YPM 1893: Not an Allosaurus fragilis?

[CAWCarcharo]

I've been looking into this particular Specimen for a while now and it doesn't sit with me as an Allosaurus fragilis Specimen as it has morphological differences that in my opinion sets it apart from other A. fragilis Specimens; the Basal portion of the Maxilla seems too convexed compared with other Allosaurus fragilis, the Basal portion of the Orbit of U-shaped unlike the V-shaped Basal portion of the Orbits of other A. fragilis Specimens, the Premaxilla is shaped with a sharper angle than the smoother, convexing shape of A. fragilis Premaxilla, the Premaxilla-Maxilla contact Suture is smooth and not angular like with A. fragilis, the Maxillary-Jugal contact Suture is smoother than the angular Suture of A. fragilis Specimens and the Dentary is more of a rounded shape that the square ended Anterior of the A. fragilis Specimens. Now, I have thought about it possibly representing a Juvenile A. fragilis Specimen but the size is much closer to that of a nearly full grown Adult A. fragilis as some smaller. Sub-Adult A. fragilis Specimens seem to have smoother, simpler Suture lines in those particular areas but this could easily be an example of those morphological features experiencing Neoteny or even Heterochrony and it may be the case or it could be that this particular Specimen experienced Neoteny or Heterochrony later into it's life but in my opinion: YPM 1893 should be reassigned to it's original Taxonomic assignment of Allosaurus ferox or as a new Allosaurus species if needed. Additionally, the area that it lived in was a drained floodplain in what is Quarry 14, Como Bluff meaning it could be specific to that kind of environment; which could explain why it is hard to find and may have not competed as well against the more common A. fragilis as other Theropoda predators around the same time like Ceratosaurus and Torvosaurus are also not as common as A. fragilis and neighbouring Quarries have turned up Allosaurus sp. material which could A. fragilis or the same Species as YPM 1893. Any opinions on the matter? I'm open to criticism .

A few links to some Websites: -
http://www.paleofile.com/Dinosaurs/Theropods/Allosaurus.asp (= Allosaurus ferox MARSH, 1896 non MARSH, 1884, assigned under A. fragilis)
http://fossilworks.org/?a=collectionSearch&collection_no=39371

[soft tissue]

it appears you aren't accounting for morphological variation or taphonomic distortion post-mortem? you would be surprised at the variation in crania across not only A. fragilis but a large number of theropod taxa.

[CAWCarcharo]

Ah... I forgot to acknowledge the Morphological variation because like you said: Allosaurus fragilis as a Species is very diverse in it's Cranial Morphology as many Palaeontologists have pointed out that the Cranial material of Allosaurus fragilis is very varied between individuals; I have considered that YPM 1893 may just be another A. fragilis it's just that the shape of the Basal portion of the Maxilla isn't like any other A. fragilis as it has a more convexing shape than the flattened out shape of an A. fragilis. And yeah, I also forgot to acknowledge the taphonomic distortion; from what I have gathered the Specimen is generally undistorted but very fair point my Friend, thanks for bringing that up, I appreciate and respect your opinion.

[Papi-Anon]

I'll piggy-back off this thread since it's Allosaurus-related.

I'm working on a sculpture of an Allosaurus head and was wondering about the crests. Most paleo art depicts it as more or less the same shape as the typical fossilized form, but I recall the Allosaurs of WWD (not Ballad of Big Al) having the crests arch above the eye sockets in a more 'cat-ear' shape. Was this something speculative on the crests' shapes in life or is there some truth to it?

[CAWCarcharo]

I believe that the current belief is that it was either just skin over the Lacrimal crests or it could have been a Keratin sheath. The shape of the crests did vary from Specimen to Specimen as Allosaurus fragilis had a diverse and largely successful population with some having rounded off crests and others having sharper or square ended crests.

[Blade-of-the-Moon]

I would say to pick a skull and work the shape of the crests from that.  It's not known what function they served , most likely a species identifier of some sort, possibly a sexual characteristic.  You could probably make of it just about anything.

