Two fossil mammaliamorph species — which are predecessors to mammals — from the Early Cretaceous Jehol Biota of northeastern China are described in a paper published online in Nature. Despite being distantly related, the species show convergent features for a digging lifestyle and represent the first scratch-diggers to be discovered from this ecosystem.
Jin Meng and colleagues describe the fossils of two distantly related species from the Early Cretaceous epoch — approximately 145 to 100 million years ago. The first, a tritylodont (a mammal-like reptile) named Fossiomanus sinensis from the Jiufotang Formation of Liaoning province, was 316 mm long and represents the first of its kind to be identified in this biota. The other, named Jueconodon cheni, is a eutriconodontan (a distant cousin of modern placental mammals and marsupials), which were common in the biota. This species, found in the Yixian Formation of Liaoning province, was smaller than Fossiomanus at 183 mm in length.
Mammals that are adapted to a burrowing lifestyle can be recognized by specialized features for digging and the authors found that, despite their distant relationship, Fossiomanus and Jueconodon displayed some of these similar features. For example, both species had shorter hind limbs compared to their forelimbs, a short tail and broad forelimbs with robust claws. They also have increased numbers of thoracic vertebrae. The authors conclude that the features shared by these two species evolved independently under similar selective pressures.
After the embargo ends, the full paper will be available at: https://www.nature.com/articles/s41586-021-03433-2
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