Hesperornis

*Hesperornis regalis*

* Jurassic Park Institute Artwork
* Robert F Walters Artwork

***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 Othniel Charles 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 Kansas and the marine shales from Canada, but the genus had probably a Holarctic distribution.

## Description

*Hesperornis* were very large birds, reaching up to 2 meters (6.5 feet) in length. They had virtually no wings, swimming with powerful hind legs. Their 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.

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 LO 9067t and bones of an undetermined species from Tzimlyanskoe Reservoir near Rostov. The small form, initially called *H. gracilis*, was later moved into a monotypic genus Hargeria, and ultimately placed in *Parahesperornis*.

## History

The first Hesperornis specimen was discovered in 1871 by Othniel Charles Marsh. Marsh was undertaking his ssecond western expedition, accompanied by ten students. The team headed to Kansas where Marsh had dug before.

## Paleoecology

*Hesperornis* primarily dove under the waves into schools of fish to snatch up fish and squid. Hesperornis was likely clumsy on terrestrial surfaces.

## Paleobiology

*Hesperornis* hunted in the waters of such contemporary shelf seas as the North American Inland Sea, the Turgai Strait and the prehistoric North Sea, 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[citation needed] 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. 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.

### Habitat

*Hesperornis* was primarily aquatic, living along shallow marine shelf seas like the Western Interior Seaway, Turgai Straight and the North Sea. Then, these waters were much warmer; subtropical. However, some *Hesperornis* have been found in inland bodies of freshwater, such as the Foremost Formation, suggesting populations moved partially or fully away from saltwater deposits at some point. H. altus is exclusive to Judith River Formation freshwaters.

### Propulsion and Gait

In terms of limb length, socket positioning and the hips form, *Hesperornis* likely swam like the modern loon. This entails swift underwater movements and awkward waddling on land. Also like the common loon, the legs were likely encased inside the bodies wall to the ankle, causing its lower legs to jut out from under its body located near its tail. This would have prevented the necessary standard bipedal gait needed for walking. Rather than walking, *Hesperornis* likely dragged itself forward via its legs, sliding its chest against the ground. However, recent studies suggest that *Hesperornis* functioned more similar to the (admittingly bipedal) cormorant.

### Juveniles

Juvenile *Hesperornis* grew very quickly at a constant rate until maturity. This is the case for modern birds, excluding enatiornithes.

### Pathology

One *Hesperornis* leg bone discovered in the 1960s, examined by David Burnham and Bruce Rothschild et al., shows prominent bite marks along the bone caused by an immature polycotylid plesiosaur, possibly *Dolichorhynchops* or similar genera. The condyle shows specific signs of infection and healing, meaning the bird escaped its predator and survived till fossilization. This finding was published in 2016, from the journal Cretaceous Research.

## Dinosaur Field Guide Description

Hesperornis ("western bird") was a flightless swimming bird with teeth. This may sound like a strange combination, but it is less weird than it seems. After all, there are flightless swimming birds today, such as the various species of penguin or the flightless cormorant of the Galápagos Islands. Birds and raptors are closely related to each other, and both types of dinosaurs diverged from a common ancestor during the Jurassic. Birds evolved the ability to fly, and most birds of the Cretaceous were fliers. The ancestors of Hesperornis, however, became swimmers that chased fish. As time went by, the wings of this group of birds became shorter and shorter, until nothing remained of each wing but a simple spike. Hesperornis swam by using its feet to push itself quickly through the water, chasing after fish and squid. Its legs were so far back on its body that it probably had problems moving on land. However, like modern penguins, Hesperornis almost certainly came up onto land to lay its eggs.

### Fun Facts

During the Late Cretaceous, most of the middle of North America was covered by a shallow tropical sea. You could have taken a boat and sailed from the Gulf of Mexico to the Arctic Ocean over lands that an now prairies!

### Trivia

Because birds are now classified as a kind of dinosaur, Hesperornis is technically a swimming dinosaur, Therefore, older books that say no dinosaurs lived in the sea are incorrect.

## Reference

1. ↑ https://phys.org/news/2014-11-penguins-cretaceous-bird-hesperornis.html