Monotoonsus

Monotoonsus is a genus of extinct lepidosaurs that lived in what is now Central Asia during the Late Cretaceous, about 90 million years ago. The genus contains a single recognized species, Monotoonsus cretaceus. Fossil material comprises skull fragments, partial jaws, and several limb bones recovered from fluvial deposits.

The name Monotoonsus combines Greek monos and tonos, chosen for the uniform patterning of the dorsal scales and the inferred single-tone coloration.

Monotoonsus was small to medium-sized for a semi-aquatic reptile, with an elongated body, a relatively short tail, and limbs adapted for semi-aquatic locomotion. The skull is narrow with a long snout and conical teeth; the dental features help distinguish it from close relatives.

While traditionally placed in Lepidosauria, its precise relationships remain uncertain due to the fragmentary remains. Some analyses suggest affinities with early teiids or other semi-aquatic lepidosaurs, but robust diagnosis awaits additional material.

The morphology indicates a semi-aquatic lifestyle, foraging in shallow rivers for fish and invertebrates. The presence of possible webbing is inferred from limb proportions, though soft tissue is rarely preserved. Reproduction and growth rates are unknown.

Fossils have been recovered from alluvial deposits that were part of a fluvial system in Late Cretaceous Asia, indicating a warm, seasonally wet environment. The species is extinct.