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

Re: Hanson 2006, Mortimer, Baeker response

Mike Taylor wrote:

I'm not sure I can agree with your position. For example, I've got pretty bored of repeatedly writing "non-neosauropod sauropod" recently; wouldn't it be nice just to define Eosauropoda as the paraphyletic group (Sauropoda - Neosauropoda) and then just refer to eosauropods?

Although "non-neosauropod sauropod" is a cumbersome term, it is also explicit. I can't see any inherent reason why this term is bad. "Non-neosauropod sauropod" tells the reader *exactly* what you mean, without having to invent a new term.

As for the paraphyletic group "Eosauropoda"... this would be difficult to define using species or specimens. You'd have to come up with a definition like "All descendents of the most recent common ancestor of A and B, but excluding all descendents of the most recent common encestor of B and C, where C is more derived than A." We have enough trouble defining MONOphyletic groups - defining PARAphyletic groups sounds like buying trouble.

> For example, I don't want to back to the bad old days when Theropoda was paraphyletic, and > birds (Aves) were excluded because they were considered too "different" to be put in with > the theropods.

That example is misleading, because the confusion arises from two differing candidate meanings (one monophyletic, the other not) of the same existing name. I agree with you that it's always bad to have multiple meanings for a name, but that is orthogonal to whether all names should refer to clades.

I don't think this example is misleading, because a lot of people do complain about the term "non-avian theropod". But if we are going to define groups by shared common ancestry (as phylogenetic taxonomy aims to do) then using paraphyletic groups is counterproductive.

I hate to disappoint you, but you are allowed to use osteological features and molecular sequences only :-) 

Aw shucks.  No 'soft anatomy' analyses, huh?    :-)

Yes!  See Recommendation 11F on page 50:

        Recommendation 11F. Clade names created by adding
        certain prefixes or suffixes to another clade name
        (the base name) should be defined in a manner
        consistent with the hierarchical relationships implied
        by the prefix or suffix and the phylogenetic
        definition of the base name (if established), unless
        doing so would be inconsistent with the predominant
        current use of a preexisting name.
        [...]

This would surely only apply to co-ordinated family-level taxa, wouldn't it? This Recommendation would only affect names ending in -oidea, -idae, -inae, -ini("superfamily", "family", "subfamily", "tribe", respectively). This appears to be the current practice anyway, so it shouldn't cause any problems - so long as these clades are defined with this hierachial principle in mind. AFAIK, there have never been "standard" suffixes for "orders", "classes", "phyla", 'kingdoms", etc - for zoological nomenclature, anyway.

        Note 11F.1. The following prefixes and suffixes imply
        greater inclusiveness than the base name: Holo-, Pan-,
        -formes, -morpha. The following prefixes imply lesser
        inclusiveness than the base name: Eo-, Eu-, Neo-,
        Proto-. The following prefixes imply mutual
        exclusivity with the base name: Pseudo-, Para-. These
        are not intended to be exhaustive lists.

Now this is a great idea. One thing that bewildered me was having the clade Suchia inside the clade Pseudosuchia - though Pseudosuchia isn't used so much these days.

I also think it's a great idea to have a clade beginning with Eu- or Neo- to be inside the corresponding more-inclusive clade, especially given the situation regarding certain dinosaur clades. For example, Ornithopoda (node-based) is defined to include _Heterodontosaurus_ but to exclude _Triceratops_. Thus, if heterodontosaurids are closer to ceratopsians than to euronithopods, then Ornithopoda is invalid, but Euornithopoda (stem-based) would continue. This is very silly.

Cheers

Tim