or if it burrowed, as well as whether or not chasmosaurines and centrosaurines had differing amounts of social behavior.[1]

As of the paper there were about 70 known species of ceratopsians.[2] The earliest known member of the clade was Yinlong downsi of the Late Jurassic of northwest China.[2] The latest was Triceratops horridus of Late Cretaceous in western North America.[2] All ceratopsians known so far have been from Laurasia with the possible exception of Serendipaceratops, which may represent an Australian neoceratopsian.[2] Countries with ceratopsian fossils include Canada, the United States, Mexico, Russia, Mongolia, China, Thailand, and Uzbekistan.[3]

Eberth wanted to review ceratopsian environment and taphonomy data because of the increasing numbers of fossils and new kinds of ceratopsians being discovered.[4] Also, translations of Asian research into English are providing useful data to work with.[4] Eberth's paper examined ceratopsian environments and taphonomy by place and time and review their implications for traditional understanding about ceratopsian dinosaurs.[4]

Eberth sorted ceratopsians into four groups.[4] The first were basal ceratopsians treated paraphyletically, next were basal neoceratopsians treated phyletically, lastly were the chasmosaurs and centrosaurs.[4] Eberth examined their stratigraphic positions, ages, number of individuals, ancient climates and environments.[4] Geological features like coal, caliche or redbeds.[4] Eberth also took note of associations with unusual geologic features like pyroclastics.[4]

Eberth conceded that many of his conclusions would be speculative and tentative due to the lack of known details.[4] He expressed hope that more research would be done on ceratopsian life habits, ecological associatios, adaptability and preservational processes over time.[4]

Eberth only regarded 13 forms of basal ceratopsian as valid. All of them are Asian and most are known from China.[5] Their age ranged from the Oxfordian to the Albian, about 60 million years worth of time.[5]

Basal neoceratopsians are more diverse than basal ceratopsians.[5] Eberth regarded 24 species fro 21 genera as valid. Archaeoceratops, Protoceratops, and Leptoceratops all had two species.[5] The basal neoceratopsians lasted from Albian to Aptian to the end of the Cretaceous, about 55 million years.[5] Most known members lived during from the iddle of the Early Cretaceous to the end of the Campanian.[5] They are known from both Asia and North America.[5] North American forms lived from the Turonian to the Maastrichtian.[5] Ceratopsids ranged in time from the Santonian to the end of the Cretaceous.[5] There are 26 genera and 31 known species of ceratopsians.[5] 11 genera and 14 species of these are centroaurines.[5] 15 genera and 17 species of these are chasmosaurines.[5] Most ceratopsids only had one species per genus, but Chasmosaurus had 3, Pachyrhinosaurus had 3, and Centrosaurus had 2.[5] All known ceratopsids were North American. All ceratopsids except for Avaceratops were 4m long or bigger.[5]

Eberth concluded that the data supported the traditional view that ceratopsians originated in Asia and were among the dominant herbivores in Late Cretaceous ecosystems.[5] He also concluded that ceratopsians did indeed experience an "explosion" of diversity during the middle Cretaceous and evolved larger body sizes.[5]

Most basal ceratopsians are found in sediments representing wetland deposits.[6] They tended to be near lakes ranging from shallow to deep.[6] Volcanic terrains also tended to be nearby.[6] These deposits were typically at the margins of basins.[6] Basal ceratopsians are also known from eolian[disambiguation needed] and alluvial settings.[6] In most of these environments rainfall was seasonal or the environments were semi-arid.[6] This raises the possibility of basal ceratopsians dying seasonally based on the weather.[6] Basal ceratopsians, especially psittacosaurs, in northeast China are associated with pyroclastic sediments deposited in lakes or near the edges of lakes.[7] The high quality of the preservation at these sites suggests the carcasses were buried rapidly and the environmental conditions inhibited both bacterial decay and infaunal scavenging.[8] Multiple articulated skeletons of Yinlong are known that seem to have been very rapidly buried by mudflows.[8] Psittacosaurs are known from a wide variety of environments from many sites in Asia .[8] This suggests they didn't have an afiinity for a particular kind of habitat.[8] However, some researchers have argued that their fossils are so commonly associated with lakes and wetlands that they may have been dependant on wet environments and unable to thrive in drier settings.[8] That basal ceratopsians stayed physically small may be further evidence of this.[8]

Basal neoceratopsians survived the longest of any of the four ceratopsian groups.[9] They are also found in the widest number of geographic locations and variety of habitats.[9] Liaoceratops is known from same pyroclastic lake deposits in Liaoning, China as Psittacosaurus.[9] Both Archaeoceratops and Liaoceratops are known from alluvial deposits left in seasaonally arid-to-subtropical environments.[10] Asiaceratops and Kulceratops are both poorly known.[11] They have been found in warm temperate paralic environments in Uzbekistan.[11] Serendipaceratops is known from Australia but there is no data available to help reconstruct its habibtat.[11]

Many different kinds of neoceratopsians are known from Asia during the late cretaceous.[11] Uzbekistan has Turanoceratops.[11] China has Magnirostris and Protoceratops.[11] Mongolia has Bagaceratops, Bainoceratops, Graciliceratops, Lamaceratops, Platyceratops, Protoceratops, Udanoceratops, and Yamaceratops.[11] Only Graciliceratops and Yamaceratops are not associated with eolian, interdune alluvial-to-paludal and distal alluvial fan deposits from semi-arid settings.[11] Graciliceratops is known from alluvial deposits left in seasonally wet and dry wetlands.[11] Yamaceratops is known from alluvial channel and interchannel sediments left in a seasonally semi-arid to subtropical setting.[11]

The presence of basal neoceratopsians in North America represents "important evidence" of ceratopsians traveling from Asia. Zuniceratops is the oldest known basal neoceratopsian from North America and dates to the Turonian.[11] Zuniceratops remains have been recovered from coal-bearing sediments representing an alluvial-to-upper coastal plain environment with a subtropical seasonally wet climate.[11] A small number of poorly preserved basal neoceratopsian remains have been recovered in the same general region as Zuniceratops.[11] The remains were associated with non-calcareous, poorly drained, and coaly alluvial-to-coastal plain sediments.[11]

Ceratopsids are only known from North America, but are diverse and lived from the Campanian to the Maastrichtian.[12] In places with abundant exposed Campanian age fossils both chasmosaur and centrosaur lived along side eachother.[12] This implies that the paleocology and habitat preferences of chasmosaurs and centrosaurines weren't so different as to drive them into different environments.[12] By the start of the Maastrichtian centrosaurs disappear from the fossil record, so they must have gone extinct sometime near the Campanian-Maastrichtian boundry.[12] The reason for the premature extinction of the centrosaurs is currently unknown.[12] The fact that chasmosaurs seem to have been less social than centrosaurs may have helped them survive whatever killed the centrosaurs.[12] Both chasmosaurs and centrosaurs seem to be associated with poorly drained alluvial to coastal plain environments.[12] This is true of Achelousaurus, Avaceratops, Centrosaurus, Einiosaurus, Pachyrhinosaurus, Styracosaurus, Anchiceratops, Arrhinoceratops, Chasmosaurus, Pentaceratops, Torosaurus, and Eotriceratops.[12] Some Campanian centrosaurs like Albertaceratops lived in better drained alluvial plain environments.[12] Some Campanian chasmosaurs, like Diceratops, likewise lived in well-drained alluvial plains.[12] Chasmosaurs like Triceratops continued preferring drier environments until the end of the Cretaceous.[12]

Most ceratopsians tend to be found in rocks deposited in environments closeley associated with water in a variety of ways.[13] These environments include such settings as lakes, alluvial or coastal plains.[13] By the Late Cretaceous many kinds of basal neoceratopsian had adapted to drier environments like marginal to fully eolian settings that were semi-arid to arid as well as seasonally wet/dry and well-drained alluvial settings across Asia and North America.[13] Neoceratopsians in Canada and Alaska both "fluorished" and diversified in the "extensive warm-temperate to subtropical wetlands that dominated the coastal lowlands along the western shore of the Western Interior Seaway."[13] This was especially true during the Campanian "where seasonality was likely of the wet and wetter variety."[13]

