Woolly mammoths possessed bizarre neck ribs which may have speeded up the process of their extinction, a new study finds.
Previous studies have found that inbreeding coupled with a changing climate was responsible for the extinction of the woolly mammoth. This mammoth species suffered from widespread birth defects in its final years on Earth. After studying 12,000-year-old mammoth fossils from the North Sea, researchers found that the giant animal possessed a "cervical" (neck) rib which is generally associated with inbreeding and adverse environmental conditions during pregnancy. The discovery led researchers to speculate that this reproductive stress could have further pushed declining mammoth populations toward ultimate extinction.
"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," Jelle Reumer, a paleontologist at the Natural History Museum of Rotterdam and Utrecht University and an author of the study, said in a statement. "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."
Cervical ribs are considered a serious deformity in humans. Ninety percent of humans with neck ribs die before reaching adulthood, according to Science Mag,
"The high incidence and large size of the cervical ribs [in woolly mammoths] indicates a strong vulnerability, given the association of cervical ribs with diseases and congenital abnormalities in mammals," the researchers noted in a study published in the journal PeerJ. "The vulnerable condition may well have contributed to the eventual extinction of the woolly mammoths."
The researchers also examined bones of 21 Asian elephants and 7 African elephants that were in museum collections in Europe. Among the 28 elephants, only one had a cervical rib. This led researchers to state that cervical ribs were 10 times more common in woolly mammoths from the North Sea than in modern elephants.
Researchers cite two possible reasons for the high incidence of cervical ribs in mammoths. One reason could be because they were interbreeding and secondly, it is a known fact that the species was struggling with famine, disease and other environmental conditions that made it difficult for female mammoths to bear healthy offspring.
"A combination of inbreeding and harsh conditions may be the most likely explanation for the extremely high incidence of cervical ribs," the research team said, according to LA Times. The animals' vulnerability "may well have contributed to the eventual extinction of the woolly mammoths."
The study was founded by Synthesys travel grants that allowed the researchers to visit the Royal Museum for Central Africa Tervuren, the Zoological Museum Copenhagen and the Natural History Museum of Stockholm.
Findings were published in the open access journal PeerJ.
