User:Abyssal/Ceratopsian habitat

Paleoenvironmental associations and taphonomy

David Eberth published a review of the stratigraphic, paleoenvironmental, and taphonomic information known about ceratopsians. He complained that such information "lacks detail" and cited a need for research focused on that topic, especially for recent Asian discoveries. 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." He also reviewed the taphonomy of some taxa.

Eberth concludes that that ceratopsians "retained a long term preferential association with wetland paleoenvironments." These environments included the areas surrounding lakes, as well as "alluvial and coastal plains." However, by the Late Cretaceous, basal forms began exploiting drier areas including habitats that were semi- to fully arid or with weather patterns divided into wet and dry seasons. Such exploitation of drier environments seems to have occurred in both Asia and North America. During the Campanian, neoceratopsians in Canada and Alaska "fluorished," experiencing an increase in taxonomic diversity. 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.

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. This focus on bonebed taphonomy was especially ture for centrosaurines. 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. Eberth stated that additional taphonomic research would be useful for reaching answers on issues of contention among paleontologists. 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.

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

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

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

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

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

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

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

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

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

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

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. Zuniceratops remains have been recovered from coal-bearing sediments representing an alluvial-to-upper coastal plain environment with a subtropical seasonally wet climate. A small number of poorly preserved basal neoceratopsian remains have been recovered in the same general region as Zuniceratops. The remains were associated with non-calcareous, poorly drained, and coaly alluvial-to-coastal plain sediments.

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

Most ceratopsians tend to be found in rocks deposited in environments closeley associated with water in a variety of ways. These environments include such settings as lakes, alluvial or coastal plains. 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. 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." This was especially true during the Campanian "where seasonality was likely of the wet and wetter variety."

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. Not only is ceratopsian taphonomy preoccupied with bonebeds but even more specifically these tend to be bonebeds where only one species predominates. Taphonomers of ceratopsian remains have even tended to neglect the study of isolated specimens occurring in the same gologic formations as bonebeds. Research on the taphonomy of Chinese and Mongolian ceratopsian specimens is particularly scarce.

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. 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. Higher in the section are tens to hundreds of psittacosaurs preserved in tuff-bearing shales that were deposited in a lake. The causes of deaths for the animals preserved in these beds are uncertain. In 2003 Guo and others suggested that emissions of toxic gases from the nearby volcanic activity caused mass deaths of local terrestrial life. Ford and Martin by contrast see the lakes as the natural habitat of Psittacosaurus, which they interpret as semi-aquatic. 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. 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. 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. Also, the depositional environment must have experience high levels of sedimentation or ver low levels of decay. Possible contributing factors to such low levels of decay could include cool or low-oxygen conditions on the lake bottom.

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. They are on display at the Mongolian Academy of Sciences in Ulanbataar. 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.

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

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.

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.

Longrich has suggested that Protoceratops was nocturnal and hid from the high daytime termperatures in burrows. During times of high sediment supply they would be entombed in their own burrows. 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.

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

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

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.

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. Ceratopsid remains he described as associated with ancient channels and overbank deposits.

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.

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

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. Chasmosaur bonebeds tended to be smaller and more often preserved in ancient channels.

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 anomalously asocial. Another explanation may be that the strata preserving such taxa had different depositional and preservational characteristics.

Centrosaur bonbeds are confined to areas of southern Alberta at least 200km up-dip from the ancient shoreline. 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. Eberth speculated that similar patterns might be uncovered in ceratopsids like Triceratops and Chasmosaurus that are known from multiple locations and stratigraphic positions.

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

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. 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. Neoceratopsians thrived and diversified in warm-temperate to subtropical wetlands of the coastal lowlands in Canada and Alaska during the Campanian.

Reference

• 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.