The story of shrews

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Posted:

18 Dec 2024

Shrews, small mole-like mammals, are widespread across the planet. There are hundreds of living shrew species from Central and North America to Europe, Asia and Africa. They are part of a group called the Soricidae, and share evolutionary history with other mammals such as moles, hedgehogs, and gymnures.

Although the outward appearance of all shrews is similar, researchers including Trinity Hall’s Dr Robert Asher have uncovered their hidden diversity through investigation of their anatomy, palaeontology and molecular biology.

The researchers discovered a novel bone in ‘Congo’ shrews (Congosorex polli) and ‘mouse’ shrews (Myosorex) from Africa. This elongated, needle-like bone projects over the back of their necks and can be as long as their forearm. Important muscles from the shoulders, neck and head attach to this bone. It does not appear to protrude beyond the skin, and despite its needle-like appearance, it lacks an obvious conduit for venom. In the samples available, it is similar in size in males and females. Although the function of this bone is yet to be confirmed, it is likely relevant to mobility of the head but researchers cannot rule out a role in defence or acoustics.

In the fossil record, shrews are usually known only from fragmentary jaws and teeth. A new, 33-million-year-old fossil from Wyoming is much more complete and shows the anatomy of this ancient shrew’s skull and forelimb. It shares several features with living shrews, such as its jaw joint. Instead of a single connection between the lower jaw and the rest of the skull, shrews’ jaws are separated into distinct upper and lower facets. Such morphology allows these species to carry out complicated yet well-coordinated chewing movements. In other regards, the new fossil differs from living shrews, for example in the anatomy of its nose and ear regions. These exhibit similarities to the nose and ear skeletons of moles and gymnures, and demonstrate the piecemeal evolution of these animals from a common ancestor, estimated to have existed over 57 million years ago.

About Dr Robert Asher

Dr Robert Asher is a Trinity Hall Fellow in Natural Sciences (Zoology), University Associate Professor and Curator of Vertebrates at the Museum of Zoology. His research focuses on how the many radiations of mammals, particularly those from the southern hemisphere, develop and are interrelated.

Original paper

Yuan H, Dickson ED, Martinez Q, Arnold P, Asher RJ. 2024 The Origin and Evolution of Shrews (Soricidae, Mammalia). Proc. R. Soc. B 291: 20241856.