Staurikosaurus

Staurikosaurus (Pronounced "STORE-ee-koh-SAWR-us", "Southern Cross lizard") is a genus of herrerasaurid[1] 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.
Paleoart of *Staurikosaurus.*
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* means "Southern Cross" (after the star constellation visible from the Southern Hemisphere) and "Lizard" (from the Greek work "saurus" meaning lizard), thus "Southern Cross Lizard." The species name *pricei* is in the honor of Colbert's fellow 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. Nonetheless, Garcia et al. (2019) referred the holotype of *Teyuwasu barberenai* as a second specimen of *Staurikosaurus pricei* (see Classification).

## Classification

Later research by Sues et al. (2011) supports that *Staurikosaurus* and the related genus *Herrerasaurus* are theropods and evolved after the sauropod line had split from the Theropoda. Mortimer points out that Benedetto (1973) and Galton (1985) were the first to recognize that *Staurikosaurus* and *Herrerasaurus* were more closely related to each other than to sauropodomorphs or avepods, placing them both in the Herrerasauridae and Herrerasauria. *Staurikosaurus* differs from *Herrerasaurus* because of its considerably smaller size (femur length of 23 centimetres (9.1 in) vs. 47 centimetres (19 in)). Sereno et al. (1993) concluded that *Staurikosaurus* was not a theropod and considered it a basal saurischian outside Theropoda and Sauropodomorpha.*Staurikosaurus* was originally incorrectly assigned by Colbert to Palaeosauriscidae, a defunct family based largely on *Efraasia*, a prosauropod dinosaur. All major phylogenetic analyses since 1994 have assigned *Staurikosaurus* to the clade Herrerasauridae, which is the current scientific consensus on classification of this genus. Bittencourt and Kellner (2009) stated that the phylogenetic position of *Staurikosaurus* is constrained by its close relationship with *Herrerasaurus ischigualastensis*, which is more complete and well known. Below is a cladogram based on the phylogenetic analysis conducted by Sues et al. in 2011, showing the relationships of *Staurikosaurus*: