Re: Eolambia and Pararhabodon (was Re: New issue of JVP 2001(2))

["Mickey Mortimer" <Mickey_Mortimer11@msn.com>]

Tim Williams wrote-

> According to Head, the cranial features regarded
> as lambeosaurine synapomorphies are erroneous interpretations of the
> material on Kirkland's part.  Certain lambeosaurine characters described
by
> Kirkland in the postcranium actually have a wider distribution within the
> Iguanodontia - like the distally expanded ischium and tall neural spines
on
> the caudals.  Head (2001) places _Eolambia_ closest to _Probactrosaurus_
> (likewise considered as non-lambeosaurine).

Here's the specifics for those without the paper-
Eolambia was described as a lambeosaurine based on the following characters
(Kirkland, 1998)-
1. absence of a premaxillary foramen
Actually present, as proved by premaxilla OMNH 28919.
2. maxillary rostral shelf (absence of paired maxillary rostral processes)
Actually present, as proved by premaxilla OMNH 28919.
3. tall neural spines on caudal vertebrae
Present in Ouranosaurus and Bactrosaurus, neither of which is a
lambeosaurine.
4. expanded distal ischium
Plesiomorphic- present in Camptosaurus, Iguanodon, Ouranosaurus,
Gilmoreosaurus and Bactrosaurus as well as lambeosaurines.
However, Head does not explain the posteriorly expanded subnarial
premaxillary process or robust humerus, also lambeosaurine synapomorphies
according to Kirkland.
It was placed in the Hadrosauridae based on-
1. narrow maxillary teeth
Actually wide, though I would prefer some quantification.
2. three or more dentary teeth per tooth position
Only two teeth per tooth position are present in Eolambia, although it is a
subadult specimen, so may have increased with age.
3. large single carina on dentary teeth
Actually, a distal secondary ridge is present.
4. angular deltopectoral crest
Plesiomorphic for iguanodonts (eg. Norman, 1998).
Head does not address other hadrosaur characters listed by Kirkland-
elevation of the dorsal maxillary process that brings the antorbital
fenestra onto the dorsal maxillary surface; narrow maxillary teeth; reduced
dorsal margin of scapular blade; no denticulate oral margin on premaxilla;
narrow mandibular condyle of quadrate.
Head also mentions that the ilium has a weak antitrochantor and the sacrum
only seven vertebrae, both more basal than hadrosaurs.  Kirkland does point
out that the sacrum is from a subadult and hadrosaurids add sacrals with
age, so this may not be valid.
The placement of Eolambia next to Probactrosaurus is very provisional, as
admitted by Head, as ony the presence of anteroposteriorly shortened
supratemporal fenestrae groups them together at present.

> Head (2001) is also inclined to scratch _Pararhabdodon_ from the
> Lambeosaurinae (referred to this group by Casanovas et al., 1999).  Among
> the rather un-lambeosaurine features of this Maastrichtian genus,
> _Pararhabdodon_ has only around 35 tooth positions in the maxilla and
> dentary, less than both hadrosaurines and lambeosaurines.

Pararhabdodon was assigned to the Lambeosaurinae based on (Casanovas, et
al., 1999)-
2. truncated, rounded maxillary-jugal contact
Head disputes this because the anterior jugal shape is the lameosaurine
character and it is uncertain how exactly this is expressed in maxillary
morphology (only the maxilla is known in Pararhabdodon).  I think this is a
bit picky, but who am I to judge...
3. angular deltopectoral crest
See above.
No argument against the presence of a medial maxillary shelf was presented,
and I lack Casanovas et al. to verify more characters weren't used to defend
hadrosaur and lambeosaurine identification.  However, Head does state
Pararhabdodon has only thirty-five maxillary and dentary tooth positions,
less than hadrosaurids.

Mickey Mortimer