| Sarcosaurus | |
|---|---|
 | |
| Skeletons of the known specimens ofSarcosaurus woodi (restored as a ceratosaur) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Neotheropoda |
| Genus: | †Sarcosaurus Andrews,1921 |
| Type species | |
| †Sarcosaurus woodi Andrews,1921 | |
| Synonyms | |
| |
Sarcosaurus (Latin:"flesh lizard") is agenus ofbasalneotheropoddinosaur, roughly 3.5 metres (11 ft) long. It lived in what is nowEngland and maybeIreland andScotland during theHettangian-Sinemurian stages of theEarly Jurassic, about 199-196 million years ago.Sarcosaurus is one of the earliest knownJurassic theropods, and one of only a handful of theropod genera from this time period. Along withDracoraptor hanigani it is one of the two described neotheropods from the lowermost Jurassic of theUnited Kingdom.[1]
Theholotype isNHMUK PV R4840 a partial skeleton that includes a posteriordorsal vertebra, partial left and rightilia, that are fused to the proximal portion of thepubis, lacking thefemoral head. The specimen shows some evidence of skeletal maturity, meaning it is not an early juvenile, but its exact ontogenetic stage cannot be ascertained.[1] Referred specimens include the non matureNHMUK PV R3542 (holotype ofSarcosaurus andrewsi) that includes a complete righttibia;WARMS G667–690, a partial skeleton of a single individual that includes posterior dorsal vertebra, middlecaudal vertebra, dorsalrib fragments, left ilium, right and left pubes,femora and tibiae, proximal end of leftfibula, probable distal half of fibula, distal portions ofmetatarsals IV, II or III proximal half of left pedalphalanx II-1, and three indeterminate bone fragments.[1][2]Sarcosaurus shares certain morphological conditions with otherneotheropods, includingLiliensternus liliensterni (collateral fossae of the metatarsal II with similar development and shape on both sides, larger ratio on the centrum) andDilophosaurus wetherilli (lateral collateral fossa is bigger than the medial one in the metatarsal, middle caudal series proportionately lower and narrower than the middle−posterior dorsal vertebra).Sarcosaurus was a bipedal predator, probably able to run fast and catch small prey. The holotype belonged to a 3.5-metre-long animal whose weight was no greater than 50–60 kg. NHMUK PV R3542 belonged to a larger animal, estimated to have had a maximum length of 5 m and a weight of 140 kg.[3]
Thefossils ofSarcosaurus were found in theLower Lias ofEngland. Thetype species,Sarcosaurus woodi, was first described byCharles William Andrews in 1921 shortly after a partial skeleton had been found by S.L. Wood nearBarrow-on-Soar, in theScunthorpe Mudstone. The generic name is derived from Greeksarx, "flesh". Thespecific name honours Wood. Theholotype,BMNH 4840/1, consists of apelvis, avertebra and the upper part of afemur. The preserved length of the femur is 31.5 centimetres (12.4 in).[4] A second species,Sarcosaurus andrewsi, was named byFriedrich von Huene in 1932,[5] based on a 445-millimetre (17.5 in)tibia, BMNH R3542, described byArthur Smith Woodward in 1908 and found nearWilmcote.[6] Confusingly von Huene in the same publication named the very same fossilMagnosaurus woodwardi. Later he made a choice forS. andrewsi to be the valid name.[7] Huene also discussed WARMS G667–690, a partial skeleton also from Wilmcote, both specimens are from theBlue Lias. In 1974S. andrewsi was reclassified asMegalosaurus andrewsi byMichael Waldman, on the probably erroneous assumption it was amegalosaurid.[8] A later study concluded the two species to be indistinguishable except for size, but other authors consider any identity to be unprovable as there are no comparable remains and conclude both species to lackautapomorphies and therefore to benomina dubia.[9] Von Huene in 1932 referred a partial skeleton from the collection of theWarwick Museum toS. woodi but the identity was unproven; in 1995 it was given the informal name "Liassaurus"[10] but this has remained anomen nudum. The specimen is likely one individual, located in the same stratiagraphic position as the holotypic specimen. Unfortunately, there are few available overlapping elements from the specimen and the holotype. Both specimens preserve a relatively complete femur: however, the features of both (an anteromedially directed head, a relatively long fourthtrochanter and a trochanteric shelf) are plesiomorphic and thus do not indicate conspecifity or clade membership. It is noted, however, that there are no features which are present in one specimen but not the other. In 2020 WARMS G667–690 was given a comprehensive redescription, which proposed that all three specimens belonged to the same species,Sarcosaurus woodi.[1]
Between the years 1980 and 2000, three fossils were discovered on a beach nearThe Gobbins inNorthern Ireland by palaeontologist Roger Byrne. Exact geologic provenance is not reported for any of the specimens, but the very dark colouration of the specimens indicate (through means of comparison to marine fossils in other Northern Irish localities) they hail fromLias Group rocks, likely from either the Planorbis Zone or the Pre-planorbis Zone of theWaterloo Mudstone Formation. Along with specimens referred to as an indeterminatedinosaur (previously referred toScelidosaurus), a tibia was recovered,BELUM K12493, referred to an indeterminateneotheropod, probably related toSarcosaurus or from an indeterminate megalosauroid. The indeterminate dinosaur femur and theropod tibia are the only known remains of dinosaurs fromIreland, which has a poor Mesozoic fossil record entirely consisting of marine localities, and the indeterminate dinosaur specimen was the first ever reported from the island.[11]
In 2023, a partial theropod specimen recovered from the lower SinemurianBroadford Beds Formation of theIsle of Skye, previously referred to a Coelophysoid-grade theropod, was reclassified as Cf.Sarcosaurus, clading withTachiraptor as a branch leading to Averostra. This specimen,NMS G.1994.10.1, consists on an isolated left tibia lacking its proximal region.[12]
Andrews originally assignedSarcosaurus to theMegalosauridae. The first to suggest a morebasal position wasSamuel Paul Welles who placed it in theCoelophysidae.[13] Later analyses resulted in either a position in theCeratosauria,[14] or in theCoelophysoidea.[15] Ezcurra (2012) foundSarcosaurus to be the most basal ceratosaur in a large unpublished analysis.[16] In 2018, Andrea Cau in the large analysis ofSaltriovenator foundSarcosaurus to be adilophosaurid with good amount of support in the data.[17] In 2020, Ezcurraet al. recoveredSarcosaurus as a close relative ofAverostra due to the presence of shared characters including an anteroventrally oriented ventral margin of the preacetabular process in lateral view on theilium and afemur with a poorly posteriorly developed fourth trochanter. Their cladogram is shown below:[1] A latter work reinforced that clade made ofSarcosaurus woodi + (Tachiraptor admirabilis + Averostra).[12]
Theholotype specimen was collected from strata (bucklandi zone,Sinemurian) that were deposited in epicontinental, shallow, marine settings affected by sea-level fluctuations and a warm, predominantly humid climate.[18] In south-westernWarwickshire, is represented by the upper part of theRugby Limestone Member (Hettangian-Sinemurian) of theBlue Lias Formation with typical lithofacies of alternatingmudrocks and generally fine-grained and frequently highly fossiliferouslimestones.[19] The Rugby Limestone Member wasdeposited at a palaeolatitude of approximately 35° N in a storm-influenced offshore setting.[20]Wilmcote was related to the eastern margin of theWorcester Graben during theEarly Jurassic and adjacent to theEast Midlands Shelf.[21] The western margin of the emergentLondon Platform at 60–80 km to the south-east was probably the principal source of terrestrial biodebris.[22]
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