| Astrophocaudia | |
|---|---|
 | |
| Caudal vertebra ofAstrophocaudia (SMU 61732) | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Clade: | †Somphospondyli |
| Genus: | †Astrophocaudia D’Emic,2012 |
| Type species | |
| †Astrophocaudia slaughteri D’Emic, 2012 | |
Astrophocaudia is anextinctgenus ofsomphospondylansauropod known from the later part of theEarly Cretaceous (Albian stage) ofTexas, United States. Its remains were discovered in thePaluxy Formation. Thetype species isA. slaughteri, described in 2012.[1]
Fragmentarysauropod remains were among the earliest dinosaurs to be named from North America in the 19th century. In particular, the generaAstrodon andPleurocoelus were named based on teeth and isolated limb or vertebral elements. Additional remains would be assigned to these genera over the course of the 19th century, most of which have either been reassigned to their own genera or considered to be dubious. Among the remains assigned to the genusPleurocoelus (itself sometimes considered ajunior synonym ofAstrodon) were the specimens SMU 61732 and SMU 203/73655, which had been discovered and excavated from thePaluxy Formation ofTexas by the paleontologistRobert Slaughter in the 1960s.[1]
Wann Langston Jr., a paleontologist who did considerable work on fossils fromTexas, assigned these specimens to"Pleurocoelus sp." in 1974, and the fossils were not fully described for several decades.[2] The remains were re-examined by the doctoral student Michael D. D’Emic, who was studying at theUniversity of Michigan at the time. His description included a comprehensive review of the sauropod remains from theEarly Cretaceous of North America includingSauroposeidon,Cedarosaurus,Brontomerus, and others. In his description, D'Emic erected the new taxonAstrophocaudia slaughteri to contain both SMU 61732 and SMU 203/73655.[1]
Thegenus name was given a twofold meaning: it is derived from severalAncient Greek words including"stropho-" meaning "twisting" or "turning","caud-" meaning "tail", and the prefix"a-", meaning "not". The genus name as a whole therefore means "non-twisting tail", in reference to the closely-connectedhyposphene-hypantrum articulation of thecaudal vertebrae. The genus name can also be translated to "star tail", using the Ancient Greek word"astron" and the above mentioned"caud", meaning "tail". This second meaning is in reference to the shape of the caudal vertebrae when viewed from behind, which have the appearance of a three-pointed star. D'Emic remarks that the name has a third meaning (although not a third translation), which is to pay homage toAstrodon, the first named sauropod from North America. Thespecies epithet"slaughteri" is in honor of Robert Slaughter, the original discoverer of the remains.[1]
Theholotype ofAstrophocaudia consists of a single tooth (SMU 203/73655) and a partial postcranial skeleton (SMU 61732). The latter specimen contains the following elements: twocervical vertebrae, a few fragments of dorsal vertebrae, 24caudal vertebrae, 20rib fragments, twochevrons, part of ascapula, a partial rightilium, and several fragments that were not able to be identified. The roughly proportional size of the bones and the lack of any repeated elements led D'Emic to conclude that all of the preserved remains likely belonged to a single individual. D'Emic did not provide an estimate of the full size ofAstrophocaudia in his description.[1] Rubén Molina-Pérez and Asier Larramendi estimated the full size of this species at 10.9 m (36 ft) long and weighing 2.85 t (6,300 lb).[3] Evan Johnson-Ransom estimated a larger size of this species at 18.3 m (60 ft) long and weighing 20 t (44,000 lb), making it comparable in size toAstrodon.[4]
Astrophocaudia is able to be distinguished from all other sauropods by the followingautapomorphies: a planar orientation of thehyposphene-hypantrum articulations relative to thezygapophyses and the presence of alamina in front of theneural arches which contacts a second lamina between, and in front of, the zygapophyses. It is further distinguished from the roughly contemporaneous sauropodsCedarosaurus,Venenosaurus,Sauroposeidon, andSonorasaurus by other characteristics of the caudal vertebrae.Astrophocaudia also possesses a preacetabular process which is slightly curved when viewed from above.[1]
In his description ofAstrophocaudia, D'Emic conducted a phylogenetic analysis which included all known sauropods from theEarly Cretaceous of North America. He notably found that fossils of the taxonPaluxysaurus bore autapomorphies ofSauroposeidon, meaning the two taxa were synonymous. He found thatAstrophocaudia belonged in apolytomy at the base ofSomphospondyli outside ofTitanosauria. An abbreviated version of the cladogram published by D'Emic is shown below next to another, more recent analysis that recovered similar results with greater resolution by Yang Han and colleagues.[1][5]
| Somphospondyli |
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