Marshosaurus

*Marshosaurus bicentisimmus*

***Marshosaurus*** is an extinct genus of medium-sized theropod dinosaur which lived during the late Jurassic period in the Morrison Formation. It lived in Utah and perhaps even Colorado, USA.
It is estimated to be a length of 4.5 meters or about 14.8 feet. Other estimates are between 5 and 6 meters. This is quite small compared to the far more famous Allosaurus. It was once thought that Allosaurus scavenged off of the more active Marshosaurus's kills. Only one species of Marshosaurus is known and that is ***Marshosaurus bicentesimus***.

Despite being so small it was built for strength. It had a fairly strong and robust skull as well as short but thick humerus (an arm bone). This means that it was well adapted for holding onto prey and physically subduing them.

This dinosaur was named after Paleontologist Othniel Charles Marsh. Another dinosaur called Othnielosaurus was also named after him and lived near Marshosaurus. It is even possible that Marshosaurus hunted Othnielosaurus. Another Jurassic predator, Ceratosaurus, was named by Othniel Charles Marsh.

## Description

*Marshosaurus* was medium-sized theropod. In 2010 Gregory S. Paul estimated its length at 4.5 metres, its weight at two hundred kilogrammes. The holotype ilium has a length of 375 millimetres. If the cranial material is correctly referred, the skull was about sixty centimetres 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.

## Discovery and naming

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 honoured 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 holotype, UMNH VP 6373, was found in a layer of the Brushy Basin Member of the Morrison Formation dating from the late Kimmeridgian, approximately 155 - 150 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.

## Classification

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 Tyrannosaurus, Velociraptor and Allosaurus. However, Roger Benson (2010) found it to be a megalosauroid in a phylogenetic analysis of Megalosaurus and 40 other theropods.

The position of Marshosaurus in the evolutionary tree, as a possible member of the Piatnitzkysauridae, is shown by the cladogram below.

## Paleopathology

One right ilium of a Marshosaurus bicentesimus is deformed by "an undescribed pathology" which probably originated as a consequence of injury. Another specimen has a pathological rib. In a 2001 study conducted by Bruce Rothschild and other paleontologists, five foot bones referred to Marshosaurus were examined for signs of stress fracture, but none were found.

## Paleoecology

Marshosaurus was one of the more medium-sized predators of its Late Jurassic age. And unlike the infamous Allosaurus, or Torvosaurus, it wasn't the apex predator, although it may have been a voracious one altogether. It likely attacked medium-sized prey, such as Othnielia, or Dryosaurus, those probably just its size. Its smaller size likely gave It the ability to attack such animals while running. It probably lived alongside other Jurassic animals, like Stegosaurus, Apatosaurus, Diplodocus, and other animals.

## JPInstitute.com Description

Marshosaurus was a medium-sized meat-eater that lived near the end of the Jurassic Period. It was discovered in the famous Cleveland-Lloyd Dinosaur Quarry, a very famous site that has produced many Allosaurusspecimens. Since this dinosaur seemed to have lived at the same time as the larger Allosaurus, it probably hunted different prey and did not compete for the same food as the larger dinosaur. Marshosaurus would rarely have won a fight with an Allosaurus!

Not enough of Marshosaurus has been uncovered to authoritatively assign it to a specific family. It has been suggested that it may be a ceratosaur or more generically, a carnosaur.

## Links

https://web.archive.org/web/20030813081654/http://www.jpinstitute.com/dinopedia/dinocards/dc\_marsh.html
https://web.archive.org/web/20080704173012/http://kids.yahoo.com/dinosaurs/325--Marshosaurus