Last updated June 28, 2018 at 9:54 am
Food, not body size, drives length of marsupial snouts.
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A study involving 16 species of kangaroos and wallabies has thrown into question one of the assumed rules governing the evolution of body shape.
Among many families of mammals there is a general trend that links body size with facial shape: in any given species group, the ones with larger bodies generally have more elongated faces.
So common is this association, that it has long been thought to be a function of biological development. One suggestion is that the process is driven by the mechanics of vocalisation: as a species grows in size, the anatomical structures needed to produce calls and cries also has to increase, producing a more elongated skull shape compared to smaller members of the same taxa.
Research led by University of New England zoologist Rex Mitchell examining the snout shapes of kangaroos, however, reveals a morphological mechanism unrelated to size.
In a paper published in the journal Proceedings of the Royal Society B, Mitchell and his colleagues report that facial form is determined by diet.
The shape and length of kangaroo and wallaby faces, the scientists report, is governed by a combination of preferred foodstuffs and the bio-mechanical methods used to gather them.
Shorter muzzles were consistently found to be associated with a diet of hard and difficult-to-break plant species. The facial shape enabled the animals to slice through the tough tissue using their incisor teeth. Conversely, long muzzles were linked to a diet of soft plants and gentle chewing.
The researchers say the discovery will be useful in at least two fields. In ecological remediation, knowing the snout size of resident roos and wallabies will inform choices regarding which vegetation species to plant. And in palaeotology, the skull shapes of fossils will inform suggestions regarding habitat, diet and behaviour.
