Catonyx is an extinct genus of ground sloth of the family Scelidotheriidae, endemic to South America during the Pliocene and Pleistocene epochs.

Unlike the latter, Catonyx possessed shorter premaxillae that formed a triangular (and not rectangular like Scelidotherium) snout tip, a pronounced rostrum bulge, a palate equipped with a median groove, and larger teeth.

In addition, the mandibular symphysis was elongated and elevated, and the posterior lobe of the lower fourth molar was more curved than that of Scelidotherium.

[7] The very first fossils of this animal were found in Upper Pleistocene strata of Brazil and were described by Lund in 1839, but for a long time there was considerable systematic confusion: the remains were gradually attributed to the genera Scelidotherium and Scelidodon.

Large, mesoherbivorous mammals in the BIR were widespread and diverse, including the cow-like toxodontids Toxodon platensis and Piauhytherium, the macraucheniid litoptern Xenorhinotherium and equids such as Hippidion principale and Equus neogaeus.

Other xenarthran fossils are present in the area as well from several different families, like the giant megatheriid ground sloth Eremotherium, the fellow scelidotheriid Valgipes, the mylodontids Glossotherium, Ocnotherium, and Mylodonopsis.

Eremotherium was a generalist, while Nothrotherium was a specialist for trees in low density forests, and Valgipes was an intermediate of the two that lived in arboreal savannahs.

[16][17] It is possible that the region alternated between dry open savannah and closed wet forest throughout the climate change of the Late Pleistocene.