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theworldofanimals.proboards.com/post/48420Allosaurus sp. (maximum size, "Epanterias amplexus" specimen)[Intro] The "Epanterias" specimen, AMNH 5767, was originally described as a sauropod by Cope in 1878, later redescribed and identified as a theropod by Osborn & Mook (1921) and as indistinguishable from
Allosaurus fragilis by Chure (2000). Due to the fragmentary nature of the material, I am tentatively treating it as
Allosaurus sp. here. The great size of the material has been noted repeatedly before (e.g. Bakker 1992, Chure 2000), but a rigorous size estimate has not been attempted aside from rough approximations (like "20% larger than any Allosaurus").
[Mat & Met] The material consists of a coracoid, axis and neural arch of the presumed first dorsal vertebra. There is also a moderate-sized mid-cervical centrum, excluded from further analysis as it does not belong to an exceptionately large individual, and hence likely not the same animal as the rest of the remains.
The originally stated measurements are a preserved height of 290 mm and width of 400 mm and width of the neural spine of 83 mm for the dorsal neural arch (Cope 1878), a height of the axis of 250 mm (Chure 2000) and a coracoid length of ~380 mm (measured digitally from figure in Osborn & Mook 1921, using the known dimensions of the dorsal neural arch in figure to the same scale for reference).
Figure 1: (A-D) AMNH 5767, Holotype of "Epanterias amplexus" Cope 1878. (
A) Axis, (
B) D1 in anterior and left lateral view. (
C) Right coracoid in proximal and lateral view. (
D) Middle cervical centrum (C6 or 7) in anterior and left lateral view. (
E-G)
Allosaurus fragilis. (
E) Axis, D1 and Coracoid of ?DINO 2560. (
F) Axis of USNM 4734. (
G) Axis and D3 of USNM 8367.
Scale Bar: 10 cm.
D1, restored based on DINO 2560:
total height 441 mm
diapophyseal width 452 mm
parapophyseal width 204 mm
centrum height 220 mm
centrum width 186 mm
centrum length(rim-rim) 123 mm
centrum length (max.) 191 mm
Axis:
centrum length
=|= excl. intercentrum ~ 100 mm
=|= incl. intercentrum 156 mm
comparative specimens:USNM 4734 (Gilmore 1920)
Axis centrum+intercentrum length 85 mm
D1 (mean of C9 and D2) centrum length e. 106 mm Coracoid:
greatest length 170 mm
(Based on skeletal reconstruction by Randomdinos¹):
TL 7.4 m
BM 1300 kg
| DINO 2560 (figures and scalebars in Madsen 1976)
Axis:
centrum + intercentrum 126 mm
D1:
centrum length 130 mm
Coracoid:
greatest length 234 mm
(based on skeletal reconstruction by ScottHartman², mass estimated from 3D-model):
TL 8.6 m
BM 1839 kg
Figure 2: Volumetric model used for mass estimate of DINO 2560, based on skeletal by Scott Hartman, dorsal view adapted from Bates 2009, specific gravity assumed to be 0.933 (grid=1 m)
| USNM 8367 (Gilmore 1920)
Axis centrum+intercentrum length 88 mm
D3 height 253 mm
(based on summed length of the 17 presacral centra preserved in both it and USNM 4734, from Gilmore 1920):
TL 7.76 m
BM 1501 kg |
We can scale up AMNH 5767 based on these three analogues.
[Results]
method scale eTL eBM
1 usnm_4734_axis_l 1.835294 13.58118 8036.378
2 4734_d1_l 1.801887 13.33396 7605.467
3 4734_coracoid 2.235294 16.54118 14519.357
4 usnm_8367_axis_l 1.772727 13.75636 8361.929
5 8367_dorsals_h 1.743083 13.52632 7949.410
6 DINO_2560_axis_l 1.238095 10.64762 3490.148
7 2560_D1_l 1.469231 12.63538 5832.460
8 2560_coracoid 1.623932 13.96581 7875.624
[Discussion & Conclusions] first of all, we can of course dismiss the 16.5 m, 14.5 t estimate. That this figure diverges so much from the others suggests there is something wrong; perhaps that USNM 4743 is a specimen with an atypically small coracoid, which we should not be assuming here.
