Antediluvian Beasts of the East : Ornithotarsus immanis

It’s morning in the woodland, 79 million years ago, and the sounds of the forest greet the rising sun. Within a cluster of Gunnera plants, a male dromaeosaurid displays his plumage to a somewhat uninterested female, while a pair of mammals dash across the earth. A sudden, triumphant bellow sends the dromaeosaurids darting into the trees, leaving the mammals to forage in peace. The bellow came from a young male Hadrosaurus foulkii, the most common dinosaur of the woodland. Typically, Hadrosaurus foulkii travel in closely-knit herds, but males are often exiled, only to return to the herd during mating season. Being solitary means that this young male Hadrosaurus foulkii lacks the protection of the herd, and is an easy kill for the predators of the forest. Yet predators aren’t the only threats in these woods.

The young male hadrosaur stops to browse on some tall shrubs, without a whim in his mind, but suddenly, with the volume of a ship horn, an immense bellow from behind the shrubs makes the young hadrosaur jump. The emperor of these forests has arrived. Meet Ornithotarsus immanis. This 39 foot, 7 ton male is twice as long and three times as heavy as the 20 foot, 2 ton young male Hadrosaurus foulkii. A whole herd of the giant hadrosaurs emerge from the forest, prompting the young Hadrosaurus to flee. These gentle giants pose no threat to the smaller hadrosaur, but instead use their bulk to tip over trees and defend themselves.

The herd of Ornithotarsus is on their way to the highlands, where they will graze on the various plants which make up the highland’s plains. But there’s a catch. The wet season, while giving life to the plants the Ornithotarsus herd will feast on, leaves the highlands wet and cold, no place for an exposed hadrosaur. These hadrosaurs, however, have a remarkable adaptation. Unlike the hadrosaurs of the lowlands, who bear scutes over their body save for the occasional bristle-like proto-feather ancestral to the order ornithischia, a thick pelt of modified proto-feathers insulate the Ornithotarsus immanis while they occupy the highlands. They are, indeed, woolly hadrosaurs.

But their are other dangers awaiting the O. immanis on their journey to the highlands. packs of dromaeosaurids occupy the highlands year-round, and harass the herd of hadrosaurs in an attempt to pick off the young. Harsh storms also pose a threat, and often young, old, and weak hadrosaurs are separated from the herd during these tempests, and are left to find their way through the woods back to the herd or die in the dark forests below the bald peaks of the mountains.

The herd advances on. So far, only two individuals have been separated from the herd, neither of which being juveniles. The herd is almost to the end of their 170 mile, 3 day long, 2500 foot verticle climb to reach the highlands. There is, however, one more challenge they must face. The rock fields of the outer highlands are a nesting site for large azhdarchid pterosaurs. With wingspans of up to 30 feet, and heads shaped like swords, these flying archosaurs can injure even adult Ornithotarsus. The hadrosaurs have also developed a trick for dealing with the pterosaurs. Ornithotarsus bellow as a means of communication, but they also use their calls as a means of intimidation. The azhdarchids, for one, are terrified of the hadrosaurs’ loud bellows, and take to the skies as soon as they hear the first call, leaving the herd to safely pass between the rock fields.

The herd finally arrives at the highlands. In front of them lie the highland plains, and they waste no time in indulging themselves, the wind howling across the expanses of plant littered earth.

What we have of Ornithotarsus consists of a partial tibia, fibula, astralagus, and calcaneum (Prieto-Marquez, Weishampel, & Horner, 2006). These remains possibly hail from the Woodbury Formation of New Jersey (Colbert, 1948). The animal itself was apparently enormous (Colbert, 1948), with an estimated length of 39 feet (Holtz, 2012). In his 1948 paper, Edwin Colbert described the animal as follows: “This seemingly represents a very large hadrosaurian, larger then any others known from the eastern Cretaceous, but until additional material is forthcoming nothing definite can be said concerning this supposed species.” Sentences like that get me excited. If Ornithotarsus was the large hadrosaur Colbert suspected it of being, it would be the largest known terrestrial-animal from the Woodbury Formation.

Ornithotarsus consists of one species, O. immanis. Like many other dinosaurs from the Eastern US, it has been considered a nomen dubium by some workers (Prieto-Marquez, Weishampel, & Horner, 2006), and a synonym of Hadrosaurus foulkii as well (Baird & Horner, 1977) (Weishampel & Horner, 1990) (Horner et. al., 2004) (Weishampel, 2006). Colbert (1948) makes a good point, noting that the fragmentary nature of the Ornithotarsus immanis material causes anything said about the animal to be tentative at best. So what exactly can we say about O. immanis, even if the statement is tentative?

