Pronunciation: MARSH-o-SOR-us
Meaning: Marsh's lizard
Author/s: Madsen (1976)
Synonyms: None known
First Discovery: Utah, USA
Discovery Chart Position: #251
Marshosaurus bicentesimus
Marshosaurus is one of the Morrison Formation's more enigmatic theropods, not least because various palaeontologists have pinpointed features reminiscent of ceratosaurs, spinosauroids, allosauroids, metriacanthosaurids and Coelurus all within its first remnant: a partial pelvis. By the 21st century, its range had been expanded from Utah to Colorado with fossils from high in the Brushy Basin Member (early Tithonian) to low in the Salt Wash Member (late Kimmeridgian). But, truth be told, it's remains aren't the best, and there's been much debate as to which bits it can legitimately lay claim to.
The first remains of Marshosaurus were described in 1976 by James H. Madsen and consist of a hatful of hip bones from Utah's Cleveland-Lloyd Quarry, three of which seemingly fit together perfectly and may belong to a single critter. In 1991 and 1993, Brooks Britt and Dan Chure referred some tail vertebrae from Colorado and a partial skeleton from Utah's Dinosaur National Monument here because they showed similar form to comparable parts from the holotype quarry that might (or might not) belong to Marshosaurus. Though yet to be fully described, the latter specimen (CMNH 21704) titillated with its short massive humerus suggestive of powerful arms. And another Di.Na.Mo specimen (DMNH 3718, housed at the Denver Museum of Nature and Science) preserved enough skull fragments to show that its snout was unusually long and shallow with a "kink" or notch similar to, but less conspicuous than, that seen in modern crocs.
Latest research has Marshosaurus pegged as a megalosauroid close to Piatnitzkysaurus, and it certainly differs from the Morrison's media hogs Allosaurus, Torvosaurus, Ceratosaurus, and anything else from this area. But whatever it may turn out to be, Marshosaurus seems to have taken a hammering during life, as a 2001 study by Bruce Rothschild concluded that its holotype is deformed, probably as a consequence of serious injury, and a rib has a pathological fracture: a bone break that occurs with minimum trauma as a result of infection or disease.
The first remains of Marshosaurus were described in 1976 by James H. Madsen and consist of a hatful of hip bones from Utah's Cleveland-Lloyd Quarry, three of which seemingly fit together perfectly and may belong to a single critter. In 1991 and 1993, Brooks Britt and Dan Chure referred some tail vertebrae from Colorado and a partial skeleton from Utah's Dinosaur National Monument here because they showed similar form to comparable parts from the holotype quarry that might (or might not) belong to Marshosaurus. Though yet to be fully described, the latter specimen (CMNH 21704) titillated with its short massive humerus suggestive of powerful arms. And another Di.Na.Mo specimen (DMNH 3718, housed at the Denver Museum of Nature and Science) preserved enough skull fragments to show that its snout was unusually long and shallow with a "kink" or notch similar to, but less conspicuous than, that seen in modern crocs.
Latest research has Marshosaurus pegged as a megalosauroid close to Piatnitzkysaurus, and it certainly differs from the Morrison's media hogs Allosaurus, Torvosaurus, Ceratosaurus, and anything else from this area. But whatever it may turn out to be, Marshosaurus seems to have taken a hammering during life, as a 2001 study by Bruce Rothschild concluded that its holotype is deformed, probably as a consequence of serious injury, and a rib has a pathological fracture: a bone break that occurs with minimum trauma as a result of infection or disease.
(Marsh's Bicentenary Lizard)
Etymology
Marshosaurus is derived from "Marsh" (for American paleontologist Othniel Charles Marsh) and the Greek "sauros" (lizard). Othnielosaurus is known from the same area as Marshosaurus, meaning a predator named for O.C. Marsh, was eating an herbivore... that was named for O.C. Marsh. The species epithet, bicentesimus, commemorates the U.S. bicentenary.
Discovery
The first fossils of Marshosaurus were discovered at Cleveland-Lloyd Quarry in the Brushy Basin Member of the Morrison Formation, Emery County, Utah, U.S.A. The holotype (UMNH VP 6373) is a left ilium (upper pelvis bone).
As well as Marshosaurus, the quarry is jam-packed with the remains of Ceratosaurus, Camarasaurus, Stegosaurus, Camptosaurus, Stokesosaurus, Allosaurus and a mystery ankylosaur, and appears to represent an ancient watering hole.
