Fossils have been found in Wales and Southern England and date from near the very end of the Late Triassic during the Rhaetian, and it is known by type and only known species T. gracilis.

It inhabited a chain of tropical, low-lying islands that made up southern Britain, along with similarly small-sized dinosaurs and abundant rhynchocephalians.

Its tail was particularly long, about twice the length of the head and body combined with an estimated 70 caudal vertebrae in total, and may have been used as a balance allowing the animal to rear up and run on its hind legs for brief periods.

[1][5] Unlike modern crocodylians, the limbs of Terrestrisuchus were very long in proportion to the body and were held upright directly beneath it.

Crush reconstructed Terrestrisuchus as a quadruped, with noticeably longer hind limbs than its forelimbs and its hips held high above the shoulder.

[7][11] Similarly, the femur of Terrestrisuchus has a distinct head that faces inwards towards the body, and fits into the hip socket at a right angle to the leg.

Its posture was further restricted to an upright gait by the calcaneal tubercle on its heel bone pointing directly backwards from the foot, unlike the back-and-sideways facing tuber of modern, sprawling crocodilians.

[12][13] The first fossils of Terrestrisuchus were discovered by Professor K. A. Kermack and Dr. P. L. Robinson in the spring of 1952, recovered from the Pant-y-ffynon Quarry located near Cowbridhe, Glamorgan in South Wales.

No osteoderms had been identified yet at the time, which Kermack regarded as representing a "missing link" between modern crocodilians and the Triassic "thecodonts".

[1] However, this classification was made prior to the invention of cladistic phylogenetic analyses, which has since demonstrated that "Sphenosuchia" is an unnatural grouping (paraphyletic), meaning that "sphenosuchians" are not all descended from a single common ancestor to the exclusion of all other crocodylomorphs.

Nonetheless, some early analyses, namely Sereno and Wild (1992), recovered a clade consisting of the two along with the South African form Litargosuchus.

Trialestes Pseudohesperosuchus Saltoposuchus Litargosuchus Terrestrisuchus Hesperosuchus Kayentasuchus Dromicosuchus Sphenosuchus Dibothrosuchus Junggarsuchus Hallopodidae Crocodyliformes In 1988, just four years after it was named, palaeontologists Michael Benton and James Clark first formally proposed that specimens of Terrestrisuchus in fact represented the juveniles of Saltoposuchus and so was a junior synonym of the latter.

[8][22] In 2003, palaeontologist David Allen identified juvenile features in Terrestrisuchus, and believed all the differing traits between it and Saltoposuchus to be ontogenetically variable, and so were otherwise indistinguishable.

[2] Saltoposuchus itself was thoroughly redescribed in 2023 by Stephan Spiekman, who identified numerous morphological differences that could not be attributed to ontogeny or to individual variation, and so rejected their synonymy.

[28] On the Pant-y-ffynnon palaeo-island, Terrestrisuchus coexisted with other archosaurs such as the similarly long-legged, enigmatic pseudosuchian Aenigmaspina, the herbivorous sauropodomorph dinosaur Pantydraco, and the coelophysoid theropod Pendraig.