Megapnosaurus

Megapnosaurus (meaning "big dead lizard", from Greek μεγα = "big", 'απνοος = "not breathing", "dead", σαυρος = "lizard") was a dinosaur of the theropod family Coelophysidae, formerly called Syntarsus (named by Raath, 1969), living during the Early Jurassic. It was renamed by American entomologist Dr. Michael Ivie (Montana State University of Bozeman), Polish Australian Dr. Adam Ślipiński, and Polish Dr. Piotr Węgrzynowicz (Muzeum Ewolucji Instytutu Zoologii PAN of Warsaw), the scientists who discovered that the genus name Syntarsus was already taken by a colydiine beetle described in 1869. Some paleontologists did not like the name Megapnosaurus, but it remains the valid name for this genus.

It is almost identical to Coelophysis, and Yates (2005) suggested that Megapnosaurus was possibly synonymous with Coelophysis.[1] In 2004, Raath co-authored two papers in which he argued that "Syntarsus" (Raath continued to use the old, invalid, name) was a junior synonym of Coelophysis.

Description
Megapnosaurus measured up to 3 meters (10 ft) long from nose to tail and weighed about 32 kilograms (70 lb). The bones of 30 Megapnosaurus individuals were found together in a fossil bed in Zimbabwe, so paleontologists think it may have hunted in packs. The various fossils attributed to Megapnosaurus have been dated over a relatively large time span- the Hettangian, Sinemurian, and Pliensbachian stages of the Early Jurassic- meaning the fossils represent either a highly successful genus or a few closely related animals all currently assigned to Megapnosaurus.

Megapnosaurus is a good example of how dinosaurs spread across the globe from their ancestral habitats (which was possibly South America). This small predator had the same basic features found in early dinosaurs, and its appearance in both Africa and the southwestern U.S. indicate that it migrated through the continents, which at the time were joined together as Pangaea. There is species-level differentiation between the African and U.S. specimens, again supporting the migration and adaptation theories.

Classification
"Syntarsus" rhodesiensis was first described by Raath (1969) and assigned to Podokesauridae.[6] The taxon "Podokesauridae", was abandoned since its type specimen was destroyed in a fire and can no longer be compared to new finds. Over the years paleontologists assigned this genus to Ceratosauridae (Welles, 1984), Procompsognathidae (Parrish and Carpenter, 1986) and Ceratosauria (Gauthier, 1986). Most recently, is has been assigned to Coelophysidae by Tykoski and Rowe (2004), Ezcurra and Novas (2007) and Ezcurra (2007), which is the current scientific consensus.

Distinguishing anatomical features
A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group.

According to Tykoski and Rowe (2004) Megapnosaurus rhodesiensis can be distinguished based on the following characteristics:
 * it differs from Coelophysis bauri in the pit at the base of the nasal process of the premaxilla
 * it differs from C. kayentakatae because the promaxillary fenestra is absent and the nasal crests are absent
 * the frontal bones on the skull are not separated by a midline anterior extension of the parietal bones
 * the anterior astragalar surface is flat
 * metacarpal I has a reduced distal medial condyle (noted by Ezcurra, 2006)
 * the anterior margin of antorbital fossa is blunt and squared (noted by Carrano et al., 2012)
 * the base of lacrimal vertical ramus width is less than 30% its height (noted by Carrano et al., 2012)
 * the maxillary and dentary tooth rows end posteriorly at the anterior rim of the lacrimal bone (noted by Carrano et al., 2012)