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Hesperornis is an extinct genus of flightless aquatic birds that lived during the Santonian to Campanian sub-epochs of the Late Cretaceous (89-65 mya). One of the lesser known discoveries of paleontologist O. C. Marsh in the late 19th century Bone Wars, it was an important early find in the history of avian paleontology. Famous locations for Hesperornis are the Late Cretaceous marine limestones from Kansasmarker and the marine shales from Canadamarker, but the genus had probably a Holarctic distribution.

Description

Restoration of H. regalis
Hesperornis was a large bird, reaching up to 2 meters (6.5 feet) in length. It had virtually no wings, and swam with its powerful hind legs. The toes were probably lobed rather than being webbed, as in today's grebes; like in these, the toes could rotate well, which is necessary to decrease drag in lobed feet but not in webbed ones such as in loons, where the toes are simply folded together.

Like many other Mesozoic birds such as Ichthyornis, Hesperornis had teeth in its beak which were used to hold prey (most likely fish). In the hesperornithiform lineage they were of a different arrangement than in any other known bird (or in non-avian theropod dinosaurs), with the teeth sitting in a longitudinal groove rather than in individual sockets, in a notable case of convergent evolution with mosasaurs.

Discovery and species

Marsh's now-obsolete 1880 reconstruction of H. regalis.
The first Hesperornis specimen was discovered in 1871 by Othniel Charles Marsh. Marsh was undertaking a second western expedition, accompanied by ten students. The team headed to Kansas where Marsh had dug before. Aside from finding more bones belonging to the flying reptile Pteranodon, Marsh discovered the skeleton of a "large fossil bird, at least five feet in height". The specimen was large, wingless, and had strong legs—Marsh considered it a diving species. Unfortunately, the specimen lacked a head. Marsh named the find Hesperornis regalis, or "great ruling bird".

Marsh headed back west with a smaller party in 1872, where he discovered another Hesperornis skeleton. This specimen had enough of its head intact that Marsh could see that the creature's bill had been lined with teeth. Along with Benjamin Mudge's find of the toothy bird Ichthyornis, Marsh was sure of the important evolutionary ramifications of the finds. In an 1873 paper Marsh declared that "the fortunate discovery of these interesting fossils does much to break down the old distinction between Birds and Reptiles". Meanwhile Marsh's relationship with his rival Edward Drinker Cope soured further after Cope accidentally received boxes of fossils, including the toothed birds, that were meant for Marsh. Cope called the birds "simply delightful", but Marsh replied with accusations Cope had stolen the bones. By 1873 their friendship dissolved into open hostility, helping to spark the Bone Wars. While Marsh would rarely go into the field after 1873, the collectors he paid continued to send him a stream of fossils. He eventually received parts of 50 specimens of Hesperornis, which allowed him to make a much stronger demonstration of an evolutionary link between reptiles and birds than had been possible before.

Of the many species described in this genus - such as the famous H. regalis or the huge H. rossicus -, not all may be valid. Some, such as H. macdonaldi, are known from very few or even a single bone and cannot be properly compared against the more plentiful (but also incomplete) remains of other similar-sized and contemporary taxa. Coniornis altus (which includes H. montana) may also belong into this genus. In addition, there are some unassigned remains, such as SGU 3442 Ve02 and LOmarker 9067t and bones of an undetermined species from Tzimlyanskoe Reservoir near Rostovmarker. The former two bones are probably H. rossicus; some remains assigned to that species in turn seem to belong to the latter undetermined taxon. (2005): Aquatic birds from the Upper Cretaceous (Lower Campanian) of Sweden and the biology and distribution of hesperornithiforms. Palaeontology 48(6): 1321–1329. (HTML abstract) The small form, initially called H. gracilis, was later moved into a monotypic genus Hargeria, and ultimately placed in Parahesperornis.

Paleobiology

Restoration of a swimming Hesperornis by J.M.
Gleeson
Hesperornis hunted in the waters of such contemporary shelf seas as the North American Inland Sea, the Turgai Strait and the prehistoric North Seamarker, which then were subtropical to tropical waters, much warmer than today. They probably fed mainly on fish, maybe also crustaceans, cephalopods and mollusks as do the diving seabirds of today. Their teeth were helpful in dealing with slippery or hard-shelled prey.

On land, Hesperornis may or may not have been able to walk. They certainly were not able to stand upright like penguins as in the early reconstructions. Their legs attached far at the back and sideways, with even the lower leg being tightly attached to the body (see photo of skeleton). Thus, they were limited to a clumsy hobble at best on land and would indeed have been more nimble if they moved by sliding on their belly or galumphing. Indeed, the leg skeleton of the hesperornithids was so much adapted to diving that their mode of locomotion while ashore, as well as where it laid its eggs and how it cared for its young is a matter of much speculation.

Some have even pointed out that it cannot be completely ruled out that these birds were ovoviviparous instead of incubating their eggs. In any case, young Hesperornis grew fairly quickly and continuously to adulthood, as is the case in modern birds, but not Enantiornithes. (1998): Bone microstructure of the diving Hesperornis and the volant Ichthyornis from the Niobrara Chalk of western Kansas. Cretaceous Research 19(2): 225-235. (HTML abstract) More young birds are known from the fossil record of the more northernly sites than from locations further south. This suggests that at least some species were migratory like today's penguins which swim polewards in the summer.

Hesperornis were preyed upon by large marine carnivores. Tylosaurus proriger specimen SDSMT 10439 contains the bones of a Hesperornis in its gut, for example.

In popular culture

Hesperornis appeared in the Episode 3 of the science fiction TV series Primeval. Here, a housewife in west London finds water spreading through the basement. She then calls a plumber. When he comes, the plumber is then killed by a frightened Hesperornis. Later a flock of these birds were shown swimming around in a tropical sea and a Hesperornis rookery was seen on the rocky shoreline. Here Hesperornis was depicted as having scales when in real life it was almost certainly covered in feathers, albeit perhaps more scale-like ones as in penguins and loons. It is also shown standing upright, which it wouldn't have been capable of.

Hesperornis was also shown in the last episode of the Walking with... series spin-off Sea Monsters, being frequently attacked and devoured by larger predators such as Xiphactinus, Squalicorax and Halisaurus and also appeared in Sea Monsters: A Prehistoric Adventure which was devoured by a Tylosaurus.

Footnotes

  1. Discussed in detail by Marsh (1880) and Gregory (1952).
  2. Thomson, 191.
  3. Thomson, 193.
  4. Wallace, 86.
  5. Thomson, 226.
  6. Wallace, 87.
  7. Wallace, 132.
  8. Mortimer (2004)
  9. (1999): Hesperornis (Aves) from Ellesmere Island and palynological correlation of known Canadian localities. Canadian Journal of Earth Sciences 36(9): 1583-1588. HTML abstract


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