Thecodontosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Thecodontosauridae

Genus:Thecodontosaurus

Species:Thecodontosaurus antiquus

Introduction

Thecodontosaurus was a small herbivorous dinosaur living in Late Triassic Europe. An early relative of the giant sauropods like Brachiosaurus, Thecodontosaurus and its close relatives were much smaller in size and lived alongside the last members of the prehistoric reptile lineage that dominated the terrestrial environment since the Permian period (roughly 299–251 million years ago), the last period of the Paleozoic era. It is one of the earliest named dinosaurs.

In the Triassic period, the continents of the world were united in a single land mass known as Pangaea. The northern and southern portions of the world were partially divided by an encroaching inland sea, known as the Tethys Seaway. Pangaea split due to tectonic movement in the Jurassic and Cretaceous periods, giving rise to northern and southern supercontinents.

As the continents split in the Jurassic, species on either side further diverged into characteristic southern and northern lineages. Ancestors of Thecodontosaurus appeared in both the southern and northern hemispheres, indicating that the species radiated while the continents were still joined by a terrestrial bridge.

Classification

According to taxonomic analysis, Thecodontosaurus belongs in the order Saurischia because of the “lizard-like” structure of its hips. From there, the species is placed in the suborder Sauropodomorpha, represented by herbivores with elongated necks and smaller heads. It is then placed into the family Thecodontosauridae, which were small, bipedal sauropodomorphs with leaf-shaped teeth. Thecodontosaurus is also sometimes placed in the Prosauropoda infraorder, a group of long-necked, small-skulled dinosaurs that were originally believed to be the ancestors of sauropods.

Cladistic analysis places Thecodontosaurus into the clade Saurpodomorpha, defined by elongated necks and smaller heads. Thecodontosaurus is considered one of the basal sauropodomorphs, a group of ancestor species that developed into a variety of species before splitting into the advanced sauropods of the Jurassic.

Anatomy

Thecodontosaurus was a small dinosaur, reaching between 1 to 1.2 meters (3.2–3.9 ft) and standing roughly 30 centimeters (12 in) at the hip. Paleontologists estimate that the animal may have weighted between 30 and 35 kilograms (66–77 lbs). Thecodontosaurus was lightly built and bipedal, whereas later members of the sauropod group would evolve into obligate quadrupedal animals.

Thecodontosaurus had five toes on both its feet and hands, with blunt, hoof-like claws on its rear feet. The animal had a relatively large head and a flexible, small neck. Thecodontosaurus had large eyes, giving it a wide field of vision, and its mouth was filled with leaf-shaped teeth to strip vegetation from low-lying plants.

Given its size and the habitat in which fossils have been discovered, Thecodontosaurus might have been cryptically colored, allowing the animal to blend in with surrounding vegetation. Paleontologists have not discovered impressions of the animal's skin, but it is likely that Thecodontosaurus was covered in fine, mosaic scales.

Intelligence

Paleontologist James A. Hopson used the ratio of brain to body mass, called the encephalization quotient (EQ), to estimate the intelligence of several groups of dinosaurs. Hopson's findings indicate that most dinosaurs fell into the range of 0.1 to 2.0 on a scale with an upper limit of 8.0, the value roughly calculated for the human brain. Dinosaurs were less intelligent, on average, than modern mammals or birds living similar lifestyles.

Although no direct EQ measurements have been calculated for Thecodontosaurus, the sauropods in general had among the lowest EQ ratings of all the dinosaurs. Thecodontosaurus had a larger skull, relative to body size, than many of the later sauropods and may have had a correspondingly higher EQ. The giant sauropods of the Jurassic relied on size and strength for defense, thereby reducing the need for advanced intelligence.

Reproduction and Population

No eggs or juvenile specimens have been found for Thecodontosauru,s and paleontologists are uncertain about the animal's reproductive behavior. Paleontologists have discovered eggs for other sauropod species, and Thecodontosaurus most likely laid eggs as well.

Later sauropods, because of their size, probably buried their eggs in vegetation for protection from weather and predators; Thecodontosaurus may have displayed similar behavior.

Diet

Examinations of the animal's dentition indicate that Thecodontosaurus was an obligate herbivore, using its leaf-shaped teeth to strip leaves and stems from plants. The Late Triassic environment in Europe supported a wide variety of plants, most of which were members of the gymnosperm variety.

In addition to ancestral conifer species like Voltziaceae, there were a variety of cycad species, which are palm-like plants that became dominant in the Jurassic. Another common variety of plants commonly called horsetails also grew into bush-like varieties and may have provided food for small herbivores like Thecodontosaurus.

Behavior

Paleontologists have uncovered evidence suggesting that some species of sauropods in the Jurassic period lived or traveled in social groups. Herding behavior is advantageous to herbivores, as it provides added protection from predators. Thecodontosaurus is known only from isolated specimens, but it is possible that the social behavior observed for sauropods evolved among their ancestors in the Triassic.

