[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Re: A few more...
>Node-based names and stem-based names yield identical clades, because any
>node can be the base of only one clade. So, for example, your Neotheropoda as
>a stem-based name may be defined as "all taxa sharing a more recent common
>ancestor with birds than with herrerasaurians." Which type of definition you
>employ is strictly a matter of convenience, perhaps depending on whether you
>know just where the root node is or not.
There seems to be some confusion here. Although it is indeed possible to
name a node rooted at the joining of two stem groups, there are not the same
Here's an example:
Reptilia (node) = the most recent common ancestor of turtles, lepidosaurs,
and archosaurs, and all of that ancestor's descendants. Includes living
taxa such as turtles, tuataras, squamates ("lizards" & snakes), crocs, and
birds, as well as nonavian dinos, other extinct archosaurs, and possibly the
ichthyosaurs and sauropterygians.
Sauopsids (stem) = reptiles and all taxa closer to reptiles than to
mammals. Includes extinct non-reptilian sauropsids such as mesosaurs,
perhaps procolophonids (may be closer to turtles), and perhaps ichthyosaurs.
The node which joins Sauropsida with its sister-taxon, Synapsida, is called
Thomas R. Holtz, Jr.
Dept. of Geology
University of Maryland
College Park, MD 20742