It’s the wet season, and flocks of Ornithomimus antiquus pour down into the lowlands from the Appalachians, their feathery bodies glimmering in the sun. The flocks have been migrating through the Appalachian mountains for months, and they’re ready to rest. Predators also arrive with the rains. Pesky dromaeosaurid packs harass the Ornithomimus, picking off the weak and the vulnerable. However, the dromaeosaurs pose no threat to the largest animals of the lowlands…
Enter Hypsibema missouriense. H. missouriense is the westernmost species of Hypsibema, and the largest animal present in the lowlands. These gigantic hadrosaurs form small herds which migrate across the plains, stripping trees and shrubs of their leaves, fruits, and seeds. Their large size means H. missourense are almost immune from attacks by predators, but the wet season brings new threats to the herd, including theropods with bigger bodies and bigger appetites.
The largest predators to come with the start of the wet season are the dryptosaurs. Full grown adults can even take down a Hypsibema missouriense, and many of the gigantic hadrosaurs have scars from fights with these killers. Armed with 3-clawed hands, a mouthful of serrated teeth, and feet like those of an eagle, these dryptosaurs are well-armed carnivores.
It’s midday in the lowlands, and a juvenile dryptosaur descends from its home on an outcrop to a nearby lake. Unfortunately for the young carnivore, a herd of Hypsibema missouriense have stopped to cool off, and do not intend to share the water. The hadrosaurs spot the juvenile, and start to bellow aggressively, signaling that they’ll charge. The juvenile knows not to instigate the titanic dinosaurs, and retreats to the safety of the adult members of its pack.
Hypsibema missouriense is the better studied and more-well known of the two Hypsibema species. Designated as the State Dinosaur of Missouri in 2004 (See reference 1 for more details), this dinosaur was originally mistaken for a sauropod (Gilmore & Stewart, 1945). This attests to the size of the known bones of H. missouriense. All the fossil caudal vertebrae of this animal in the Smithsonian’s collection are almost 10 centimeters (3.9 inches) in length.
The size of H. missouriense‘s caudal vertebrae suggest an animal of similar size to H. crassicauda. However, none of the H. missourense caudal vertebrae above equate to 10 centimeters in length, whereas the caudal vertebrae of the Hypsibema crassicauda type specimen does (the H. crassicauda vertebrae is actually slightly longer then 10 centimeters. Go check out my post here for an image of the type specimen). The longest vertebrae in the image above (rightmost row, second down) comes in at approximately 9.8 centimeters in length. If we compare that with this 10 centimeter caudal vertebrae attributed to H. crassicauda, we realize that the length of the H. missouriense specimen is 96% of the H. crassicauda specimen. Using the length determined by Holtz and Rey (2007) for H. crassicauda (I should note that Holtz and Rey refer to H. missouriense as Parrosaurus, which was placed in the genus Hypsibema by Baird & Horner (1979)), which they determined was 49.2 feet, we can make an approximate estimate of the length of the H. missouriense holotype. We find a length of 47.2113 feet (96% of 49.2 feet) for the holotype of H. missouriense. That’s slightly smaller then H. crassicauda , but still gigantic for a hadrosaur.
The caudal vertebrae above aren’t the only material we have from H. missouriense. A fragmentary dentary and predentary are known from this animal (Weishampel et. al., 2007)(Check out this page at the Bollinger County Museum’s website to see the partial dentary), as well as some phalanges (see below). From the more complete remains of H. missouriense, we can better understand how the giant hadrosaurids of Appalachia lived.
During the time of Hypsibema missouriense, Missouri was situated in the southwest of Appalachia. Here, the Appalachians gave way to lowlands, which eventually dipped into the Western Interior Seaway.
75 million years ago (Campanian Stage of the Late Cretaceous) the Appalachians were eroding away. The elements slowly chipped away at these mountains, almost flattening them into the lowlands they gave way to. H. missouriense would have been witness to the last of the Cretaceous Appalachian mountains.
