Woolly Rhino’s Neck Ribs Offer Clue Into Extinction

Arrows indicate large articulation facets of cervical ribs on a fossil cervical vertebra of a woolly rhino of Naturalis, Leiden. (Frietson Galis)

(CN) – A developmental abnormality that contributed to the extinction of woolly rhinos could serve as an indicator of at-risk populations among modern rhinoceros species, several of which are already considered endangered or threatened.

Dutch researchers report the connection Tuesday after examining the remains of woolly rhinos from the North Sea, which revealed a strong association between a “cervical rib” and the ultimate demise of these late Pleistocene animals. Their study was published in the open-access journal PeerJ.

While the cervical rib – a rib attached to a cervical vertebra – is harmless by itself, the condition is often linked to adverse environmental conditions during pregnancy and inbreeding.

The team argues that screening modern rhinos for such a defect could facilitate more effective intervention strategies.

“Our study suggests that monitoring the health of the vertebrae in rhinos has the potential to timely detect developmental errors that indicate the level of extinction risk,” said co-author Frietson Galis, an evolutionary developmental biologist at the Naturalis Biodiversity Center at Leiden University in the Netherlands.

Authors Alexandra van der Geer (left) and Frietson Galis (right) investigating a vertebra of a woolly rhino. (Jacques van Alphen)

The researchers also note that the lack of cervical ribs in modern samples does not mean that current rhino species are healthy or safe, as museum collections are based on specimens that were collected at least 50 years ago.

The team investigated the demise of woolly rhinos after Galis found a surprisingly high percentage of cervical ribs in woolly mammoth specimens as part of an earlier study.

“This aroused our curiosity to also check the woolly rhino, a species that like the woolly mammoth lived during the late Pleistocene and similarly died out,” said lead author Alexandra van der Geer, a researcher at the Naturalis Biodiversity Center. “Our work now shows that there was indeed a problem in the woolly rhino population.”

Rhino populations are dwindling worldwide, particularly over the past couple decades, leading to near extinction of several species. The western black rhino and a subspecies of the Javan rhino are now completely extinct.

Restoration of the woolly rhinoceros by Charles R. Knight, 1916.
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