marshosaurus Archives - The Big Dinosaur Podcast

Episode 76 is also about Marshosaurus, a carnivorous theropod named after Charles Marsh.

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In this episode, we discuss:

More than 14,000 bones were found in the Cleveland-Lloyd Quarry in Utah in the 1960s. Most of them were from Allosaurus, but there were also two new theropods. James Madsen named both: Stokesosaurus and Marshosaurus
Madsen named the species Marshosaurus bicentesimus in 1976, to honor Charles Marsh and the bicentennial of the U.S.
The holotype consists of an upper pelvis bone and pieces of upper jaw; at least three individuals were found, and the bones included the pubic bone, and jaw fragments

Madsen didn’t think there were enough bones to prepare and study, but the bones found were different from other dinosaurs found in the Cleveland-Lloyd quarry, including a small Allosaurus
Bits of Marshosaurus were found in other dinosaur bonebeds (included more skull material, a partial vertebral column)
In the 90s, more fossils were referred to as Marshosaurus; in 1991 Brooks Britt referred tail vertebrae (looked like non-identified tail vertebrae from Cleveland-Lloyd), in 1993 a partial skeleton was referred (spines resembled non-identified spines from the Cleveland-Lloyd quarry; the partial skeleton was described in more detail in 1997

At first, Madsen didn’t know where to place Marshosaurus phylogenetically, and put it as Theropoda incertae sedis (in episode 54 we explained that incertae sedis means it’s unclear where in the group it falls)
Later analysis found Marshosaurus to be part of Avetheropod (group of bird-like theropods, includes Tyrannosaurus, Velociraptor, Allosaurus); but in 2009 Roger Benson said it was a megalosauroid, based on newly referred Megalosaurus specimens
Roger Benson in 2010 included Marshosaurus in Megalosauroidea, as a basal member (group includes predators such as sail-backed Spinosaurus and other dinosaurs like Torvosaurus and Megalosaurus

But very little is known still about Marshosaurus (like how did it live so close to larger predators like Allosaurus and Torvosaurus)
Medium-sized carnivorous theropod that lived in the late Jurassic
Gregory Paul estimated Marshosaurus to be about 14.8 ft (4.5 m), and weighed 440 lb (220 kg), and the skull was about 24 in (60 cm) long

Other theropods found include Ceratosaurus, Ornitholestes, Torvosaurus; other dinosaurs include Stegosaurus, Brachiosaurus, Camarasaurus, Camptosaurus (herbivores may have gotten stuck in the mud when trying to cross, and it became a death trap for the carnivores, who smelled the dead dinosaurs, but then became trapped too)
Probably very strong
Had short, thick arms that it probably used to hold on to prey

One right ilium (uppermost and largest bone in pelvis) has an “undescribed pathology”, probably from an injury
Marsh has another dinosaur named after him, Othnielosaurus (named in 2007); a small herbivore ornithipod that lived around the same time and place as Marhosaurus, so may have been prey sometimes
In 2012, Carrano et. al named the family Piatnitzkysauridae (which includes megalosauroid tetanurans)

Includes Piatnitzkysaurus, Condorraptor, Marshosaurus (and is a sister taxa to Megalosauria)
Lived in the Jurassic in Argentina and the U.S.
Fun fact: The IOC World Bird List recognizes 10,637 extant bird species among 2,289 genera. This is pretty similar to the estimated number of non-avian dinosaur genera (estimated at 1800 including those still undiscovered). But all 2200+ of the bird genera are alive right now, whereas the dinosaur genera were spread out over more than 150Ma and many of them only lasted a few million years.

I Know Dino Podcast Show Notes: Marshosaurus (Episode 76)