Stokesosaurus

*Stokesosaurus clevelandi*

***Stokesosaurus*** (meaning "Stokes' lizard") is a genus of small (around 3 to 4 meters in length) early tyrannosaur from the Late Jurassic period of Utah and England. It was named after Utah geologist William Lee Stokes. Remains possibly referable to *Stokesosaurus* have been recovered from stratigraphic zone 2. of the Morrison Formation.

## History

From 1960 onwards Utah geologist William Lee Stokes and his assistant James H. Madsen excavated thousands of disarticulated *Allosaurus* bones at the Cleveland-Lloyd Dinosaur Quarry in Emery County, Utah. During the early 1970s Madsen began to catalogue these finds in detail, discovering that some remains represented species new to science. In 1974 Madsen named and described the type species *S. clevelandi*. Its generic name honors Stokes. The specific name refers to the town of Cleveland, Utah, near where it was found.

The holotype (UUVP 2938) consists of a hip bone, originally thought to belong to the possible early tyrannosaur *Iliosuchus*, as well as several vertebrae and a partial braincase. Another ilium referred to this dinosaur is lost but may actually belong to the related *Aviatyrannis*, and a premaxilla thought to belong to *Iliosuchus* is actually from *Tanycolagreus*.

A second species, *Stokesosaurus langhami*, was described by Roger Benson in 2008 based on a partial skeleton. The skeleton consists of an "associated partial skeleton represented by a complete pelvis" as well as a partially complete leg, and neck, back, and tail vertebrae. This second skeleton was discovered in 1984 in Dorset, was mentioned in several papers, but was not formally described until 2008. The new species was named in honor of Peter Langham, who collected the specimen. The new specimen was discovered in strata dating from the Tithonian, the final stage of the Late Jurassic, meaning the fossil is around 150 million years old.

*Stokesosaurus* and *Tanycolagreus* are about the same size, and it is possible that the latter is a junior synonym of the former. However, the ilium (the best known element of *Stokesosaurus*) of *Tanycolagreus* has never been recovered, making direct comparison difficult.

## Classification

In 1974 Madsen assigned *Stokesosaurus* to the Tyrannosauridae. However, modern cladistic analyses indicate a more basal position. In 2012 the study by Brusatte and Benson recovered *Stokesosaurus* as a basal member of the Tyrannosauroidea, and closely related to *Eotyrannus* and *Juratyrant*.

## Paleoecology

### Habitat

The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, ranges between 156.3 million years old (Ma) at its base, to 146.8 million years old at the top, which places it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels and floodplains.[18] This formation is similar in age to the Solnhofen Limestone Formation in Germany and the Tendaguru Formation in Tanzania. In 1877 this formation became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope.

### Paleofauna

The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs such as *Camarasaurus*, *Barosaurus*, *Diplodocus*, *Apatosaurus* and *Brachiosaurus*. Dinosaurs that lived alongside *Stokesosaurus* included the herbivorous ornithischians *Camptosaurus*, *Dryosaurus*, *Stegosaurus* and *Othnielosaurus*. Predators in this paleoenvironment included the theropods *Saurophaganax*, *Torvosaurus*, *Ceratosaurus*, *Marshosaurus*, *Ornitholestes* and[19] *Allosaurus*, which accounting for 70 to 75% of theropod specimens and was at the top trophic level of the Morrison food web. Other animals that shared this paleoenvironment included bivalves, snails, ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphans, and several species of pterosaur. Examples of early mammals present in this region, were docodonts, multituberculates, symmetrodonts, and triconodonts. The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests of tree ferns, and fern (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer *Brachyphyllum*.

## JPInstitute.com Description

Stokesosaurus may have been the first member of the family that included T. rex. Very few bones of this dinosaur have been found and they don't seem to match up with the other meat-eating dinosaurs that lived at the same time and place. It lived with the much larger Allosaurus and would have had to compete with it for food.

Known only from a few bones, this dinosaur provides tantalizing clues to the possible evolution of the tyrannosaur lineage. Discovered in the famous Cleveland-Lloyd quarry, scientists hope to find more of this creature among the many thousands of fossils discovered this bone bed. Until the discovery of a braincase, it was thought that Stokesosaurusmight have belonged to the ceratosaurs.

## Links

https://web.archive.org/web/20030405114802/http://www.jpinstitute.com/dinopedia/dinocards/dc\_stoke.html

## References

1. ↑ 1.0 1.1 Template:Cite journal
2. ↑ Foster, J. (2007). "Appendix." *Jurassic West: The Dinosaurs of the Morrison Formation and Their World*. Indiana University Press. pp. 327-329.
3. ↑ Template:Cite journal
4. ↑ Template:Cite journal
5. ↑ Template:Cite journal
6. ↑ 6.0 6.1 Benson, R.B.J. (2008). "New information on *Stokesosaurus*, a tyrannosauroid (Dinosauria: Theropoda) from North America and the United Kingdom." *Journal of Vertebrate Paleontology*, **28**(3):732-750. doi: 10.1671/0272-4634(2008)28[732:NIOSAT]2.0.CO;2.
7. ↑ Foster, J. (2007). *Jurassic West: The Dinosaurs of the Morrison Formation and Their World*. Indiana University Press. 389pp.