tgamble

Dinosaurs weren't reptiles? How's that? Archie is said to have reptilian features and bird features and also be a transitional between dinosaurs (which weren't reptiles?) and birds. I'm confused! <img src="confused.gif" border="0">

Peez

The problem is that "Reptilia" is not a monophyletic group (it is not defined by one common ancestor). Extant reptiles are members of at least three monophyletic groups, and it becomes a semantic argument as to which groups should be included. Meanwhile, the dinosaurs are not a monophyletic group either, as traditionally recognized. In order to make dinosaurs monophyletic, birds would have to be considered dinosaurs. In order to make reptiles monophyletic, birds, dinosaurs, Ichthyosaurs, Plesiosaurs, and perhaps mammals would have to be considered reptiles (this is the group known as Amniotes).

Meanwhile, the author's sister is not a fungus because we have defined the fungi as members of a Kingdom of organisms with a common ancestor, and we humans are members of a different Kingdom with its own common ancestor. Neither reptiles nor dinosaurs are defined in this way, rather they are grouped together based on shared features. So, are dinosaurs reptiles? Really a semantic argument.

Peez

Boro Nut

Are suggesting they were Jewish?

MrDarwin

It depends on how you define "reptile". In classical taxonomy, largely following "folk" taxonomy, reptiles are a group that by definition excludes mammals and birds--two groups that we now know evolved from within the group commonly known as "reptiles". Reptiles are creatures that are cold-blooded, generally covered with scales, and lack wings, feather, hair, and warm-bloodedness. But these characteristics are primitive characteristics, and were characteristics of the ancestral birds and mammals--so "Reptilia" has been defined not on the basis of unique characteristics that the creatures have but rather on the characteristics they are lacking. It would be a bit like defining "mammals" to exclude bats because they have wings, and other mammals do not.

We know that life has a phylogeny and a series of relationships--based on the fundamental evolutionary concepts of common ancestry and divergence over time--but it's entirely arbitrary how we recognize these relationships and what labels we put on the various groups we recognize within this series of relationships. How we recognize groups--drawing lines around them and naming them--often depends on patterns of extinction, and whether "intermediate" or "transitional" forms still exist. Many groups, like "reptilia", break down entirely once we examine the fossil record because we see the early birds and mammals, and discover that they are much more like "reptiles" than living birds and reptiles.

There has been a fundamental shift in the last couple of decades in the way that taxonomic groups are defined and named. I don't want to go too much into cladistics, but suffice to say that the idea now is that once you are a member of a group, you will always be a member of that group; you simply can't evolve out of being a member of a group that you originated in. And in the cladistic concept of "monophyly" these groups should always be named to include all their elements, no matter how much some of them may have evolved to become different from the other members of the group.

MrDarwin

BTW if anybody ever writes an "Icons of Creationism" the picture on this booklet, showing a tyrannosaurus in the same landscape as a human city, should be featured prominently. Where is the evidence that dinosaurs and humans ever existed together? It's entirely in the minds of creationists, yet numerous creationist publications and websites show images of humans and dinosaurs co-existing.