A newly discovered species, Militocodon lydae, which is thought to be the size of a mouse and weigh up to 455 grams, may be the ancestor of all modern hoofed animals, known as ungulates.

This small mammal, which lived around 65 million years ago, shortly after the extinction of the dinosaurs, was identified from part of a skull and jaw recovered from the Corral Bluffs fossil site in Colorado.

The discovery is reported in a new study published in the Journal of Mammalian Evolution. The researchers believe that M. lydae fills crucial gaps in our understanding of the Periptychidae family of primitive mammals, which became prominent after the extinction of the dinosaurs, points out Science Alert.

Skull of a new periptychid mammal from the lower Paleocene Denver Formation of Colorado (Corral Bluffs, El Paso County) - Journal of Mammalian Evolution
The Periptychidae, an extinct group of archaic ungulates (‘condylarths’), were the most speciose eutherian mammals in the earliest Paleocene of North America, epitomizing mammalian ascendency after the Cretaceous–Paleogene (K–Pg) mass extinction. Although periptychids are mostly known from fragmentary gnathic remains, the Corral Bluffs area within the Denver Basin, Colorado, has yielded numerous exceptionally well-preserved mammalian fossils, including periptychids, from the earliest Paleocene. Here we describe a partial cranium and articulated dentaries plus an additional unassociated dentary fragment of a small-bodied (~273–455 g) periptychid from ca. 610 thousand years after the K–Pg mass extinction (Puercan 2 North American Land Mammal ‘age’) at Corral Bluffs. Based on these new fossils we erect Militocodon lydae gen. et sp. nov. The dentition of M. lydae exhibits synapomorphies that diagnose the Conacodontinae, but it is plesiomorphic relative to Oxyacodon, resembling putatively basal periptychids like Mimatuta and Maiorana in several dental traits. As such, we interpret M. lydae as a basal conacodontine. Its skull anatomy does not reveal clear periptychid synapomorphies and instead resembles that of arctocyonids and other primitive eutherians. M. lydae falls along a dental morphocline from basal periptychids to derived conacodontines, which we hypothesize reflects a progressive, novel modification of the hypocone to enhance orthal shearing and crushing rather than grinding mastication. The discovery and thorough descriptions and comparisons of the partial M. lydae skull represent an important step toward unraveling the complex evolutionary history of periptychid mammals.
SpringerLinkLucas N. Weaver
Surprise! This Tiny Animal May Be The Long-Lost Ancestor of Cows, Pigs, And Deer
Meet the newly discovered species Militocodon lydae: Thought to be about the size of a rat and weighing up to 455 grams or 16 ounces, this small mammal is the likely ancestor of all modern hoofed animals, called ungulates.
ScienceAlertDavid Nield

The team used sophisticated scanning techniques, 3D reconstructions and tooth comparisons to accurately place M. lydae on the evolutionary tree. The teeth, used for cutting and crushing rather than grinding, suggest that this small creature could be an ancestor of today's cows, pigs and deer.

Despite the importance of this discovery, researchers have only found a few fossils of M. lydae in the last eight years. More discoveries and studies are needed to confirm that this animal is indeed what it is supposed to be. The researchers acknowledge that ongoing discoveries and studies of archaic ungulates from the early Paleocene will probably reveal more specimens that challenge existing taxonomic classifications.

Tracing the evolution of animals immediately after the disappearance of the dinosaurs has been a challenge due to the scarcity of fossils from this period. This period marked rapid and widespread diversification in the animal kingdom, particularly in mammals. After the asteroid impact and the extinction of the dinosaurs, mammals such as M. lydae took the opportunity to thrive.

The discovery and description of a fossil mammal skull represents a significant step in documenting the first diversification of mammals after the Earth's last mass extinction.