Thecodontosaurus was partially bi-pedal, likely using its rear legs for speed when trying to evade predators. The front legs were also strong and the animal likely used all four legs when moving slowly.

Habitat and Other Life Forms

The global environment was warmer than the modern period during most of the Triassic and sea levels remained low. Conifers and cycads dominated the tall plant species across the world.

There were a wide variety of small reptiles and amphibians in Late Triassic Europe, in addition to a few lineages of the dicynodonts, or “mammal-like” reptiles that were among the dominant terrestrial animals throughout the Permian and Triassic periods.

The sauropodomorphs were one of the largest herbivore groupings in the Late Triassic and, by the Early Jurassic, became the largest herbivore lineage in the world. In addition to Thecodontosaurus, a variety of sauropodomorph species lived in Triassic Europe, including Plateosaurus and Ruehleia. Other groups of reptiles were also developing during this time, including one of the first known turtles, Proganochelys.

Predatory animals in late Triassic Europe included a few theropod predators, like Saltopus and Velocipes.

As the dinosaurs were evolving into a variety of species, the first crocodilian ancestors also radiated during this time, producing both aquatic and terrestrial predator species. Saltoposuchus was one of the crocodilian predators that lived alongside the sauropodomorphs.

Recent research also suggests that Thecodontosaurus's habitat may have been tropical islands, with lush vegetation, rather than dry uplands that were arid in nature, as originally thought.

Based on this research, it has been further suggested that because of its island inhabitation, Thecodontosaurus may have, in fact, been a dwarfed version of another dinosaur, Plateosaurus.

Research

Thecodontosaurus fossils were first found in Bristol, England, in 1836, with additional contributions in 1890. The type species, T. antiquus, was established in 1843. (It was, in fact, one of the earliest-named dinosaurs.) The early specimens of Thecodontosaurus were lost after World War II—the remains were largely destroyed by German bombing raids over Britain—but specimens (a partial juvenile skeleton) were later recovered in other European fossil beds. It is widely held, however, that this newly discovered dinosaur, Thecodontosaurus caducus (2003), may be claimed a different kind of dinosaur altogether, called Pantydraco. Revisions to the Sauropodomorpha group have been furthered by discoveries of new Thecodontosaurus specimens, comprising at least 13 partial skeletons, discovered between 1836 and 2007.

Bibliography

Books:

Briggs, Derek E. G., and Peter R. Crowther. Paleobiology II. Wiley-Blackwell, 2001.

Carpenter, Kenneth. Eggs, Nests and Baby Dinosaurs: A Look at Dinosaur Reproduction. Indiana UP, 1999.

Chinsamay-turan, Anusuya. Microstructure of Dinosaur Bone: Deciphering Biology with Fine-Scale Techniques. Johns Hopkins UP, 2005.

Fastovsky, David E., and David B. Weishampel. Dinosaurs: A Concise Natural History. Cambridge UP, 2009.

Fastovsky, David E., and David B. Weishampel. Evolution and Extinction of the Dinosaurs. Cambridge UP, 2005.

Horner, Jack, and James Gorman. How to Build a Dinosaur: Extinction Doesn’t Have to Be Forever. Dutton, 2009.

Horner, John R., and Edwin Dobb. Dinosaur Lives. Mariner Books, 1998.

"Introduction to Psrosauropods." University of California, Berkeley, www.ucmp.berkeley.edu/diapsids/ saurischia/prosauropods.html. Accessed 8 May 2020.

Lucas, Spencer G. Dinosaurs: The Textbook. 2nd ed., McGraw Hill, 2004.

Mannion, Philip D., and Paul Upchurch. “Completeness Metrics and the Quality of the Sauropodomorph Fossil Record through Geological and Historical Time.” Paleobiology, vol. 36, 2010, pp. 283–302.

Martin, Anthony J. Introduction to the Study of Dinosaurs. 4th ed., Blackwell, 2006.

Naish, Darren, and David M. Martill. “Dinosaurs of Great Britain and the Role of the Geological Society of London in their Discovery: Basal Dinosauria and Saurischia.” Journal of the Geological Society, vol. 164, 2007, pp. 493–510.

Skawiński, Tomasz. "A Re-Evaluation of the Historical 'Dinosaur' Remains from the Middle-Upper Triassic of Poland." Historical Biology, vol. 29, no. 4, June 2017, pp. 442–472. Academic Search Complete, search.ebscohost.com/login.aspx?direct=true&db=a9h&AN=121235081&site=eds-live. Accessed 8 May. 2020.

Weishampel, David B., Dodson, Peter, and Halszka Osmolska. Dinosauria. 3rd ed., University of California Press, 2007.

Wedel, Mathew J. “Vertebral Pneumaticity, Air Sacs, and the Physiology of Sauropod Dinosaurs.” Paleobiology, vol. 29, 2003, pp. 243–55.