Archaeopteryx and Dino-Bird Evolution

Erm, yeah. Or rather, convergence. Only the chicks have wing claws. It's a defense mechanism. Hoatzin live in riverside/swamp trees and they're pretty lousy fliers. When threatened, chicks dive into the water to escape, then use the wing claws to climb back up. The only other significant trait "shared" with Archy is a reduced breastbone. This adaptation is a trait reduction - flight sacrificed (apparently) to accommodate a really large digestive pouch that functions exactly like a rumen (foregut fermentation). One of the only obligate folivores.I know a lot of people have compared Archy and the Hoatzin, but "sharing many features" may be stretching it a bit. Us Evilutionists need to be more careful than most when it comes to streatching a point with the creos.

No prob. It actually IS a good argument for homology (the claws) and adaptive reduction (the sternum). We've got a family group (~flock) of hoatzin living on a river island in the reserve I'm working with on the Rio Napo. I love telling people, "If you squint your eyes a bit, you can briefly glimpse 100 million years ago the ancestors of the ancestors of modern birds." When I'm talking to folks in the field, I allow myself a bit of fancy now and then. When we're talking to our resident carpet-chewers, however, we have to be a bit more careful.I owe THAT lesson to our very own Wounded King. And a painful lesson it was...

You can't win Coragyps. He's got the Revised Quote Book and is already on the "H"'s.

Guess what? You're right (doesn't it feel good to be justified?). Try Scott, GB 1980, "The primate caecum and appendix vermiformis: a comparative study.", J. of Anatomy 131:549-63

quote:

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The examination of the caecum of two groups of cynomolgus and rhesus monkeys, two orang-utans and a chimpanzee, as well as an extensive review of the available literature, confirmed that the length of the caecum, relative to that of the colon, decreased as the position of the species in the primate scale rose. Although absent in prosimians and New World monkeys, there was evidence that the appendix vermiformis began to develop in certain Old World monkeys and became fully developed in the anthropoid apes, showing that, far from being a vestigial organ, it has actually developed progressively in primates.

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I think it's very interesting that this author downplays the "vestigial" nature of the appendix in certain primates. However, I think he's using a misleading definition of vestigial. As you suggested, it depends on the lineage - and the diet to which they are adapted. For instance, colubine monkeys (old world), are primarily folivores and have developed a foregut digestive system - completely doing away with an appendix, which the lineage never developed (although it does have a caecum). Another major lineage of folivorous monkeys - the Cebidae (new world) - are hindgut fermenters and have only a caecum. Great apes appear to be the only lineage of primates that have developed an appendix. (see, for example, BANR 2003, "Nutrient Requirements of Non-Human Primates", NAP, ppg 22-26). In humans, out of all the hominins, the appendix is highly reduced, probably related to the change in diet when our ancestors left the forest for savannah in the Pliocene. Although still serving a dietary function in the great apes, the only apparent function in humans is as a small part of our immune system - IOW a coopted function, which is my definition of vestigial.

Sorry. How about I add, "Unlike the anthropoids noted above, folivorous birds like the hoatzin have never developed an appendix. Hoatzin digestive systems use a fermentation sack in the foregut similar to the rumen of even-toed ungulates. Although fossil evidence of archosaurian herbivore digestion is limited to non-existent, modern folivorous reptiles such as the iguanids and a few turtles are all hind-gut fermenters relying on a cecum for digestion. Since the vast majority of modern birds, whether fructivores, insectivores, nectarvores or opportunistic omnivores do not posess either appendix or caecum, we can probably conclude that if birds developed from dinosaurs, then they derived from a non-herbivore lineage rather than an archosaur. This lends some further evidence to the dromaeosaur origin of birds - a lineage which includes Archeopteryx."

I know. I was just trying to be a smart ass. Guess it didn't work.This message has been edited by Quetzal, 05-05-2006 08:55 AM

You didn't really just claim that platypus are birds, did you?abe: I see Dr. Jones beat me to this one. Hey, at least it shows people are reading your posts...Edited by Quetzal, : No reason given.