All mammals–humans and giraffes, mice and dolphins–have the same number of vertebrae. Manatees (and sloths, but they don’t matter in Marine Science Today) are a unique exception to this rule. New research published in BioMed Central’s open access journal EvoDevo shows how different species have evolved their unique necks.
Reptiles, amphibians and birds have varying number of vertebrae in their necks, but mammals, regardless of shape or size, have seven. Abnormal numbers of vertebrae are usually correlated with an increased risk in stillbirth, childhood cancer and neuronal problems in mammals, often associated with physical problems due to misplaced or crushed nerves, muscles and blood vessels.
The skeletons of manatees were compared to dugongs and hyraxes. Interestingly, about half the dugongs and a couple of hyraxes had an abnormal number of neck vertebrae and all had other skeletal abnormalities.
Dr. Galis from the Netherlands Centre for Biodiversity Naturalis said, “We think that it is the slow lifestyle and low metabolic rate which has allowed evolution to alter the neck length of [manatees] without any of the side effects seen for other mammals. Their low metabolic rates protect them from cancer and their low activity rates protect them from thoracic outlet syndrome.”
Copyright © 2011 by Marine Science Today, a publication of OceanLines LLC