Earth’s earliest primates were tree dwellers, according to a team of paleontologists led by Dr. Stephen Chester, an assistant professor at Brooklyn College, City University of New York.
Skeleton composite of Torrejonia wilsoni: most elements of the composite skeleton are in ventral view, but some elements are oriented differently to better illustrate articular surfaces. Descriptions and orientations of skeletal elements organized from left to right and then from top to bottom: (a) cranial fragment of R frontal in dorsal, left lateral, right lateral views; cranial fragment of parietals in dorsal, ventral views; (b) R maxilla M1–M3 in occlusal view; L maxilla P4, M2-M3 in occlusal view; R dentary p2–m2 in buccal, lingual, occlusal views; (c) R distal humerus in ventral, dorsal, distal views; R distal radial epiphysis in distal view; R proximal radius in proximal, ventral, lateral, dorsal, medial views; R proximal ulna in ventral, lateral, dorsal, medial views; (d) R scapula fragment in ventral, lateral, dorsal views; L proximal humerus in proximal, ventral, lateral, dorsal, medial views; (e) R partial astragalus in dorsal, lateral, plantar, medial, proximal, distal views; R calcaneus in dorsal, lateral, plantar, medial, proximal, distal views; R cuboid in dorsal, lateral, plantar, medial, proximal, distal views; (f) R partial innominate in ventral, lateral, dorsal, medial views; concretion with proximal femora and L tibia with L proximal femur in ventral view, R proximal femur in ventral view; R tibia in ventral, lateral, dorsal, medial, distal views; L distal femur in ventral, lateral, dorsal, medial, distal views. Scale bars – 1 cm. Image credit: Chester et al, doi: 10.1098/rsos.170329.
Dr. Stephen Chester and co-authors analyzed a partial skeleton of Torrejonia wilsoni, a small primate that lived in what is now western North America around 62 million years ago (early Paleocene).
The skeleton was found in the Nacimiento Formation, San Juan Basin, New Mexico, by Dr. Thomas Williamson, curator of paleontology at the New Mexico Museum of Natural History & Science, and his twin sons, Taylor and Ryan.
It consists of over 20 separate bones, including parts of the cranium, jaws, teeth, and portions of the upper and lower limbs.
The study shows that Torrejonia wilsoni — a member of an extinct group of primates called plesiadapiforms — had skeletal features adapted to living in trees, such as flexible joints for climbing and clinging to branches.
Previously, paleontologists had proposed that plesiadapiforms were terrestrial, based on details from cranial and dental fossils consistent with animals that nose about on the ground for insects.
“This is the oldest partial skeleton of a plesiadapiform, and it shows that they undoubtedly lived in trees,” said Dr. Chester, lead author of the paper reporting the results in the journal Royal Society Open Science.
“We now have anatomical evidence from the shoulder, elbow, hip, knee, and ankle joints that allows us to assess where these animals lived in a way that was impossible when we only had their teeth and jaws.”
The study supports the hypothesis that plesiadapiforms, which first appear in the fossil record shortly after the extinction of non-avian dinosaurs, were the earliest primates.
The team also contends that the new data provide additional evidence that all of the geologically oldest primates known from skeletal remains, encompassing several species, were arboreal.
“To find a skeleton like this, even though it appears a little scrappy, is an exciting discovery that brings a lot of new data to bear on the study of the origin and early evolution of primates,” said senior author Prof. Eric Sargis, of Yale University.
“Palaechthonids, and other plesiadapiforms, had outward-facing eyes and relied on smell more than living primates do today — details suggesting that plesiadapiforms are transitional between other mammals and modern primates.”
Source: sci.news
