Thoughts (and concerns) about Epidendronosaurus

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

Greetings,

Have seen the Epidendronosaurus paper, and am both impressed and a bit
concerned.

My concern is NOT that it is an artificial composite: the way the various
pieces extend from one block to the next argue against it.  My concern is
the possibility that it is a natural chimera: that there are more than one
taxon represented in this specimen.

The first thing that struck me is that there is no counterslab shown.  For
fossils in this mode of preservation, that information can be wonderfully
important.

The second is that the sclerotic ring shows no sign of being composed of
separate ossifications, as in typical dinosaurs.  There is no sign of
segmentation in the ring.  Puzzling.

I am very dubious of the nature of the "tail impression": no part of the
tail is preserved, only an apparent impression in (admittedly) the proper
position between the (unquestionably theropod) hindlimbs.

The mandible has large prongs described as the articular, but look for all
the world to me as the coronoid processes of typical lepidosaurs.  The broad
arc of the mandibles, too, reminds me more of lizards and sphenodontians
than of dinosaurs.  Too bad there are no close ups of the jaws: I'd love to
know if it has thecondont (or acrodont, or whatever) dentition.

And the big problem: the manus.  It is not found in articulation.  The long
isolated digit is interpreted as digit III, preseriving phalanges III-1 to
III-4.  However, there is not evidence at present to show that their "III-1"
isn't really a metacarpal II, in which case the longest digit here would be
digit II (as in theropods typically).  Futhermore the only digit for which
some of the elements seem to be in place is in the proper position for digit
III, although they identify it as digit II.

I offer these observations only as hypotheses: I'm not committed to them.
They have just begun to describe members of this new fauna (this critter is
NOT from the Yixian, but from the (interpreted as stratigraphically older,
possibly Late Jurassic) Daohugou Formation.

Looking forward to seeing Czerkas' critter for comparison.

                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