MEANING: Western bird
PERIOD: Late Cretaceous
CONTINENT: North America
The cormorant-like Hesperornis lived throughout the Campanian age, and possibly the early Maastrichtian age, of the Late Cretaceous period. It reached up to 1.8 m in length, had virtually no wings, and swam with its powerful hind legs. It is unknown whether Hesperornis had lobed toes similar to modern-day grebes, or webbed toes as seen in most aquatic birds. Hesperornis had teeth as well as a beak. The teeth were present along nearly the entire lower jaw and the back of the upper jaw. Studies of the bone surface show that at least the tips of the jaws supported a hard, keratinous beak similar to that found in modern birds.
Hesperornis is from the Cretaceous. The Cretaceous is a geological period that lasted from about 145 to 66 million years ago. It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct flora and fauna, while dinosaurs continued to dominate on land. The world was ice free, and forests extended to the poles. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras.
Hesperornis is a Paravian. The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. The Archaeopteryx has famously been known as the first example of a bird for over a century, and this concept has been fine-tuned as better understanding of evolution has developed in recent decades.
Like other theropods, all paravians are bipedal, walking on their two hind legs. Most of the earliest groups were carnivorous, though some smaller species are known to have been omnivores. Paravians generally have long, winged forelimbs, though these have become smaller in many flightless species. The wings usually bore three large, flexible, clawed fingers in early forms. Over time, the fingers became fused and stiffened in some lineages, and the claws reduced or lost. An increasingly asymmetric wrist joint allowed the forelimbs to elongate and an elaboration of their plumage eventually allowed the evolution of flapping flight possible.