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Jurassic Morrison Marshosaurus Tooth with Allosaurus Tooth VF-JC-24-003

Jurassic Morrison Marshosaurus Tooth with Allosaurus Tooth VF-JC-24-003

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Marshosaurus bicentesimus with Allosaurus sp.

Morrison Formation Brushy Basin Member

Upper Jurassic

Moffat County, Colorado

 

Here is an outstanding and large example of the very rare Morrison carnivorous dinosaur Marshosaurus.  The tooth is 5.2 cm long and 2 cm wide at the base.  The tooth is slender in cross-section and the serrations are smaller than other Morrison carnivorous dinosaurs.  The serrations on the mesial carina of the tooth extend one half of the distance from tip to the base.  These features are diagnostic of the genus.  The serrations on both the carinae are very distinct and in good condition. There are abrasions from adjacent teeth seen on both the lingual and buccal sides of the tooth.  The tip is restored (1.5 mm) and there is a small patch of restoration near the base of the lingual side of the tooth.  Another small (3 mm) patch of restoration is present along the distal carina 1.5 cm below the tip.  There has been filling of tiny natural fractures.

A small piece of original matrix attaches an Allosaurus tooth to the Marshosaurus tooth.  It is 2 cm long and 1.2 cm wide at the base of the tooth.  Restoration can be seen filling several natural fractures.  The entire specimen is in its original position as collected.

Marshosaurus was medium sized for a theropod. In 2010, Gregory S. Paul estimated its length at 4.5 meters and its weight at two hundred kilograms. The holotype ilium has a length of 375 millimeters. If the cranial material is correctly referred, the skull was about sixty centimeters long.

In 2012, Matthew Carrano established one autapomorphy, a unique derived trait of the holotype: the suture between the pubic peduncle and the pubic bone is convex, curving upwards, at the front and concave at the rear.

During the 1960s, over fourteen thousand fossil bones were uncovered at the Cleveland-Lloyd Quarry in central Utah. The majority of these belonged to Allosaurus but some were of at least two theropods new to science. In 1974 one of these was named by James Henry Madsen Jr. as the genus Stokesosaurus.

In 1976 the second was by Madsen named as the type species Marshosaurus bicentesimus. The generic name honored the nineteenth century paleontologist Professor Othniel Charles Marsh, who described many dinosaur fossils during the Bone Wars. The specific name was chosen in honor of the bicentennial of the United States of America.

The holotypeUMNH VP 6373, was found in a layer of the Brushy Basin Member of the Morrison Formation dating from the late Kimmeridgian, approximately 155 - 152 mya. It is a left ilium, or upper pelvis bone. The paratypes consisted of three bones: the ischia UMNH VP 6379 and UMNH VP 380 and the pubic bone UMNH VP 6387. Three ilia and six jaw fragments were provisionally referred. The material represents at least three individuals.

In 1991 Brooks Britt referred tail vertebrae from Colorado, because they resembled non-identified tail vertebrae fragments from the Cleveland-Lloyd Dinosaur Quarry.   In 1993 a partial skeleton, CMNH 21704, from the Dinosaur National Monument was referred because its spines resembled non-identified spines from the Cleveland-Lloyd Dinosaur Quarry.   This specimen was more completely described in 1997.

Madsen originally was unsure about the phylogenetic position of Marshosaurus, placing it as Theropoda incertae sedis. Some later analyses showed Marshosaurus to be a member of Avetheropoda, a group of more bird-like theropods including TyrannosaurusVelociraptor and Allosaurus. However, Roger Benson (et al., 2009)  found it to be a Megalosauroid, using a lot of newly found characters of referred Megalosaurus specimens.

The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, ranges between 156.3 million years old (Ma) at its base, to 146.8 million years old at the top, which places it in the late OxfordianKimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as a semiarid environment with distinct wet and dry seasons. The Morrison Basin where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels and floodplains. This formation is similar in age to the Solnhofen Limestone Formation in Germany and the Tendaguru Formation in Tanzania. In 1877 this formation became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope.

 

Allosaurus was a large bipedal predator. Its skull was large and equipped with dozens of sharp, serrated teeth. It averaged 8.5 m (28 ft) in length, though fragmentary remains suggest it could have reached over 12 m (39 ft). Relative to the large and powerful hind limbs, its three-fingered forelimbs were small, and the body was balanced by a long and heavily muscled tail. It is classified as an allosaurid, a type of carnosaurian theropod dinosaur. The genus has a complicated taxonomy, and includes an uncertain number of valid species, the best known of which is A. fragilis. The bulk of Allosaurus remains have come from North America's Morrison Formation, with material also known from Portugal and possibly Tanzania. It was known for over half of the 20th century as Antrodemus, but study of the copious remains from the Cleveland-Lloyd Dinosaur Quarry brought the name Allosaurus back to prominence and established it as one of the best-known dinosaurs.

 

As the most abundant large predator in the Morrison Formation, Allosaurus was at the top of the food chain, probably preying on contemporaneous large herbivorous dinosaurs and perhaps even other predators. Potential prey included ornithopods, Stegosaurids, and Sauropods. Some paleontologists interpret Allosaurus as having had cooperative social behavior, and hunting in packs, while others believe individuals may have been aggressive toward each other, and that congregations of this genus are the result of lone individuals feeding on the same carcasses. It may have attacked large prey by ambush, using its upper jaw like a hatchet.

 

The skull and teeth of Allosaurus were modestly proportioned for a theropod of its size. Paleontologist Gregory S. Paul gives a length of 845 mm (33.3 in) for a skull belonging to an individual he estimates at 7.9 m (26 ft) long. Each premaxilla (the bones that formed the tip of the snout), held five teeth with D-shaped cross-sections, and each maxilla (the main tooth-bearing bones in the upper jaw) had between 14 and 17 teeth; the number of teeth does not exactly correspond to the size of the bone. Each dentary (the tooth-bearing bone of the lower jaw) had between 14 and 17 teeth, with an average count of 16. The teeth became shorter, narrower, and more curved toward the back of the skull. All of the teeth had saw-like edges. They were shed easily and were replaced continually.

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