Showing posts with label abelisauroidea. Show all posts
Showing posts with label abelisauroidea. Show all posts

Friday, July 24, 2020

Elaphrosaurus

Type Species: Elaphrosaurus bambergi
Classification: Dinosauria – Saurischia – Theropoda – Ceratosauria – Neoceratosauria – Abelisauroidea – Noasauridae – Elaphrosaurinae 
Time Period: Late Jurassic 
Location: Africa
Diet: Carnivore   

The lithe theropod Elaphrosaurus has a storied taxonomic history. It’s known from a single nearly-complete specimen from the Kimmeridgian stage in Africa, but this specimen lacks a head – and heads are notoriously helpful when it comes to classification. Elaphrosaurus had anatomical features similar to different theropod lineages; was it a ceratosaur? a coelophysoid? was it, perhaps, the ancestor of the later Cretaceous ostrich-mimic theropods? The current consensus is that Elaphrosaurus was a ceratosaur closely related to the beaked Limusaurus of the earlier Oxfordian stage of the Late Jurassic. Because we lack Elaphrosaurus’ skull, and because it’s assumed to have a close relationship with the omnivorous or herbivorous Limusaurus, Elaphrosaurus’ dietary preferences are dense with speculation; but, as we shall see, evidence from its long neck may give us a clue. 

Elaphrosaurus is known from the African Tendagu Formation, but possible remains have been discovered in North America, hinting at a wide distribution throughout Gondwana and western Laurasia. This theropod was twenty feet long with slim, long legs; slender forelimbs with three digits each; a lightweight, shallow-chested body; a long, stiff tail; and a long, relatively stiff neck. This was the shortest theropod dinosaur in stature, at least when you go by the height of the hips compared to the creature’s overall length. Several Coelophysis-like teeth were discovered among Elaphrosaurus’ remains; though these have been attributed to Elaphrosaurus (and they may very well belong to Elaphrosaurus!) most scientists believe these were deposited by scavengers enjoying this specimen’s long-lost flesh. Although Elaphrosaurus’ neck was long, the design of the neck vertebrae indicate that I was much less flexible than those of other theropods. It likely supported a rather small skull. These traits argue against Elaphrosaurus being a predator of large prey; perhaps it hunted early ornithopods? The other theory is that Elaphrosaurus, like its (assumed) close relative Limusaurus, was omnivorous or even herbivorous. 

a pack of Elaphrosaurus attack a juvenile sauropod in Late Jurassic Africa
(this is assuming, of course, that
Elaphrosaurus was a predator!)

Wednesday, July 15, 2020

Limusaurus


Type Species: Limusaurus inextricabilis
Classification: Dinosauria – Saurischia – Theropoda – Ceratosauria – Neoceratosauria – Abelisauroidea – Noasauridae – Elaphrosaurinae 
Time Period: Late Jurassic
Location: China
Diet: Omnivorous to Herbivorous   

The theropod Limusaurus was a slender animal about six feet long in adulthood. It had a long neck and legs and very small three-fingered hands. Its name literally means “impossible to extricate from mud,” in reference to the Shishugou Formation mud pits in which these specimens died. Limusaurus is fascinating in that this dinosaur underwent a dramatic morphological transformation as it aged: while juveniles were toothed, these teeth were completely lost and replaced by a beak as they reached adulthood! The change to toothlessness in adults likely corresponded to a dietary shift from omnivory to herbivory, a theory bolstered by the fact that gastroliths (stomach stones) were found in adults. Since many specimens were found together, it’s possible that Limusaurus lived in groups. These theropods were similar to the Cretaceous ornithomimids as well as the Triassic non-dinosaurian shuvosaurids; thus at least three times within the archosaur lineage, these herbivorous adaptations evolved separately in instances of convergent evolution (in which different organisms, unrelated, evolve similar traits to deal with similar environmental pressures).