What led to wooly mammoths' extinction

Researchers have suggested that neck ribs in woolly mammoths can provide clues about their decline and eventual extinction.

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 per cent versus 3.3 per cent).

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.

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. We knew these were just about the last mammoths living there, so we suspected something was happening," said Jelle Reumer, one of the authors on the study.

The incidence of abnormal cervical vertebrae in mammoths is much higher than in the modern sample, strongly suggesting a vulnerable condition in the species. Potential factors could include inbreeding (in what is assumed to have been an already small population) as well as harsh conditions such as disease, famine, or cold, all of which can lead to disturbances of embryonic and fetal development.

Given the considerable birth defects that are associated with this condition, it is very possible that developmental abnormalities contributed towards the eventual extinction of these late Pleistocene mammoths.

The study has been published in the open access journal PeerJ.