Megapnosaurus (meaning "big dead lizard", from Greek μέγα = "big", ἄπνοος = "not breathing", "dead", σαῦρος = "lizard") is an extinct monospecific genus of coelophysid theropod dinosaur that lived around 199-188 million years ago during the early part of the Jurassic Period in what is now Africa. The species was a small to medium-sized, lightly built, ground-dwelling, bipedal carnivore, that could grow up to 2.2 m (7.2 ft) long and weigh up to 13 kg (29 lb). It was originally given the genus name Syntarsus, but that name was later determined to be preoccupied by a colydiine beetle (itself now absorbed into the genus Cerchanotus). The species was subsequently given a new genus name, Megapnosaurus, by Michael Ivie, Ślipiński, & Węgrzynowicz in 2001. Some studies have classified it as a species within the genus Coelophysis, but this interpretation has been challenged by more subsequent studies and the genus Megapnosaurus is now considered valid.
Discovery and history The first fossils of Megapnosaurus were found in 1963 by a group of students from Northlea School on Southcote Farm in Nyamandhlovu, Zimbabwe (then Rhodesia). Michael Raath, the describer, was shown the fossils by school staff in 1964 and over several weeks, was excavated from the Forest Sandstone, the layers dating to the early Jurassic. The type specimen (QG 1) consisted of a well preserved postcranial skeleton, missing only the skull and cervical vertebrae. In another sandstone block, a few fossils of another specimen intermixed with the bones of a prosauropod, likely Massospondylus. Later in 1968, Raath and D. F. Lovemore discovered additional Jurassic rock layers northeast of the type locality of Southcote Farm. These rock layers were then known as the Maura River Beds, but due to the strata bearing fossils of Massospondylus, the beds were determined to be the same age as those of the Forest Sandstone. This second locality produced many articulated partial skeletons of Massospondylus, but only fragmentary postcranial remains of Megapnosaurus. Raath would name the animal in 1969, dubbing it Syntarsus rhodesiensis, after the fused tarsal bones in its foot. Still in search of complete skeletons, Raath continued searching in the Jurassic rocks of Zimbabwe until finding what would become the most productive S. rhodesiensis-bearing locality near the Chitake River in 1972. The quarry contained hundreds of bones of at least 26 individuals from many growth stages, making it one of the most productive quarries for African theropods. The quarry contained several skulls and cervical vertebrae, elements missing in previously collected specimens, and some specimens even preserved gastralia, sexual dimorphism, and gut contents. The fossils were described in detail by Raath in his thesis in 1977, including skeletal and musculoskeletal reconstructions of S. rhodesiensis. All specimens collected from Southcote, Maura River, and Chitake River now reside at the Queen Victoria Museum.
Possible & reclassified Megapnosaurus remains In 1989, a second species of "Syntarsus" was proposed as Syntarsus kayentakatae, a description by Timothy Rowe of a well preserved skull and partial remains of postcranial skeleton. The fossils came from the early Jurassic strata of the Kayenta Formation in Arizona, United States. The phylogenetic position of "Syntarsus" kayentakatae is debated, with a position in Megapnosaurus, Coelophysis, or a making a new genus being proposed. The next year Darlington Munyikwa and Raath described a partial snout of "S." rhodesiensis from the Elliot Formation in South Africa, but the material has been referred to Dracovenator. A "Syntarsus" specimen was discovered in the United Kingdom in the 1950s and consisted of several postcranial elements. The specimen have now been referred to a new genus and species, Pendraig milnerae in 2021. A partial coelophysoid sacrum and several additional elements from the Early Jurassic of Mexico were described as a new species of "Syntarsus", "Syntarsus" "mexicanum", in 2004. The remains were not given proper description in their naming and are likely from an indeterminate coelophysoid. Fragmentary coelophysid specimens (FMNH CUP 2089 and FMNH CUP 2090) from the Lufeng Formation of southern China have been identified as cf. Megapnosaurus, though phylogenetic analyses cannot be conducted due to poor preservation. A partial skeleton described from the Moenave Formation was listed with the name Syntarsus "moenavensis" by Tykoski in 2005, attributing the name to the describers of the specimen, though the name was not used in their study.
Description
Megapnosaurus rhodesiensis measured up to 2.2 m (7.2 ft) long from nose to tail and weighed up to 13 kg (29 lb). It was a lean, elongated species of theropod dinosaur with an S-shaped neck, long hind limbs that resembled the legs of large birds such as the secretarybird, shorter forelimbs with four digits on each hand unlike most later theropods, and a long tail. While still lean, it sported a more robust frame than other members of Coelophysoidea. Its lithe and superifically bird-like body lead to M. rhodesiensis being one of the first dinosaurs to be portrayed with feathers, though there is no direct evidence that it actually had feathers. The bones of at least 30 M. rhodesiensis individuals were found together in a fossil bed in Zimbabwe, so paleontologists think it may have hunted in packs. The various fossils attributed to this species 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 Coelophysis. Specimen UCMP V128659 was discovered in 1982 and referred to Megapnosaurus kayentakatae by Rowe (1989), as a subadult gracile individual and later, Tykoski (1998) agreed. Gay (2010) described the specimen as the new tetanurine taxon Kayentavenator elysiae, but Mortimer (2010) pointed out that there was no published evidence that Kayentavenator is the same taxon as M. kayentakatae.
Classification The cladogram below was recovered in a study by Ezcurra et al.. (2021).
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