The headless rider would soon befriend an Asian ankylosaurus; where the former tends to miss its head, these dinosaurs are often found without their bodies. The lack of ankylosaur bodies has even plagued paleontologists, eager to learn more about how the hefty herbivores became club-tailed, heavily armored tanks.
Now an international team of researchers has described the post-cranial remains of an ankylosaurus from the Gobi Desert in Mongolia, enhancing paleontologists’ understanding of the diversity and evolution of this family. The team suggests that ankylosaurs may have used tombs for defensive or strategic purposes. Their research on a Cretaceous Ankylosaurus – which is not yet to be associated with any particular species, as ankylosaurs are described by their skulls, and this skeleton was found without one – was published today in scientific reports.
These ankylosaur fossils are embedded in a chicken nugget-shaped mold. It has been dead for about 70 million years, and although it was discovered some 50 years ago, it wasn’t until 2008 that an excavation team had enough resources and time to analyze the fossil. It was transported to a South Korean laboratory in 2012 for preparation and returned to Mongolia four years later.
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“Articulated armored dinosaur body skeletons are quite rare,” Yuong-Nam Lee, a paleontologist at Seoul National University in South Korea and a co-author of the paper, said in an email. “The nearly complete skeleton we have recently studied provides valuable information about their evolution and behavior. By comparing our specimen to other related dinosaurs, we now know that the armored dinosaurs of Asia developed rigid bodies and reduced the number of pedal phalanges [toes] through time.”
You may think that a rigid-bodied ankylosaurus isn’t news. But Lee’s team found that this Mongolian dinosaur was even less flexible than its ankylosauride cousins from North America, perhaps to support their longer tails or because of their fused vertebrae. The reduced clove count, the authors wrote, likely came about as an adjustment to support their heavier weight. This would also have reduced the animals’ mobility, making the Asian ankylosaurs even more tank-like than previously thought.
Perhaps most importantly, the paleontology team claims that ankylosaurs may have been built for digging. That skeletal rigidity would have stabilized the animal when it was digging with its front legs, they wrote, and the slight curvature of its toes would have given its front legs a trowel-like shape. The authors don’t suggest that ankylosaurs were burrowing animals per se – more that when confronted with a ferocious theropod, they could dig ditch-like depressions and settle down, leaving only their bony skin exposed to the surface. Lee compares this behavior to modern horned lizards.
“We are curious to see if juvenile ankylosaurs were also able to dig,” said Lee. Baby ankylosaurs don’t have elaborate body armor, and this must have made them vulnerable to predators. If the babies could dig, it seems possible to live in underground spaces like armadillos do today. “
This is speculative, but having a well-articulated skeleton gives future paleontologists a little more to look at than a thick skull. The study authors found perforated holes in the skeleton, evidence of dermestide beetles, which are known for their appetite for rotting meat. That suggests the animal may have been lying post-mortem for at least a while.
“Digging like modern elephants for minerals, food, or water, I could see it, as this behavior has also been suggested for sauropods,” said ReBecca Hunt-Foster, the unaffiliated paleontologist for Dinosaur National Monument in Utah. with the new paper. “They may also have used their digging to dig out nests. However, behavior can be difficult to deduce from body fossils alone. “
The researchers also found five phalanges of theropods embedded in the ribs of the ankylosaurus – it’s clear this dinosaur had good reason to wear so much protection.