Archive for April 6th, 2014

Wooster’s Fossil of the Week: A brontothere jaw fragment (Miocene of South Dakota)

April 6th, 2014

Titanotherium proutiiThis fossil has been sitting in a glass case outside my office door for nearly three decades. Only this year — in the desire to find more Fossils of the Week — did I bother to open the cabinet and take it out for a looksie. On the reverse was a 19th century label: “Titanotherium proutii, Badlands, SD”. That started me on a complicated journey through the literature to see just what sort of creature bore these magnificent molars, as well as the history of its discovery.
Titanotherium proutii occlusalIn this occlusal (meaning the biting surface) view you can see in the beautiful flowing lines of the hard (dark) and softer (light) enamel that there are some serious cracks repaired with a dodgy yellowish glue. The specimen is very fragile — that glue has probably been holding it together for well over a century. These are classic plant-eating teeth for both cutting and grinding leaves, roots and small branches.
TitanotheriumThe animal represented here is a titanothere, a large extinct mammal common in what would become the Badlands of South Dakota during the Paleogene. Above is a recreation of a relative of our species: Megacerops (Titanotherium) robustum. (The artist who drew this illustration in 1912 was Robert Bruce Horsfall, 1869-1948.) The titanotheres, now better known as brontotheres, were roughly the size and shape of rhinoceroses, but were actually more closely related to horses. They had elephant-like feet, inwardly-curved skull caps, and impressive horns on the nose.

I usually delight in tracking down taxonomic histories (the technical history of scientific names), but Titanotherium proutii has defeated me. The history of this taxon is convoluted beyond recovery — a sad tale of mistakes, misplaced fossils, specimens given multiple names, and over-zealous “splitting” of taxa. In other words, typical middle 19th century vertebrate paleontology. Mader (1998) says that Titanotherium Leidy 1853 (or 1852?) is a nomen dubium or “doubtful name”. Even the species, which later became Palaeotherium proutii, is nomen dubium. The names are simply worthless to science. I have been unable to figure out what the accepted name for our fossil now is.
Joseph_LeidyJoseph Leidy (1823-1891) named Titanotherium and (maybe) T. proutii (there is dispute as to who named it first). Leidy was a well known American biologist and paleontologist who taught first at the University of Pennsylvania and then Swarthmore College. He described and named the first nearly-complete dinosaur skeleton, Hadrosaurus foulkii. (It was found in the Cretaceous of New Jersey and he named it in 1858.) Leidy was also an early supporter of Charles Darwin and his the new theory of evolution, early enough for this to be an unpopular position. Edward Drinker Cope was one of his students, which forever places him at the beginning of the famous “Bone Wars” between Cope and Othniel Charles Marsh, which raged from 1877 to 1892. That epic conflict actually began in the New Jersey marl pits where Leidy’s hadrosaur was found. Leidy thus leaves us with a mixed legacy of discoveries, innovations and insights mixed with errors and folly. Just the sort of character we would expect on the frontier of a new science in a new country.
Leidy1Leidy’s 1853 (Plate XVI) figure of a jaw fragment of “Titanotherium proutii“.

References:

Leidy, J. 1853. The ancient fauna of Nebraska: or, a description of remains of extinct Mammalia and Chelonia, from the Mauvaises Terres of Nebraska. Smithsonian contributions to knowledge, vol. 6. Washington, Smithsonian Institution.

Mader, B.J. 1998. Brontotheriidae. In: C.M. Janis, K.M. Scott, and L.L. Jacobs (eds.), Evolution of Tertiary Mammals of North America 1: 525-536.

Mihlbachler, M.C., Lucas, S.G. and Emry, R.J. 2004. The holotype specimen of Menodus giganteus, and the “insoluble” problem of Chadronian brontothere taxonomy. Paleogene Mammals. New Mexico Museum of Natural History and Science Bulletin 26: 129-135.

Warren, L. 1998. Joseph Leidy: the last man who knew everything. Yale University Press, New Haven; 303 pages.