Many mammoths had an extra rib growing from the vertebrae in their necks, a sign of inbreeding in modern animals, say European researchers.
The findings suggest inbreeding may have contributed to the decline and eventual extinction of the hairy giants.
Researchers recently noticed that the remains of woolly mammoths from the North Sea often possess a ‘cervical’ (neck) rib—in fact, 10 times more frequently than in modern elephants (33.3% versus 3.3%).
In modern animals, these cervical ribs are often associated with inbreeding and adverse environmental conditions during pregnancy.
If the same factors were behind the anomalies in mammoths, this reproductive stress could have further pushed declining mammoth populations towards ultimate extinction.
Mammals, even the long-necked giraffes and the short-necked dolphins, almost always have seven neck vertebrae (exceptions sloths, manatees and dugongs), and these vertebrae do not normally possess a rib.
A cervical rib itself is relatively harmless but its development often follows genetic or environmental disturbances during early embryonic development. They are strongly associated with stillbirths and multiple congenital abnormalities.
Researchers from the Rotterdam Museum of Natural History and the Naturalis Biodiversity Center in Leiden examined mammoth and modern elephant neck vertebrae from several European museum collections.
“It had aroused our curiosity to find two cervical vertebrae, with large articulation facets for ribs, in the mammoth samples recently dredged from the North Sea,” said Jelle Reumer, one of the authors on the study published today in the open access journal PeerJ.
“We knew these were just about the last mammoths living there, so we suspected something was happening. Our work now shows that there was indeed a problem in this population.”