Datousaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Mamenchisauridae

Genus:Datousaurus

Species:Datousaurus bashanensis

Introduction

Datousaurus belongs to one of the most populous and widely spread dinosaur groups known—the herbivorous sauropods. The sauropods included many of the largest land animals yet discovered, though Datousaurus ranked along the middle of the sauropod scale in size. Datousaurus is remarkable because it remains something of a mystery. Research has been limited to two incomplete skeletons and one possible, but uncertain, set of jaws.

Though found among one of the richest fossil beds in China, along with numerous other sauropod specimens, Datousaurus fossils have not yielded enough information to identify its family with great certainty or to draw specific conclusions regarding much of its life. Scientists continue to debate many aspects of its anatomy and its existence. Though it appears to be a close relative of Shunosaurus, a well-known Middle Jurassic sauropod, fossils of which were found in the same excavation site, more evidence must be found to form a complete picture of this dinosaur.

Classification

Paleontologists rely largely on the hierarchical Linnaean system, developed by Carl Linnaeus in 1735, to classify dinosaurs. This system comprises different tiers of classification (class, order, genus, and species) based on shared characteristics within each grouping. Species, the lowest tier, is based on the most specific shared traits.

Within the Linnaean system, dinosaurs are split into two orders, Ornithischia and Saurischia, based on their skeletal structure. Datousaurus falls into the saurischian order, which comprises dinosaurs known for more lizard-like hip skeletons, as opposed to the more bird-like hips of ornithischians. Specifically, saurischian dinosaurs have pelvic, or hip, bones that are angled down and forward, like modern lizards, rather than down and back, like modern birds.

Fossil evidence for Datousaurus is sufficient to further classify the dinosaur as a member of the Sauropodomorpha suborder, whose herbivorous members are recognized as large, four-legged dinosaurs with long necks. Datousaurus can further be identified as a member of the Sauropoda infraorder. These large terrestrial dinosaurs thrived during the Middle and Late Jurassic periods (174–145 million years ago) and continued into the Cretaceous. They were also quadrupedal, with small heads relative to their long necks and large body.

Despite little fossil evidence, some experts have placed the Datousaurus in the family group Mamenchisauridae. Other experts, however, believe that not enough fossil evidence has been uncovered to assign Datousaurus to a specific family group. For this reason, they classify its family assignation as incertae sedis, meaning “of uncertain placement.” This phrase is used when a dinosaur cannot be appropriately placed within a particular taxonomic group or system.

Scientists may also use another classification system, called phylogenetic or cladistic classification. This system classifies animals in family trees, called cladograms, grouped by common ancestry. Each split in the tree creates a new group based on shared physical traits. Within this system, Datousaurus belongs to the Sauropoda clade, but it is uncertain along which further branches the dinosaur should fall.

Anatomy

Paleontologists must rely on two partial skeletons, both lacking skulls, to conduct anatomical studies of Datousaurus. Though some scientists believe a partial skull, primarily the jaw, belonging to Datousaurus has been unearthed, it is inconclusive and also yields limited data. Available fossil evidence suggests that Datousaurus possessed the large, four-legged body, including long neck and tail, of the sauropods. Datousaurus appears to have been much smaller than many of its contemporaries, including Shunosaurus, the fossils for which were found in the same excavation. It had fewer vertebrae than its larger relatives, and if the jaw is correctly identified, it had a characteristically small head with a smaller number of spoon-shaped, plant-eating teeth.

Dinosaurs have generally been regarded as cold-blooded animals, like modern lizards, though the term can be deceptive. Modern lizards are ectothermic, meaning that they rely on the sun to warm their bodies. Though science has traditionally held dinosaurs, specifically non-avian dinosaurs, to be ectothermic, evidence suggests that some might have been endothermic, meaning that they could heat their bodies from within by consuming food. Scientists continue to debate whether sauropods such as Datousaurus might have been ectotherms or endotherms, or something in between.

Intelligence

Slower-moving herbivores tend to fall lower on the EQ scale than their faster, carnivorous, predatory counterparts. The sauropods, with their vast bodies and small heads, are believed to have fallen on the lowest end of that scale. Sauropods, including Datousaurus, likely ranked around 0.2 on the EQ scale.

Reproduction and Population

Little is known about reproduction among sauropods such as Datousaurus. Existing evidence indicates that most (or all) dinosaurs were oviparous, like modern lizards and birds. This means that they reproduced by laying eggs. However, fossilized egg evidence is limited for sauropods. Only recent finds, begun in the 1980s, have uncovered embryonic sauropods and what are believed to be their associated eggshells. This evidence seems to confirm that at least some, if not all, sauropods were oviparous, though scientists continue to search for further fossil support.

Discoveries made in Argentina indicate that eggs were hidden beneath mounds of vegetation, likely to keep them warm and protect them from predators. Additional evidence must be uncovered to draw conclusions regarding the post-natal treatment of hatchlings. Many other plant-eating herd dinosaurs, such as hadrosaurs and ceratopsians, are believed to have stayed with and cared for their hatchlings for some time, but current fossil evidence is indeterminate for sauropods.

The large numbers of collective fossils finds for sauropods and their wide geographic distribution across six continents suggests that the dinosaurs ranged in great numbers. Scientists believe sauropods to have been one of the dominant species during the Jurassic period, though their numbers appear to have declined in the Cretaceous. However, limited fossil evidence exists for Datousaurus, which may mean that this particular species did not reach the numbers of its relatives.

