National Geographic

Gnarly Fossil Tells of a Torn Dinosaur Tail

Fossil bones are vestiges of once-living animals. It’s easy to forget that sometimes. Reconstructed skeletons and isolated bones can appear as static objects that now do little more than collect dust. That’s why I’m fascinated by paleopathologies. Recorded in bone, traces of prehistoric disease and trauma speak to critical moments in the lives of extinct creatures. A tattered dinosaur tail is one such symbol of ancient injury.

Described by Munich, Germany’s Ludwig-Maximilians-Universität München paleontologist Richard Butler and coauthors in the latest Journal of Vertebrate Paleontology, the appendage in question belonged to a sauropodomorph dinosaur who roamed Early Jurassic South Africa between 200 and 175 million years ago. Exactly what species the dinosaur was is difficult to discern, but, Butler and colleagues note, the animal’s anatomy is consistent with Massospondylus – a long-necked, small-headed, bipedal dinosaur that was an archaic cousin of the famous, giant sauropods like the later Diplodocus. Based on skeletal proportions, the researchers expect that this Massospondylus could have been about 20 feet long, but was undoubtedly shorter. A mass of messy, fused tail bones indicate that this was a truncated dinosaur.

A reconstruction of Massospondylus at the Natural History Museum, London. Photo by Ballista, image from Wikipedia.

While dinosaur tail length likely varied within and between species, similar sauropodomorph dinosaurs typically have between 45 and 50 tail vertebrae. The injured Massospondylus only had 25, with the latter three wrapped up in a mass of reactive bone growth. Paleontologists have noted similar pathologies among other dinosaurs before. One unlucky hadrosaur was missing the last foot of its tail, and a specimen of the predatory Majungasaurus described by Andrew Farke and Patrick O’Connor was missing the last ten tail vertebrae when it died. Pathologies on such specimens indicate that injury or disease accounts for the shortened tails rather than preservation or sampling.

What could have caused such a devastating injury? Butler and coauthors lay out two scenarios. Perhaps a prior injury and devastating infection could have severed the back third of the dinosaur’s tail. Then again, the dinosaur’s tail could have been broken or torn off in a short, sharp traumatic event. “Really, we can’t be certain about what caused this pathology,” Butler says, but he and his coauthors suspect that the sauropodomorph’s tail was quickly ripped off. “We think a traumatic event is more likely for the reason that the neural arch of the final preserved vertebra appears to have been sheared in two, then later fused together again, but with the posterior part of the vertebra slightly displaced relative to the anterior part,” Butler explains, and this pathological clue “suggests some kind of violent impact, most plausibly an attack by a predator.”

“It’s even more speculative to try and propose possible candidates” for the attacking dinosaur, Butler cautions, but he and his colleagues note that the 20-foot-long predator Dracovenator was found nearby in the same stratigraphic horizon. We can’t know whether a Dracovenator was responsible for the injury, or even if any predator ran off with the tail of the poor dinosaur, but, for now, Dracovenator remains on the list as a possible culprits.

Supposing that a predator really did tear the tail of Massospondylus, we know that the carnivore didn’t kill their victim. The sauropodomorph survived long enough for new bone to grow and suppurative abscesses to form. Healing must have been incredibly painful for the dinosaur, but the degree to which its last three tail bones fused underscores the fact that the Massospondylus survived for a long time after the injury. Despite all the caution and caveats, the dinosaur’s gnarly tail gives us just that much more insight into a tragic prehistoric life.

Reference:

Butler, R., Yates, A., Rauhut, O., Foth, C. 2013. A pathological tail in a basal sauropodomorph dinosaur from South Africa: evidence of traumatic amputation? Journal of Vertebrate Paleontology. 33, 1: 224-228

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