Staurikosaurus (Pronounced /ˌstɔɹ̠ikoʊˈsɔɹ̠ʌs/, STOR-ree-koh-SOR-ruhs; "Southern Cross lizard") is a genus of herrerasaurid[1] dinosaur from the Late Triassic of Brazil, found in the Santa Maria Formation.

[2] 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.

[6] This dentition suggests that Staurikosaurus could catch and hold prey, as well as slice and tear flesh to aid in mechanical digestion.

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.

[9] Novas (1993) added that Staurikosaurus is distinguished from other dinosaurs based on the presence of a distal bevel on anterior margin of its pubis.

[12] The first known specimen of Staurikosaurus (MCZ 1669) was recovered from the Paleontological Site Jazigo Cinco of the Santa Maria Formation,[5] Rio Grande do Sul, southern Brazil.

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.

[14] 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.

[15] 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.

[19]Staurikosaurus was originally incorrectly assigned by Colbert to Palaeosauriscidae, a defunct family based largely on Efraasia, a prosauropod dinosaur.

[21] Phylogenetic analysis by Sues, Nesbitt, Berman and Henrici, in 2011, exclude Eoraptor, and include Chindesaurus along with Herrerasaurus as more derived than Staurikosaurus.

[29] However, the combination (that is, the simultaneous presence) of the five characters listed by Garcia et al.[14] is not present in any of the aforementioned dinosauriforms, and therefore remains unique between "Teyuwasu" and Staurikosaurus.

The contemporaneous occurrence of basal theropods Staurikosaurus, Herrerasaurus, and Eoraptor with the ornithischian Pisanosaurus suggests that the main carnivorous and herbivorous lineages were established during the middle part of the Carnian stage.