The Big Dinosaur Podcast

Episode 291 is all about Opisthocoelicaudia, a late cretaceous titanosaur that may have been able to rear up on its hind legs.

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In this episode, we discuss:

News:

• A new analysis of dozens of tyrannosaur specimens splits its growth into 5 major phases source
• The asteroid that wiped out the dinosaurs hit at just the right angle to do the most possible damage source
• The dueling dinosaurs appear to be going exclusively to the surface rights owners source
• A set of chinese “chicken claw prints” turned out to be Jurassic dinosaur tracks source
• Japanese researchers claim to have found the world’s smallest dinosaur egg fossil source
• The NHM in London shared details about Qhemegha, South Africa and its importance in dinosaur paleontology source
• The TV show Dinosaurs is coming to Disney+ this fall source
• Dinosaur Batman uses the name B. rex for one character, it’s not a shoebill or the T. rex specimen MOR 1125 that go by the same name source
• Filming for Jurassic World Dominion has resumed source

The dinosaur of the day: Opisthocoelicaudia

• Sauropod that lived in the Late Cretaceous in what is now Mongolia (Gobi Desert)
• Estimated to be about 37 to 43 ft (11.4 to 13 m) long
• Many different weight estimates, ranging from 8.4 tonnes to 25.4 tonnes
• Had a small head, long neck, and quadrupedal
• Had a medium-length neck about 16 ft (5 m) long
• Gregory Paul in 2019 found there were 10 dorsals, the number found in titanosaurs
• Had a long tail
• Had a flexible back, and a strong pelvic region
• Had bony projections on the top of its spine (like Diplodocus)
• Had short limbs, proportionally, and forelimbs were about 2/3 the length of the hindlimbs, that were fairly flexible
• Foot claws were all about the same size
• May have used its tail like a third leg when it reared up, which meant it had a flexible tail (the thick pelvis, may show it was strong enough to rear up)
• Originally thought to have a straight back, but in 2007 Daniela Schwarz and others found the back may have dipped towards the rear, and that the shoulder blade inclined at a steeper angle
• Type species is Opisthocoelicaudia skarzynskii
• Genus name means “posterior cavity tail” and refers to the opisthocoelian structure of the anterior caudals, which means the vertebrae at the anterior (facing forward) of the tail were concave on their posterior (facing rearward) sides and convex on their anterior sides, to form ball-and-socket joints
• Because of this, may have been able to rear on to its hindlegs
• Species name is in honor of Wojciech Skarzynski, who prepared the type specimen
• Nearly complete skeleton found (no head or neck) in 1965 during a joint Polish-Mongolian expedition
• Holotype was an adult, and found on its back, with most vertebrae still connected, though left limb and rib bones were found to the right of the body, and the right limb and rib bones and were found on the left side of the body
• Tooth marks on the skeleton, probably means large carnivores ate the carcass and may have removed the missing parts (head and neck)
• Bite marks found in the pelvis and right femur
• Because of the completeness of the skeleton, probably died close to where it was found, possible there was a flood that moved the body and covered it in sediment
• A juvenile part of shoulder also found
• Part of a tail and come claws also have been referred to Opisthocoelicaudia
• Described by Maria Magdalena Borsuk-Bialynicka in 1977
• Found in the Nemegt Formation
• Hard to move the fossils, had stone blocks that had to be moved about 1900 ft (580 m) on metal sledges made of petrol drums, then put onto trucks
• Packed skeleton into 35 crates, that weighed 12 tons
• Holotype was part of the collection at the Institute of Paleobiology in Warsaw, then later went back to Mongolia, and is now at the Institute of Geology of the Mongolian Academy of Sciences in Ulaanbaatar
• Other sauropod found in Nemegt is Nemegtosaurus, known from one skull
• Opisthocoelicaudia skull is not known, so some scientists think Opisthocoelicaudia and Nemegtosaurus are synonymous (if synonymous, would be named Nemegtosaurus because Nemegtosaurus was named first, in 1971)
• Nemegtosaurus found in the same expedition, but thought to be from a different clades (Nemegtosaurus originally classified as Dicraeosaurinae, Opisthocoelicaudia as Camarasauridae). Now both dinosaurs thought to be titanosaurs and Opisthocoelicaudia is now classified as Saltisauridae
• Phil Currie and others in 2018 found some postcranial fossils in the quarry where Nemegtosaurus was found, which may have belonged to the holotype. Helped support the idea that Nemegtosaurus and Opisthocoelicaudia were synonymous
• Other scientists think femora found are Nemegtosaurus and that the femora is different from Opisthocoeliucaudia, making them two distinct dinosaurs
• Sauropod footprints have been found in the Nemegt Formation, with skin impressions, probably either Opisthocoelicaudia or Nemegtosaurus
• Skin impression of the foot print show non-overlapping scale, also claw impressions
• Footprints found were very large, so probably made by a dinosaur larger than the type specimen of Opisthocoelicaudia
• Other dinosaurs that lived at the same time and place include tyrannosaurid Tarbosaurus, ornithomimosaur Deinocheirus, sauropod Nemegtosaurus, troodontid Borogovia, ankylosaur Tarchia
• Other animals that lived at the same time and place included fish, turtles, crocodiles, and birds

Fun Fact: Lots of dinosaur movies show sauropods avoiding stepping on small animals, but it would have been hard for them to simultaneously watch their feet and where they were going.