Fossils have been found in Paleocene aged rocks of the Iullemmeden Basin in West Africa,[1] Campanian–Maastrichtian (Late Cretaceous) Shendi Formation of Sudan[2] and Maastrichtian (Late Cretaceous) through Danian (Early Paleocene) strata in New Jersey, Alabama and South Carolina.

The other North American species (i.e. H. fraterculus, H. ferox and H. natator) are therefore considered nomina vana (i.e. empty names).

[7][2] Hyposaurus lived in a shallow, near shore marine environment and has many aquatic adaptations [4] In 2009, the disorganized phylogeny of crocodyliforms was treated and reliable diagnostic traits established, but remaining questions are unanswered.

[9] The genus name is meant to describe the unique "hypapophyseal keel extended on the ventral surface of the centrum".

[11] The species was named Hyposaurus derbianus after professor Orville Derby, the director of the department of Geology at the National Museum of Brazil.

[12] The three main differences between the axial skeletons of Hyposaurus and modern crocodylians are the tall neural spines, vertically oriented thoracic ribs and osteoderm which lack external keels.

[3] The short transverse process on the caudal vertebrae implies the tail did not move vertically, indicating that Hyposaurus was not a diving animal.

[3] Moreover, Dyrosaurids generally are hypothesized to have pitch correction where the pleural cavity is pushed towards the back side to produce a more horizontal stance while submerged in water.

[3] Buffetaut proposed Dyrosaurids laid their eggs on land and only after they have fully grown moved to coastal waters.

[12] Citing vague distinctions, Jove and colleagues,[1] attempted to reclassify the genus Hyposaurus based on diagnostic characteristics and sort of taxonomic troubles.

[1] The paper focuses on the at least 5 species of Hyposaurus or Congosaurus known from the Paleocene of the Iullemmeden Basin of Western Africa (Mali, Niger, Nigeria).

[1] A paper by Hastings and colleagues described a new skull of a dyrosaurid crocodyliform, found in the Cerrejón Formation of northern Colombia.

Analysis supports an African origin to Dyrosauridae, with dispersal and radiation in South America in the Late Cretaceous or very early Paleocene.

[13] In 2016, Salih and colleagues reported the first Hyposaurus fossil found in the Campanian to Maastrichtian Shendi Formation of Sudan.

[2] This fossil is different from other specimens of Hyposaurus because it has a larger eighth alveolus (bony socket for tooth root), smaller interveolar space between the ninth and tenth alveoli, and a ridge along the dorsal side of the mandible.