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Description
Marshosaurus bicentesimus

The Morrison Formation of the Rockies and Great Plains of the United States is a treasure trove of Late Jurassic fossils. It's also home to some of the most iconic dinosaurs in the world; Stegosaurus, Diplodocus, and Allosaurus once thrived in the American West. However, within these iconic taxa are among the most obscure predators that ever walked the earth: Marshosaurus bicentesimus.

History:

In the 1960s, expeditions from Salt Lake City were sent to the Cleaveland Lloyd Quarry to uncover theropod fossils. They largely succeeded in recovering many new bones and fragments of Allosaurus. However, among the Allosaur fossils, they also found a handful of fragments and fossils that were unlike any Allosaurus fossil.

Roughly a decade later, James Henry Madsen of the Utah Museum of Natural History described two new species of theropod dinosaur after he looked over the fossils found in these expeditions. The first, in 1974, consisting of a pelvis, was labeled Stokesosaurus, a tyrannosaur; however, its description is a profile for another day.

The other was an assemblage of partially articulated bones discovered from the quarry. Consisting of a nearly complete pelvis, cervical vertebrae, partial tail vertebrae and a relatively complete skull with only the rear of the mandible and part of the orbits missing. Madsen analyzed this fossil for a further two years. Mainly because Madsen was unsure of what this was as it had traits resembling Allosaurs and Tyrannosaurs. Ultimately, he classified it as "Incertae Sedis," meaning "of uncertain placement" in Latin. However, he did give it a name. Madsen decided to dub the species Marshosaurus bicentesimus. The generic name honors Othniel Charles Marsh, a successful yet controversial paleontologist of the Bone Wars of the late 19th century who helped discover and name numerous dinosaur fossils in the 1890s. The specific name is a Latinized version of the word "Bicentennial" since it was the bicentennial of the United States of America; thus, "Marsh's bicentennial lizard."

The holotype was dubbed UMNH VP 6373, and in the intervening years more specimens were described from the Morrison Formation. Among them is a find from the Dinosaur National Monument on the Utah-Colorado border consisting of a handful of vertebrae. As the vertebrae were similar to the holotype, these fossils, labeled CMNH 21704, were also assigned to this genus.

Taxonomy:

As previously mentioned, this dinosaur was of uncertain placement for a long time, hence its classification. In 2010, Dr.Roger Benson, in a redescription of Megalosaurus, labeled Marshosaurus as a basal Megalosauroid. He was mainly noting the similarities in the vertebrae as a diagnostic factor.

In 2019, during the description of Asfaltovenator from Jurassic Argentina, this was refined further as a member of the funnily named Piatnitzkysauridae. A group of basal Allosaurs closer to Megalosaurs than Allosaurus itself.

As of now, the lattermost classification still stands; however, where the broader group of Piatnitzkysauridae stands is still open to debate.

Description:

Marshosaurus itself was a relatively medium to small theropod in the Morrison Formation. Roughly 14 to 17 feet long, about 5ft tall, and 500-600lbs based on the highest estimates. To put this in perspective, Marshosaurus would've been an eighth the size of Allosaurus or Torvosaurus.

However, it would've had the standard carnosaur/Allosaur body plan. A skull filled with blade-like serrated teeth, a decently muscled torso, forelimbs tipped with three fingers, powerful legs counterbalanced with a tail.

The skull shape of this animal is up for debate as the holotype's skull is somewhat deformed, according to the description. Some choose a more allosaur-shaped skull, others a distinctive tyrannosaur-esque skull, or, like in this profile, a long megalosaur-esque skull. As its basal relations stand, the author of this profile elected to restore it after that.

Pathology:

In recent finds, paleontologists noted pathologies on the ribs associated with Marshosaurus. The ribs were deformed through unknown means, perhaps due to a failed hunt or fight. Interestingly, though, many specimens of the contemporary Allosaurus and Ceratosaurus have pathologies of feet being injured or infected. None of which appear on Marshosaurus. This could be due to preservation biases. However, it could also imply that Marshosaurus hunted in ways that mitigated foot injury.

Habitat and Environment:

The habitat of this medium theropod was in the Morrison Formation some 155-152,000,000 years ago. The environment was a scrubby seasonal floodplain environment. Rivers, floodplains, and fern prairies dominated the region 152,000,000 years ago. Interspersed between the climate would have been forests and groves consisting of primitive conifers like Monkey-Puzzle, Sequoia, cycad, primitive pine trees, and tree ferns. All of this flora would have been prevalent with seasonal wet and dry seasons in the Morrison.

Present in the region would have small ornithopods like Nanosaurus or Drinker. Giant sauropods like Brachiosaurus, Diplodocus, Brontosaurus, and Camarasaurus. As well as larger ornithischians like Camptosaurus, Uteodon and Dryosaurus. The most recognizable herbivores would have been Stegosaurs, like Stegosaurus itself and Alcovasaurus—moreover, the more defensively armored cousins, the basal nodosaurs Mymoorapelta and Gargoyleosaurus.