If Ornithotarsus immanis does hail from the Woodbury Formation, it is likely this gargantuan hadrosaur co-existed with the smaller H. foulkii. These animals might have co-existed by exploiting different food sources in the same I have suggested before concerning other hadrosaur genera. So what of (tentative) classification? Prieto-Marquez, Weishampel, & Horner, (2006) classified Ornithotarsus immanis as an indeterminate hadrosaurid, and based on Colbert’s statement, this seems to be the best we can do in terms of the classification of Ornithotarsus immanis until more complete specimens are discovered.

Hadrosaurus foulkii fossils displayed at the Philadelphia Academy of Natural Sciences, Drexel University. Photo from Wikipedia.

Casts of Hadrosaurus foulkii fossils displayed at the Philadelphia Academy of Natural Sciences, Drexel University. Photo from Wikipedia.

Besides Hadrosaurus, a variety of other animals are known from the Woodbury Formation. Hence the fact that the Woodbury Formation is a marine deposit, specimens of the shark Scapanorhynchus texanus, the fish Enchodus, and the sea turtle Catapleura repanda have been collected from the formation (Gallagher, 1993).

Scapanorhynchus texanus teeth. Photo by the author, 2015.

Scapanorhynchus texanus teeth. Photo by the author, 2015.

Ornithotarsus immanis (if the remains do persist to the Woodbury Formation) is also the temporally oldest hadrosaur I’ve discussed so far. The Woodbury Formation is estimated to have been deposited between 80.5 and 78.5 million years ago (Gallagher, 2005). That beats out Hypsibema crassicauda of the Ellisdale site (=Marshalltown Formation, ~72 million years ago). The Hypsibema of the James King Marl Pits (= Black Creek Formation, ~84.9-70.6 million years ago) may have existed at the same time as Ornithotarsus. 

O. immanis was but one of the first giant hadrosaurs of the continent Appalachia. Hadrosaurs would thrive until the end of the Cretaceous, diversifying into a menagerie of forms on multiple continents. The fate of Ornithotarsus would be burial at sea, its remains eroding away until nothing but fragments remained to be found.

Ornithotarsus immanis by the author. Pencils on paper, 2015.

Ornithotarsus immanis by the author. Pencils on paper, 2015.

For more on gigantic hadrosaurids, see these articles:

Antediluvian Beasts of the East : Hypsibema missouriensis 

Antediluvian Beasts of the East : Hypsibema crassicauda 

References 

1. Prieto−Márquez, A.; Weishampel, D. B.; Horner, J. R. .2006. “The dinosaur Hadrosaurus foulkii, from the Campanian of the East Coast of North America, with a reevaluation of the genus.” Acta Palaeontologica Polonica 51(1): 77–98. 

2.Colbert, E.H.  .1948. “A hadrosaurian dinosaur from New Jersey.” Proceedings of the Academy of Natural Sciences of Philadelphia 100: 23–27.

3.Holtz, T. R. Jr; Rey, L. V. .2007. Dinosaurs: the most complete, up-to-date encyclopedia for dinosaur lovers of all ages. New York: Random House. (Updated during 2012) link: PDF .

4. Baird, D.; Horner, J. R. .1977.” A fresh look at the dinosaurs of New Jersey and Delaware.” The Bulletin of the New Jersey Academy of Science 22(2):50. 

5. Weishampel, D. B. ; Horner, J. R. .1990. “Hadrosauridae.” In D. B. Weishampel, H. Osmolska, and P. Dodson (eds.), The Dinosauria. Berkeley: University of California Press. p. 534-561.

6. Weishampel, D. B. .2006. “Another look at the dinosaurs of the East Coast of North America.” III Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno, Salas de los Infantes, Burgos, Spain. Colectivo Arqueológico-Paleontológico Salense Actas:129-168.

7.Gallagher, W. B. .1993. “The Cretaceous/Tertiary mass extinction event in the North Atlantic coastal plain.” The Mosasaur 5:75-154

8. Gallagher, W. B. .2005. “Recent mosasaur discoveries from New Jersey and Delaware, USA: stratigraphy, taphonomy and implications for mosasaur extinction.” Netherlands Journal of Geosciences 84(3): 241.

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