Eardasaurus

Before formal naming or identification, this organism was known as the following on this wiki:
**OUMNH J.02247**

## Statistics

### Diet

Carnivorous

*Eardasaurus* is an extinct genus of pliosaur that lived in England during the Middle Jurassic.

## History

Eardasaurus was discovered in a gravel pit near Yarnton, Oxfordshire from the Oxford Clay Formation and was unnamed for many years. The holotype is OUMNH PAL-J.02247 (prev. OUMNH J.02247), decently complete cranium and postcranium. It derives from the Old English eard, meaning "home", "native soil" or "dwelling" and the traditional epithet meaning "lizard", based on the etymology of the village of Yarnton. The specific epithet is after H. Phillip Powell, who was a former Assistant Curator at the Oxford University Museum of Natural History. It was formally named by Ketchum and Benson (2022).

## Description

*Eardasaurus* is known from a partial atlas-axis complex, a skull, mandible and 56 postaxial vertebrae, 18 cervicals, 3 pectorals, 24 dorsals, 4 sacrals and 8 caudals. The centra, neural arches, cervicals and ribs are disarticulated. This may suggest that the holotype was immature, as these elements would have been fused if it was mature. The neurocentral sutures are often unfused in large thalassophoneans, however, which may suggest that this trait may not be reliable for determining age. The genus is differentiated by a maxilla with 34-35 alveoli (which is a large amount), "fluted" ornamentation at the jugal and squamosal and a "lacrimal" that is dorsoventrally slender and has a posterior rod-like projection, which are all autapomorphies. It is also differentiated from other pliosaurs by a suite of cranial and postcranial traits.

## Classification

A 2010 paper on *Peloneustes philarchus* taxonomy and cranial anatomy releases few information on OUMNH J.02247, which was then-unnamed. First, OUMNH J.02247 represents an unnamed taxon alongside NHMUK R2439 and BEDFM 1999.201 (now known as *Marmornectes*). These three, alongside *"Pliosaurus" andrewsi*, *Simolestes vorax* and *Kronosaurus queenslandicus*, are poorly-preserved, which leads to the region's hazy anatomical knowledge. The splenial somewhat encloses a foramen that is narrow at the dorsoventral that is dorsal to the angular's medial exposure. Between the angular, surangular, coronoid eminence and dentary, there is a wide opening, that penetrates the lateral mandibular surface. The latter is present in OUMNH J.02247 and *"Pliosaurus" andrewsi*. Hilary F. Ketchum and Roger B. J. Benson (2011), in the naming paper of *Marmornectes candrewi*, found the placement of pliosaurid taxa including OUMNH J.02247, reduced to genera:

In 2022, Ketchum and Benson formally named the taxon as Eardasaurus powelli. They recover it as in the "Middle Jurassic thalassophonean pliosaurid" grouping as slightly more derived than *Peloneustes*, and as a sister group to *"Pliosaurus" andrewsi*, *Simolestes*, *Pliosaurus* and brachauchenines. They recover:

## Paleobiology

Prominent apicobasal enamel ridges that extend to the distal crown surfaces form cutting ridges similar to carninae, which indicates enhanced cutting function that is often suggestive of a macropredatory diet. These are seen in many other groups and other pliosaurs as well, though rare for plesiosaurs. These are much finer than in *Liopleurodon* and *Makhaira* and have a very weak serration-like texture. The authors found these structures missing in some taxa and unreported in others. These suggest that this type of dental morphology is more widespread in pliosaurs, and possibly plesiosaurs as a whole .

## Paleoecology

At the time of naming, *Eardasaurus* would have been the sixth (or seventh is *Pachycostasaurus* is included) pliosaur known from the Oxford Clay Formation. It is known from the Middle Callovian *Kosmoceras jason* Zone of the Peterborough Member, Oxford Clay Formation. These pliosaurs include itself, *Pachycostasaurus*, *Liopleurodon*, *Marmornectes*, *Peloneustes*, *"Pliosaurus"* and *Simolestes*. Other plesiosaurs, cryptoclidids, are known from the formation. Pachycormiformes, ichthyosaurs and thalattosuchians swam the waters while dinosaurs such as iguanodons, stegosaurs, ankylosaurs, sauropods, megalosaurids, metriacanthosaurids and some ootaxa are known to have been terrestrial. The fish and invertebrate assemblage (cephalopods such as belemnites, gastropods and bivalves such as *Gryphaea*) is diverse.

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 https://www.app.pan.pl/archive/published/app67/app008872021.pdf
2. ↑ https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1475-4983.2011.01050.x
3. ↑ https://www.palass.org/publications/special-papers-palaeontology/archive/86/article\_pp109-129
4. ↑ https://en.wikipedia.org/wiki/Oxford\_Clay