The First Mammal in Evolutionary History

April 14, 2013 in Trivia

Species Hadrocodium wuiHadrocodium wui is the name given to the first true mammal identified so far in our natural history. According to William J. Cromie of the Harvard University Gazette, its discovery was reported in the journal Science in May, 2001 by Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh; Crompton; and Ai-Lin Sun, formerly of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.

This finding originates with the discovery of the skull of a shrew-like animal the size of a paper clip. The discovery pushes back the origin of mammals, including humans, to 195 million years ago ─ versus 150 million years ago as previously believed.

While dinosaurs still dominated the earth, these small creatures already had become part of the ecosystem.

According to Cromie, they were “diminutive insect-eating animals, part reptile, part something new. When a meteor strike or some other unknown calamity wiped out the giant reptiles and many other animals some 65 million years ago, the shrew-like  newcomers prospered. They began evolving into different types of mammals and eventually gave rise to everything from field mice to elephants, whales, and humans.”

H e continued, “The new fossil was found in YunnanProvince in southern China more than 10 years ago. Ai-Lin Sun brought it to the United States when she came to Harvard as a visiting professor. Nothing much happened to the little skull, securely encased in rock, until William Amaral of Harvard’s Museum of Comparative Zoology carefully freed the skull from its rock entombment. Zhe-Xi Luo did a major analysis of the skull. Based on his work, the three scientists concluded that H. wui either is, or is very close to being, the oldest known true mammal and a missing link between reptiles and mammals.”

As explained by the Carnegie Museum of Natural History, the species’ name “Hadrocodium wui” refers to “its exceptionally large brain (hadro is Greek for ‘large and full,’ and codium is Greek for ‘head’).”

“Mammals differ from non-mammalian vertebrates by possessing a very large brain and an advanced ear structure,” according to Zhe-Xi Luo, Carnegie’s Curator of Vertebrate Paleontology. “It has been a challenge for scientists to trace the origins of these important mammalian features in the fossil record. Previously, these important mammalian traits could only be traced to the Late Jurassic … The discovery of Hadrocodium pushes back their origins by some 45 million years to the Early Jurassic.”

According to findings published in Science, paleontologists from the University of Texas at Austin, Carnegie Museum of Natural History and St. Mary’s University in San Antonio have concluded that “mammals first evolved their characteristic large brains to enable a stronger sense of smell.”

As reported in 2011 by the University of Texas at Austin’s Jackson School of Geosciences, “This latest study is the first to use CT technology, similar to medical scanners, to reconstruct the brains of two of the earliest known mammal species, both from the Jurassic fossil beds of China. The 3D scans revealed that even these tiny, 190-million-year-old animals had developed brains larger than expected for specimens of their period, particularly in the brain area for smell.”

These mammalian or close ancestors may go back even further. According to the Lunar and Planetary Institute of the Universities Space Research Association, some fossils of early mammals ─ small, shrew-like animals that probably lived in caves or burrows and hunted insects and small reptiles at night ─ are more than 200 million years old.