CHIMAERA AVIMIMUS

[darren.naish@port.ac.uk]

What a fun time is to be had in Germany. All these bizarre new 
pterosaurs.. and dare I mention the work on theropods that was done? 
Be patient, you will be informed in time..

_Avimimus portentosus_, as is well known, was not found as an 
articulated specimen, but as bits and pieces scattered over about 5 
square km. Matt Troutman writes..

>    Perle has said the skull is that of a juvenile oviraptorid. The 
> carpometacarpus and ulna are that of a bird ( Parvicursor has been 
> suggested ) and the pelvis and rest of the body is up for grabs ( I 
> think oviraptorid too ).

The premax referred to _A. portentosus_ may be from a hadrosaur, as 
Norman indicated in WDO (1990). It is toothless and has 
denticulations like those seen on some ornithopod beaks. It is of 
incidental interest that Chatterjee thought these structures to be 
teeth, thus thought _Avimimus_ to be toothed, and thus included an 
incorrect character coding in his cladistic analysis of _Protoavis_. 

I'm unsure about the hind limbs of _Avimimus_. There is a fourth 
trochanter, thus the limb is not from a bird. Oviraptorosaurs also 
lack a fourth trochanter (_Microvenator_ apparently only has a scar 
in this location. Ostrom (1970) asserts no fourth troch. is
present), but Barsbold (1983) reported one for _Oviraptor_, and 
Barsbold, Maryanska and Osmolska (1990) therefore wrote as if _all_ 
oviraptorosaurs have one. I do not have Barsbold's paper to hand - 
can someone verify the presence of this feature in _Oviraptor_? If it 
is there, it presumably marks a reversal. It is definitely absent in 
all of the well preserved 3-D oviraptors the AMNH team have prepped.

Dromaeosaurids, including _Deinonychus_, DO have a fourth trochanter, 
despite Ostrom (1976) and (just about) every other author that 
followed. Thus lack of a fourth troch. is NOT an unambiguous 
synapomorphy of Maniraptora, but only of Aves. Notably, the femur of 
_Avimimus_ is like that of dromaeosaurids, _Unenlagia_, 
_Archaeopteryx_ and troodontids in having a 'posterior trochanter'. 
Chiappe has also identified this feature in enantiornithine birds.

_Avimimus_ is somewhat like some oviraptorosaurs in having a robust, 
'finger-shaped' lesser trochanter that is well separated from the 
greater trochanter by a marked furrow. However, this feature is 
variable in oviraptorosaurs: in _Microvenator_ it is very tall 
(higher than the greater troch.), while in _Chirostenotes_ it is 
described by Sues (1997/8) as being more distally located than in any 
other Cretaceous theropod.

So, is the hindlimb of _Avimimus_ from an oviraptorosaur? I still 
don't know.

And will you Americans please publish and figure all of the 
_Ornitholestes_ material some time! For such a well known theropod 
it's incredibly poorly known.

Matt also listed this as a character seen only in Aves..

>  7) Hypertrophy of the forelimb. 

Well, it's a subjective character (like some of Gauthier's early 
ones.. viz, 'neural spines large', 'skull large') - but have you seen 
the arms on 'Bambi'/'_Linsterosaurus_'? Judging from a skeletal 
reconstruction Pete Buchholz sent me, the arms on this critter are of 
_Archaeopteryx_-like proportions. The animal is from the Two Medicine 
Fm. (Campanian) and was found jumbled with hadrosaur bones. Pete 
has previously discussed it extensively on this list, and in 
_Dinosaur Discoveries_.

I drove through a place in Europe called Buchholz the other day.

"You drive all night, and you see a light, and it comes right down 
and lands on the ground, and out comes the man from Mars, and you try 
to run but he's got a gun, and he shoots you dead, and he eats your 
head, and now you're in the man from Mars, you go out at night, 
eating cars"

God knows why I learnt that at the age of 16.

DARREN NAISH
darren.naish@port.ac.uk