Sarcosaurus

Pelvis and parts of femur and dorsal vertebra

The holotype is NHMUK PV R4840 that includes a posterior dorsal vertebra, partial left and right ilia, that are fused to the proximal portion of the pubis, lacking the femoral head. This specimen shows indicators of maturity, altrought it´s ontogenetic stage cannot be constrained.[1] Referred specimens include the non mature NHMUK PV R3542 (holotype of "Sarcosaurus andrewsi") that includes a complete right tibia; WARMS G667–690, a partial skeleton of a single individual that includes posterior dorsal vertebra, middle caudal vertebra, dorsal rib fragments, left ilium, right and left pubes, femora and tibiae, proximal end of left fibula, probable distal half of fibula, distal portions of metatarsals IV, II or III proximal half of left pedal phalanx II-1, and three indeterminate bone fragments.[1][2] Sarcosaurus has different morphological convergences with other Neotheropods, such as Liliensternus liliensterni (collateral fossae of the metatarsal II with similar development and shape on both sides, larger ratio on the centrum) Dilophosaurus 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 a catch small prey. The holotype belonged to a 3.5 m long animal whose weigth wasn´t beyond 50-60 Kg. The referred Sarcosaurus andrewsi belongs to a larger animal, whose maximun estimate has been 5 m long and a weigth of 140 Kg.[3]

The Fossils of Sarcosaurus were found in the Lower Lias of England. The type species, Sarcosaurus woodi, was first described by Charles William Andrews in 1921 shortly after a partial skeleton had been found by S.L. Wood near Barrow-on-Soar. The generic name is derived from Greek sarx, "flesh". The specific name honours Wood. The holotype, BMNH 4840/1, consists of a pelvis, a vertebra and the upper part of a femur. The preserved length of the femur is 31.5 centimetres (12.4 in).[4] A second species, Sarcosaurus andrewsi, was named by Friedrich von Huene in 1932,[5] based on a 445 millimetres (17.5 in) tibia, BMNH R3542, described by Arthur Smith Woodward in 1908 and found near Wilmcote.[6] Confusingly von Huene in the same publication named the very same fossil Magnosaurus woodwardi. Later he made a choice for S. andrewsi to be the valid name.[7] In 1974 S. andrewsi was reclassified as Megalosaurus andrewsi by Michael Waldman, on the probably erroneous assumption it was a megalosaurid.[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 lack autapomorphies and therefore to be nomina dubia.[9] Von Huene in 1932 referred a partial skeleton from the collection of the Warwick Museum to S. woodi but the identity is unproven; in 1995 it was given the generic name "Liassaurus"[10] but this has remained a nomen 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 fourth trochanter 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.

Andrews originally assigned Sarcosaurus to the Megalosauridae. The first to suggest a more basal position was Samuel Paul Welles who placed it in the Coelophysidae.[11] Later analyses resulted in either a position in the Ceratosauria,[12] or in the Coelophysoidea.[13] Ezcurra (2012) found Sarcosaurus to be the most basal ceratosaur in a large unpublished analysis.[14]. In 2018, Andrea Cau in the large analysis of Saltriovenator found Sarcosaurus to be a dilophosaurid with good amount of support in the data.[15] Finally, on 2020 Ezcurra et al. recovered all the specimens assigned to the genus on a single species, Sarcosaurus woodi, and was recovered as one of the most immediate sister-taxa to Averostra due to synapomorphies like anteroventrally oriented ventral margin of the preacetabular process in lateral view on the illium, femur with poorly posteriorly developed fourth trochanter, etc.[1] It was also recovered as the nearest taxon to the also lower liassic Tachiraptor admirabilis, both on lineage leading to Averostra. Phylogenetic relationships where left as:

Holotype 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.[16] In south-western Warwickshire is represented by the upper part of the Rugby Limestone Member (Hettangian-Sinemurian) of the Blue Lias Formation . with typhical lithofacies of alternating mudrocks and generally fine-grained and frequently highly fossiliferous limestones.[17] the Rugby Limestone Member was deposited at a palaeolatitude of approximately 35° N in a storm-influenced offshore setting.[18] Wilmcote was related to the eastern margin of the Worcester Graben during the Early Jurassic and adjacent to the East Midlands Shelf.[19] The western margin of the emergent London Platform at 60−80 km to the south-east was probably the principle source of terrestrial biodebris.[20]

• Timeline of coelophysoid research

• Liassaurus

• Sarcosaurus in the Dino Directory