Re: antorbital fenestra in _Triceratops_

[Dinogeorge@aol.com]

In a message dated 98-09-09 00:47:53 EDT, jconrad@lib.drury.edu writes:

<< I was recently in Chicago and at the field museum I noticed that one of the
 skulls of _Triceratops_ retained an antorbital fenestra.  Is this truly a
 retained characteristic, a reversal, or a new character independently
 derived?  I've seen it in some photos and/or diagrams of other _Triceratops_
 skulls.   >>

Be sure that (1) the skull is complete and unbroken between the orbits and
narial opening, and not unnaturally perforated; and (2) you're not mistaking
the huge narial opening for an antorbital fenestra(!). In _Triceratops_ and
other ceratopids, the only remnant of the external antorbital fenestra was the
indentation of the antorbital fossa >right in front< of the orbit. Some
protoceratopids (e.g., _Leptoceratops_) retained an actual opening, albeit a
small one, within a fairly prominent antorbital fossa. According to Witmer
(1997), ceratopids did retain an >internal< antorbital fenestra, but this is
typically covered over and can't be seen externally. (It's when the internal
and external fenestrae meet within the fossa that you get the actual opening
in the muzzle, bounded by lacrimal, maxilla, and jugal. Sometimes a little
foramen manages to open up from exterior through to interior at the juncture
of these three bones, and this may be what you've seen. This is apparently an
individual thing, perhaps a juvenile or subadult feature.)