Two new species of Cretaceous mammal relatives discovered in China Paleontology

Fossiomanus sinensis i Jueconodon cheni, two related mammal species, which lived about 120 million years ago (Early Cretaceous), were well adapted to phosphorus life and were the first “scratch diggers” known from Jehol Biota, which is mainly distributed in the western province of Liaoning and neighboring areas in the northeast. China.

The dioramic landscape illustrates the early Cretaceous Jehol biota with an emphasis on mammals. Image credit: Chuang Zhao.

Jueconodon cheni is a eutriconodont, a distant relative of modern mammals and placental clocks, and was 17.8 cm (7 inches) long.

Fossiomanus sinensis is a herbivorous mammal-like animal called tritylodontid and was 31.6 cm (12.2 inches) long. It is the first such species identified in Jehol Biota.

“Early Cretaceous Jech biota created many well-preserved fossils that provided a lot of information about the morphology and evolution of early mammals,” said Dr. Jin Meng of the American Museum of Natural History and colleagues.

“The two new species expand the diversity of the mammalian set and increase its morphological disparity, as they show unequivocal evidence of convergent adaptation to the phosphorus way of life.”

“These two samples also provide an opportunity to learn more about the biology (such as axial skeletal development) of these extinct forms.”

Fossiomanus sinensis (top right) and Jueconodon cheni in their lairs.  Image credit: Chuang Zhao.

Fossiomanus sinensis (top right) and Jueconodon cheni in their lairs. Image credit: Chuang Zhao.

Mammals that are adapted to burial have special digging properties. Dr. Meng and co-authors found some of these features – such as shorter limbs, strong forelimbs with robust arms and a short tail – in both Fossiomanus sinensis i Jueconodon cheni.

These characteristics especially indicate the type of digging behavior known as “scratching”, which is mainly achieved with the claws of the front limbs.

“There are many hypotheses about why animals dig into the ground and live underground,” said Dr. Meng.

“To protect against predators, to maintain a temperature that is relatively constant, or to find food sources such as insects and plant roots.”

“These two fossils are a very unusual, deep-temporal example of animals that are not closely related, and yet both have developed highly specialized digger characteristics.”

Holotypes Fossiomanus sinensis (left) and Jueconodon cheni (right).  Abbreviations: cl - clavicle, cor - coronoid process of dental tooth, dental, ds - dental symphysis, fe - femur, fi - fibula, hu - humerus, il - ilium, man - manus, nap - anterior nasal process, nuc - nuchal ridge , eye - occipital condyle, r - rib (with number), ra - radius, sc - scapula, tibia - tibia, ul - ulna, upc - upper postcanin, for - zygomatic arch;  (r) and (l) in parentheses denote right and left, respectively.  Scale bars - 10 mm.  Image credit: Mao et al., Doi: 10.1038 / s41586-021-03433-2.

Holotypes Fossiomanus sinensis (left) and Jueconodon cheni (right). Abbreviations: cl – clavicle, cor – coronoid process of dental tooth, dental, ds – dental symphysis, fe – femur, fi – fibula, hu – humerus, il – ilium, man – manus, nap – anterior nasal process, nuc – nuchal ridge , eye – occipital condyle, r – rib (with number), ra – radius, sc – scapula, tibia – tibia, ul – ulna, upc – upper postcanin, for – zygomatic arch; (r) and (l) in parentheses denote right and left, respectively. Scale bars – 10 mm. Image credit: Mao and others., doi: 10.1038 / s41586-021-03433-2.

Fossiomanus sinensis i Jueconodon cheni they also share another unusual feature: an elongated spine.

Typically, mammals have 26 vertebrae from neck to hip. However, Fossiomanus sinensis had 38 vertebrae, doc Jueconodon cheni had 28.

To try to determine how these animals got their elongated trunks, paleontologists turned to recent studies in developmental biology.

They found that the variation could be attributed to mutations in genes that determine the number and shape of vertebrae at the beginning of animal embryonic development.

“These fossils shed light on the evolutionary development of the axial skeleton in mammals, which has been the focus of numerous studies on vertebrate evolution and developmental biology,” they said.

Discovery Fossiomanus sinensis i Jueconodon cheni was published in a journal Nature.

_____

F. Mao and others. Phosoriality and evolutionary development in two Cretaceous mammals. Nature, published online April 7, 2021; doi: 10.1038 / s41586-021-03433-2

Source