Epachthosaurus
Epachthosaurus (meaning "heavy lizard") was a genus of dinosaur from the Late Cretaceous. It was a titanosaurid sauropod. Its fossils have been found in Central and Northern Patagonia in South America.
Discovery and naming[]
The type species, E. sciuttoi, was described by Powell in 1990.
The holotype specimen is MACN-CH 1317, which consists of an incomplete caudal vertebrae. Another specimen, the paratype MACN-CH 18689, contains a natural cast of six articulated caudal vertebrae, the partial sacrum, and a fragmentary pubic peduncle from the right ilium.
A new specimen was found recently. The specimen is UNPSJB-PV 920. During field research conducted as a part of the project ‘‘Los vertebrados de la Formación Bajo Barreal, Provincia de Chubut, Patagonia, Argentina,’’ people from the Laboratorio de Paleontologia de Vertebrados of the Universidad Nacional de la Patagonia recovered a well preserved, articulated skeleton of a medium-sized sauropod. This specimen includes a complete, articulated skeleton only missing the skull, neck, four or five cranial dorsal vertebrae, and several distal caudals. The specimen, one of the most complete titanosaurian skeletons known, was referred to the genus Epachthosaurus.
A nearly complete skeleton was described in 2004.
Description[]
The bones assigned to it by Powell in 1990 were, originally, assigned to Antarctosaurus sp., and then to Argyrosaurus superbus?, before being named as a new taxon.
Distinguishing characteristics[]
Below is a list of autapomorphies that distinguish Epachthosaurus from other genera:
- middle and caudal dorsal vertebrae with unique articular processes extending ventrolaterally from the hyposphene;
- a strongly developed intraprezygapophyseal lamina, and processes projecting laterally from the dorsal portion of the spinodiapophyseal lamina;
- hyposphene-hypan-trum articulations in caudals 1–14;
and a pedal phalangeal formula of 2-2-3-2-0.
The genus shares the following apomorphies with various titanosaurians:
- caudal vertebrae with ventrally expanded posterior centrodiapophyseal laminae;
- six sacral vertebrae;
- an ossified ligament or tendon above the sacral neural spines;
- procoelous proximal, middle, and distal caudal centra with well-developed distal articular condyles;
- semilunar sternal plates with cranioventral ridges;
- humeri with squared proximolateral margins and proximolateral processes;
- unossified carpals;
- greatly reduced manual phalanges;
- nearly horizontal, craniolaterally expanded iliac preacetabular processes;
- pubes proximodistally longer than ischia;
- and transversely expanded ischia.
Classification[]
Epachthosaurus is known to be in the basal titanosaurian because of the procoelous caudal vertebrae.
Below is a phylogenetical cladogram showing the position of Epachthosauruswithin Titanosauria:
| Titanosauria |
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The cladogram below follows Mocho et al.(2019), placing Epachthosaurus within Lithostrotia, instead of a basal titanosaur.
| Lithostrotia |
|