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Re: biggest predators (Allosauridae wins)



Juergen Peters wrote-

> www.dinodata.net lists this as Epanterias amplexus. Which name is the
> presently valid one? And how is Saurophaganax related to it?
> Is the latter also a valid genus yet?

Here's the deal with the big Morrison allosaurids.  First of all, note that
Allosaurus fragilis got quite large itself, reaching 9.5 meters long and
weighing 2.3 tons.  But we're interested in the really big allosaurids.
Epanterias amplexus was named by Copein 1878 (as a sauropod!) based on AMNH
5767 (axis, cervical centrum, dorsal centrum, dorsal neural arch and spine,
coracoid, distal metatarsal IV).  Scaling the coracoid gives an estimated
length of 12.1 meters and a weight of 4.5 tons for this specimen.  Paul
synonymized this species with Allosaurus to form the new combination
Allosaurus amplexus in his book Predatory Dinosaurs of the World.
Saurophagus maximus was named by Ray in 1941, based on postcrania from
Oklahoma.  This was not described properly and is therefore a nomen nudum,
in addition to being preoccupied (Swainson 1831).  Hunt and Lucas (1987)
later designated a tibia (OMNH 4666) as the lectotype.  Chure (1995)
determined the atlas, dorsal vertebrae and chevrons referred to Saurophagus
are actually distinguishable from Allosaurus fragilis.  They show the
following autapomorphies:
- atlas lacks prezygapophysis for proatlas, does not roof over neural canal
- dorsal vertebrae with horizontal lamina along base of each side of neural
spine arising from spine base cranially, free caudally
- chevrons craniocaudally expanded distally
As Saurophagus is preoccupied and based on an indeterminate tibia, he gave
the vertebrae, chevrons and other postcranial material associated with it a
new name- Saurophaganax maximus.  The holotype is OMNH 001123, a dorsal
neural arch.  Material referred to this species includes a postorbital, two
quadrates, three teeth, an atlas, cervicals, caudal centra, chevrons, an
ilium, a pubis, an ischium, a humerus, manual phalanges and unguals, a
femur, a tibia and pedal elements.  Chure also determined the type material
of Epanterias amplexus could not be distinguished from Allosaurus or
Saurophaganax, so it is a nomen dubium.  The femur and tibia suggest a
length of 10.2-10.5 meters and a weight of 2.7-3.1 tons, while the humerus
suggests a length of 13 meters and a weight of 6 tons.  Smith (1998)
published a morphmetric analysis of Allosaurus and determined that
Saurophaganax maximus plotted on the same growth curve as Allosaurus
fragilis, but because it can be distinguished by morphological characters,
retained the species as Allosaurus maximus.  Williamson and Chure reported
another large Morrison allosaurid, this one being known from sacral and
caudal vertebrae, chevrons, an ilium, ischium, femur, tibia, fibula and
pedal phalanges (NMMNH P-26083).  Its size is estimated to be 9.8-10 meters
and its weight 2.5-2.7 tons.  Bakker has also reported an "Epanterias"
skull.

Cope, E. D. 1878.  A new opisthocoelous dinosaur.  Amer. Naturalist xii p.
406.
Ray, Grace Ernestine 1941.  Big for his day.  Nat. Hist. 48 36-39, illustr.
Chure, D., 1995. ``A reassessment of the gigantic theropod Saurophagus
maximus from the Morrison Formation (Upper Jurassic) of Oklahoma, USA,''
Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers,
Beijing, China Ocean Press: 103-106.
Smith, D. K., 1998. "A morphometric analysis of Allosaurus," Journal of
Vertebrate Paleontology 18(1): 126-142 [April 10, 1998].

Mickey Mortimer