Environment, forced change in habitat determine burrowing capacity of mammals: Study

November 14th, 2007 - 3:00 am ICT by admin  
According to University of Oregon palaeontologist Samantha Hopkins, environmental influences and forced changes in habitat play a significant role in determining the physique and physical attributes of burrowing mammals.

In a talk at the annual meeting of the Geological Society of America, Hopkins presented preliminary findings of one line of her research.

She said that moles and mole rats are examples of mammals that have adapted to moving soil in rocky, root-packed soils, in opposition to most other burrowing mammals that prefer softer, dryer sandy soils.

“It requires a lot of morphological adaptation, a lot of tradeoffs, to be good at digging. Burrowing mammals acquire a complex of features that lets them handle whole days moving soil. They make for a great case for understanding convergent evolution because in spite of how difficult it is to do this — in spite of all the costs of doing this — it seems to be worthwhile enough that many mammals have done it through time,” Hopkins said.

Convergent evolution is the development of similar characteristics, necessary for survival, among unrelated organisms in the same environmental conditions.

Hopkins studies living burrowers as well as the fossil records of such mammals, living and extinct worldwide, to understand why some choose to live — and dig for their food and to avoid predators — in harsher regions.

Conventional thinking, she said, is that mammals evolved into burrowers after being driven into grassland habitats, where going into the soil is their only option to eat or escape in the absence of trees.

Fossils found in the field or in museum collections allowed Hopkins to examine and compare the structure of burrowing mammals’ shoulders, skulls, legs, feet and claws to get clues of what features developed and possibly at what points in time these skeletal changes occurred.

In her talk, Hopkins briefly described known methods of burrowing, including scratch, head-lift, incisor and humeral rotation.

As a doctoral student at the University of California, Berkeley, Hopkins studied the fossil record of the extinct burrowing mammal Ceratogaulus, the only horned member of the digging group Mylagaulidae.

The gopher-like rodents used the head-lift technique, in which they use the tips of their snouts, powered by enlarged neck muscles, to drive into soil.

As part of her dissertation, she showed in the Proceedings of the Royal Society B in 2005 that the horns were used for defense against predators — not to help with the digging as had been previously theorized.

Existing head-lift diggers include marsupial moles, blind mole rats and mole voles. More common land-dwelling burrowers, which use a variety of techniques, are badgers, ground squirrels, burrowing owls, aardvarks, nutria, kangaroo rats, shrews, prairie dogs and armadillos.

The National Science Foundation and the National Evolutionary Synthesis Center are funding Hopkins’ research. (ANI)

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