Earliest brood care by a vertebrate

The earliest-known example of brood or parental care by a vertebrate was exhibited by a lizard-like fossil reptile named Dendromaia unamakiensis. It constitutes a new genus and species of varanopid (a type of synapsid reptile) that lived 305 million years ago, during the Carboniferous Period, in what is now Nova Scotia, Canada. This new species is known from a partial fossil consisting of the fossilized remains of a large (presumably adult) specimen and a smaller (presumably younger) specimen. The smaller one was found beneath the larger one's upper leg bone, and was encircled by the larger one's tail – an entwinement that according to the research team who documented the discovery suggests that the two animals were curled up together in a den consisting of a hollowed-out lycopsid plant stump, thus indicating brood care of the smaller by the larger.

Prior to this discovery, the earliest-known example of brood care in a vertebrate also featured a varanopid species, but one that existed approximately 40 million years later, during the Guadalupian (middle Permian) period, in South Africa.

The fossil of the two D. unamakiensis specimens was discovered by researchers from Carleton University in Ontario, Canada, who formally documented it and named its new species in a paper published by the journal Nature Ecology & Evolution in December 2019.