Taphonomic research on ceratopsians has been so heavily focused on bonebeds that science's knowledge of the subject is patchy, complicating the ability of researchers to make generalizations about it the way that it's possible to generalize about ancient environmental associations.[14] Not only is ceratopsian taphonomy preoccupied with bonebeds but even more specifically these tend to be bonebeds where only one species predominates.[15] Taphonomers of ceratopsian remains have even tended to neglect the study of isolated specimens occurring in the same gologic formations as bonebeds.[15] Research on the taphonomy of Chinese and Mongolian ceratopsian specimens is particularly scarce.[15]

One assemblage of psittacosaurs from the Lujiatun beds of the Yixian Formation seems to have been buried quickly by a kind of volcanic mudflow occurring near the site of a volcanic eruption.[16] There is some controversy as to whether or not the mudflow burying the psittacosaurs was caused by the volcanic eruption itself or if the sediments were reworked by water sometime later.[16] Higher in the section are tens to hundreds of psittacosaurs preserved in tuff-bearing shales that were deposited in a lake.[16] The causes of deaths for the animals preserved in these beds are uncertain.[16] In 2003 Guo and others suggested that emissions of toxic gases from the nearby volcanic activity caused mass deaths of local terrestrial life.[16] Ford and Martin by contrast see the lakes as the natural habitat of Psittacosaurus, which they interpret as semi-aquatic.[16] They support their case by noting that Psittacosaurus specimens are very frequently preserved in shales deposited in lakes, their gastroliths, as well as aspects of their anatomy and functional morphology.[16] Eberth observed that any hypothesis purporting to explain the taphonomy of psittacosaur specimens must account for their high frequency of well-preserved articulated specimens but rarity of isolated remains.[16] Further the evidence indicates that the psittacosaurs preserved in lake shales lacked significant periods of time floating in their depositional environment due to bloating of the carcass, as such a scenario would result in body parts being frequently missing from the fossils.[16] Also, the depositional environment must have experience high levels of sedimentation or ver low levels of decay.[16] Possible contributing factors to such low levels of decay could include cool or low-oxygen conditions on the lake bottom.[16]

The fighting dinosaurs specimen consisting of a Protoceratops and associated Velocirapter discovered Tugriken Shireh are the most discussed ceratopsian association and possibly the most famous associated dinosaurs.[17] They are on display at the Mongolian Academy of Sciences in Ulanbataar.[17] Some researchers have interpreted the animals involved as interacting in life in such a manner as to kill them both. Others have interpreted the Velociraptor as being buried while scavenging an already dead Protoceratops.[17]

In 1997 Fastovsky and others showed that many of the entombed Protoceratops at Tugriken Shireh were buried on the lee side of prograding[disambiguation needed] dunes.[17] They proposed that these specimens spent some time exposed to open air and drying but were finally rapidly buried by wind-blown sand.[17]

In 1998 Loope and other proposed that the dinosaurs including Protoceratops of the Djadokhta at Ukhaa Tolgod were buried in sandslides that were more common during periods of wetter climate than normal.[17]

The range in preservation and facies associations in the Djadokhta deposits of China and Mongolia suggest that both sandstorms and mass sediment flow contributed to the beds fossils, including basal neoceratopsians.[17]

Longrich has suggested that Protoceratops was nocturnal and hid from the high daytime termperatures in burrows.[17] During times of high sediment supply they would be entombed in their own burrows.[17] Eberth termed this an "elogant solution" that explained the high quality preservation of Protoceratops in the formation and why they are found 3 dimensional standing positions.[18]

James Kirkland found evidence that Protoceratops and other dinosaur carcasses were consumed by carrion eating beetles at Tugriken Shireh.[19]

In 1970 Sternberg published a study that commented on ceratopsid taphonomy.[20] He observed that isolated skulls of ceratopsian dinosaurs were common in Dinosaur Provincial Park sediments.[20] They are actually more common than isolated potcranial remains.[20] Sternberg attributes this discrepency to scavenging theropods preferring to eat from ceratopsid postcrania. Ceratopsid skulls were also very durable and would have rsisted decomposition and reworking.[20]

Sternberg interpreted the park's bonebeds as resulting from large numbers of ceratopsid carcasses accumulating in a swamp where they were trampled by other dinosaurs.[20]

In 1971 Dodson concurred with Sternberg on the abundance of ceratopsid skulls being higher than their postcrania. He also stated that young ceratopsids were uncommon in the park.[20] Ceratopsid remains he described as associated with ancient channels and overbank deposits.[20]

In 2005 Eberth and Currie suggested that many of the dinosaurs at DPP were killed in large coastal flooding but only the carcasses rapidly buried in river channels ended up fossilizing.[20]

Much taphonomic research has been dedicated to monodominant ceratopsid bonebeds.[20] Eberth describes the proposed scenarios for their formations as "remarkably consistent" between different studies.[20] These deposits are typically interpreted as herds of social ceratopsids being killed by calamitous weather like severe floods or droughts.[20] Most have found that the carcasses were exposed after death, trampled, reworked by water leading to the beds devloping a "complex taphonomic signature".[20]

Hunt and Farke have argued that although the sample size of chasmosaur bonebeds is small there may be quantifiable difference in the size of the biocoenoses and thanatocoenoses the beds preserve.[20] Chasmosaur bonebeds tended to be smaller and more often preserved in ancient channels.[20]

Eberth infers that a tendency to sociality is primitive for ceratopsids because of the length of its stratigraphic range, from Barremian to Aptian. That some well-studied ceratopsians, like Triceratops, are generally not known from bonebeds may suggest these species were anomolously asocial.[20] Another explanation may be that the strata preserving such taxa had different depositional and preservational characteristcs.[20]

Centrosaur bonbeds are confined to areas of southern Alberta at least 200km up-dip from the ancient shoreline.[20] This ordered distribution of bonebed locations has been interpreted as implying that these centrosaurs lived alone or in small family groups, possibly while nesting, near the shoreline and joined together in larger herds during or after migrations further inland.[20] Eberth speculated that similar patterns might be uncovered in ceratopsids like Triceratops and Chasmosaurus that are known from multiple locations and stratigraphic positions.[20]

Further taphonomic work might help clarify whether or not Psittacosaurus was fully aquatic or fully terrestrial.[21]

Ceratopsians seem to have preferred wetland environments for most of their evolutionary history as evidence by their remains being found in deposits left in environments on coastal plains, in alluvial fans, and lakes.[22] Basal neoceratopsian began living near or within environments that were deposited by wind-blown sediment with seasonal wet-dry, semi-arid, or arid conditions by the Late Cretaceous.[22] Neoceratopsians thrived and diversified in warm-temperate to subtropical wetlands of the coastal lowlands in Canada and Alaska during the Campanian.[22]


Psittacosaurus[edit]

Tracy L. Ford and Larry D. Martin published a study urging scientists to reconsider traditional reconstructions of Psittacosaurus as a terrestrial biped from "seasonally dry alluvial to desert paleoenvironments" and give "more seriou[s]" consideration to the proposal that Psittacosaurus had a semi-aquatic lifestyle.[23] After reviewing previous research and examining specimens, Ford and Martin concluded that the most parsimonious interpretation of the data suports the semi-aquatic hypothesis.[23] Facts the researchers interpreted as favorable to the idea include:

  • Hundreds of Psittacosaurus specimens being preserved in lake deposites found in Northeastern China.[23]
  • Specimens exhibiting "natural resting and sprawling positions that suggest an ability to lift the hind limb in preparation for a swimmer's 'kick'."[23]
  • High nostrils and eye sockets.[23]
  • Range of motion for forelimbs "consistent with a swimming stroke".[23]
  • Muscle scars on the back of the metatarsals suggestive of strong flexor muscles.[23]
  • Tail was "long with deep chevrons".[23]
  • A possibly skin-covered "'bristle-like' integumentary structure" ran along the midline of the tail near its base.[23]

The authors propose multiple means by which psittacosaurs could swim, including thrusting with the hindlimbs, paddling with the forelimbs, and using an eel-like "undulating motion of the tail" for propulsion.[23] Psittacosaurus was diverse, abundant, and known from a wide range of paleoenvironments.[23] Ford and Martin see parallels for its habitat diversity in other modern semi-aquatic lifeforms from among both reptiles and mammals.[23] Reptiles include lizards of the families agamidae, scincidae, and varanidae.[23] Mammal families include the caviids and castorids.[23]

Prior to the Dinosaur Renaissance, many groups of dinosaurs were considered semi-aquatic, including sauropods and hadrosaurs.[24] Afterward, Ford and Martin felt an interpretation of dinosaurs as "strictly terrestrial" emerged as the "new orthodoxy" among dinosaur paleontologists.[24] However, they noted that some more recent research have interpreted some dinosaurs as semi-aquatic, including Baryonyx, some Early Cretaceous North African sauropods, and some ankylosaurs.[25] Protoceratopsians were reinterpreted by Tereschenko as being semi-aquatic because he thought their vertebral columns, especially in the tail, could be used for swimming.[26] The idea of semi-aquatic protoceratopsians had been previously suggested in 1970 by Rinchen Barsbold, and in a 1940 paper by Brown and Schlaikjer.[26]

In 2002, a Psittacosaurus specimen found in Liaoning, China with bristle-like integumentary structures was described.[26] Although these structures have been interpreted by previous researchers as feather or quill-like structures that performed a display-related function.[26] Ford and Martin say that the specimen "fired [their] imaginations" and inspired an "alternative explanation" consistant with their hypothesized semi-aquatic lifestyle for Psittacosaurus.[26]

Ford and Martin characterize the semi-aquatic lifestyle hypothesis as "not radical" and trace its history to earlier proposals made by scientists like Rozhdestvensky,[disambiguation needed] Suslov,[disambiguation needed] Phil Currie, Averianov and others.[26] The scientific community's reluctance to accept the hypothesis was attributed to the association of Psittacosaurus fossils with dry paleoenvironments.[26] However, Ford and Martin feel that since Psittacosaurus fossils are found from a variety of habitats these environmental associations are not enough to convincingly argue that psittacosaurs were "obligate terrestrial forms."[26]

Rozhdeventsky argued that since the finger bones of Psittacosaurus were flattened from the top and bottom that in life they may have had webbed fingers that may have allowed them to swim.[27] Rozhdeventsky also thought that the presence of a sclerotic ring was suggestive of aquatic habits, but since modern terrestrial vertebrates like birds also have sclerotic rings Ford and Martin reject this suggestion as supporting their hypothesis.[27] In 1983, Suslov argued that psittacosaurs lived in around water because the Khamryn-Us site in Mongolia preserve many psittacosaurs in sediments deposited by a lake.[27]

Phil Currie suggested to the authors in 1997 that psittacosaur gastroliths were used for ballast rather than for processing food.[27] He noted that psittacosaurs are often found preserved in lake sediments and that their sophisticated teeth and jaws should preclude a need for additional processing by the gastroliths.[27] The author's found Averianov to support the arguments and conclusions of other researchers who subscribe to the semiaquatic lifestyle hypothesis.[28]

Suslov noted in 1983 that more Psittacosaurus specimens have been discovered from lake deposits than from other type of environment.[29] Most Psittacosaurus specimens have been recovered from three Early Cretaceous lakes, the Qinyang Lake of the modern Ordos Plateau, a lake formerly located in the Junggar Basin, and the lake sediments of the Khamryn-Us site.[29] In 2007 additional "tens of specimens" were reported from "volcano-lacustrine deposits in western Liaoning."[29]

The type specimen of Psittacosaurus was discovered with its hind legs flexed and raised up toward its body.[30] The forelimbs were strecthed back, palm-side up along its sides. In 1982, Cooms argued that this posture was unnatural for the species and formed after deather and burial.[30] In 2001, Brinkman and others described a specimen of P. xinjiangensis in a similar posture and argued that this was the animal's life resting position.[30] Faux[disambiguation needed] and Padian also argued that this posture was the animal's resting position in life, and that the posture was "not consistent with opisthotony".[30] Ford and Martin concurred that the flexed and raised legs represented Psittacosaurus's life resting posture.[30]

The second documented Psittacosaurus specimen, the type of Protiguanodon mongoliensis, was found with its arms outstretched and its legs sprawling.[31] In 2007 Phil Senter interpreted the position of the arms as resulting from the humerus being dislocated from the glenoid.[31] However, because the sprawling posture is so common among Psittacosaurus specimens, Ford and Martin thought it may represent a natural part of their life range of movement.[31] The sprawled-legs-with-outstretched-arms position has been seen in the type specimen of P. sinensis (of Shantung's Laiyang Beds) and referred specimens of P.xinjiangensis from both Liaoning and Delunshan.[31] An adult Psittacosaurus specimen of indeterminate species was described in 2004 in paleontology.[31] This specimen was accompanied by 34 babies, many of whom had the sprawling posture.[31] Lizards, salamanders and crocodilians often adopt similarly splayed-limbed postures while swimming and the authors interpeted this common ground as evidence that psittacosaurs may have swam as well.[31]

The proportionally long hindlimbs of psittacosaurus have traditionally interpeted as implying a bipedal gait. Most Psittacosaurus species have a femoral head angled 30 degrees to the shaft of the bone, contrary to almost all bipedal dinosaurs wose femoral heads would be at a 90 degree angle.[32] This angle would have given Psittacosaurus the ability to sprawl its hindlimbs.[32] The cartilage cap of the joint also would have covered part of the femur's dorsal surface.[32] In dinosaurs whose femoral heads were positioned at right angles, the cartilage would have been limited to the femoral head itself.[32]

Psittacosaurus had very flexible knees and mesotarsal joints The mesotarsal joits were flexible enough to allow the entire bottom of the surface to contact the ground while the dinosaur was resting.[32] In 1982 Coombs saw this lower body flexibility as being related to the small size of the animal.[32] Ford and Martin see this lowerbody flexibility as being a possible adaptation of the leg for an effective swimmig stroke, providing and increased rage of motion at the knee and allowing the foot to participatei the motion.[32]

Psittacosaurus's metatarsals were bound by ligaments.[33] The rear side of these metatarsals bear "large" scars left at the sites where the flexor muscles attached.[34] This suggests that these muscles were powerful enough to be useful for more than walking.[35] Ford and Martin suggested that such powerful muscles would be "ideal for digging or swimming".[35] Psittacosaurus had proportionally long toes compared to similarly sized ornithopods.[35] Its phalanges and toe claws were flat.[35]

The Psittacosaurus forepaw is flat and some scientists have speculated that it might have been webbed since the bones comprising it were flat.[36] Its third digit is the longest on the hand and is more robust than is typical for a ceratopsian.[36] The fourth finger was so short as to be useless.[36] Ford and Martin rejected previous workers' suggestions that it was used while walking on all fours or grasping.[36]

A ridge on the far end of the metacarpals would prevent the digits from flexing far enough to allow Psittacosaurus to walk on all fours.[36] When Psittacosaurus flexed its first finger, the digit would bend towards the middle of the animal's palm.[36] If Psittacosaurus did have webbed hands then this motion may have been useful for folding the webbing during the return stroke while swimming.[36] The authors saw traits shared between Psittacosaurus and other swimming vertebrates like seals, dolphins, penguins and sea turtles.[36] These included parallel, closely positioned metacarpals and short, stocky phalanges.[36] The authors speculated that the forepaw of Psittacosaurus may have been bound by thick skin like the flippers of sea turtles.[36]

The anatomy of Psittacosaurus's humerus suggests the presence of large deltoid/pectoralis muscles that could have been useful for swimming.[36] The radius and ulna in Psittacosaurus didn't cross each other.[36] The anatomy of the radius and ulna in Psittacosaurus would have prevented it from turning its palms to face completely downwards or upwards.[36] Instead, they would have been limited to facing the midline of the body. Ford and Martin argue this is an additional feature that would have made Psittacosaurus a capable swimmer.[36]


In 2007 Phil Senter examined he range of motion in ceratopsian forelimbs permitted by their anatomy. He observed that because Psittacosaurus neimongoliensis and P. mongoliensis couldn't completely flex their elbows the forelims could not be used for walking.[37] He concluded that Psittacosaurus used its forelimbs to "clutch objects to its body".[38] Ford and Martin disputed this concluusion and instead iterpreted Psittacosaurus's range of forelimb motion as supporting their use for swimming.[38]

Psittacosaurusu mongoliensis generally had longer hindlimbs in proportion to their front limbs compared to the species from Liaoning.[39] Ford and Martin argue that these differences are due to variation in levels of adaptation to the water among Psittacosaurus species.[39] They contend that species with proportionally shorter front limbs spent more time in the water.[39] The narrow, body with short ribs may have lent a streamlined character to Psittacosaurus's body that would have "reduce[d] drag while swimming".[39]

