Staurikosaurus (Pronounced /ˌstɔɹ̠ikoʊˈsɔɹ̠ʌs/, STOR-ree-koh-SOR-ruhs; "Southern Cross lizard") is a genus of herrerasaurid dinosaur from the Late Triassic of Brazil, found in the Santa Maria Formation.
Description
Colbert (1970) described Staurikosaurus as a small and agile, bipedal predator. Staurikosaurus lived during the late-Carnian and early-Norian stage, of the Late Triassic, approximately 225 million years ago—which makes it one of the earliest dinosaurs known. Its length is measured at 2.2–2.25 metres (7 ft 3 in – 7 ft 5 in) long, but Gregory S. Paul presented a lower length estimate of 2.1 metres (6 ft 11 in) and a body mass estimate of 12 kilograms (26 lb). Staurikosaurus was small in comparison to later theropods like Megalosaurus. The type specimen has long but relatively slender limb bones. There exists a very incomplete fossil record of Staurikosaurus, consisting of most of the spine, the legs and the large lower jaw. However, dating from such an early period in the dinosaurs' history and being otherwise so primitive, most of Staurikosaurus' other features as being primitive also can be reconstructed. For example, Staurikosaurus is usually depicted with five toes and five fingers—very simple features of an unspecialized dinosaur. However, since the skeletal structure of the legs is known, it can be seen that Staurikosaurus was a quick runner for its size. It also had just two vertebrae joining the pelvis to the spine, a distinctly primitive condition. The available teeth for Staurikosaurus bear a morphology that strongly suggests a carnivorous diet. The teeth are all serrated, laterally compressed, and caudally curved (i.e. the top of each tooth is curved back toward the throat). This dentition suggests that Staurikosaurus could catch and hold prey, as well as slice and tear flesh to aid in mechanical digestion. The tail of Staurikosaurus was relatively long (with more than 40 vertebrae) compared to the rest of its body and was held straight and off the ground as it ran. The rear part of Staurikosaurus's tail is stiffened by features of the tail vertebrae. Ostrom (1969a) considered this adaptation to serve as a dynamic stabilizer facilitating the animal's leaping and running.
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 Sues (1990), Staurikosaurus can be distinguished based on the following 14 features: (i) a mandible almost as long as the femur, suggesting a proportionately large head; (ii) a fairly deep but thin dentary with 13 to 14 teeth and with a well-developed retroarticular process; (iii) a vertebral column with 9 to 10 cervical, 15 dorsal, 2 sacral, and more than 40 caudal vertebrae. Staurikosaurus is considered to be more primitive than any other dinosaur because only two sacral vertebrae are present; (iv) an elongated 3rd, 4th, and 5th cervical vertebrae, which represents a primitive condition; (v) cranial cervical vertebrae that lack epipophyses; (vi) the absence of accessory intervertebral articulations; (vii) a slender scapular blade that is not expanded proximally; (viii) a large and plate-like coracoid; (ix) a humerus featuring a prominent deltopectoral crest (represents a primitive condition) as well having distinctly expanded articular ends; (x) an ilium with an extensively developed medial wall of a semiperforate acetabulum (like Herrerasaurus, but unlike any other dinosaur); (xi) a long pubis, two-thirds the length of the femur; (xii) hollow limb bones that feature fairly thick walls; (xiii) a robust femur with an S-shaped shaft: and (xiv) a tibia and fibula slightly longer than the femur. Novas (1993) added that Staurikosaurus is distinguished from other dinosaurs based on the presence of a distal bevel on anterior margin of its pubis. Langer and Benton (2006) noted that Staurikosaurus can be distinguished based on the anterior trochanter being reduced to a scar. Bittencourt and Kellner (2009) also noted that the proximal fibula has a medial sulcus, which is unique to Staurikosaurus pricei.
Discovery and occurrence
Staurikosaurus is named after the "Southern Cross" the star constellation visible from the Southern Hemisphere (from the Greek "Stauros" meaning cross and "saurus" meaning lizard), thus "Cross Lizard". The species name pricei is in the honor of paleontologist Llewellyn Ivor Price. The first known specimen of Staurikosaurus (MCZ 1669) was recovered from the Paleontological Site Jazigo Cinco of the Santa Maria Formation, Rio Grande do Sul, southern Brazil. Staurikosaurus was found in mid-Carnian sediments. The genus name refers to the star constellation "The Southern Cross", pictured in the coat of arms of Brazil and only visible in the Southern Hemisphere—when Staurikosaurus was described in 1970, it was unusual to find dinosaurs in the Southern Hemisphere. The specific name honors the Brazilian paleontologist Llewellyn Ivor Price, who discovered it in 1936. It was described by Edwin Harris Colbert, working at the American Museum of Natural History. The rarity of Staurikosaurus remains may be a result of it being uncommon while alive, or because it lived in an environment like a forest, where fossils rarely form. However recent evidence indicates that the ecosystem was probably more dry. Nonetheless, Garcia et al. (2019) referred the holotype of Teyuwasu barberenai as a second specimen of Staurikosaurus pricei (see Classification).
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