| Eotyrannus | |
|---|---|
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| Known skeletal elements | |
 | |
| Skeletal diagram | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Tyrannoraptora |
| Superfamily: | †Tyrannosauroidea |
| Clade: | †Pantyrannosauria |
| Genus: | †Eotyrannus Huttet al., 2001 |
| Species: | †E. lengi |
| Binomial name | |
| †Eotyrannus lengi Huttet al., 2001 | |
| Synonyms | |
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Eotyrannus (meaning "dawn tyrant") is agenus oftyrannosauroidtheropoddinosaur hailing from theEarly CretaceousWessex Formation beds, included inWealden Group, located in the southwest coast of theIsle of Wight,United Kingdom. The remains (MIWG1997.550), consisting of assorted skull, axial skeleton and appendicular skeleton elements, from a juvenile or subadult, found in a plant debris clay bed, were described by Huttet al. in early 2001.[1] The etymology of the generic name refers to the animal's classification as an early tyrannosaur or "tyrant lizard", while the specific name honors the discoverer of the fossil.
The exact location of the discovery of theholotype specimen has not been revealed due to its importance and the possibility of new material to be collected as the coastline recedes. From what is mentioned in the description, the specimen was found on the southwestern coast of the Isle of Wight, betweenAtherfield Point andHanover Point. In 1995, local collector Gavin Leng brought a claw he had found along the coastline to Steve Hutt who worked at the old Museum of Isle of Wight Geology atSandown. Gavin Leng revealed the location of where the claw was discovered, and over the next few weeks the site was carefully excavated, and the fossils removed in a hard matrix. Over the next few years the specimen was carefully researched with scientists from theUniversity of Portsmouth, and with help from theNatural History Museum.[2]
Eventually in 2001,Eotyrannus was given its name along with its specific epithet in honour of Mr. Leng.[1] The material was described briefly in 2001 by Hutt et al. In July 2018Darren Naish, a colleague of Hutt who helped produce the preliminary description, created aGoFundMe fundraiser in order to release a monograph of the specimen, which received well over its goal.[3] The monograph was eventually published in the journalPeerJ in 2022.[3]
A number of characters present in the holotypic specimen are unique to the genus. These include: Therostral end of dentary possessing a concave notch housing the mostmesial alveolus and a dorsally-directed prong on the rostromesial margin of the notch, curving lateral furrows on the lateral surface of the dentary, a surangular with a hypertrophied gutter-like concavity near the rostrodorsal border, with the caudal end of the concavity containingforamina that perforate the body of the surangular, a low coronoid process on the surangular with a concave area located caudodorsally, and an ulna and radius with a tear-drop shaped cross-section at the mid-shaft.[3]
The holotypic specimen was disarticulated prior to fossilisation, with many elements of its skeleton scattered throughout the assemblage: none of the vertebral column is preserved in articulation and those vertebrae that are preserved consist of separated neural arches and centra, signifying that the holotype was an immature individual.
Due to the relative low-quality preservation of many of the skeletal elements, numerous pieces discovered have been difficult to identify: these include unidentifiedcranial elements, as well as an “ulna” which has since been recognised as thedistal part of thetibia. Before the proper identification of this fragment,Eotyrannus was reconstructed with much longer tibiae, which influenced the early reconstructions of the animal.
Many of the characters also presented as unique to the genus in the diagnosis of Hutt et al. (2001) are in fact widespread throughoutTyrannosauroidea, for example the presence of 'serrated carinae on D-shaped premaxillary teeth' is far from unique toE. lengi. Furthermore, neither the presence of a laterally flattened rostral region to themaxilla nor a pronounced rim to theantorbital fossa are unique to the genus.[4]
Although the specimen itself measures up to 4.5 m (15 ft) in length, it doesn't represent the size of an adult; the specimen likely belongs to a subadult due to the lack of fusion regarding the neurocentral and sacral sutures.[3]
The discovery ofEotyrannus corroborates the notion that early tyrannosauroids were gracile with long forelimbs and three-fingered grasping hands, although the somewhat large size of the animal either means that early evolution for this clade was carried out at a large size orEotyrannus developed large size independently.[5] The find of this animal in Europe puts in question to the purported Asian origin for these animals along withNorth AmericanStokesosaurus andEuropeanAviatyrannis arguing for a more complex biogeography for tyrannosauroids.[6]
Below is a cladogram by Loewenet al. in 2013 that includes most tyrannosauroid genera.[6]
A 2014 analysis foundEotyrannus to be amegaraptoran closely related to taxa likeMegaraptor.[7]
The 2022 osteology by Naish and Cau by comparison, classifiesEotyrannus as an intermediate gracile tyrannosauroid more closely related to the true tyrannosaurids; more advanced than proceratosaurids, stokesosaurids andYutyrannus, but without the characteristics of more advanced genera. Simultaneously, the description ofEotyrannus' placement in the family suggests that Megaraptora are tyrannosauroids as well, even though it was found thatEotyrannus is not a megaraptoran itself according to the authors' research, with Megaraptora representing a second wave of large-bodied tyrannosauroids that were important members of the world's ecosystem, one that may have originally slowed the evolutionary radiation of tyrannosaurids initially.[3]
In 2024, Andrea Cau recoveredEotyrannus as a sister taxon ofProceratosauridae, distant in relation fromMegaraptora.[8]
TheWessex Formation, whereEotyrannus was found, was considered to have been warm and humid, similar to the present-dayMediterranean. However, there is evidence of a phase of increasing aridity during the lateBarremian to earlyAptian whenEotyrannus lived. In theWessex Basin, sedimentological evidence, as well as fossils such as mud-cracks, suggests that the area experienced a warm, equablepaleoclimate with a mean annual temperature of 20–25 °C with low seasonal rainfall. Watson and Alvin (1996) and Allen (1998) showed that theWessex Formation flora was both fire and drought resistant and suggested that it was adapted to a seasonal climate with periods of marked aridity. Evidence for a wet season is provided by the frequent occurrence of fungal decay in plant material from the plant debris beds.[9]
TheWessex Formation possessed a wide array of fauna, including many other dinosaurs such as thecarcharodontosaurianNeovenator, thecompsognathidAristosuchus; the medium sizespinosauridsRiparovenator andCeratosuchops; the basalneornithischianHypsilophodon; the ornithopodsIguanodon,Mantellisaurus,Brighstoneus, andValdosaurus; the sauropodsOrnithopsis,Eucamerotus, andIuticosaurus; and theankylosaurPolacanthus. There were many contemporary mammal species whichEotyrannus likely fed on, including thespalacotheriidYaverlestes and theeobaataridEobaatar.[citation needed]
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