Five specimens of Psittacosaurus have been documented with preserved gastroliths.[40] Psittacosaurus mongoliensis gastroliths are known from AMNH 6544, which had 63, and AMNH 6253, which had more than fifty. A P. mazongshanensis specimen, IVPP V 12165, had 36.[40] Two other specimens of unidentified species have been reported in the scientific literature as having an unspecified number of gastroliths as well.[40] Gastroliths are used for either ballast or to aid digestion.[40] Phil Currie has argued that Psittacosaurus was unlikely to need gastroliths for digestion because in every species except P. mazongshanensis the teeth were self-sharpening.[40] Ford and Martin agreed with Currie's assesment.[40]

The most complete known Psittacosaurus tail was that belonging to AMNH 6254 which had 43 vertebrae.[41] The vertebrae near the base of the tail were taller than they were long while near the end they were longer than tall.[41] The tail overall has been described as long.[41] The transverse processes near the base of the tail were long and shaped like those of a crocodile.[41] The chevrons are likewise long, making it deep and additionally similar to a crocodile's.[41] The tail vertebrae's neural spines are tall, with P. sinensis having especially tall spines.[42] In both P. mongoliensis and P. sinensis the neural spines of the vertebrae farther along the length of the tail are flat and "fan-shaped".[43] This configuration may have left the tail somewhat laterally compressed. Lizards who swim have similarly laterally compressed tails. Paul Sereno has interpreted some aspects of Psittacosaurus's tail vertebrae morphology as inhibiting its ability to move side-to-side.[43] The authors disagreed with this interpretation however, since many articulated Psittacosaurus specimens have tails that curl to one side.[43]

Psittacosaurus had high eye sockets and nostrils.[44] These are common adaptations that allow a swimming animal to breathe and see outside of the water while mostly submerged.[44] Similar configurations are seen in crocodillians, Hippopotamus, and capybara.[44]

Psittacosaurus skin impressions have been documented from Liaoning, China.[45] SMF R 4970 is a Psittacosaur specimen preserved with skin impressions along the rear part of the leg from the ankle up to the hip. The leg was preserved in a flexed position.[45] The authors interpreted the SMF R 4970 skin impressions as indicating a thick layer of soft tissue along the rear side of the legs which would have "increased [their] surface area when using the hid limbs for swimming".[45] MV53 preserves Psittacosaurus skin along the side of the belly. Cross sections of the preserved skin indicate that it was "thick and strong" and was composed of seven layer of collagen fibers.[45] Lingham-Solair interpreted this thick skin as serving a defensive purpose by protecting Psittacosaurus from predators.[45] Ford and Martin suggest that in addition to or instead of protecting Psittacosaurus from predators the thick skin would have provided additional strength to the limbs and tail as an adaptation for swimming.[45]

In 2002 Mayr and others reported the observation of about "[one hundred] bristle-like integument structures" on the tail of a Psittacosauuruus specimen catalogued as SMF R 4970.[46] These structures were ony found growing from the middle of the tail's upper surface, near its base.[46] Each individual bristle originates near the vertebrae, so they were deeply anchored in the animal's soft tissue.[46] Further, while some researchers have interpreted them as resembling protofeathers, others see evidence that they were stiff keratinous tubes.[46] Although these previous workers saw the structures as serving a display function, Ford and Martin interpretd them as supporting a tail fin like that seen in salamanders and tadpoles.[46] They felt the stiffness other researchers ascribed to the structures was due to the requirements of a larger body size in contrast to the relatively flexible structures found in amphibians.[46]

The forelimbs of Psittacosaurus had a wide range of side-to-side motion and may have provided the animal with maneuverability while swimming.[47] This sort of behavior would resemble that found in "lift-based labriform fish, wrasses, parrotfishes, sturgeons, and chimeras."[47]

Ford and Martin note that Averianov has proposed that Psittacosaurus may have have "crawl[ed] [through] the mud searching for aquatic plants" of lakes and rivers.[48] The authors note that the range of environments their hypothesis proposes for the Psittacosaurus species of varying limb length ratios is comparable to those of modern animals like "agamid, scincid, and varanid lizards" as well as castorids.[48]

Lourinhanosaurus is known to have had gastroliths.[40]

Basal neoceratopsians[edit]

Yuong-Nam Lee, Michael J. Ryan and Yoshitsugu Kobayashi

In 2008 a new basal neoceratopsian was discovered in South Korea's Albian-aged Tando beds in the Tando basin.[49] Koreaceratops had very tall neural spines in its tail that were over five times as tall as their respective centra.[49] It also had a unique ridge running from front to back on its ankle bone dividing it into two depressions.[49] Evolutionarily, a phylogenetic analysis positioned Koreaceratops between Archeoceratops and more derived neoceratopsians.[49] The tall neural spines of the tails of Koreaceratops, Montanoceratops, Udanoceratops, Protoceratops, and Bagaceratops all seem to be convergences rather than inherited from a common ancestor.[49] These elongated neural spines were an important derived trait in non-ceratopsid neoceratopsians.[49] This may be an adaptation for swimming.[49] The evolution of quadrupedality in ceratopsians was gradual.[49] The group began as obligate bipeds and gradually gained the ability to walk on all fours.[49] By the time the Coronosaurs had evolved ceratopsians could no longer walk on two legs in any capacity.[49]

The presence of the rostral bone has been called the most easily recognizable trait of the ceratopsids.[50]

Possible psittacosaurid remains are known from Thailand.[50]

Nearly all Asian ceratopsian genera are known from the Gobi desert region.[50]

China's Sinoceratops zhuchengensis was the first ceratopsid found outside of Santonian to Maastrichtian aged strata in North America.[50]

Koreaceratops was the first ceratopsian dinosaur from the Korean peninsula.[51] It was also the easternmost occurence of a Eurasian ceratopsian.[52] Albian strata preserve very few known basal neoceratopsian fossils.[52]

Koreaceratops is named after Korea. The species epithet hwaseongensis refers to Hwaseong city.[53]

KIGAM VP 200801 is the holotype.[54] The specimen is housed by the Korea Institute of Geoscience and Mineral Resources, Vertebrate Paleontology, Daejeon.[54] the specimen preserves a nearly complete tail, both ischia, and the far ends of the hindlimb and feet.[54] The Tando Basin is very small, being only about 25 square kilometers in area.[55] It dates back to the Cretaceous and was discovered in 1972.[55] It was officially named the Tando Basin by Park and others in 2000.[55] Most of the sediments in the basin are clastic rocks mostly purple colored fine grained siltstones and sandstones.[55] There are also thin sandstones and thick congolmeratic sandstones in the lower part of the Tando beds.[55] The upper part of the formation has well-bedded tuffaceous rocks and cherty mudstones.[55]

The authors regarded the Tando beds as a proper geologic formation, but they need to establish a type location and publish a full description.[55] Outcrops of the Tando beds can be found on several small islands in the basis like Tando, Buldo, Ttakseum, Goreyom, and Seoksan islands.[55]

In 2008 a Hwaseong city public official noticed the fossils in a block of rock in the rock-filled Tando embankment dam.[55] The block was 80 centimeters by 60 centimeters by 80 centimeters and was composed of reddish colored finegrained sandstone.[55] The Tando embankment dam was built in 1994 with rocks from Tando and Buldo quarries.[55] The rocks preserving the fossils most closely resemble those of the lower Tando beds.[55] In 2001, Choe and others reported six ornithopod tracks from the tuffaceous sandstone in the upper Tando beds.[55] Regional volcanic activity have modified local sedimentary rocks via heat and oxidation, which has prevented researchers from recovering palynomorphs that might be used to date the formation.[55] Nevertheless in 2004, Yi and others reported Potassium-Argon plagioclase and biotite age of three andeitic tuff samples from the upper Tando beds.[55] They found that the beds were 103 million years old, give or take 500,000 years. This puts them within the Albian age of the late Early Cretaceous.[55]

Apart from the tip of the tail, its neural spines were five times as tall as their respective centra.[56] A ridge running from front to back divided the astragalus into two fossae.[56] The calcaneum was triangular in shape and was 1.5 times as long as the astragalus from front to back when viewed from the side that faced the animal's body.[56]

The hind legs were nearly articulated. The near ends of the tibiae and fibulae are sharply cut off at the end of the block.[57] This likely means the rest of the skeleton was presentbefore the block was broken up at the quarry.[57] The tail is nearly complete and preserved 36 vertebrae.[57] Four or five vertebrae from the the end of the tail might be missing, but the tail's very tip is preserved although detached from the rest of the specimen.[57] The tail was about 813 mm long.[57]

The fibula is more gracile than the tibia in all known ceratopsians.[58]

