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Climate Change Helped These Giant Dinosaurs Colonize Australia

A warming period may have helped these enormous dinosaurs wander from South America to Australia via Antarctica.
Concept art of Savannasaurus elliottorum based on the type specimen ("Wade") and comparisons with titanosaurs from around the world. Image: Travis Tischler / © Australian Age of Dinosaurs Museum of Natural History

The most massive animals ever known to walk on land were the titanosaurs, a group of long-necked, plant-eating dinosaurs that spread widely across Cretaceous Earth. Some titanosaurs measured over 120 feet from head to tail and are estimated to have weighed around 140,000 pounds, equivalent to a mid-sized commercial airplane. If ever there was an embodiment of the wisdom of eating your vegetables, it was these gargantuan herbivores.

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Now, research published Thursday in Scientific Reports announces the discovery of two extraordinary Australian titanosaur specimens from the Winton Formation in Queensland. While these aren't the first titanosaurs found in Australia—indeed, titanosaur remains have been recovered from every continent on Earth—they open a fascinating window into this dinosaur family's colonization of Australia.

One of the fossilized skeletons represents an entirely new genus and species that has been named Savannasaurus elliottorum (nicknamed "Wade" in honor of the renowned Australian paleontologist Mary Wade, who died in 2005 while the specimens were being excavated).

The other fossil set belongs to a previously known species called Diamantinasaurus matildae, and includes the first cranial remains of a sauropod—the scientific name for these iconic long-necked dinosaurs—that have ever been found in Australia. Sauropod skulls are notoriously rare in the fossil record, because their heads were small and delicate compared to more robust skeletal features like vertebrae, femurs, or pelvic girdles. Headless sauropods are also thought to be common because the skulls were prone to posthumously detaching from the body and getting carried away by natural forces like water currents or scavengers.

Fossils recovered from Diamantinasaurus matildae. Image: Travis Tischler / © Australian Age of Dinosaurs Museum of Natural History

These newly announced titanosaurs lived some 95 million years ago, in what is now the Winton Formation in Queensland. Based on the fossils, the study's lead author Stephen Poropat, a sauropod specialist based at the Australian Age of Dinosaurs Natural History Museum, estimates that Savannasaurus and Diamantinasaurus probably measured between 12 to 16 meters (around 40 to 50 feet) in length. The animals would have tipped the scales at around 44,000 pounds, though Savannasaurus was much broader across the hips than Diamantinasaurus.

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While those dimensions may seem pretty impressive by today's megafauna standards, paleontologists have to grade these herbivores on a curve. "As far as titanosaurs are concerned, both Savannasaurus and Diamantinasaurus are medium-sized, and towards the smaller end of the spectrum," Poropat told me.

"Titanosaurs like Dreadnoughtus, Futalognkosaurus, Argentinosaurus and Puertasaurus were much larger, in some cases exceeding 25 meters in length whereas other titanosaurs like Saltasaurus, Neuquensaurus, and especially Magyarosaurus and Lirainosaurus were relatively small, probably not exceeding 10 meters in length."

The fact that a 10-meter-long titanosaur is considered small shakes, at least relative to its cousins, speaks volumes about the the way these animals pushed the upper limits of size during their long reign on Earth.

But beyond the excitement of identifying such well-preserved fossils, Poropat and his co-authors say the find informs the broader history of titanosaur migration during the Cretaceous Period, especially their arrival in the unique paleoenvironment of Mesozoic Australia.

Titanosaurs were incredibly successful explorers, and their remains have been recovered from every continent on the planet, including Antarctica. But in Australia, they appear to be missing from the fossil record until around 110 million years ago, suggesting that they may not have made the trek down under until a particularly opportune geological moment.

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READ MORE: Recently Discovered Titanosaur Is So Huge, It Barely Fits into a Museum

"Although the absence of evidence of sauropods in these southeast Australian sediments is not necessarily evidence of their genuine absence, it should be borne in mind that no sauropods are yet known from palaeolatitudes higher than 66° in either hemisphere," Poropat noted.

In other words, the Earth's polar regions may have proved a little too chilly for these otherwise worldly animals. But according to the new study, there is persuasive floral evidence for a warming period around 110 million years ago, which may have allowed titanosaurs to pass from South America to Australia by way of Antarctica, which connected those continents at the time.

The continental drift. GIF: Algol/YouTube

"The Winton Formation itself, from which Savannasaurus and Diamantinasaurus were derived, is characterised by floras co-dominated by angiosperms and conifers, with ferns the next most diverse and abundant group, and ginkgoes, horsetails, and bennettitales also present but relatively rare," said Poropat. "Various analyses on leaf margins and wood growth suggest that the Winton region was warm and wet, and rather seasonal during the Cenomanian [the period lasting from 94 million to 100 million years ago]."

It's pretty mind-boggling to imagine these colossal animals radiating out across Antarctica as the larger Gondwanan continent was slowly splitting up under their feet. Poropat is already looking into studies on other Australian sauropods, like the Early Cretaceous genus Austrosaurus, which might further elucidate the migration patterns of titanosaurs, as well as their relationship to the global diaspora of titanosaurs during the Mesozoic.

Poropat next to Savannasaurus bones. Image: Judy Elliott / © Australian Age of Dinosaurs Museum of Natural History

"The next step that I plan to take is to reassess sauropods from Australia that are slightly older than Savannasaurus and Diamantinasaurus," he said. "It is my hope that a thorough revision of Austrosaurus, and of other Australian Early Cretaceous sauropod specimens, will shed some light on where titanosaurs like Savannasaurus and Diamantinasaurus came from, and when they did so."

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