Diet

Datousaurus and other sauropods were herbivores. Their vast body size indicates that they likely had to spend a great deal of their time eating, and they could not afford to be selective about the vegetation that they consumed. Scientists continue to debate the preferred posture of sauropods when feeding, but their long necks suggest that they were able to consume vegetation both high and low in a wide circumference. The Middle and Late Jurassic periods were dominated largely by ferns and gymnosperms, such as cycads and conifers; flowering plants, or angiosperms, did not appear until the Cretaceous, when the numbers of sauropods began to decline, being replaced by smaller herbivores such as hadrosaurs and ceratopsians.

Behavior

The few remains found for Datousaurus make it difficult to assess the social habits or behavior of the dinosaur. However, communal fossil beds for related sauropods and the discovery of many collectively assembled sauropod footprints suggest that some sauropods were social dinosaurs that moved in herds. Some evidence also suggests that sauropods might have moved in interspecies herds. Herd behavior is common among plant-eating dinosaurs, as it provides individual members of a group with additional defense against predators. Some scientists have suggested that the isolated finds for Datousaurus indicate that this particular species of sauropod might have been more solitary than many of its contemporary relatives. The wide geographic distribution of sauropods also suggests that they might have been migratory animals who moved from place to place in search of food.

Habitat and Other Life Forms

Datousaurus lived during the Middle Jurassic period in what is now China. At the time, however, its home was part of a changing landscape. For millions of years, the modern continents had formed one giant landmass, known as the supercontinent Pangaea. During the Late Triassic period, this giant landmass began the slow process of breaking apart into what would become two new supercontinents, Gondwana and Laurasia. With these tectonic shifts, the landscape and climate of the dinosaurs changed as well. Previously dry and arid lands become tropical and subtropical forests, jungles, and wetlands. New oceans emerged and vast areas of land likely flooded.

The Jurassic habitat was one rich with plant and animal life. The climate, including in China where Datousaurus and many other Jurassic fossils have been unearthed, was likely warm and humid much of the time. Lush, green forests of ferns, cycads, conifers, and other plant life covered much of the land, providing ample food for the large herbivores that thrived during this time. It was during this period that dinosaurs came to dominate the faunal landscape.

Fossil evidence from the Dashanpu Formation and other nearby regions reveals not only a large sauropod population, but also many other dinosaurs, including theropods, stegosaurs, pterosaurs, and ornithopods, as well as remains of fish and amphibians. Jurassic China was very diverse, and Datousaurus and other sauropods likely shared their habitat with many other herbivores. They were likely hunted or scavenged by carnivorous theropods and carnosaurs.

Research

Study of Datousaurus relies on the remains of two partial skeletons, without skulls, and on a set of jaws that is believed to have belonged to one of the skeletons. These finds were made by Dong Zhiming in an interval of the Dashanpu Formation, known as the Lower Shaximao Formation, near Sichuan, China. The discovery was made, along with that of thousands of other bones, during an excavation between 1979 and 1981. Dong identified these specific fossils as a new species, Datousaurus bashensis, in 1983. However, research based on the fossils is incomplete, and doubt remains as to whether the partial skull (jaw) belongs to one of the identified skeletons.

However, the Dashanpu Formation has yielded many other valuable finds, including numerous fossils evidencing a thriving sauropod community in the region. The same excavation also unearthed the remains of Shunosaurus lii, a contemporary sauropod of Datousaurus. The finds for Shunosaurus were much more numerous—twenty skeletons and five skulls—and the two dinosaurs may have been close relatives.

The very first sauropod discovery made was of a successor relative, Cetiosaurus conybeari, in 1841. English paleontologist Richard Owen studied two partial skeletons and later included them in a new group of reptiles he called “Dinosauria.”

Since the mid–nineteenth century, hundreds of fossil finds have been made for the sauropods on every continent except Antarctica. Additional finds from southern China include several species of Mamenchisaurus from the Late Jurassic, two species of Omeisaurus that were contemporary to Datousaurus, and the contemporary Abrosaurus. Shunosaurus, Mamenchisaurus and Omeisaurus have been classified as members of the Eusauropoda family, while Abrosaurus is identified as belonging to the Macronaria clade.

Bibliography

"Another Look at the Dinosaurs of the East Coast of America." Center for Functional Anatomy and Evolution, Johns Hopkins University School of Medicine, 2006, www.hopkinsmedicine.org/fae/DBWpdf/R88‗2006Weishampel.pdf. Accessed 2011.

Carpenter, Kenneth. Eggs, Nests, and Baby Dinosaurs. Indiana UP 1999.

Cox, Barry, et al. Simon & Schuster Encyclopedia of Dinosaurs & Prehistoric Creatures. Simon & Schuster, 1999.

"Datousaurus." Natural History Museum, www.nhm.ac.uk/discover/dino-directory/datousaurus.html. Accessed 5 May. 2020.

"Dinobase." University of Bristol, dinobase.gly.bris.ac.uk. Accessed 2011.

Jerison, H. J. “Brain Evolution and Dinosaur Brains.” American Naturalist, vol. 103, 1969, pp. 575–88.

"Paleportal." UC Museum of Paleontology, University of California, Berkeley, ucmp.berkeley.edu. Accessed 2011.

Richardson, Hazel. Dinosaurs and Prehistoric Life. DK Publishing, 2003.

Weishampel, David B., et al, editors. Dinosauria. University of California Press, 2007.

Wright, Rebekah A. "Were Dinosaurs Bird Brains." University of Arizona Geosciences, 2002, www.geo.arizona.edu/~rwriht/abs2002.html. Accessed 2011.

Zimmer, Carl. “Dinosaurs.” Discover, vol. 26, no. 4, 2005, pp. 32. Canadian Reference Centre , search.ebscohost.com/login.aspx?direct=true&db=rch&AN=16382092&site=eds-live. Accessed 5 May 2020.