These bones belong to a creature that lived at the very end of the reign of the dinosaurs. The creature, with its kin, watched the asteroid fall. However, who were its kin? Did this animal belong to the royal family of T. rex the tyrant king, or was it a competing prince? Meet Nanotyrannus, one of the most hotly debated, controversial creatures in all paleontology.
Nanotyrannus is in the middle of a bit of a paternity dispute. Does it belong to the same species as Tyrannosaurus rex, and merely represent a juvenile, or is the Nano its own, distinct creature? For ages before Nanotyrannus arrived on the scene, North America commonly supported several large predator species at a time. Each predator fulfilled different ecological niches. In the Jurassic, the large predators Allosaurus, Torvosaurus, and Ceratosaurus all coexisted, splitting the prey between them. In the time just before Nanotyrannus, two different tyrannosaurs also split the menu. There is debate, however, as to whether the pattern of diversity continued to the end of the dinosaurs' reign. While large and small tyrannosaurs have been found from the Nano's time, many scientists believe that the skeletons of the smaller tyrant bear so much similarity to T. rex that they may be juveniles of the same species. If true, this would mean that Tyrannosaurus was so dominant during its time that it drove out all other large predator competition. According to this hypothesis, the large Tyrannosaurus would fill the large predator niche, and the subadult Tyrannosaurus would elbow their way into the medium predator niche (all the more impressive considering the size of their elbows). Could one species have taken over such a large swathe of the ecosystem, eliminating other competitors? Or do some of the smaller tyrannosaurs from the time belong to a different species, as had been the pattern for so long?
With each new find, paleontologists continue to debate the distinctness of Nanotyrannus. Whichever side wins out, the results will enrich the story of the Cretaceous. If Nanotyrannus is its own creature, it will add to our picture of the diversity of its environment. If not, it will add a layer of richness to the tragedy of the dinosaurs' demise. Dinosaurs had faced mass extinction events before. However, at each prior extinction the dinosaurs had maintained strong diversity going into the event. Many species were wiped out, but in the past there were so many species that a few would manage to survive cataclysm and begin anew in the next period. Some scientists argue that the lack of dinosaur diversity at the end of the Cretaceous made it harder for them to bounce back as they had done before. Perhaps, by taking over so many niches and eliminating other species, T. rex may have contributed to a lack of diversity that prevented dinosaurs as a whole from recovering after the K-T extinction event. While many other factors went into the extinction, the creature could have been in part a victim of its own success. Such a story might contain a lesson for earth's current apex species- even tyrants can benefit from sharing.