Alamosaurus: measuring 21 meters long, this titanosaur is the largest land animal ever known to have lived in North America

Today, the largest land animal in North America is the bison, which can measure nearly 4 meters (13 feet) in length and weigh up to two grand pianos. But as much as we love bison, they pale in comparison to the largest land animal to ever roam the continent: Alamosaurus.

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Part of the aptly named titanosaurs – a group of ridiculously gigantic, long-necked sauropod dinosaurs – this enormous lizard was estimated to have been 21 meters (70 feet) long, and although it’s difficult to determine the weight of an object based on fossils, the upper end of the estimation scale puts it at up to 80 tonnes. That’s about 40 times heavier than today’s great icons, giraffes.

Scientists discovered the giant for the first time Alamosaurus in 1921, after geologist John B. Reeside, Jr. came across a huge fossil specimen near the Ojo Alamo Formation in New Mexico, which would eventually give the dinosaur its name.

From this, the researchers were able to determine that Alamosaurus lived during the late Cretaceous period, from about 70 million years ago until 65 million years ago, when that pesky asteroid ended the reign of the dinosaurs.

What is particularly intriguing Alamosaurus is that it appeared in North America after a 30-million-year gap in the fossil record known as the “sauropod hiatus.” During this period, there appear to have been no sauropods on the continent, the exact reasons for which are open to debate. Perhaps an argument between a group of sauropods caused them to flee in opposite directions, perhaps they became extinct, or it could be that no sauropod remains were preserved during this time – their transformation into fossils is not guaranteed.

“The process of fossilization is a very rare process,” Dr Susannah Maidment, a senior researcher in the Vertebrates, Anthropology and Palaeobiology Division at the Natural History Museum, London, told IFLScience. “Sometimes we preserve items like skin and other soft tissues like feathers, which usually requires a very unique set of burial conditions, often very rapid burial.”

While it was a matter of extinction and reintroduction, however, some scientists believe that the sauropod hiatus ended with Alamosaurus migrating north from what is now South America. This is a reasonable theory; At the time, South America was largely titanosaur country, home to 37-meter-long giants like Patagotitan.

We can’t say for sure (okay, maybe we can rule out the sauropod group breakup theory), but hey, at least now we know that North America managed to retain at least one giant dinosaur before they all disappeared.