Re: RESTORABLE RECENTLY-DISCOVERED ORNITHODIRANS

[Pieter.Depuydt@rug.ac.be]

'RaptorRKC' asked:
> To all:
> 
> I am just curious ... how many ornithodirans discovered in, say, the past
> five years are known well enough to restore with a relatively small margin of
> error?  Well-preserved crania or skeletons at least 1/4 complete are the ones
> I am looking for.  A list of the taxa would be most appreciated.
 
You probably mean 'basal ornithodirans' as Ornithodira consists of 
Pterosauria, Dinosauria (Dinosauromorpha in fact) (plus birds of 
course) and all descendants of their most common ancestor.
As far as I know, apart from the basal theropod Eoraptor 
lunensis, no new basal ornitodirans have been discovered in the 
past five or ten years; however the known taxa have been restudied, 
especially by Sereno and Arcucci. Here's a try of a list, not meant 
as a rigorous taxonomic overview:

Marasuchus lilloensis, erected by Sereno in 1994 as a new genus for 
material formerly assigned to' Lagosuchus talampayensis' (the 
holotype of which is a possible dinosauromorph, alas without 
synapomorphies, so 'nomen dubium'). This taxon is known by reasonably 
complete material (vertebrae, forelimbs, pelvis, hindlimbs without 
feet, maxilla and braincase). According to Sereno a dinosauromorph, 
so more close to Dinosauria than to Pterosauria.

Lagerpeton chanarensis, described by Romer in the seventies I 
think, restudied by Sereno in 1993: pelvis plus articulated hindlimb, 
and some presacral vertebrae. Sereno states this is a quite derived 
dinosauromorph with unique autapomorphies probably linked to a
saltatory locomotion.

Pseudolagosuchus major, named by Arcucci in 1987 or something: 
badly eroded though diagnostic material constituting of a partial 
hindlimb without feet and some vertebrae. Probably a 
dinosauromorph.

These three taxa are found in the Middle Triassic Chanares formation, 
Argentina.

 ?Scleromochlus taylori, known from natural molds in sandstone from 
Elgin (Lossiemouth sandstone), Late Triassic.
Traditionally considered as 'pterosaur ancestor', this taxon was 
restudied by Sereno, who provided a quite new restoration (in SVP 
Memoir 2) of a gracile biped akin to Marasuchus. As many details are 
not known, its place within Ornitodira (closer to pterosaurs or to 
dinosaurs?) is not certain, it might not even be an ornithodiran.

Of course there is Eoraptor lunensis, represented by a virtually 
complete skeleton from the Late Triassic Ischigualasto formation 
(Sereno, Forster, Rogers and Monetta, Nature 7Jan1993), which 
is (according to the authors) a very basal theropod probably very 
much resembling the common dinosaur ancestor. The 
contemporaneous Herrerasaurus ischigualastensis is already a much 
more derived theropod.

Primitive pterosaurs such as Eudimorphodon and Peteinosaurus are 
already very derived, with many adaptations related to piscivory and 
flight.

Longisquama and Sharovipteryx are very poorly known, and am not aware 
of any rigourous taxonomic analysis which includes this forms. They 
may turn out to be ornitodirans though.

Any corrections or comments on this posting will be very appreciated.

Regards,

Pieter Depuydt