In competition were numerous theropods like Torvosaurus, Ceratosaurus, and the most common theropod, Allosaurus. These dinosaurs were among the top predators in the region.

Competing more directly with Marshosaurus would've been smaller predators like the basal maniraptoran Ornitholestes, the basal tyrannosaur Stokesosaurus, and the small basal troodontids Koparion and Hesperornithoides were present in the region too. Crocodilians from the goniopholid family, like Amphicotylus, would've filled the niche of aquatic predators in the region's rivers, lakes, and ponds.

Also, peculiarly, there would've been terrestrial crocodilians like Fruitachampsa and Hallopus functioning in the niche similar to monitor lizards or even reptilian coyotes of the Morrison.

Pterosaurs would have been the only flying vertebrates around, with Mesadactylus and Kepodactylus being found in the Morrison environment.

Finally, there would've been small mammals consisting of rodent-like Multituberculates and larger Eutriconodonts filling the niche of ferrets and raccoons of the Morrison formation.

Regarding what niche Marshosaurus filled, it's possible they hunted smaller ornithopods and juvenile theropods and sauropods—scampering through the forest and prairies, snatching them up in their maws. It would've been the wolf or mountain lion of the Morrison.

Extinction:

Marshosaurus would vanish by the end of the Jurassic. The extinction of this predator is unknown but is likely down to climate change.

Marshosaurus' discovery sheds further light on the Morrison's ecosystem. A smaller predator is scampering in the shadow of predators like Allosaurus and Torvosaurus. On top of being named after one of the most prolific (and controversial) paleontologists of the 19th century and named in the bicentennial year, Marshosaurus is an interesting theropod of the American West.
___________________________________________________________________________________________

Ahhhh... I love getting a new base mesh to play with. Easily one of the most unique and obscure Morrison Theropods. Seriously, there's next to no depiction of this animal in media. I saw this guy in a display case next to an Allosaur at the Carnegie Museum in Pittsburg a year and a half back. So here, I decided to do it justice properly.

Will this be in PMP? Normally I'd say no, but here it actually will. Replacing another animal from the original version of PMP. However, this scene of it eating a an Allosaurus chick... It won't be quite like this.

Model and Skin by Tyranachu, modified by me:
Torvosaurus V2 (2023) - The ZT2 Round Table

Description
Marshosaurus bicentesimus

The Morrison Formation of the Rockies and Great Plains of the United States is a treasure trove of Late Jurassic fossils. It's also home to some of the most iconic dinosaurs in the world; Stegosaurus, Diplodocus, and Allosaurus once thrived in the American West. However, within these iconic taxa are among the most obscure predators that ever walked the earth: Marshosaurus bicentesimus.

History:

In the 1960s, expeditions from Salt Lake City were sent to the Cleaveland Lloyd Quarry to uncover theropod fossils. They largely succeeded in recovering many new bones and fragments of Allosaurus. However, among the Allosaur fossils, they also found a handful of fragments and fossils that were unlike any Allosaurus fossil.

Roughly a decade later, James Henry Madsen of the Utah Museum of Natural History described two new species of theropod dinosaur after he looked over the fossils found in these expeditions. The first, in 1974, consisting of a pelvis, was labeled Stokesosaurus, a tyrannosaur; however, its description is a profile for another day.

The other was an assemblage of partially articulated bones discovered from the quarry. Consisting of a nearly complete pelvis, cervical vertebrae, partial tail vertebrae and a relatively complete skull with only the rear of the mandible and part of the orbits missing. Madsen analyzed this fossil for a further two years. Mainly because Madsen was unsure of what this was as it had traits resembling Allosaurs and Tyrannosaurs. Ultimately, he classified it as "Incertae Sedis," meaning "of uncertain placement" in Latin. However, he did give it a name. Madsen decided to dub the species Marshosaurus bicentesimus. The generic name honors Othniel Charles Marsh, a successful yet controversial paleontologist of the Bone Wars of the late 19th century who helped discover and name numerous dinosaur fossils in the 1890s. The specific name is a Latinized version of the word "Bicentennial" since it was the bicentennial of the United States of America; thus, "Marsh's bicentennial lizard."

The holotype was dubbed UMNH VP 6373, and in the intervening years more specimens were described from the Morrison Formation. Among them is a find from the Dinosaur National Monument on the Utah-Colorado border consisting of a handful of vertebrae. As the vertebrae were similar to the holotype, these fossils, labeled CMNH 21704, were also assigned to this genus.

Taxonomy:

As previously mentioned, this dinosaur was of uncertain placement for a long time, hence its classification. In 2010, Dr.Roger Benson, in a redescription of Megalosaurus, labeled Marshosaurus as a basal Megalosauroid. He was mainly noting the similarities in the vertebrae as a diagnostic factor.

