Eotyrannus

Credit: Van Johnson-Ransom on DeviantArt.

*Eotyrannus* is an extinct genus of tyrannosauroid theropod dinosaur lived in the Isle of Wight during the Early Cretaceous.

## History

The discovery location of the holotype is not revealed since it has the possibility to provide future fossil material (later revealed to be a site called Grange Chine, Grange CHine Sandstone from plant debris bed L11), though the original description says it was found on the southwestern coast of the Isle of Wight between Atherfield and Hanover Points. In 1995, collector Gavin Leng brought a claw to Steve Hutt, disclosing the discovery location and having it carefully excavated within the next few weeks. It was prepared for the next few years and published by Hutt et al. (2001). *Eotyrannus* means 'dawn tyrant', with the specific epithet after Leng. Darren Naish and Andrea Cau created a GoFundMe in order to author a monograph of the genus, which released in 2022. The holotype is IWCMS: 1997.550 (prev. MIWG1997.550), crania, cerivals, dorsals, sacrals, scapulocoracoid, rib fragments, parts of the ilium and much of the fore- and hindlimbs.

## Description

IWCMS: 1997.550 (crania, axial skeleton and appendicular elements) is a juvenile or subadult about 4.5 meters long and around 91-227 kilograms; it is the holotype. It was found in a plant debris clay bed and described by Hutt et al. (2001). The holotype was disarticulated, and many elements were scattered. None of the vertebrae were articulated, and the neural arches were split from the centra. This splitting is a natural trait suggesting this individual was immature. It was found many of the diagnosing features were common to Tyrannosauroidea (such as serrated carinae on D-shaped premaxillary teeth, a rim on the antorbital fossa and a laterally-flattened rostrum). This low-quality preservation makes identification difficult. This has led to some crania and an "ulna" being confused; the "ulna" was the distal portion of the tibia. These have influenced early paleoart of *Eotyrannus*. Ornithopod remains were found alongside the holotype.

It bears a scapulocoracoid that is tyrannosaurid-like, long-handed with gracile distal hindlimbs, had nasals that are thickened, fused and pneumatic, a premaxilla with a steep anterior border, a tyrannosaurid-like quadrate, U-shaped premaxillary teeth in cross section and a shorter preantorbital ramus. This demonstrates that *E. lengi* was not a longirostrine, suggesting that this trait is a distinct evolutionary style in tyrannosauroids, not making it a synapomorphy. This indicates that the clade was not always specialized for robust bone-crushing snouts. Strange curving furrows on the lateral of the dentary, a large and block-like humeral entepicondyle and a tibia with a distoproximally-aligned channel that is laterally positioned on the distal are all autapomorphies of *Eotyrannus*. The femur, pubis, ischium and most of the caudal skeleton are not preserved.

## Classification

Naish and Cau (2022) find that no theropods from the Wesex can be subsumed into *Eotyrannus*, although the fragmentary holotype renders this uncertain. It was mid-sized as all basal tyrannosaurs, being ~4.5 meters long. They confirm Hutt et al. (2001)'s suggestions that it is a non-tyrannosaurid tyrannosauroid, being one of the closest known of these basal genera to those who clade with Tyrannosauridae. They also suggest megaraptorans are affiliated with tyrannosauroids as often postulated, resolving them as a second wave of large tyrannosauroids that highlights the diversity of Tyrannosauroidea. Two overlapping characters of the ilia in *Eotyrannus* and *Juratyrant* (posterodorsally-inclined vertical ridge and the vertical ridge terminating before reaching the dorsal margin) are peculiar because the two are not closely related. Naish and Cau (2022) find:

## Paleoecology

The Wessex was very warm and humid, comparable to the present Mediterranean. An aridity phase in the Late Barremian and Early Aptian, where Eotyrannus is reported, is found, however. Sedimontology suggests a warm and equable paleoclimate with a mean annual temperature of 20-25° Celsius with low seasonal rainfall. Watson and Alvin (1996) and Allen (1998) postulate that the Wessex flora was fire and drought resistant, suggesting adaptation to a seasonal climate with marked aridity. A wet season is evidenced by frequent fungal decay in plants from plant debris beds. It coexisted with *Neovenator*, *Aristosuchus*, *Riparovenator*, *Ceratosuchops*, *Hypsilophodon*, *Iguanodon*, *Mantellisaurus*, *Brighstoneus*, *Valdosaurus*, *Ornithopsis*, *Eucameratus*, *Iuticosaurus*, *Polacanthus* and others. *Eotyrannus* likely fed on *Yaverlestes* and *Eobataar*.

## References

1. ↑ https://www.sciencedirect.com/science/article/abs/pii/S0195667101902526?via%3Dihub
2. ↑ https://www.nhm.ac.uk/discover/dino-directory/eotyrannus.html
3. ↑ https://australian.museum/learn/dinosaurs/fact-sheets/eotyrannus-lengi/
4. ↑ 4.0 4.1 4.2 4.3 https://peerj.com/articles/12727/
5. ↑ 5.0 5.1 https://en.wikipedia.org/wiki/Eotyrannus
6. ↑ https://www.sciencedirect.com/science/article/abs/pii/S0195667101902526?via%3Dihub
7. ↑ https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429784
8. ↑ https://twitter.com/NHMdinolab/status/1487110460264615945
9. ↑ https://twitter.com/NHMdinolab/status/1487113337888456704