Hesperornithes is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genera such as Hesperornis, Parahesperornis, Baptornis, Enaliornis, and Potamornis, all strong-swimming, predatory divers. Many of the species most specialized for swimming were completely flightless. The largest known hesperornithean, Canadaga arctica, may have reached a maximum adult length of 2.2 metres (7.2 ft).
Ichthyornis is an extinct genus of toothy seabird-like ornithuran from the late Cretaceous period of North America. Its fossil remains are known from the chalks of Alberta, Alabama, Kansas, New Mexico, Saskatchewan, and Texas, in strata that were laid down in the Western Interior Seaway during the Turonian through Campanian ages, about 95–83.5 million years ago. Ichthyornis is a common component of the Niobrara Formation fauna, and numerous specimens have been found.
Hesperornis is a genus of cormorant-like Ornithuran that spanned throughout the Campanian age, and possibly even up to the early Maastrichtian age, of the Late Cretaceous period. One of the lesser-known discoveries of the paleontologist O. C. Marsh in the late 19th century Bone Wars, it was an early find in the history of avian paleontology. Locations for Hesperornis fossils include the Late Cretaceous marine limestones from Kansas and the marine shales from Canada. Nine species are recognised, eight of which have been recovered from rocks in North America and one from Russia.
The Smoky Hills are an upland region of hills in the central Great Plains of North America. They are located in the Midwestern United States, encompassing north-central Kansas and a small portion of south-central Nebraska.
Niobrarasaurus is an extinct genus of nodosaurid ankylosaur which lived during the Cretaceous 87 to 82 million years ago. Its fossils were found in the Smoky Hill Chalk Member of the Niobrara Formation, in western Kansas, which would have been near the middle of Western Interior Sea during the Late Cretaceous. It was a nodosaurid, an ankylosaur without a clubbed tail. It was closely related to Nodosaurus.
Baptornis is a genus of flightless, aquatic birds from the Late Cretaceous, some 87-80 million years ago. The fossils of Baptornis advenus, the type species, were discovered in Kansas, which at its time was mostly covered by the Western Interior Seaway, a shallow shelf sea. It is now known to have also occurred in today's Sweden, where the Turgai Strait joined the ancient North Sea; possibly, it occurred in the entire Holarctic.
Polarornis is a genus of prehistoric bird, possibly an anserimorph. It contains a single species Polarornis gregorii, known from incomplete remains of one individual found on Seymour Island, Antarctica, in rocks which are dated to the Late Cretaceous.
Neogaeornis is a controversial prehistoric genus of diving bird. The single known species, Neogaeornis wetzeli, was described from fossils found in the Campanian to Maastrichtian Quiriquina Formation of Chile. It lived about 70-67 million years ago. It remains known from the single tarsometatarsus described in 1929 by Lambrecht, and today housed in the Paläontologisches Institut und Museum in Kiel, Germany.
Enaliornis is a genus of hesperornithine which lived during the late Albian to the early Cenomanian, making them the oldest known hesperornithines. Fossils have been found near Cambridge, England. Due to its lack of certain hesperornithid apomorphies, they were much more "conventional" birds and were initially held to be Gaviiformes (loons/divers).
Eoalulavis is a monotypic genus of enantiornithean bird that lived during the Barremian, in the Lower Cretaceous around 125 million years ago. The only known species is Eoalulavis hoyasi.
Parahesperornis is a genus of prehistoric flightless birds from the Late Cretaceous. Its range in space and time may have been extensive, but its remains are rather few and far between, at least compared with its contemporary relatives in Hesperornis. Remains are known from central North America, namely the former shallows of the Western Interior Seaway in Kansas. Found only in the upper Niobrara Chalk, these are from around the Coniacian-Santonian boundary, 85–82 million years ago (mya).
Pasquiaornis is a prehistoric flightless bird genus from the Late Cretaceous. It lived during the late Cenomanian, between 95 and 93 million years ago in North America.
Toxochelys is an extinct genus of marine turtle from the Late Cretaceous period. It is the most commonly found fossilized turtle species in the Smoky Hill Chalk, in western Kansas.
During the time of the deposition of the Niobrara Chalk, much life inhabited the seas of the Western Interior Seaway. By this time in the Late Cretaceous many new lifeforms appeared such as mosasaurs, which were to be some of the last of the aquatic lifeforms to evolve before the end of the Mesozoic. Life of the Niobrara Chalk is comparable to that of the Dakota Formation, although the Dakota Formation, which was deposited during the Cenomanian, predates the chalk by about 10 million years.
During most of the Late Cretaceous the eastern half of North America formed Appalachia, an island land mass separated from Laramidia to the west by the Western Interior Seaway. This seaway had split North America into two massive landmasses due to a multitude of factors such as tectonism and sea-level fluctuations for nearly 40 million years. The seaway eventually expanded, divided across the Dakotas, and by the end of the Cretaceous, it retreated towards the Gulf of Mexico and the Hudson Bay.
Brodavis is a genus of freshwater hesperornithiform birds known from the Late Cretaceous of North America and Asia. It was first described and named by Larry D. Martin, Evgeny N. Kurochkin and Tim T. Tokaryk in 2012 and assigned to a new monogeneric family, Brodavidae. Four species were described and assigned to Brodavis.
Luis María Chiappe is an Argentine paleontologist born in Buenos Aires who is best known for his discovery of the first sauropod nesting sites in the badlands of Patagonia in 1997 and for his work on the origin and early evolution of Mesozoic birds. He is currently the Vice President of Research and Collections at the Natural History Museum of Los Angeles County and director of the museum's Dinosaur Institute. He was a postdoctoral researcher at the American Museum of Natural History, New York after immigrating from Argentina. Chiappe is currently the curator of the award winning Dinosaur Hall at the Natural History Museum of Los Angeles County, an adjunct professor at the University of Southern California, BBC advisor and author of scientific and popular books.
Tingmiatornis is a genus of flighted and possibly diving ornithurine dinosaur from the High Arctic of Canada. The genus contains a single species, T. arctica, described in 2016, which lived during the Turonian epoch of the Cretaceous.