The clacaneum is firmly fused to the astragalus medially.[59] Metatarsal I is the shorted and metatarsal III was the longest and most robust.[59]

Recent phylogenetic research had been based off of a list of 133 characters.[60] The hypodigm of Koreaceratops can only be coded for 6 of these characters.[60] The discovery of Koreaceratops inspired the researchers to add three more; the ratio of mid-tail neural spines to their centra, the width of the near side of an ungual compared to the far end, and tail vetebrae with neural spines longer than chevrons.[60]

Their analysis found that Koreaceratops was placed phylogenetically between Archaeoceratops and a clade including Cerasinops and more advanced ceratopsians.[61]

Although most distinguishing characteristics of ceratopsians are known from their skulls, the authors had to identify Koreaceratops as a ceratopsian based on postcranial characters due to the absence of a skull among its fossils.[62] The foot of Koreaceratops is too long and slender to be a ceratopsid and its chevrons being shorter than its neural spines rule out the possibility that it is a psittacosaurid.[62]

Koreaceratops is the first basal neoceratopsian known from Korea.[62] It is the easternmost example of the group in Eurasia.[62] It's also the oldest neoceratopsian to have the deep tail profile.[62] The next oldest example is Udanoceratops which lived 20 million years later.[62] It's late Albian age makes an important contribution to filling a chronological gap wtih few known ceratopsian remains that exists from the late Albian to the Santonian.[62] The basal neoceratopsian Asiaceratops from the Cenomanian of Uzbekistan and Turanoceratops from Uzbekistan.[62]

No other basal neoceratopsians neural spines are as long or located so far along the tail as in Korreaceratops.[62] Montanoceratops from the early Maastrichtian of Montana has a complete tail that is "leaf shaped".[62] The fifteenth tail vertebrae has its longest neural spine.[62] This is only four times as high as its vertebral centrum.[62] The highest neural spine in the vertebrae of Koreaceratops is close towards the tip of the tail.[62]

The neural spines of Udanoceratops tchizhovi are only three times as high as their centra.[62] Its tall spines are also positioned closer to the tail base than in Koreaceratops.[62] Its unguals were more hooflike than Koreaceratops's slender pointed unguals.[62]

Protoceratops hellenikorhinus from China's Bayan-Mandahu Formation was named in 2001 for a skull found by the Sino-Belgian expeditions.[62] Protoceratops hellenikorhinus had more hoof-like unguals than Koreaceratops.[62] Its mid-tail vertebrae had circular or flattened neural spines that were only four times as large as their centra.[62]

Bagaceratops rozhdeventsky from the Campanian Barungoyot Formation.[62] Its neural spines are five times as tall as its centra, it's most distinguishing characteristic.[62] This is similar to Koreaceratops, however Bagaceratops has short, wider feet and more hoof-like unguals.[62]

Koreaceratops has claw-like unguals. Cerasinops and Graciliceratops also have claw like unguals.[63]

The midcauda neural spine to centrum ratios of Koreaceratops, Montanoceratops, Udanoceratops, Protoceratops, and Bagaceratops are 3, 2, 1, 2, 3 respectively.[63] The tall neural spines of the basal neoceratopsians was lost secondarily in the ceratopsids.[63]

Coronosaurs have hoof-like unguals.[63] The general trend in ceratopsian evolution was toward larger body sizes, heavier weights, and shorter limbs and tails. Feet became shorter and more robust.[63] Metatarsals, phalanges and unguals all became shorter and thicker.[63]

In 2008 Tereschenko devised a classification scheme for ceratopsian unguals based on their length to width ratios.[63] "Claws" are twice as long or more as they are wide.[63] "Unuglo-hooves" are 1.5 to 2.0 times as long as they are wide.[63] "Hoof" unguals are less than 1.5 tiomes as long as they are wide.[63]

There is no controversy about the fact that Ceratopsids were quadrupeds.[63] However, more primitive ceratopsians' means of locomotions have been more controversial.[63] In 1978 Coombs argued that the ratio in length between forelimbs Leptoceratops and Protoceratops suggested they spent at leats some of their time walking on all fours.[63] In 2007 Senter performed an analysis of forelimb anatomy and range of motion and agreed.[63] In 2008 Tereschenko concluded that they were obligatory quarupeds.[63] In 2007 Senter observed differences in the forelimbs of Protoceratops and Leptoceratops.[63] In Protoceratops the palms face rearward as would be expected for typical quadrupedal locomotion.[63] However the palms of Leptoceratops seemed to naturally face inward and would need to be re-oriented in order to walk on all fours.[63] Protoceratops was also a bulkier animal than Leptoceratops and therefore likely better adapted to walking on all fours.[63]

The development of unguals resembling the hooves of many larger herbivorous quadrupeds seems to have occurred as ceratopsians became more quadrupedal.[63]

The evolution of large skulls in ceratopsians may have been the precipitating factor that led to them becoming quadrupeds.[64] There is a strong correlation between the ratio between the length of the skull and hind limb (including the foot) of a ceratopsian and its manner of locmootion.[65] In coronosaurs this ratio is about 0.7 while the bipedal Psittacosaurus and Cerasinops have ratios of less than 0.4.[65] The ratios of Montanoceratops, Prenoceratops, and Leptoceratops range betwen 0.60 and 0.65, indicating they were intermediate between the former groups.[65] The researchers predicted based on its phylogenetic position that when more Koreaceratops fossils are found it will have a skull length to hind limb length ration indicating bipedal habits.[65]

The authors believe that quadrupedality gradually evolved in ceratopsians Forms like Cerasinops and probably Koreaceratops were bipedal.[65] By the appearance of Graciliceratops and Leptoceratops ceratopsians had gained the ability to spend some of their time on all fours.[65] By the appearance of the coronosaurs they achieved full quadrupedality.[65] They achieved this by evloving larger skulls, longer bodies, more robust hands and hoof-like unguals.[65]

In 1925 Gregory and Mook suggested that the large feet and tall neural spines in the tail of Protoceratops were adaptations for swimming.[66] In 1974 Barsbold also felt that Protoceratops was semi-aquatic due to its high neural spines.[66] In 1997 Bailey reinterpreted the tall tail spines as adaptations for storing fat and water on its tail to make survival easier in its desert habitat.[66] In 2008 Tereschenko again echoed the interpretation that the tall tail with heterocoelous vertebrae in Protoceratops and its relatives were adaptations for swimming.[66] Also the associations in the Djadokhta Formation between Protoceratops and lake and pond deposits.[66] Of these Tereschenko concluded that Bagaceratops was ost completely adapted for aquatic behavior.[66] He argued that in decreasing swimming ability were Protoceratops, Udanoceratops, and Leptoceratops as the most terrestrial.[66] If these lines of reasoning are correct then the authors conclude that Koreaceratops would be a good swimmer.[66]

Complicating the idea that Protoceratops and its relatives were proficient swimmers are the many Protoceratops specimens found in wind-blown deposits that still posess the "deep tail" thought to be related to swimming abilities.[66] Also, psittacosaurs have long been speculated to have an aquatic component to their behavior and are frequently found preserved in lake deposits yet lack the deep tail that's supposedly evidence for similar habits in Protoceratpos and its relatives.[66] An additional complication is that some taxa have deep tails, are known from sedimentary rock deposited by flowing water, and yet are thought to be the least aquatically inclined.[66]

In 2010 Nick Longrich proposed that Protoceratops was nocturnal and spent the day hidden in burrows to escape the heat of the day.[66] This hypothesis was proposed to explain the existence of articulated Protoceratops specimens discovered in upright standing postures.[66] The tall neural spines of the narrow tail under this interpretation are adaptations for shedding heat while it was active.[66]

The authors noted that the tail of Koreaceratops was consistent with interpretations of it as a capable swimmer, but called the evidence overall "equivocal".[66] They proposed that future evidence about its environment may better inform future discussions on the topic.[66]

Ceratopsids[edit]

In 2010 Jordan C. Mallon and Robert Holmes published a description of a partial ceratopsid skeleton.[67] The remains preserved enough useful anatomical information to identify the specimen as a chasmosaurine, but not enough to determine what genus or species it was.[67] Its stratigraphic origins in the second unit of the Horseshoe Canyon Formation suggest that it was either an Anchiceratops or Arrhinoceratops.[67] This specimen has unique anatomical characteristics of the limbs and ribs.[67] It had a unique vertebral count; 10 neck vertebrae, 13 thoracic vertebrae, 12 sacral vertebrae and 39 tail vertebrae.[67] It unique features and "unusually robust" build suggest that it was a semi-aquatic hippo-like animal.[67] Mallon and Holmes find additional support for this hypothesis from its depositional setting, which was a estuary during the Cretaceous.[67]

