Animal Species:Appalachiosaurus montgomeriensis

Pronounced ap-uh-LAY-chee-oh-SOR-us mont-gom-uri-en-sis.

The genus name Appalachiosaurus means 'lizard from Appalachia', in reference to the  mountain region where the fossils were found. Montgomeri honours Alabama's Montgomery county and ensis is the Latin suffix meaning 'from'.

Appalachiosaurus montgomeriensis is the first and most complete theropod tyrannosaur known from the eastern USA. It is smaller than its relatives Albertosaurus and Gorgosaurus.

Appalachiosaurus montgomeriensis

Ralph Daily © Ralph Daily

Standard Common Name

Alabama tyrannosaur

Identification

The only known individual, the type specimen, was a juvenile that was about two-thirds fully grown.

Appalachiosaurus montgomeriensis had a long, narrow skull with a shallow jaw and probably short, stunted arms with two fingers. Although the forelimbs of Appalachiosaurus are poorly known, large tyrannosaurids are characterised by proportionally small forelimbs and two-fingered hands, so it's believed that's the case for this species. Early reconstructions gave it long arms with three fingers, but they been corrected.

Similar to the arrangement in the Asian Alioramus altai, this North American tyrannosaur had six low crests along the top of its long snout.

Although discovered in 1982, it wasn’t until 2005 that palaeontologists determined that the type specimen represented an entirely new genus and species of small tyrannosaurid dinosaur and first used the name Appalachiosaurus montgomeriensis.

Size range

7-8 metres long

Distribution

Appalachiosaurus montgomeriensis  lived in a densely wooded rainforest in what is now the Appalachian region in Montgomery County, Alabama, USA, during the Late Cretaceous, about 80-76 million years ago.

Habitat

During much of the Late Cretaceous, North America was divided by the Western Interior Seaway. Eastern tyrannosaurs like Appalachiosaurus and Dryptosaurus had no interactions with their more advanced western cousins.

Large seeds found in Alabama suggest Appalachiosaurus lived in a rainforest-like environment with a closed canopy.

Feeding and Diet

Appalachiosaurus montgomeriensis was a predatory dinosaur that lived among a small community of eastern North American dinosaurs.

Experts believe the moderate size of this dinosaur, and the type of habitat it lived in, would have forced Appalachiosaurus to be an ambush predator. The densely wooded forests may have prevented Appalachiosaurus from reaching its potential top speeds, instead it may have waited amongst the trees for prey to approach. Estimates suggest it may have only reached a maximum speed of around 13 km/hr when chasing prey in enclosed areas, but it could possibly have engaged in long distance pursuits. 

Detailed studies of this species' skull and jaw, reveal more information on feeding strategies. Based on its estimated bite force, Appalachiosaurus likely was not a habitual bone cruncher like Tyrannosaurus rex, but was more likely to have focused on the flesh of prey. Its teeth were also well equipped for raking down and backwards with its jaws into flesh. Evidence also suggests Appalachiosaurus would have been able to dispatch prey of equal or greater body size to themselves - finds near the location of Appalachiosaurus fossils include large and heavily armoured dinosaur species. However, because of the small skull it likely used lateral shaking to dismember prey rather than repeated biting. 

Other behaviours and adaptations

The type specimen of Appalachiosaurus, as well as one of Albertosaurus, bears evidence of bite marks from the crocodilian Deinosuchus  . The hunter was also the hunted (or possibly scavenged!).

Fossils

It's not often that dinosaurs are dug up in the southeastern USA, so the discovery of Appalachiosaurus was big news. The fossil, believed to be of a juvenile, measured about 7 metres long, and the living dinosaur probably weighed a bit less than a ton.

The type specimen was found by Auburn University geologist David King in eastern North America, Montgomery County, Alabama, in July 1982. It is about 40 percent complete and includes parts of the skull and mandible (lower jaw), several vertebrae, parts of the pelvis, and most of both hind limbs. It is the property of the Department of Geology and Geography at Auburn University and is currently housed at the McWane Center in Birmingham, where parts of it are frequently on public display. Both genus and species were named in 2005 by palaeontologists Thomas Carr, Thomas Williamson and David Schwimmer.

As with all Late Cretaceous eastern North American dinosaurs, the fossils of Appalachiosaurus montgomeriensis were found in marine sediments, more specifically chalk, made of fine clay and marine plankton that formed at water depths of over 100 hundred metres. Scientists believe that Appalachiosaurus died on land before its carcass was washed out to sea, perhaps during a storm. This theory is based on the fact fossil plankton and other marine fossils were entombed in the rock with the dinosaur specimen. Also, some of the heavy bones were missing, probably lost while the carcass floated before burial.

Era / Period

Cretaceous Period

What does this mean?

Evolutionary Relationships

Scientists are yet to agree on this species' position within the superfamily.

The first phylogenetic analyses using cladistics, performed before the animal was named, found Appalachiosaurus to be a member of the Albertosaurine subfamily of Tyrannosauridae, which also includes Albertosaurus and Gorgosaurus. The original published description in 2005 also included a cladistic analysis, and claimed A. montgomeriensis to be a basal tyrannosauroid outside of Tyrannosauridae.

More recently, it has again been proposed that the species is member of the Albertosaurine subfamily, and at least one scientist considers it a possible species of Albertosaurus as it is structurally similar to its western cousin.

Classification

Species:
montgomeriensis
Genus:
Appalachiosaurus
Subfamily:
Albertosaurinae
Superfamily:
Tyrannosauroidea
Suborder:
Theropoda
Order:
Saurischia
Superorder:
Dinosauria
Class:
Reptilia
Phylum:
Chordata
Kingdom:
Animalia

What does this mean?

References

Carr, T.D.; Williamson, T.E.; Schwimmer, D.R. (2005). "A new genus and species of tyrannosauroid from the Late Cretaceous (middle Campanian) Demopolis Formation of Alabama". Journal of Vertebrate Paleontology 25 (1): 119–143.

Jovanelly T.J. & Lane L. (2012), "Comparison of the Functional Morphology of Appalachiosaurus and Albertosaurus", The Open Geology Journal 6: p. 65-71.

 


Melissa Murray
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