Dongoconodon () is an extinct genus of early mammal in the order Eutriconodonta known from the Early Cretaceous (Barremian–Aptian age) Jiufotang Formation of China. The genus contains a single species, Dongoconodon platycauda, known from a nearly complete skeleton missing part of the left forelimb. Dongoconodon has a unique pattern of replacement teeth (polyphydonty) compared to most mammals. Several anatomical features, such as evidence for webbed hands and a flattened tail, indicate it had a semiaquatic ecology.
Discovery and naming
The Dongoconodon fossil material was collected by Junyou Wang in 2016 from outcrops of the Jiufotang Formation (Changzigou locality) near Sanjiazi Town in Lingyuan city, Liaoning Province, China. The specimen is housed in the Inner Mongolia Museum of Natural History, where it is permanently accessioned as specimen IMMNH-PV01700. It consists of a nearly complete, articulated skeleton including the skull, preserved on a single slab. The only missing elements are the left humerus, ulna and radius, three bones of the forelimb.
In 2026, Shundong Bi and colleagues described Dongoconodon platycauda as a new genus and species of eutriconodont based on these fossil remains, designating IMMNH-PV01700 as the holotype specimen. The generic name, Dongoconodon, honors Chinese scientist Junshe Dong and his contributions to vertebrate paleontology research. This is combined with the common eutriconodont suffix (), from the Greek () and (). The specific name, platycauda, combines the Greek (), meaning , with the Latin , meaning tail, referencing the distinctive tail morphology.
Description and palaeobiology
The D. platycauda holotype represents an individual with an estimated body mass of . The skull is flattened but generally triangular in shape and broadest toward the back. The mandible is robust. The jaw shape and caniniform incisors are reminiscent of the related gobiconodontids, suggesting a carnivorous diet involving the active catching and ripping of prey items. The tooth replacement pattern of Dongoconodon is unusual, with multiple generations of teeth indicative of polyphyodonty (continuous replacement of teeth). This contrasts with nearly all other mammals, which are diphyodont (two sets of teeth), and is instead similar to the pattern in many reptiles.
Dongoconodon further exhibits a suite of unique adaptations to a semiaquatic ecology, consistent with features seen in extant semiaquatic mammals. The hands and feet are long and broadened in relation to the limbs, as in the platypus. The arrangement and structure of the phalanges, meta/carpals, and meta/tarsals indicate the digits could be spread, increasing surface area and improving the stroke for swimming. The manual (hand) phalanges bear flanges on the dorsal surfaces, similar to the platypus, marking the attachment points for webbing between the digits. The proximal caudal (tail) vertebrae are broad and flattened, while the vertebrae toward the tip of the tail were longer and more round. This structure is most similar to the extant nutria, where part of the tail is flattened, but the rest is long and tapered.
Classification
Bi et al. (2026) included Dongocondon in a phylogenetic matrix to test its affinities and relationships. It was recovered as the sister taxon to a clade including Spinolestes, Gobiconodon, and Repenomamus, which together comprise the family Gobiconodontidae. These taxa, along with several others, form the early-diverging mammal clade Eutriconodonta. These results are displayed in the cladogram below:
References