[stargatedalek]

I'm working on a sculpture of an Allosaurus head and was wondering about the crests. Most paleo art depicts it as more or less the same shape as the typical fossilized form, but I recall the Allosaurs of WWD (not Ballad of Big Al) having the crests arch above the eye sockets in a more 'cat-ear' shape. Was this something speculative on the crests' shapes in life or is there some truth to it?

Honestly, it was probably done to look more dramatic. They are far beyond reasonable speculation for the genus let alone within a given species.

[Blade-of-the-Moon]

If your looking for references , i would suggest the Dinosaur Revolution/Dinotasia model

[Papi-Anon]

If your looking for references , i would suggest the Dinosaur Revolution/Dinotasia model

Thanks, all of you. That clears things up quite a bit. I should correct my previous statement, though: it's actually a CAD model of the head I'm designing, which I'll post in the Dino Art section in my thread (I changed my name from 'Crash'). Also have previews of a stylized velociraptor action figure being printed from Shapeways at the moment.

[soft tissue]

let us not be too conservative. what is to say that allosaurids did not possess exaggerated keratinous sheaths for their lacrimals?

[CAWCarcharo]

Exactly, absence of proof isn't proof of absence; the modern day Theropoda Ave Genus of Casuarius possess a Keratin or Keratinous skin covering over the Casque. It could have occurred in all Extinct Theropod species like Allosaurus fragilis and the other Sister species of Allosaurus fragilis but who truly knows.

[stargatedalek]

Exactly, absence of proof isn't proof of absence; the modern day Theropoda Ave Genus of Casuarius possess a Keratin or Keratinous skin covering over the Casque. It could have occurred in all Extinct Theropod species like Allosaurus fragilis and the other Sister species of Allosaurus fragilis but who truly knows.

It's still highly unlikely they would become thickened horizontally to the point of growing at an angle adjacent to the underlying bone structure as seen in WWD.

[CAWCarcharo]

Ah yes, the structure of the Lacrimal in the WWD Model is pretty much fused over the top of Orbit and is connected to the Post-Orbital like the JP Tyrannosaurus rex Female; that's why I consider the look of the WWD Allosaurus as a very poor references for Allosaurus anatomy.

[Papi-Anon]

Ah yes, the structure of the Lacrimal in the WWD Model is pretty much fused over the top of Orbit and is connected to the Post-Orbital like the JP Tyrannosaurus rex Female; that's why I consider the look of the WWD Allosaurus as a very poor references for Allosaurus anatomy.

Good point. I always liked the way it looked as a kid, but I prefer accuracy a bit more.

One last Allosaurus question dealing with the crests:

Has there been any consistency of the crests being more/less 'pronounced' depending on the sex of the specimen? I recall reading that it's believed the female specimens lack fused pubic bones while the males have them fused. Has there been any pattern of crests' forms or sizes in males vs females? Or were the crests not sexually dimorphic features?

[CAWCarcharo]

I've looked at a few assigned A. fragilis Specimens and there seems to be a correlation in most individuals; though it is not consistent with all Specimens so it's a bit unreliable but it a theory I have as I have seen it: short, deep snouted Specimens seem to have larger and more pronounced Lacrimal crests meaning that these are possibly representatives of Male morphs and the longer, shallower snouted Specimens have less pronounced Lacrimal crests meaning that these are possibly Female morphs. I wouldn't use this as fact though it's a start.

[Blade-of-the-Moon]

Have we a 100% proved that the fused pubic bones are a sign of gender one way or the other?

[stargatedalek]

Have we a 100% proved that the fused pubic bones are a sign of gender one way or the other?

Definitely have not.

[CAWCarcharo]

I think the 'Pubic Bone Fusion Hypothesis' should be compared with Modern Aves in order to see if Modern-Day Theropoda (Birds) have this sort of dimorphism and whether it's based on Sex or whether the unfused Pubic Bones in A. fragilis Specimens can be attributed to ontogenic or taphonomic means.