The nature of cladistics (birds and dinosaurs)
kinman2 at YAHOO.COM
Fri Nov 19 11:50:30 CST 2004
Of course Reptilia is one of the easiest paraphyletic groups to maintain---it's so darn obvious and useful!!! Most useful paraphyletic groups aren't nearly that obvious, so Reptilia is a more clear-cut and well-known example. Unfortunately that also makes it the most common target of strict cladism.
As for Velociraptor, there is mounting evidence that they had small ancestors that could fly (microraptorines). So the velociraptorines are not all that much different than any other bird group (such as ratites) that returned to the ground and abandoned such flight capability. On the other hand, tyrannosaur ancestors hadn't gotten to the flight stage (just simple protofeathers for thermoregulation and brooding of eggs). The evolution of flight feathers from protofeathers is one of the major evolution events of the Mesozoic (flowering plants are another). Velociraptor and Corvus share these complex feathers, similar eggshell microstructure, and lots of other synapomorphies (which are lacking in tyrannosaurs, non-coelurosaur saurischians, and ornithischians).
If you dig deeper, there really is some method to what you may consider Kinmanian madness. Where biologists ultimately draw the line between reptiles and birds remains to be seen (the Chinese fossils just keep on coming), perhaps even maintaining the traditional cut-off at Archaeopteryx (some analyses show it spliting off BEFORE velociraptorines and microraptorines!). But that little bit of quibbling (exactly where to draw the line) is a minor nuisance compared to the taxonomic quagmire the strict cladists are making of it. They certainly seem to have failed to effectively communicate the big differences between tyrannosaur ancestors and velociraptor ancestors (structure of the feathers, eggshell microstructure, non-flight vs. flight, and so on). If early Velociraptor fossils had shown the feathers (the way they were preserved in Archaeopteryx), it too would probably have been classified as a wing-clawed bird right at the very start (although secondarily grounded, like moas or elephant-birds).
Honestly, I don't have a clue what you are talking about--the situation to me seems exactly opposite. It's easy to maintain a paraphyletic Reptilia when the closest known relatives of birds are crocodilians, but with all the new fossil finds, we are facing a situation where some would claim (if I understand one of your previous posts correctly) that Velociraptor is a bird and Tyrannosaurus is a reptile. The value of classifying the latter, but not the former, in a major group with turtles and cynodonts totally escapes me. What differences can Velociraptor (or even Corvus) possibly have from Tyrannosaurus that they would be more important than both their similarities with Tyrannosaurus and its differences from cynodonts.
More information about the Taxacom