Estimated at over eight meters long, Tarchia is one of the largest ankylosaurids currently known, rivalling even the more famous Ankylosaurus. In fact given that Ankylosaurus is still known only from partial remains, Tarchia may one day actually prove to be the biggest. Tarchia was named along with another large, but slightly smaller ankylosaurid called Saichania, and although quite similar to one another, there are a number of identifiable differences between the two, particularly differences associated with the skull proportions. Despite these differences however, both Tarchia and Saichania both share bulbous bone growths that are present across the tops of their skulls. A North American ankylosaurid called Nodocephalosaurus also has these bumps, strongly suggesting a possible relationship with Tarchia and Saichania.
Tarchia possessed a wide cropping beak across its mouth that allowed large amounts of vegetation to be indiscriminately pulled into the mouth. These plants would have likely been quite tough considering that Tarchia lived in an arid climate that was near desert in places, and would have required a large degree of processing in the mouth. Evidence for this comes from the teeth which show occlusion wear, basically meaning that the teeth of the upper and lower jaws regularly made contact. Like other ankylosaurids Tarchia had teeth more suited to chopping, and with every up and down movement of the jaw, the food in the mouth would be chopped into smaller and smaller pieces. This was not just to help swallowing but to increase the efficiency of digestion as the teeth chopping the food would provide a greater surface area to be exposed to the digestive acids of the stomach, greatly enhancing the nutritional gain.
Tarchia also had a hard palate and a network of air passages in the snout which would have helped to moisten the dry air of its ecosystem before it reached its lungs. This would greatly reduce the amount of water lost through the process respiration, a vital adaptation considered the climate that Tarchia lived in. Additionally the presence of the hard palate (unknown in most dinosaurs, but seemingly common in ankylosaurids) meant that Tarchia could still breathe while it processed food in its mouth.
Time Period: The Early Maastrichtian Stage of the Late Cretaceous.
Locale: The lower Kirtland Formation of New Mexico.
Name: “Knob-headed lizard.”
Ankylosaurs were perhaps the classic armored dinosaurs. Maybe Stegosaurus and kin get a bit more press, but the ankylosaurs were a bit more long-lived and heavily armored. They were around since the Late Jurassic, living side by side with their predecessors, who may have even been driven to extinction by them. They dominated the earth, particularly Laurasia, for most of the Cretaceous, and were especially successful because of their protective armor. I’ve covered Minmi, a distant cousin of Nodocephalosaurus, in the first post of my Dinodissertations series, and it, like Nodocephalosaurus, had important geographical implications.
The fauna of Western North America and Eastern Asia during the last stages of the Cretaceous Period were very similar, hinting at repeated migrations from one continent to the other. With the exception of the therizinosaurs, most groups present in one of these areas were also present in the other. Note: Chasmosaurine ceratopsians were not very widespread in Late Cretaceous Asia to our knowledge, but this may change following later remains. This was likely due to consistent migration from one area to another, and these movements have been happening since the Early Late Cretaceous, where creatures like Nothronychus and Zuniceratops were present in both places.
Nodocephalosaurus seems to have been the representative of an ankylosaurian movement from Asia to America, and was morphologically similar to Tarchia and Saichania, two other large ankylosaurs from Asia. It shows that even very late in the Cretaceous, migrations back and forth from Asia and North America were frequent. Saurolophus is another example of such migrations, because it has been found in Mongolia and the United States.
Nodocephalosaurus may have belonged in a family with Tarchia and Saichania, but some disagree, saying that it should just be given a classification as an Ankylosauridae incertae sedis. Whatever the case, the animal remains one of the most striking examples of faunal similarities between joined continents in the Latest Cretaceous, when the world as we know it did not yet exist.