[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Campbell's even crazier than a MANIAC? (archeopteryx



Still, a leaping animal would essentially begin with a ballistic trajectory, and I have a hard time imagining an intermediate structure that would be advantageous. I would think a leap would lead to low drag structures and forelimb positions...

...I just cannot imagine evolution acting on anything aerodynamic in a terrestrial ancestor without preexisting aerodynamic adaptations, unless that ancestor is falling (be it a cliff or tree)

The catch here is that the ancestral condition for some groups, birds in particular, may include some sort of exapted foil. Forelimb feathers are becoming increasingly well known for a range of maniraptorans outside Aves, including taxa which were clearly terrestrial. Phylogenetically speaking, the current bracket places forelimb "proto-wings" at a node rather near the base of Maniraptora (perhaps even outside that).



don ohmes wrote:

If "easier" is defined as "a larger and more diverse feedstock of 'flight-candidate' organisms", then gravity-driven evolution _is_ easier. In other words, any animal that might fall or pounce from a high place has the potential to evolve at least passive flight. The same cannot be said of all ground-dwellers, most of which would need to evolve leaping ability first, at a minimum.

So, essentially, we might predict that a greater percentage of powered flyers would come from arboreal lineages than terrestrial ones. In practice, this doesn't seem to have worked out - birds seem to have a mostly terrestrial ancestry (with some semi-arboreal members possibly present), and bats seem to have an arboreal ancestry, while pterosaurs and insects are somewhat equivocal at present. All told, there is not a clear bias towards arboreal ancestry. This could be because of the small sample (only four origins of powered flight), or it could be that terrestrial lineages have a greater chance of producing flyers than we might otherwise expect. It could also be that derivation of powered flight is actually rare among arboreal lineages, even though gliders are rather common. Quite a few of the living arboreal gliders would lose gliding efficiency through airfoil oscillation, so the actual 'flight-candidate' pool might be smaller than it appears.


Cheers,

--Mike


Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280-0181 habib@jhmi.edu