This specimen was discovered at a Horseshoe Canyon Formation field site near Rumsey, Alberta near the end of summer on a 1925 expedition led by Charles M. Sternberg to the Red Deer River valley.[68] Apart from the mostly missing skull, the specimen was both complete and articulated.[68] Sternberg identified the specimen as belonging to Anchiceratops, although in 2010 Mallon and Holmes noted that he didn't provide a justification for this referral.[68] The specimen was prepared to be used as a panel mount in 1929 and provided a skull from a cast of the Anchiceratops longirostris type specimen.[68] Paleontologists Mallon and Holmes have expressed surprise that this high quality specimen hasn't received detailed examination in the scientific literature, although it received brief treatment in 1933 by Lull.[68] Postcranial remains of ceratopsids that are both complete and articulated are so rare that only one other specimen, described by Brown in 1917, is of "comparable quality".[68]

This specimen is catalogued as CMN 8547.[69] The body is complete, but only fragments of its frill remain of the skull.[69] Sternberg reported the presence of the front portion of the animal's snout in his 1925 field notes, but in their 2010 description of the material, Mallon and Holmes could not find it.[69] The unguals of the left hand's first and third toe are missing, although their former presence with the specimen is documented by photographs from the field and of the original panel mount.[69]

CMN 8547 was discovered on the east side of the Red Deer River 10.3 km southwest of Rumsey at a field locality catalogued as TMP locality L1508.[70] Stratigraphically speaking, the fossils were recovered from near the top of unit 2 of the Horseshoe Canyon Formation.[70] This horizon lay 26 m below Carbon coal zone, also known as coal seam 11.[70] CMN 8547 was also 16 m below a bed of oyster fossils that comprised part of the Drumheller Marine Tongue.[70]

CMN 8547 preserves four fragments of its frill, each of which is "flattened".[71] Sternberg originally described these as originating from the frill's left side, but in 2010 Mallon and Holmes argued that they cam from the right side of the animal's frill based on their curvature.[71] In thickness these fragments range from 28 to 30 mm at the edges of the frill and 7-10mm at the thinnest points.[71] Two of the fragments originated from the edge of the frill where it had a "scalloped" appearance.[71] Mallon and Holmes observed 3mm deep scarring on one of the frill fragments that was left by vascular sulci that ran roughly parallel to one another.[72] These features have been documented in other ceratopsians "but are especially pronounced" in derived chasmosaurines like Anchiceratops longirostris, as seen in the specimen CMN 8535 and Arrhinoceratops brachyops, as seen in ROM 796.[73]

When CMN 8547 was discovered, the specimen was laying on its right side with its left flank exposed.[74] The panel mount was prepared for an exhibit in the Canadian Museum of Nature's Talisman Energy Fossil Gallery.[74] Because the specimen is a panel mount, scientists can only examine its right side.[74] This has hindered multiple attempts at describing the specimen's anatomy in detail, including Mallon and Holmes' 2010 description. [75]

Distortion to the specimen after its burial was "minima[l]", but in order to accurately reconstruct the anatomy of CMN 8547 for thewir 2010 description, Mallon and Holmes had to position the shoulder blade at 45 degrees to the horizontal, space the ribs more widely, and rotate the ischium downward.[76] The vertebral column of CMN 8547 is 4.05m long, with a total of 74 vertebrae.[76] This resemble the vertebrae counts estimated by other workers for different kinds of ceratopsid. Centrosaurus has been estimated as having 77 vertebrae.[76] In 1933 Lull estimated the vertebral count of Chasmosaurus belli at 76 although no full vertebral column is known for this species.[76] The vertebrae of CMN 8547 are spaced roughly 1-2 cm apart except for the far end of the tail where they are spaced closer together.[76]

The distinction between the vertebrae of the neck and body has been a subject of contention for paleontologists.[76] Most researchers define neck vertebrae as those vertebrae with parapophyses on their vertebrae rather than their neural arches.[76] A few have historically defined neck vertebrae based on "the short, straight ribs they support".[76] This minority approach is problematical because "ribs are rarely preserved articulated with their supporting vertebrae".[76] For the sake of consistency with the majority of workers and the aforementioned shortcoming, Mallon and Holmes used the parapophysis-based definition for neck vertebrae rather than the minority rib-based definition.[76]

A ceratopsid neck is usually comprised of 6 typical vertebrae and a syncervical composed of 3 fused vertebrae, although some workers have historically misinterpreted it as being composed of 4 vertebrae.[76] Therefore a typical ceratopsid has 9 total neck vertebrae.[76] However, Mallon and Holmes argue that the syncervical of CMN 8547 is truly comprised of four vertebrae, unlike previous misinterpretations of fosslis that produced the same number.[77] This would make CMN 8547's neck vertebrae count of 10 completely unique among known ceratopsids.[78]

Mallon and Holmes in 2010 defined throacic vertebrae as those with parapophyses on their neural arches.[78] Most ceratopsids have 12 thoracic vertebrae.[78] In 1986 Ostrom and Wellnhofer inaccurately restored Triceratops as having 14 thoracic vertebrae.[78] CMN 8547 has 13 thoracic vertebrae.[78] Plaster hindered Mallon and Holmes' ability to determine whether or not the last thoracic vertebra is co-ossified to the first sacral like Centrosaurus, although it is possible.[78] In 1933 Lull termed this configuration a dorsosacral.[78]

Mallon and Holmes describe the synsacrum as "relatively long" in CMN 8547.[78] Most ceratopsids have 10 sacral vertebrae, but CMN 8547 has twelve.[78] Pentaceratops is known to have 11.[78] The neural spines of CMN 8547's sacral vertebrae are "braced... by a tendon trellis".[78] However, these fossilized tendons were damaged during preparation making it impossible for Mallon and Holmes to compare the tendon trellis of CMN 8547 with those of other ceratopsians.[78] CMN 8547 had 39 tail vertebrae.[78] This number is intermediate between Pentaceratops sternbergii, which had 30 and Centrosaurus apertus, which had 46.[78] P. sternbergii and C. apertus are the only known ceratopsid species with complete tails.[78]

CMN 8547 had unusually thick ribs.[78] They average 39 mm thick from front to back at their midpoints.[78] In Chasmosaurus russeli the average width and midlength is 37 mm and in Styracosaurus it's 27 mm midlength.[78] CMN 8547 is larger than both even though Chasmosaurus russel has been estimated to be about 1.25 times as massive as CMN 8547.[78] Styracosaurus albertensis has been estimated to be 1.5 times as massive as CMN 8547.[78] The ribcage has been described as compact and rigid, although this is partially due to postburial distortion which gives an exagerated appearance of compaction and rigidity by compressing the ribs together.[78]

The shoulder blade was discovered angled at 64 degrees to the horizontal, although Mallon and Holmes interpret it as being more likely that in life this angle was closer to 45 degrees.[79] They compared its outline to those of Triceratops horridus and Pentaceratops sternbergii.[79] The shoulder region of CMN 8547 was general typical compared to other ceratopsids.[79] One of the potential sternal plates discovered near the shoulder region may be allochthonous in origin.[79]

In their 2010 description of CMN 8547, they described its forelimb as being more "stout" than is typical for a ceratopsid.[79] It humerus is almost as long as the typical ceratopsid value but is more robust.[79] The absence of a medial tubercle in the humerus of CMN 8547 distinguishes it from all other ceratopsians.[79] Mallon and Holmes dismissed the idea that this absence is attributable to post mortem damage on the specimen because the medial tubercle is absent on both humeri in field photos and the surface where it should be present seem "complete".[79]

CMN 8547's radius was typical for ceratopsids, but its ulna is unusual.[79] One notable trait is its prominen olecranon process compared to centrosaurines.[79] CMN 8547 preserved two carpal bones, like most ceratopsids.[79] These carpals were probably distal carpals three and four.[79] The bones of its forepaw were unusually short and wide.[79] These elements were generally more "robust" than those found in Centrosaurus apertus, Chasmosaurus belli, or Chasmosaurus irvinensis.[79] Otherwise the forepaw is typical for ceratopsids and has the usual phalangeal formula of 2-3-4-3-2.[79]

