Lagosuchus

The type species Lagosuchus talampayensis was first described by Alfred S. Romer in 1971, who considered it a "pseudosuchian" (then a collection of various non-dinosaurian "thecodonts").[1] In 1972 he named a second species, Lagosuchus lilloensis, known from a larger and more well-preserved skeleton.[2] A later review by Jose Bonaparte in 1975 synonymized the two species and considered Lagosuchus intermediate between "pseudosuchians" and saurischian dinosaurs.[3]

Modern authors now consider at least L. lilloensis to be firmly on the lineage of archosaurs leading to dinosaurs.[4] However, the genus Lagosuchus is regarded by some to be dubious. Paul Sereno and Andrea Arcucci considered L. talampayensis to be undiagnosable in a 1994 study, and reclassified L. lilloensis as a new genus, Marasuchus.[5] In 2019, the holotype skeleton of L. talampayensis was redescribed by Federico Agnolin and Martin Ezcurra who determined it to not only be diagnostic, but indistinguishable from specimens of Marasuchus lilloensis, and so supported the synonymy proposed by Bonaparte.[6] Additionally, the dating of its formation is unclear; recent research has dated the Chañares to the early Carnian stage of the Late Triassic.[7]

Artist's impressions and skeletal restoration

Lagosuchus is known from very incomplete remains (only a hind leg plus a shoulder blade and vertebrae can be definitely assigned to it). However, features of the leg show that it was a lightly built archosaur, and is notable for its long slender legs and well-developed feet - features it shares with certain dinosaurs. These features, as well as comparisons to close relatives, suggest that it could run on its hind legs for short periods, although it probably moved on all fours most of the time. Lagosuchus was likely an agile predator that could use speed to chase its prey and to escape larger predators.[8] Lagosuchus was about the size of a ferret.[9]