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The final chapter of the dinosaur story is a tale that spans two very different worlds, each a vast supercontinent dominated by its own unique mix of predators and herbivores.
Fossil remains of a plant eater common to one of the two main land masses have been unexpectedly unearthed in rocks belonging to the other, prompting paleontologists to wonder how he managed to make such a leap.
“It was completely out of place, like finding a kangaroo in Scotland,” says paleontologist Nicholas Longrich of the University of Bath, who led a study on the recent discovery.
This misplaced “kangaroo” was actually a type of crested duckbill browser recently classified as a hadrosaurid (of a lambeosaurine variety to be precise).
About 66 million years ago, as the Cretaceous period neared its catastrophic end, hadrosaurs of many different varieties were among the most common herbivorous dinosaurs.
At least, that was the case with the supercontinent Laurasia, a mass that would later split to give us today’s continents of North America, Europe, and much of Asia.
Across the ocean, a separate land mass known as Gondwana was instead ruled by a variety of clumsy, long-necked sauropods.
The remains of these giants are commonly found in places like Africa, India, Australia, and South America.
Where Hollywood would have seen fit to mix the two groups, vast expanses of water between continents and long periods of isolation meant by the late Cretaceous, duckbills and long necks would only powerfully mix in distinct regions, as in what is today Europe.
This new member of the hadrosaurid family may be just a new exception.
Based on little more than a few pieces of jaw and a handful of teeth extracted from a phosphate mine in Morocco, the discovery is proof that at least one of these animals must have strayed further from Laurasia than was suspected possible.
Ajnabia jaw and tooth fossil. (Longrich et al., Cretaceous Research, 2020)
Well maybe not wandering as much as paddling.
“It was impossible to walk in Africa,” Longrich says.
“These dinosaurs evolved long after continental drift divided continents and we have no evidence of land bridges. Geology tells us Africa was isolated from the oceans. If so, the only way to get there is. the water”.
Late Cretaceous hadrosaur discoveries in Europe and Africa, with Ajnabia at number 6. (Longrich, et al., Cretaceous Research, 2020)
The idea is not as far-fetched as it might seem at first glance. Hadrosaurs look comfortable near aquatic environments and come in all shapes and sizes. Some have measured up to 15 meters (45 feet) in length, with large tails and powerful legs capable of making them competent swimmers.
At a length smaller than 3 meters (9 feet), this hadrosaur may have had a little more difficulty running a marathon that could have included hundreds of kilometers of open water.
But theories about smaller animals rapidly crossing oceans on floating rafts of vegetation abound: why not a relatively small dinosaur?
“Events once in a century are likely to happen many times. Ocean crossings are necessary to explain how lemurs and hippos got to Madagascar, or how monkeys and rodents went from Africa to South America,” says Longrich.
By combining the Arabic word for foreigner with the name of the famous Greek seafarer, scientists have nicknamed hadrosaurus Ajnabia odysseus.
The same assembly that contained the file Ajnabia Jaw gave up a few other dinosaur bones, including the Gondwana staples of titanosaurs and carnivorous theropods called abelisaurs.
That may not be enough to reimagine the split between Cretaceous supercontinents in the moments before an asteroid changed everything. But it should give us enough pause to say that an ocean would be an insurmountable barrier.
“As far as I know, we are the first to suggest ocean crossings for dinosaurs,” says Longrich.
This research was published in Cretaceous research.
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