The pelvis of CMN 8547 fairly typical for ceratopsids.[79] However, is ischium is unusually robust compared to Chasmosaurus belli, Agujaceratops mariscalensis, and Pentaceratops sternbergii.[80]

CMN 8547 has longer hindlegs relative to the size of its ribcage than Centrosaurus apertus.[81] Its femur does not appreciably differ in length from other ceratopsid, but is thicker.[81] The tibia and fibula of CMN 8547 are proportionally similar to those of other ceratopsids.[81] Its toe phalanges were more "robust" than those of Styracosaurus albertensis due to being shorter and wider.[81]

As of 2010 only four ceratopsid species have been documented in the Horseshoe Canyon Formation.[82] The only known centrosaurine from the formation is unit 1's Pachyrhinosaurus canadensis.[83] Mallon and Holmes characterize the stratigraphic distribution of centrosaurs in the Horseshoe Canyon Formation as "wid[er]" than centrosaurines.[84] Anchiceratops ornatus and Arrinoceratops brachyops are both known from units 1 and 2 of the Horseshoe Canyon Formation.[84] Eotriceratops xerinsularis is known from the middle of unit 5.[84]

From the time Lull, in 1933, endorsed Sternberg's 1925 referral of CMN 8547 to Anchiceratops no researcher has questioned its identity.[84] Of the three known Horseshoe Canyon chasmosaurs, Eotriceratops's frill morphology least consistent with the fragments belonging to CMN 8547.[84] Anchiceratops and Arrhinoceratops both have more similar frills and are known from the same unit of the formation as CMN 8547.[84] Nevertheless, CMN 8547 preserves little information that would be useful for classifying at the genus or species level.[85] Further, Mallon and Holmes noted that there were very few reliable characters to even distinguish Anchiceratops and Arrhinoceratops as different kinds of dinosaur.[86]

The extreme rarity of postcranial ceratopsian fossils in the Horseshoe Canyon Formation complicates the identification of CMN 8547.[86] The only specimen besides CMN 8547 with significant postcranial material is ROM 1493.[86] This specimen preserves a skull and part of a forelimb.[86] One of its forelimb elements is a badly weathered incomplete humerus.[86] This humerus has a large deltopectoral crest like that found in CMN 8547.[86] ROM 1493 has been referred to both Arrhinoceratops and Torosaurus, so CMN 8547 might be attributable to them as well, although Mallon and Holmes state that "more conclusive evidence is needed" to be sure.[86]

Mallon and Holmes speculated that Sternberg's original referral of CMN 8547 to Anchiceratops might have been due to its status as the only known Edmontonian ceratopsid at the time rather than any distinguishing anatomical traits.[86] Mallon and Holmes examined some of Sternberg's correspondance from the time period archived at both the Royal Ontario Museum and the Canadian Museum of nature and found no evidence that Sternberg new of the only recently named Arrhinoceratops.[86]

Mallon and Holmes speculated that the increased numbers of vertebrae before the tail and the low count of tail vertebrae compared to Centrosaurus apertus suggests changes in the devlopmental process of the animal.[86] Four of the tail vertebrae could have joined the rear of the sacral vertebrae while two of the front sacral vertebrae could have joined the thoracis vertebrae.[86] This devlopmental hypothesis explains the distribution and number of vertebrae for each segment of the spinal columns.[86] Similar developmental changes could have been at work to form Pentaceratops sternbergii's proportional long neck and body but short tail.[86] However, it's likely that in the case of P. sternbergii this process was "less pronounced".[86] Mallon and Holmes cautioned that without additional articulated skeletons to examine it can't be determined whether vertebrae counts varied by individual within this species.[86]

In 1959 Langston concluded that Anchiceratops was common only in areas where other ceratopsids were based their depositional environments and his own personal observations in the field.[87] He hypothesized that Anchiceratops lived only in "marshy" environments in low elevation areas characterized by mainly reductive chemistry.[87] Langston noted that in CMN 8547 its long nose could have been useful for keeping its nostrils above the surface using its frill as a counterbalance.[87] He saw CMN 8547's stocky body and short limbs as evidence it was a "sluggish" protected from predators by the water and isolation of its environment.[87]

The idea that ceratopsids might be semi-aquatic lost traction in the scientific community many years ago.[87] Mallon and Holmes, however, contend that recent arguments in favor of ceratopsids living primarily in wetland habitats call for more attention to be given to the idea.[87] Crocodilians are the closest semi-aquatic modern relatives of ceratopsians, yet their specialized body plans and smaller sizes weaken comparisons between them.[87] Hippos might be a modern analogue for what a semi-aquatic ceratopsid would be like in life.[87] Some researchers have cautioned against ascribing excessive similarities with mammals to dinosaurs, but CMN 8547's has physical features in common with hippos.[87] Other ceratopsians have features in common with hippos as well that may suggest a semi-aquatic lifestyle.[87] Many of the potential adaptations for a semi-aquatic mode of existence in CMN 8547 could be beneficial for a terrestrial animal.[87] However, Mallon and Holmes interpret the large number of candidate adaptations for semi-aquatic living in CMN 8547 as a strong cumulative case that it did so.[87] They argue that the strong arm and chest muscles in CMN 8547 and its "stout proportions" were useful for maneuverability in the mud of its early Maastrichtian lowland swamp habitat.[87] It depositional environment supports this interpretation since the rock's bearing the fossil were deposited in an estuary, the highest of such deposits found in the Drumheller Marine Tongue.[87] Further, there were oysters associated with CMN 8547.[87] In 2008, Tereschenko argued that the heterocoelous vertebrae found near the base of ceratopsids' tails and tall neural spines near their middle for sculling through the water were adaptations for a semi-aquatic mode of life.[87] Mallon and Holmes noted that CMN 8547 did not provide support for this interpretation.[87] However, Mallon and Holmes also cautioned researchers to "limit speculation" about ceratopsid aquatic behvior based on sedimentological evidence since ceratopsids are also known from environments with well-drained soils as well.[87]

The uniqueness of CMN 8547's anatomy stands out among ceratopsians, which typically only varied from eachother in skull anatomy.[88] Mallon and Holmes cautioned other researchers against relying on cladistic analyses that used CMN 8547 as a basis for Anchiceratops's postcranial anatomy.[88] Mallon and Holmes describe evidence that some ceratopsids may have been semi-aquatic as "an increasing body of sedimentological, microsite, and paleosol data."[89]

Footnotes[edit]

