Young Dinosaur Found in Ancient Mud Pit Is New Species of ‘Small Giant,’ Fossils Suggest

kaatedocus siberi

A young sauropod that met its death mired in an ancient mudflat may have been small for its kind — that is, the size of a modern humpback whale — but it was a member of an early, newly identified species that may hold lessons about some of the largest animals that ever lived, a new study says.

The dinosaur’s fossilized remains were found more than 20 years ago in the compressed sediments of what’s now north-central Wyoming. But back in the Late Jurassic, the region was a mucky lowland prone to seasonal droughts and muddy spells.

Kaatedocus sauropods mired in mud
An artist’s rendering depicts the demise of Kaatedocus in the mudflats of what’s now northern Wyoming. (Illustration by Davide Bonadonna (Milan))

This climatic mixture made it a death trap for the giant, lumbering plant-eaters like the newfound sauropod.

But it also turned the site into a fossil bonanza, now known as the Howe Quarry, from which dozens of dinosaurs have been hauled, including some of the largest species known to have ranged the Ancient West, like Diplodocus and Barosaurus. [Read about another “dinosaur death trap” recently excavated in Utah.]

But some of those specimens, first excavated in the early 20th century, have since been lost, and the quarry itself sits in the less-explored northern reaches of the fossil-rich rock strata, known together as the Morrison Formation, that span the intermountain West.

So the new species from the quarry may fill some important gaps in the story of ancient plant-eaters, according to paleontologist Emanuel Tschopp.

Tschopp, who has just completed his graduate studies at the New University of Lisbon, says the specimen is likely an early form of diplodocid — the group of seismic, crane-necked herbivores that included some of the longest animals the planet has ever seen.

“The finding of yet another diplodocid genus [in the region] shows that diplodocid diversity, even though high, is still underestimated,” Tschopp said in an interview.

Excavated from among the quarry’s deepest layers, the fossil dates back some 150 million years, and its basal, or primitive, features suggest it belonged to a kind of “sister” genus to other ancestral giants like Supersaurus and Barosaurus, Tschopp said.

And although diplodocids are known for their earth-shaking size, this specimen — likely a subadult — was no more than 14 meters long and probably didn’t have much more growing to do.

Thus it was given the name Kaatedocus, from the diminutive “kaate-” in the Crow Indian language.

And indeed, when Tschopp and Dr. Octávio Mateus of Lisbon’s Museu da Lourinhã, first published their findings last year, some fossil-watchers staked out positions as to whether the specimen was in fact a juvenile Barosaurus.

“Further studies indicate that Kaatedocus is indeed a different genus from Barosaurus, although very closely related,” Tschopp said.

kaatedocus
If you can get past its winsome smile, you’ll note the bony structures around the eyes of Kaatedocus that are among the species’ distinctive features, according to the study authors. (Illustration by Davide Bonadonna)

“The proposition that Kaatedocus could be a juvenile Barosaurus was made … based on earlier, very short reports without description or detailed assessment of what this material actually was.”

Tschopp and Mateus’ findings were recently published in the Journal of Systematic Paleontology.

Among the dinosaur’s signal features, he said, are bony, U-shaped notches between the frontal bones, and a pair of distinctive spurs that flare out from near the bottom of each eye.

“The lateral spur in front of the eyeball probably provided some protection of the eye when feeding in dense vegetation,” Tschopp noted, “and the more rounded snout compared to Diplodocus or Apatosaurus indicates that Kaatedocus was probably a more specialized feeder than the other two genera.

“By looking for high-quality food in dense vegetation, additional protection by such a spur might have been needed.”

The most distinguishing trait, he said, was not in the dinosaur’s skull but in the shape of its upper vertebrae, where the two vertical features that erupt the top of each, called neural spines, grew straight up and parallel to each other.

kaatedocus skull
The new genus and species Kaatedocus was identified by a skull and upper vertebrae excavated from the Howe Quarry in the early 1990s. (Courtesy Tschopp et al., JSP)

“In Apatosaurus and Diplodocus, or also Barosaurus, these neural spines diverge widely in the last few neck vertebrae,” he said.

Taken together, these traits suggest a unique genus, Tschopp said, which hints at even greater diversity of diplodocid dinosaurs in the Howe Quarry, and elsewhere in the northern stretches of the West’s fossil-rich Morrison.

“The appearance of  new taxa in the northern exposures of the Morrison … shows that there’s still great potential to find new dinosaurs, and that the fauna of the Morrison might have been different in northern and southern regions,” he said.

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Emanuel Tschopp, & Octávio Mateus (2013). The skull and neck of a new flagellicaudatan sauropod from the Morrison Formation and its implication for the evolution and ontogeny of diplodocid dinosaurs Journal of Systematic Palaeontology DOI: 10.1080/14772019.2012.746589

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