Quetzalcoatlus, the largest of all pterosaurs, also has a very confusing classification. It is known from North America’s Latest Cretaceous deposits, but during this time there were a great number of rock formations, many of which had some kind of azhdarchid.
Some of these were indeed species of Quetzalcoatlus while others were probably not. In fact many of these genera are actually unclassified.
They all date back to around 68 to 66 million years ago, to the Lancian Age of the Maastrichtian. At this time the Western Interior Seaway was beginning to disappear at last and only a small arm of it was left behind. This was known as the Pierre Seaway.
During this time there was a continental climate, which much more stability than earlier faunas in both Appalachia and Laramidia. This resulted in a rather warm, temperate North America, a climate that seems to have dominated much of the western United States.
The best Lancian formations are Hell Creek, Lance, Frenchman, Laramie and a few others. In these areas were bayous and backwaters somewhat like those in the Everglades. The foliage was quite similar as well, with towering swamp cypresses, ferns, horsetails and duckweed growing in and around the water.
Land plants included conifers of the genus Metasequoia as well as Araucaria in higher regions. There was also dogwood, katsura, palmetto, oak and magnolia in these areas.
We know that the Lance Formation was far swampier than the Hell Creek, and filled with numerous avialan genera. Hell Creek, Lance and Scollard were part of a broad coastal plain with biomes as numerous as forests, floodplains, oxbow lakes and swamps.
The fauna here mostly consisted of famous non-avialan dinosaurs like the all-time favorites Triceratops and Tyrannosaurus.
However even here there were a few specific changes going on. Triceratops contains two species, T. horridus and T. prorsus. The latter is known from the upper Hell Creek and has a shorter frill and thicker, more robust features in comparison to the earlier T. horridus.
Triceratops lived alongside another, much rarer ceratopsian called Torosaurus, and a smaller genus named Leptoceratops. Torosaurus is quite common south of the Hell Creek area but also exists in many of the places where its more famous cousin is found. Triceratops and Torosaurus have even been regarded as being the same animal although more recently this hypothesis was crushed.
Taxonomic messes are commonplace with Hell Creek taxa. Even Tyrannosaurus did not manage to escape this fate. Its remains were first known as ‘Manospondylus gigas’.
This name comes from Edward Drinker Cope, but the discoverer thought that they belonged to a horned dinosaur. Later Henry F. Osborn, who named T. rex, noted the similarity between the two but did not synonimize them. Later it was discovered that they were one and the same.
Remains of young Tyrannosaurus have also been known by different names, including Nanotyrannus and Stygivenator. The difference is quite understandable, for young T. rex went through a series of growth stages during their lifetime. They started out as small and lanky but after an incredible teenage growth spurt, ended up as powerful, muscular adults. Dromaeosaurid remains have always been rare and fragmentary. Only the Hell Creek remains were classified and now constitute a genus called Acheroraptor.
Teeth and other remains are still known all over the remains of these coastal plains, but are as yet unclassified. As recently as a few days ago, a new genus was revealed to the public.
This Hell Creek dromaeosaur was Dakotaraptor steini, a massive animal of 5 meters in length and roughly 400 kilograms. It probably existed in the same niche as teenage and preteen Tyrannosaurus of the same size class, although it was probably not advisable to compete with adults head-on.
Oviraptorid genera Anzu and Leptorhynchos are unknown from Lance, Scollard or Frenchman. Anzu in particularly is another grossly enlarged coelurosaur, up to 2 meters tall and 4 meters long. The oviraptorids would have been omnivores or herbivores. The same goes for ornithomimids like Ornithomimus and Struthiomimus.
The waters of these areas were ruled by many small crocodilians. These include the alligator Brachychampsa with its crushing teeth, and the somewhat gharial-like Thoracosaurus.
While the horned dinosaurs browsed on shrub-level foliage, the versatile switch-feeder, able to browse from trees and from close to the ground, was the massive hadrosaur Edmontosaurus. Synonyms include Anatotitan, used for the very largest and oldest specimens, and the famous Anatosaurus, a much older name. However this is certainly not a new problem.
The genus Edmontosaurus annectens was, for a long time, regarded as being a separate genus called Thespesius, named by Charles Sternberg in 1925.
Also we have the two ornithopods Thescelosaurus and Edmontosaurus in all these formations.
The armored dinosaurs Ankylosaurus and Denversaurus both lived in these areas.
The Canadian Scollard Formation also dates back to this time, as do the Javelina and North Horn Formations of Texas and Utah respectively.
The very largest species of Quetzalcoatlus, Q. northropi, is often shown coexisting with T. rex in Hell Creek but in reality the Hell Creek azhdarchid might have been either Q. sp, or something else. Q. northropi is from the southern states of North America, as is a smaller, unnamed species.
The larger animal did coexist with the largest non-avialan dinosaur in North America. This gigantic beast is Alamosaurus sanjuanensis.
Alamosaurus is not named after the Battle of the Alamo but instead the Ojo Alamo Formation of New Mexico. It is often thought of as the very last sauropod of all, lasting till the end of the Mesozoic Era.
Indeed Ojo Alamo runs from 69 to 66 million years ago. Alamosaurus is known from rather good remains, including juvenile animals and immense adults of over 30 to 40 meters long and 80 tonnes. The largest individuals are the most fragmentary, and were only discovered very recently.
This giant was one of the commonest herbivores in southern North America, with remains known from Utah and Texas as well as in New Mexico. However as an adult it might have been almost untouchable, even with Tyrannosaurus as the apex predator. The two species of Quetzalcoatlus were second fiddle to the big theropod, picking up small animals off the ground.
Quetzalcoatlus northropi itself was up to 5 meters tall and 250 kilograms in weight, with a wingspan of 10 meters, making it the largest flying animal of all time.
However thanks to its classification history, a number of remains have been ascribed to this genus, both large and small. In fact most Quetzalcoatlus species are only moderate in terms of azhdarchid size.