Ichnotaxa (was RE: dino tracks near Syracuse?)

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> R. Irmis
>
> <<Interestingly, the paper I have here says that direct fossile evidence
> takes presedence over indirect evidence, and thusly the name _Coelophysis_
> is retained and _Grallator_ dropped.>>
>
> Actually, there is really no way in the world we can assign these
> footprints
> to Coelophysis.  Pretty much any theropod the size of the footprints could
> have made them.  Therefore, Grallator is most certainly retained.  It is
> what is refered to as a form genus, and refers to the form of the
> footprint,
> since we cant refer to any body fossil genus.

It wouldn't matter if every single _Grallator_ track ended with a dead
_Coelophysis_: BOTH names would be retained!!

_Grallator_ is not, nor has ever been, the name of a dinosaur.  It is the
name of a type of dinosaur track.  Animal footprints, burrows, scratch
marks, and other trace fossils have traditionally been given their own set
of Linnean-style taxonomic names.  These names do NOT apply to the track
maker: they only apply to the track form itself.

So if _Coelophysis_ were to produce three or four different track forms (as
well it could: normal walking, walking on very soft substrate, walking on
the metatarsal pads, etc.), each would have its own "ichnotaxon" name.
Similarly, as nearly every basal theropod would likely produce the same kind
of tracks as _Coelophysis_, those tracks would ALL be _Grallator_.

Personally I think the tradition of retaining a Linnean-style ichnotaxonomy
was foolish; trace fossils are biogenic sedimentary structures, and not
slices or branches of the tree of life.  Certainly they deserve to be named
(just as other sedimentary structures are).  However, the practice of using
the same style of names for sedimentary structures as we use for slices or
branches of the tree of life (true taxa) is misleading, as this discussion
has shown.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796