“The most aesthetically pleasing skulls of any carnivorous dinosaur” 1
1. Quote by Dr W. Scott Person
The most complete Allosaurus skull known to exist
One of the most impressive fossil presentations that has ever appeared on the market, preserving the finest known skull2 of the iconic apex predator of the Jurassic.
The fossilised remains of a mature Allosaurus; a remarkably complete assemblage consisting of skull, mandibles and post-cranial elements, with full legal documentation, detailed CT scans and high resolution 3D models.
This skull possesses all the wonderful aesthetic qualities associated with Allosaurus, such as the slimline head, prominent nasal crests, flaring lacrimal bones, curved maxillae and recurved, serrated teeth. It is a perfect illustration of palaeontologist Dr W. Scott Persons’s statement that Allosaurus skulls are “the most aesthetically pleasing skulls of any carnivorous dinosaur”.3
2. Dr Mark Loewen, personal communication, 2 May 2022.
3. “Allosaurus Head to tail”, Ask a Paleontologist,
3.05 min: watch the video here.
Allosaurus: Top predator of the Jurassic
Of all dinosaurs, Allosaurus is undoubtedly one of the most formidable and well-known. The apex predator of the Late Jurassic, it could reach up to five meters in height, twelve meters in length and weighed around two tonnes. Its long tail helped it keep its balance as it roamed the floodplains of the United States and Western Europe, around 157 - 145 million years ago.
Allosaurus had an unusually strong skull, characterised by a very light, fenestrate architecture and highly mobile jaw. Using its extremely strong neck muscles, it likely used its mouth as a slashing weapon to inflict deep lacerations into the flesh of its prey:
“[During] attack or feeding, Allosaurus generally used a high velocity impact of the skull into its prey; an analogue would be a person wielding a large, heavy hatchet. Aided by sharp, recurved teeth and powerful neck musculature driving the skull downwards and then imparting a retractile force, portions of flesh were sliced, torn away and swallowed.” 4
This high impact “slash and tear” hunting and feeding style allowed Allosaurus to ambush much larger dinosaurs such as stegosaurs and sauropods.
During feeding, Allosaurus easily lost its teeth, which were rapidly and continuously replaced, at a frequency of around 100 days. The present specimen shows several germ and newly erupted teeth.
4. Emily J. Rayfield, et al., “Cranial design and function in a large theropod dinosaur”, Nature (22 February 2001), vol.409, p.1035.
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Image 1:
Saggital CT of right mandible of the present Erupted tooth.
Image 2:
Right dentary specimen, showing germ tooth.
Image 3:
Distinctive banding of the Morrison Formation at Dinosaur National Monument, near Dinosaur, Colorado
The Morrison Foundation – and the Great Dinosaur Rush
Allosaurus remains have been identified in both North America and Portugal. About 75% of all Allosaurus fossils have been recovered from the Morrison Formation, a Late Jurassic rock unit extending over 1 million square kilometres in the western United States.5
In the mid-late 1800s, it became the locus of the Bone Wars, a scientific rivalry between palaeontologists Othniel Charles Marsh and Edward Drinker Cope, often referred to as the “Great Dinosaur Rush”. Numerous dinosaur genera were first discovered in the Formation, such as Brontosaurus and Stegosaurus, respectively discovered at Como Bluff, Wyoming, and north of the town of Morrison, Colorado, after which the Formation is named.
The first Allosaurus fossils to be discovered were caudal vertebrae found by geologist Ferdinand Vandeveer Hayden in 1869, near Granby, Colorado. However, on examining specimens from Cañon City, Colorado, Marsh noticed that the vertebrae were different from those of other dinosaurs known at the time. Thus, he named the new beast Allosaurus (“different lizard”) in 1877.
5. The Formation centres mostly around Wyoming, Colorado, and Utah.
Allosaurus jimmadesni – even older, even rarer
Whilst the term Allosaurus usually refers to the type species Allosaurus fragilis, which appeared circa 150 million years ago, an older species, Allosaurus jimmadseni, was recently described from specimens previously thought to belong to fragilis.6
Jimmadseni lived around 5 million years prior to fragilis, making it the oldest species of Allosaurus in the United States. Its skull presents several unique features: “In particular, whereas the ventral margin of the jugal of Allosaurus fragilis has pronounced sigmoidal convexity, the ventral margin is virtually straight in Allosaurus jimmadseni. The paired nasals of Allosaurus jimmadseni possess bilateral, blade-like crests along the lateral margin, forming a pronounced nasolacrimal crest.” 7
Furthermore, Allosaurus jimmadseni fossils are much rarer. All confirmed Allosaurus jimmadseni remains, including the present skull, originate from the lower part of the Morrison Formation, in Utah, Wyoming, and Colorado, and more particularly from the geological unit known as the Salt Wash Member. The significance of finding a new species in such an intensely studied formation cannot be overstated and highlights the paucity of the fossil record.
6. The study, authored by Daniel J. Chure and Mark A. Loewen in 2020, is based on thirty years of observation of Allosaurus remains: Daniel J. Chure and Mark A. Loewen, “Cranial anatomy of Allosaurus jimmadseni, a new species from the lower part of the Morrison Formation (Upper Jurassic) of Western North America”, PeerJ (2020),8:e7803 DOI 10.7717/peerj.7803. Its name was chosen in honour of palaeontologist James J. Madsen (d. 2009) and his important work on Allosaurus. Madsen is known for having unearthed more Allosaurus bones than anyone else in history, and he authored the seminal monograph Allosaurus Fragilis: A Revised Osteology (1976).
7. Daniel J. Chure and Mark A. Loewen, (2020), p. 1.
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