Hesperornithes
| Hesperornithes Temporal range: Late Cretaceous, 99.6–66 Ma |
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| Restored skeleton of Hesperornis regalis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Ornithurae |
| Clade: |
†Hesperornithes Fürbringer, 1888 |
| Subgroups | |
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| Synonyms | |
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Hesperornithiformes Sharpe, 1899 |
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Hesperornithiformes Sharpe, 1899
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 over 1.5 metres (4.9 ft).
Hesperornitheans were the only Mesozoic avialans to colonize the oceans. They were wiped out in the Cretaceous–Paleogene extinction event, along with enantiornitheans and all other non-avian dinosaurs, as well as many other diverse plant and animal groups.
Most of what is known about this group rests on analyses of single species, as few provide sufficiently complete fossils for analysis. Although some of the smaller and more primitive species, like those belonging to the subgroups Enaliornithidae and Brodavidae, might have been able to fly, the larger hesperornithids like Hesperornis and Baptornis had only vestigial wings. As in the case of modern foot-propelled diving birds, the femur and metatarsus of these animals were short, whereas the tibia was long. The legs were also set far back on the body, as in loons, grebes or penguins. Hesperornithids must have been powerful swimmers and divers but extremely ungainly on the land, and probably spent little time ashore except to nest. They were rather long-bodied, and measured about 6 feet (180 cm) long.
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