Marasuchus lilloensis (previously considered Lagosuchus talampayenisis, Romer 1971), Ladinian, Middle Triassic, ~230 mya, ~40cm was a small dinosauriform widely considered a sister taxon to Herrerasaurus outside the Dinosauria. Here Marasuchus nests within the Dinosauria. It was derived from a sister to Tawa and Segisaurus and phylogenetically preceded Procompsognathus.

Smaller and distinct from Tawa, the skull of Marasusuchus had a maxilla with a straight ventral rim and shorter teeth.

The cervicals rose in a stronger S-curve. Distinct from other theropods two sacrals were retained. The caudals stretched out to over three times their diameter as the tail became more gracile.

The scapulocoracoid was robust overall. The ilium anterior process was squared-off with a dorsally concave margin. Digits 1 was shorter than metatarsal 2. The foot was relatively longer and narrower with more asymmetrical digits.

Agnosphitys cromhallensis (Fraser et al. 2002) is known from a selection of uncrushed bones, all of which resemble those from Marasuchus, but slightly larger with a relatively longer rostrum and shorter arms. These two represent a separate and distinct lineage of theropods.

Guaibasaurus candelariensis (Bonaparte et al., 1999; UFRGS PV0725T; Late Triassic) is known from an articulated skeleton lacking a neck and skull. Originally considered a basal theropod, later studies allied it with basal sauropodomorphs. Here this specimen nests as a basal theropod in a rarely studied clade between Segisaurus and Marasuchus. A pellvis with a tall ilium and long pubis attributed to Guaibasaurus does not match this specimen, which appears to have a long ilium and short broad pelvis. Creating taxonomic chimaeras may be the problem with earlier studies.

Agnolin F and Martinelli AG 2012. Guaibasaurus candelariensis (Dinosauria, Saurischia) and the early origin of avian-like resting posture. Alcheringa. 36 (2): 263–267.

Bonaparte JF;Ferigolo J and Ribeiro AM 1999. A new early Late Triassic saurischian dinosaur from Rio Grande do Sol state, Brazil. Proceedings of the Second Gondwanan Dinosaur Symposium, National Science Museum Monographs. 15: 89–109.

Bonaparte JF, Brea G, Schultz CL and Martinelli AG 2007. A new specimen of Guaibasaurus candelariensis (basal Saurischia) from the Late Triassic Caturrita Formation of southern Brazil. Historical Biology, 19(1): 73-82.

Fraser NC, Padian K, Walkden GM and Davis LM 2002. Basal dinosauriform remains from Britain and the diagnosis of the Dinosauria. Palaeontology. 45(1), 79-95.

Langer MC; Bittencourt JS and Schultz CL 2011. A reassessment of the basal dinosaur Guaibasaurus candelariensis, from the Late Triassic Caturrita Formation of south Brazil. Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 101 (3–4): 301–332.

Paul GS 1988. Predatory dinosaurs of the world (464). New York: Simon and Schuster.

Romer AS 1971. The Chanares (Argentina) Triassic reptile fauna X. Two new but incompletely known long-limbed pseudosuchians: Brevoria 378: 1-10.

Romer AS 1972. The Chanares (Argentina) Triassic reptile fauna. XV. Further remains of the thecodonts Lagerpeton and Lagosuchus: Breviora 394: 1-7.

Sereno PC and Arcucci AB 1994. Dinosaurian precursors from the Middle Triassic of Argentina: Marasuchus lilloensis gen. nov. Journal of Vertebrate Paleontology, 14: 53-73

wiki/Marasuchus
wiki/Agnosphitys
wiki/Guaibasaurus