Earliest birds acted more like turkeys than common cuckoos

November 14th, 2007 - 8:33 am ICT by admin  
According to Christopher Glen of the University of Queensland, all fossil species, representing evolutionary lineages from non-flying ancestors to early flying birds, had claws more like modern birds that spend most of their time on the ground.

The researchers claim that the evolutionary ancestors of birds primarily made their living off the ground rather than in trees.

“The claws of Mesozoic birds and their immediate ancestors, the non-avian theropods, are relatively ’straight’-most like [those] of birds that are now either specialized for walking on the ground or have a preference for it, rather than the highly curved claws of birds that spend a lot of time in trees,” says Glen.

In their study, Glen and his colleagues suggest that part of the problem is the loose categorization of many living bird species as either ground- or tree-dwellers on the basis of their hind limbs when, in reality, these are not mutually exclusive alternatives.

Rather, they said that birds exhibit differing degrees of ground- and tree-based behaviours and would be better placed along a continuum according to the proportion of time spent on ground versus tree foraging.

To test the idea, Glen’s group first analyzed the toe claws of 249 species of recent birds, revealing that their claw curvatures increase, becoming more hooked, as tree foraging becomes more predominant. They then compared the claw curvatures of modern birds to those of the fossilized ancestors of birds.

“Since claw angle is independent of body size and the evolutionary relationships among species, it is a reliable indicator of the predominant behaviour reliant upon hind-limb locomotion, and can make an important contribution to reconstructing the ‘ecomorphology’ of fossil species. Our findings suggest early birds foraged predominantly on the ground, rather than supporting previous suggestions of arboreal claw adaptations, which appear to have evolved later in the lineage,” they concluded. (ANI)

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