The holotype skeleton of L. talampayensis is fairly fragmentary, but it does possess some traits suggesting that Lagosuchus was a probable dinosauriform, closely related to dinosaurs.

[6][3] 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").

[4] A later review by Jose Bonaparte in 1975 synonymized the two species and considered Lagosuchus intermediate between "pseudosuchians" and saurischian dinosaurs.

Paul Sereno and Andrea Arcucci considered L. talampayensis to be undiagnosable in a 1994 study, and reclassified L. lilloensis as a new genus, Marasuchus.

As a result, they supported the synonymy proposed by Bonaparte, referring specimens of Marasuchus lilloensis back to Lagosuchus talampayensis.

[1] Gregory S. Paul inferred that Lagosuchus was one of the smallest Triassic archosaurs, with a weight of about 167 g, similar in size and ecology to a weasel or ferret.

[9] Thomas Holtz estimated that Lagosuchus could have obtained a total length of 1.7 ft (51 cm) and a weight similar to that of a pigeon (50-500 g).

In addition, they both have trapezoidal neural spines with thickened upper edges which expand forwards and backwards to contact those of adjacent vertebrae.

[3] The scapula (shoulder blade) was narrow, with a slightly expanded upper tip and a thick longitudinal ridge on its inner surface.

[1] The pelvis (hip) is similar to that of Marasuchus, with a thin pubis and a plate-like ischium which has a large ridge on its rear edge.