This leaves us with the following viable estimates:
method scale eTL eBM
1 usnm_4734_axis_l 1.835294 13.58118 8036.378
2 4734_d1_l 1.801887 13.33396 7605.467
4 usnm_8367_axis_l 1.772727 13.75636 8361.929
5 8367_dorsals_h 1.743083 13.52632 7949.410
6 DINO_2560_axis_l 1.238095 10.64762 3490.148
7 2560_D1_l 1.469231 12.63538 5832.460
8 2560_coracoid 1.623932 13.96581 7875.624Based on this, we can be fairly confident that AMNH 5767 is among the largest, if not the largest known jurassic theropod specimen, with a length of at least 10.6 m and a mass of at least 3.5 t.
The mean TL of these is 13.1 m. Mean body mass is 7022 kg. The median is 13.5 m and 7875 t.
Estimate 6, based on the DINO 2560 axis is also a little suspicious in terms of how it diverges quite a bit from where the other figures tend to cluster. If we ignore estimate 6 as well, out mean becomes 13.5 m and 7610 kg, the median 13.6 m and 7913 kg. Scaling up Bates’ model of Big Al (7.6 m, ~1.5 t) to 13.5 m gives ~8.4 t, roughly in agreement with this.
As a plausibility test, we can compare the dorsal vertebra to those of other giant theropods, vertebral diameter having been previously proposed as a reliable indicator of body mass:
Figure 3: (
A, B) First dorsal vertebrae of giant theropods (
A) cf.
Allosaurus sp. (AMNH 5767) and (
B)
Tyrannotitan chubutensis (MPEF-PV 1157, Canale et al. 2015). (
C) Fourth dorsal vertebra (anteriormost preserved dorsal) of
Tyrannosaurus rex (FMNH PR 2081, Brochu 2003).
Scale bar: 10cm
In conclusion, it appears probable that AMNH 5767 is the largest Jurassic theropod specimen, among the largest theropod specimens yet discovered, as suggested by Bakker (1992). Interesting enough, there seems to be an increased ocurrence of very large allosaurids at the very top of the Morrison formation (e.g. Chure 1995, Williamson & Chure 1996).
References:
Bakker, R. T., J. Siegwarth, D. Kralis, and J. Filla. 1992: Edmarka rex, a new, gigantic theropod dinosaur from the middle Morrison Formation, Late Jurassic of the Como Bluff outcrop region. Hunteria 2:1–24.
Bates, K. T. 2009: How big was ‘Big Al’? Quantifying the effect of soft tissue and osteological unknowns on mass predictions for Allosaurus (Dinosauria: Theropoda). Palaeontologia Electronica 12:1–33.
Bates, K. T., R. B. Benson, and P. L. Falkingham. 2012: A computational analysis of locomotor anatomy and body mass evolution in Allosauroidea (Dinosauria: Theropoda). Paleobiology 38:486–507.
Brochu, C. A. 2003: Osteology of Tyrannosaurus rex: insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. Journal of Vertebrate Paleontology 22:1–138.
Canale, J. I., F. E. Novas, and D. Pol. 2015: Osteology and phylogenetic relationships of Tyrannotitan chubutensis Novas, de Valais, Vickers-Rich and Rich, 2005 (Theropoda: Carcharodontosauridae) from the Lower Cretaceous of Patagonia, Argentina. Historical Biology 27:1–32.
Chure, D. J. 1995: A reassessment of the gigantic theropod Saurophagus maximus from the Morrison Formation (Upper Jurassic) of Oklahoma, USA. 6th Symposium on Mesozoic terrestrial ecosystems and biotas, short papers. Edited by A.-L. Sun and Y.-Q. Wang. China Ocean Press, Beijing, China:103–106.
Chure, D. J. 2000: A new species of Allosaurus from the Morrison Formation of Dinosaur National Monument (UT-CO) and a revision of the theropod family Allosauridae. Ph. D. dissertation, Columbia University.
Cope, D. E. D. 1878: On a new opisthocoelous dinosaur. Annals and Magazine of Natural History 2:194–194.
Gilmore, C. W. 1920: Osteology of the carnivorous Dinosauria in the United States National museum: with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus. US Government printing office.
Madsen, J. H. 1976: Allosaurus fragilis: a revised osteology. Utah Geological and Mining Survey Bulletin 109:1–163.
Osborn, H. F., and C. C. Mook. 1921: Camarasaurus, Amphicoelias, and other sauropods of Cope. Memoirs of the American Museum of Natural History 3:247–387.
Williamson, T. E., and D. J. Chure. 1996: A large allosaurid from the Upper Jurassic Morrison Formation (Brushy Basin Member), west-central New Mexico. Museum of Northern Arizona, Bulletin 60:73–79.
