Top Dog

[creature386]

Aramberri could have been a juvenile after all? Am I the only one who finds that kinda ironic?

[theropod]

Nope, me too.

[Grey]

I remember that Frey once said me he didn't see any evidence for paedomorphy in the specimen.

[theropod]

It is certainly strange that such a large number of giant pliosaurs have unfused vertebrae (the interpretation not withstanding), but cranial fusion would appear to be an independent line of reasoning.
So lets resume the facts:
• Some pliosaurs have extensively fused skulls, others don’t
• In several smaller specimens (e.g. BRSMG Cc332, P. brachydeirus and brachyspondylus skulls) these are less fused than in larger ones (e.g. P. macromerus, BRSMG Cd6172; Knutsen 2012, Sassoon et al. 2012).
• UANL-FCT-R2, by contrast, has unfused cranial sutures (Buchy 2007).

• Furthermore, in at least one specimen of the genus Pliosaurus vertebral fusion does occur (Knutsen 2012)

–––References:
Buchy, Marie-Céline: Mesozoic marine reptiles from north-east Mexico: description, systematics, assemblages and palaeobiogeography. Karlsruhe (2007)
Knutsen, Espen M.: A taxonomic revision of the genus Pliosaurus (Owen, 1841a) Owen, 1841b. Norwegian Journal of Geology, Vol. 92 (2012); pp. 259-276
Sassoon, Judyth; Noè, Leslie F.; Benton, Michael J.: Cranial Anatomy, taxonomic Implications and Palaeopathology of an Upper Jurassic Pliosaur (Reptilia: Sauropterygia) From Westbury, Wiltshire, UK. Palaeontology, Vol. 55 (2012); 4; pp. 743-773

[Grey]

So this would mean that the specimens BRSMG Cc332, P. brachydeirus and brachyspondylus were ontogenically older than UANL-FCT-R2, despite the later being way larger ?

The fact this specimen is totally unfused both in its vertebral column and its skull is quite impressive.

[theropod]

Feb 22, 2015 0:09:07 GMT 5 Grey said:

So this would mean that the specimens BRSMG Cc332, P. brachydeirus and brachyspondylus were ontogenically older than UANL-FCT-R2, despite the later being way larger ?

No, these are other examples of non-fusion of mandibular and cranial elements:

knutsen2012 said:

In the relatively small skulls such
as P. brachydeirus (OUMNH J.9245) and P. brachyspon-
dylus (CAMSM J.35991), the coronoid is not fused to
the medial face of the dentary, in contrast to the larger
skull P. macromerus (NHMUK 39692), in which they
are firmly fused.

I.e. these specimens could be ontogenetically younger than the NHM P. macromerus or the larger of the Westbury pliosaurs, which are the specimens that may be more mature than the Aramberri pliosaur.

[Grey]

So, an educated guess regarding the thread question ?

[theropod]

The data do not clearly show one animal to be bigger and more formidable, so that guess wouldn't be very educated.

[Grey]

Wouldn't you bet on one at least ?

[theropod]

Feb 22, 2015 13:46:40 GMT 5 Grey said:

Wouldn't you bet on one at least ?

If I can't make an educated guess, I sure as hell wouldn't bet. This is science, not sports.
As I've remarked previously for Livyatan and Megalodon, and as apppears to now once more realistically apply to pliosaurs too, the data are not sufficient to establish such a thing.

[Grey]

The difference would be that most of the data suggesting pliosaurs as contenders are based on unpublished, undescribed or offline information (giants teeth and vertebra, most likely status of Aramberri). The largest published pliosaurs rather top at 12-13 m, 15 m if using the initial estimate for Aramberri.

Megalodon and Livyatan at 18 m and 13.5-17.5 m do have properly published data, even if the ecology and sampling population of Livyatan is deficient.

Apprently, Physeter is now acknowledged to have reached 24 m in some extreme cases, but I would question if these specimens were necessarilly as heavy as scaling from normal-sized individuals would suggest.

[theropod]

Well, there is the problem, a bunch of hard-to-compare data with variable amounts of detail and credibility. We’ve all been tempted to make premature conclusions on this matter in the past, and it seems the situation has, if anything, become more difficult now.

Anyway, regarding the Aramberri specimen, if it is immature we still have to be cautious, the last few years have taught me to be more sceptical of estimates that base on juveniles (the reason why there are usually no estimates for adult body size deduced from these, e.g. in the cases of Cryolophosaurus, Eustreptospondylus, Baryonyx…), so regardless of its ontogenetic stage I would not use it to speculate about 20-30m pliosaurs as I did the last time.
It is plausible that the 3D model and brachaucheniids used by McHenry are not a good representation of pliosaurid proportions, overestimating their relative head size and vertebral size, but without properly described remains that’s once more something to be cautious about.
Has Noè responded to your inquiries about the proportional discrepancies between the figures for the Tübingen Liopleurodon given in the 2003 paper and your communications pointing to a 1:6 ratio?

There are the teeth, for which the question is whether they really tell us anything, and there are the giant vertebrae, which it would be very helpful to see a description of.

[Grey]

Noé didn't clearly explain me, only he still suggests a range of 15-18 m for the Cumnor mandible, regardless of the accurracy of the reconstruction.

Regarding the thread question, again I need to determinate if there are others cases where a 15 m individual was juvenile...

[Grey]

From Cruickshank and A new species of pliosaurid reptile from the Early Cretaceous Birdrong
Sandstone of Western Australia 1997 :


Maturity of specimens
A question as to whether the specimens
described here are juvenile or not deserves
comment. The limb bones are all very well ossified
and do not give the impression of being from
young animals. However the neural arches of the
two other species of Leptocleidlls are firmly fused to
their centra, and certainly these two specimens
must be regarded as 'adult'. Notwithstanding these
observations, the specimen of Pliosaurus
brachyspondylus described by Taylor and
Cruickshank (1993) is a very large animal (skull
length ca 2m), the skull sutures were well fused,
and yet the cervical vertebrae did not have their
neural arches fused. It is unlikely that an observer
would have called that animal, if seen alive,
"juvenile'. We prefer to regard these specimens
from the Birdrong Sandstone as being sub-adult,
probably being close to fully grown when they
died.

Here again if we compare, both the cranial and backbone elements of the Aramberri are unfused. This reinforces even more the plausibility of juvenile status ?

[theropod]

Hmm, that’s strange.
The individual described by Taylor and Cruickshank is BRSMG Cc332, the smaller one of the Westbury Pliosaurus sp. and the same BRSMG Cc332 referred to as showing a similar degree of fusion to the smaller OUMNH J.9245 and CAMSM J.35991 by Knutsen, i.e. these all ought to represent an ontogenetic stage earlier than that of P. macromerus or BRSMG Cd6172.