In 2019, during the description of Asfaltovenator from Jurassic Argentina, this was refined further as a member of the funnily named Piatnitzkysauridae. A group of basal Allosaurs closer to Megalosaurs than Allosaurus itself.

As of now, the lattermost classification still stands; however, where the broader group of Piatnitzkysauridae stands is still open to debate.

Description:

Marshosaurus itself was a relatively medium to small theropod in the Morrison Formation. Roughly 14 to 17 feet long, about 5ft tall, and 500-600lbs based on the highest estimates. To put this in perspective, Marshosaurus would've been an eighth the size of Allosaurus or Torvosaurus.

However, it would've had the standard carnosaur/Allosaur body plan. A skull filled with blade-like serrated teeth, a decently muscled torso, forelimbs tipped with three fingers, powerful legs counterbalanced with a tail.

The skull shape of this animal is up for debate as the holotype's skull is somewhat deformed, according to the description. Some choose a more allosaur-shaped skull, others a distinctive tyrannosaur-esque skull, or, like in this profile, a long megalosaur-esque skull. As its basal relations stand, the author of this profile elected to restore it after that.

Pathology:

In recent finds, paleontologists noted pathologies on the ribs associated with Marshosaurus. The ribs were deformed through unknown means, perhaps due to a failed hunt or fight. Interestingly, though, many specimens of the contemporary Allosaurus and Ceratosaurus have pathologies of feet being injured or infected. None of which appear on Marshosaurus. This could be due to preservation biases. However, it could also imply that Marshosaurus hunted in ways that mitigated foot injury.

Habitat and Environment:

The habitat of this medium theropod was in the Morrison Formation some 155-152,000,000 years ago. The environment was a scrubby seasonal floodplain environment. Rivers, floodplains, and fern prairies dominated the region 152,000,000 years ago. Interspersed between the climate would have been forests and groves consisting of primitive conifers like Monkey-Puzzle, Sequoia, cycad, primitive pine trees, and tree ferns. All of this flora would have been prevalent with seasonal wet and dry seasons in the Morrison.

Present in the region would have small ornithopods like Nanosaurus or Drinker. Giant sauropods like Brachiosaurus, Diplodocus, Brontosaurus, and Camarasaurus. As well as larger ornithischians like Camptosaurus, Uteodon and Dryosaurus. The most recognizable herbivores would have been Stegosaurs, like Stegosaurus itself and Alcovasaurus—moreover, the more defensively armored cousins, the basal nodosaurs Mymoorapelta and Gargoyleosaurus.

In competition were numerous theropods like Torvosaurus, Ceratosaurus, and the most common theropod, Allosaurus. These dinosaurs were among the top predators in the region.

Competing more directly with Marshosaurus would've been smaller predators like the basal maniraptoran Ornitholestes, the basal tyrannosaur Stokesosaurus, and the small basal troodontids Koparion and Hesperornithoides were present in the region too. Crocodilians from the goniopholid family, like Amphicotylus, would've filled the niche of aquatic predators in the region's rivers, lakes, and ponds.

Also, peculiarly, there would've been terrestrial crocodilians like Fruitachampsa and Hallopus functioning in the niche similar to monitor lizards or even reptilian coyotes of the Morrison.

Pterosaurs would have been the only flying vertebrates around, with Mesadactylus and Kepodactylus being found in the Morrison environment.

Finally, there would've been small mammals consisting of rodent-like Multituberculates and larger Eutriconodonts filling the niche of ferrets and raccoons of the Morrison formation.

Regarding what niche Marshosaurus filled, it's possible they hunted smaller ornithopods and juvenile theropods and sauropods—scampering through the forest and prairies, snatching them up in their maws. It would've been the wolf or mountain lion of the Morrison.

Extinction:

Marshosaurus would vanish by the end of the Jurassic. The extinction of this predator is unknown but is likely down to climate change.

Marshosaurus' discovery sheds further light on the Morrison's ecosystem. A smaller predator is scampering in the shadow of predators like Allosaurus and Torvosaurus. On top of being named after one of the most prolific (and controversial) paleontologists of the 19th century and named in the bicentennial year, Marshosaurus is an interesting theropod of the American West.
___________________________________________________________________________________________

Ahhhh... I love getting a new base mesh to play with. Easily one of the most unique and obscure Morrison Theropods. Seriously, there's next to no depiction of this animal in media. I saw this guy in a display case next to an Allosaur at the Carnegie Museum in Pittsburg a year and a half back. So here, I decided to do it justice properly.

Will this be in PMP? Normally I'd say no, but here it actually will. Replacing another animal from the original version of PMP. However, this scene of it eating a an Allosaurus chick... It won't be quite like this.

Model and Skin by Tyranachu, modified by me:
Torvosaurus V2 (2023) - The ZT2 Round Table