H. missouriense itself hails from the Chronister site, a Campanian age deposit, which, in some places, constitutes as a bone bed (Fix & Darrough, 2004). During the Campanian, the Chronister site was a body of fresh water, possibly some sort of lake or wetland (Fix & Darrough, 2004). The Chronister site is very special, as it is the only locality in Missouri which produces terrestrial vertebrate remains dating to the Mesozoic (Fix & Darrough, 2004). Among the vertebrates are turtles, such as Adocus, the large amphibian Habrosaurus, and the crocodilian Leidyosuchus (Fix & Darrough, 2004). Along with H. missouriense, dromaeosaurids and tyrannosaurids make up the dinosaur fauna (Fix & Darrough, 2004). What interests me about this site, however, is its location on the western coast of Appalachia 72 million years ago.
Many Late Cretaceous localities, such as the Ellisdale site (New Jersey) and Phoebus Landing (North Carolina), have yielded the remains of not only dinosaurs, but turtles, amphibians, lizards, fish, and other vertebrates. When it comes to the fossil record from western Appalachia (I am referring to the continent), we aren’t so lucky. The Chronister site gives us the unique opportunity to study what life was like on the eastern shores of the Western Interior Seaway. Yet Chronister’s close proximity to this inland sea might have caused the downfall of its native residents. When this seaway pulled a reverse-Moses, the dinosaurs of Chronister were right there in the midst of Laramidian species, some of which may have outcompeted natives like Hypsibema missouriense. Of course, we can’t be sure what happened, as we simply do not have localities in the Central and Midwestern US which preserve Maastrichtian dinosaur bones from Appalachia. For now, the fate of western giant hadrosaurids like H. missouriense is a mystery.
Although we might never know what eventually happened to the giant hadrosaurids of western Appalachia, the future looks positive for the Chronister dig site. Excavations of this locality are currently being conducted by the Bollinger County Museum of Natural History. New specimens are constantly being unearthed, and the site’s bone bed will surely continue to yield exciting vertebrate fossils, along with those of plants and invertebrates. The secrets of Appalachia’s far west are finally being revealed.
For more on gigantic hadrosaurids and Appalachian localities, see these articles:
1. “The State Dinosaur”. State Symbols of Missouri. Missouri Secretary of State. URL: http://www.sos.mo.gov/symbols/symbols.asp?symbol=dino. Accessed June 28, 2015.
2. Gilmore, C. W.; Stewart, D. R. .1945. “A New Sauropod Dinosaur from the Upper Cretaceous of Missouri”. Journal of Paleontology 19 (1): 23–29.
3. “Hypsibema missouriensis” Collections Search Center, Smithsonian Institution. Smithsonian Institution. URL: http://collections.si.edu/search/results.htm?q=Parrosaurus . Accessed June 28, 2015.
4. “Hypsibema crassicauda” Collections Search Center, Smithsonian Institution. Smithsonian Institution. URL: http://collections.si.edu/search/results.htm?q=Hypsibema+crassicauda . Accessed June 28, 2015.
5. Baird, D.; Horner, J. R. .1979. “Cretaceous dinosaurs of North Carolina”, Brimleyana 2: 1-28.
6. Weishampel, D. B.; Dodson, P.; and Osmólska, H. (eds.). 2007. The Dinosauria, 2nd Edition. Berkeley: University of California Press. p. 443.
7. “Hypsibema missouriense” Collections Search Center, Smithsonian Institution. Smithsonian Institution. URL: http://collections.si.edu/search/results.htm?q=Hypsibema%20missouriense&tag.cstype=all . Accessed June 28, 2015.
8. Fix, M. F.; Darrough, G. .2004. “Dinosauria and associated vertebrate fauna of the Late Cretaceous Chronister site of southeast Missouri.” Geological Society of America Abstracts with Programs 36 (3): 14.