  1. ^ a b c d e f g h i j k l m n o "Abstract," Eberth (2010); page 428.
  2. ^ a b c d "Introduction," Eberth (2010); page 428.
  3. ^ "Introduction," Eberth (2010); pages 428-429.
  4. ^ a b c d e f g h i j "Introduction," Eberth (2010); page 429.
  5. ^ a b c d e f g h i j k l m n o p "Who's Who, Where, and When?" Eberth (2010); page 429.
  6. ^ a b c d e f g "Paleoenvironmental Associations: Basal Ceratopsians," Eberth (2010); page 429.
  7. ^ "Paleoenvironmental Associations: Basal Ceratopsians," Eberth (2010); pages 429-430.
  8. ^ a b c d e f "Paleoenvironmental Associations: Basal Ceratopsians," Eberth (2010); page 430.
  9. ^ a b c "Paleoenvironmental Associations: Basal Neoeratopsians," Eberth (2010); page 430.
  10. ^ "Paleoenvironmental Associations: Basal Neoeratopsians," Eberth (2010); pages 430-431.
  11. ^ a b c d e f g h i j k l m n "Paleoenvironmental Associations: Basal Neoeratopsians," Eberth (2010); page 431.
  12. ^ a b c d e f g h i j k "Paleoenvironmental Associations: Neoeratopsians," Eberth (2010); page 431.
  13. ^ a b c d e "Paleoenvironmental Summary," Eberth (2010); page 431.
  14. ^ "Taphonomic Patterns," Eberth (2010); pages 431-432.
  15. ^ a b c "Paleoenvironmental Summary," Eberth (2010); page 432.
  16. ^ a b c d e f g h i j k "Taphonomic Patterns: Basal Ceratopsians," Eberth (2010); page 432.
  17. ^ a b c d e f g h i "Taphonomic Patterns: Basal Neoceratopsians," Eberth (2010); page 432.
  18. ^ "Taphonomic Patterns: Basal Neoceratopsians," Eberth (2010); pages 432-433.
  19. ^ "Taphonomic Patterns: Basal Neoceratopsians," Eberth (2010); page 433.
  20. ^ a b c d e f g h i j k l m n o p q r s "Taphonomic Patterns: Neoceratopsians," Eberth (2010); page 433.
  21. ^ "Taphonomic Summary," Eberth (2010); page 434.
  22. ^ a b c "Conclusions," Eberth (2010); page 434.
  23. ^ a b c d e f g h i j k l m n o "Abstract," Ford and Martin (2010); page 328.
  24. ^ a b "Introduction," Ford and Martin (2010); page 328.
  25. ^ "Introduction," Ford and Martin (2010); pages 328-329.
  26. ^ a b c d e f g h "Introduction," Ford and Martin (2010); page 329.
  27. ^ a b c d e "Previous Arguments in Support of Semi-Aquatic Psittacosaurs," Ford and Martin (2010); page 329.
  28. ^ "Previous Arguments in Support of Semi-Aquatic Psittacosaurs," Ford and Martin (2010); pages 329-330.
  29. ^ a b c "Previous Arguments in Support of Semi-Aquatic Psittacosaurs," Ford and Martin (2010); page 330.
  30. ^ a b c d e "Resting," Ford and Martin (2010); page 330.
  31. ^ a b c d e f g "Sprawling," Ford and Martin (2010); page 330.
  32. ^ a b c d e f g "Hindlimbs," Ford and Martin (2010); page 331.
  33. ^ "Pes," Ford and Martin (2010); page 331.
  34. ^ "Pes," Ford and Martin (2010); pages 331-332.
  35. ^ a b c d "Pes," Ford and Martin (2010); page 332.
  36. ^ a b c d e f g h i j k l m n "Forelimbs," Ford and Martin (2010); page 332.
  37. ^ "Forelimb Movement," Ford and Martin (2010); pages 332-333.
  38. ^ a b "Forelimb Movement," Ford and Martin (2010); page 333.
  39. ^ a b c d "Body Proportions," Ford and Martin (2010); page 333.
  40. ^ a b c d e f g "Gastroliths," Ford and Martin (2010); page 333.
  41. ^ a b c d e "Tail," Ford and Martin (2010); page 333.
  42. ^ "Tail," Ford and Martin (2010); pages 333-334.
  43. ^ a b c "Tail," Ford and Martin (2010); page 334.
  44. ^ a b c "Nares and Orbit," Ford and Martin (2010); page 334.
  45. ^ a b c d e f "Skin," Ford and Martin (2010); page 334.
  46. ^ a b c d e f "Bristle-Like Structures," Ford and Martin (2010); page 335.
  47. ^ a b "The Nature of Psittacosaur Swimming," Ford and Martin (2010); page 335.
  48. ^ a b "Conclusions," Ford and Martin (2010); page 336.
  49. ^ a b c d e f g h i j "Abstract," Lee, Ryan and Kobayashi (2010); page 39.
  50. ^ a b c d "Introduction," Lee, Ryan and Kobayashi (2010); page 39.
  51. ^ "Introduction," Lee, Ryan and Kobayashi (2010); pages 39-40.
  52. ^ a b "Introduction," Lee, Ryan and Kobayashi (2010); page 40.
  53. ^ "Etymology," Lee, Ryan and Kobayashi (2010); page 40.
  54. ^ a b c "Holotype," Lee, Ryan and Kobayashi (2010); page 40.
  55. ^ a b c d e f g h i j k l m n o p "Type Locality and Geological Setting," Lee, Ryan and Kobayashi (2010); page 41.
  56. ^ a b c "Diagnosis," Lee, Ryan and Kobayashi (2010); page 41.
  57. ^ a b c d e "Description," Lee, Ryan and Kobayashi (2010); page 41.
  58. ^ "Description," Lee, Ryan and Kobayashi (2010); page 42.
  59. ^ a b "Description," Lee, Ryan and Kobayashi (2010); page 43.
  60. ^ a b c "Phylogenetic Analysis," Lee, Ryan and Kobayashi (2010); page 44.
  61. ^ "Phylogenetic Analysis," Lee, Ryan and Kobayashi (2010); page 45.
  62. ^ a b c d e f g h i j k l m n o p q r s t u v "Discussion," Lee, Ryan and Kobayashi (2010); page 45.
  63. ^ a b c d e f g h i j k l m n o p "Behavioral Inferences," Lee, Ryan and Kobayashi (2010); page 47.
  64. ^ a b c d e f g "Abstract," Mallon and Holmes (2010); page 189.
  65. ^ a b c d e f "Introduction," Mallon and Holmes (2010); page 189.
  66. ^ a b c d "Systematic Paleontology: Material," Mallon and Holmes (2010); page 190.
  67. ^ a b c d "Systematic Paleontology: Locality and Horizon," Mallon and Holmes (2010); page 190.
  68. ^ a b c d "Description of CMN 8547: Skull," Mallon and Holmes (2010); page 190.
  69. ^ "Description of CMN 8547: Skull," Mallon and Holmes (2010); pages 190-191.
  70. ^ "Description of CMN 8547: Skull," Mallon and Holmes (2010); page 191.
  71. ^ a b c "Description of CMN 8547: Postcranium," Mallon and Holmes (2010); page 191.
  72. ^ "Description of CMN 8547: Postcranium," Mallon and Holmes (2010); pages 191-192.
  73. ^ a b c d e f g h i j k l "Description of CMN 8547: Postcranium," Mallon and Holmes (2010); page 192.
  74. ^ "Description of CMN 8547: Postcranium," Mallon and Holmes (2010); pages 192-194.
  75. ^ a b c d e f g h i j k l m n o p q r s t u "Description of CMN 8547: Postcranium," Mallon and Holmes (2010); page 194.
  76. ^ a b c d e f g h i j k l m n o p "Description of CMN 8547: Postcranium," Mallon and Holmes (2010); page 195.
  77. ^ "Description of CMN 8547: Postcranium," Mallon and Holmes (2010); pages 195-196.
  78. ^ a b c d "Description of CMN 8547: Postcranium," Mallon and Holmes (2010); page 196.
  79. ^ "Discussion: Taxonomic Affinities of CMN 8547," Mallon and Holmes (2010); page 196.
  80. ^ "Discussion: Taxonomic Affinities of CMN 8547," Mallon and Holmes (2010); pages 196-197.
  81. ^ a b c d e f "Discussion: Taxonomic Affinities of CMN 8547," Mallon and Holmes (2010); page 197.
  82. ^ "Discussion: Taxonomic Affinities of CMN 8547," Mallon and Holmes (2010); pages 197-198.
  83. ^ a b c d e f g h i j k l m n o "Discussion: Taxonomic Affinities of CMN 8547," Mallon and Holmes (2010); page 198.
  84. ^ a b c d e f g h i j k l m n o p q r "Discussion: Semi-Aquatic Ceratopsids," Mallon and Holmes (2010); page 199.
  85. ^ a b "Discussion: Significance of CMN 8547," Mallon and Holmes (2010); page 199.
  86. ^ "Discussion: Significance of CMN 8547," Mallon and Holmes (2010); pages 199-200.

Reference[edit]

  • Eberth, D.A., 2010. Ceratopsians: A Review of Paleoenvironmental Associations and Taphonomy. In, Ryan, M.J., Chinnery-Allgeier, B, and Eberth, D.A., eds. New Perspectives on Horned Dinosaurs: The Ceratopsian Symposium at the Royal Tyrrell Museum, September 2007. Indiana University Press, Bloomington, Indiana, p. 428–446.
  • Ford, Tracy L.; Martin, Larry D. (2010). "A semi-aquatic life habit for Psittacosaurus". New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium. Bloomington and Indianapolis: Indiana University Press. pp. 328–339. ISBN 978-0-253-35358-0. {{cite book}}: Unknown parameter |editors= ignored (|editor= suggested) (help)
  • Lee, Yuong-Nam; Ryan, Michael J. and Kobayashi, Yoshitsugo (2011). "The first ceratopsian dinosaur from South Korea". Naturwissenschaften. 98 (1): 39–49. doi:10.1007/s00114-010-0739-y. PMID 21085924.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • Mallon, J. C., and R. B. Holmes, 2010. Description of a complete and fully articulated chasmosaurine postcranium previously assigned to Anchiceratops (Dinosauria: Ceratopsia). In M. J. Ryan, B. J. Chinnery-Allgeier, and D. A. Eberth (eds.), New Perspectives on Horned Dinosaurs. Indiana University Press, Bloomington, Indiana.
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