The terrorist attacks on September 11, 2001 overshadowed the discovery of a remarkable fossil site in southeastern Missouri that occurred on that very day when a road-building crew uncovered Riverbluff Cave. This cave is 220 feet long and the fossiliferous Pleistocene-age sediments were 18 feet thick. On the first day of discovery workers found 15 foot high claw marks made by the extinct giant short-faced bear (Arctodus simus). I posted a photo of those marks on the blog entry just previous to this one. The cave is now closed to the public and only scientists with permits are allowed to study inside, though there is a public museum dedicated to the find.
Riverbluff Cave, Missouri. The cave is closed to the public. It’s a beautiful rock outcropping.
Fossils apparently began accumulating in Riverbluff Cave about 970,000 BP. The fossil deposition lasted until 55,000 BP when a rockfall sealed the cave. Scientists found mammoth bones dating to 660,000 BP here. The website for the Riverbluff Cave Museum erroneously reports this as the oldest mammoth fossils found in North America. This claim is not even close. Mammoth fossils dating to 1.36 million years ago were found in Bruneau, Idaho 60 years ago, and I think there have been mammoth fossils found in Florida that are older than that. This early mammoth species is known as the southern mammoth (Mammuthus meridionalis). However, Riverbluff Cave does have some unique features found nowhere else. Scientists found 25 beds scratched out by bears that formerly denned here. This is also the only place in the world where tracks of the extinct flat-headed peccary (Platygonus compressus) are still intact. Strange as it may seem, fossil millipedes dating to the Pleistocene were unknown from that era until they were discovered here. In addition to these unusual features, the cave offers scientists a mountain of data, including bear and peccary coprolites, hair from extinct mammals, and scores of bones from large and small mammals, birds, reptiles, and amphibians. Plus, the rocks forming the surface of the cave contain Paleozoic echinoderm (starfish) fossils.
Claw mark made by an extinct species of lion–Panthera atrox.
Hoof marks made by flat-headed peccaries.
Fossil sites in southwestern Missouri
There used to be 6 springs on a Pomme de Terre River terrace in southwestern Missouri before construction of a dam flooded them. Luckily, scientists were able to study each in detail in advance. These springs acted as bogs that attracted and preserved many species of animals but especially semi-aquatic mastodons whose remains were so abundant that scientists could thoroughly study changes in their anatomy over time from specimens excavated here. Pollen, plant, and animal fossils accumulated in Jones Spring beginning 75,000 BP and lasting until the present, providing an almost continuous ecological record. During the middle of the Wisconsinian Ice Age, a warm interstadial allowed hardwood forests to flourish on rich soils, while jack pine predominated on thin and sandy soils in this region. Jack pine no longer occurs south of Michigan. Macrofossils of oak, maple, dogwood, plum, cherry, elm, hickory, honey locust, osage orange, ash, juniper, and jack pine were excavated from Jones Spring. Pollen indicates an environment of 20%-30% pine, 10% oak, 5% grass, 5% composities, 5% ragweed, and 35% other plants. This composition of species suggests an environment prone to frequent fire. Osage orange and honey locust, not coincidentally, bore fruit dependent on mastodons for propagation, explaining their abundance here. Later, as the climate cooled, spruce forests replaced the oak and pine woodlands, but by the latter stages of the Ice Age, oak and other hardwoods began to recolonize the region, and they co-existed with spruce in forests that have no modern analogue. Jack pine never recolonized the region, demonstrating the haphazard nature of plant distribution. Vertebrate fossils found here included mastodon, mammoth, Harlan’s ground sloth, camel, horse, donkey, tapir, long-horned bison, woodland musk-ox, saber-tooth, raccoon, ducks, alligator, and box turtle. The presence of alligator, which no longer ranges this far north, may be evidence of warmer winters during the mid-Wisconsinian interstadial than occur here today. However, it’s possible alligators simply haven’t recolonized the region since the LGM.
There were 2 Trollinger Springs. The remains of at least 15 mastodons were excavated from these springs in addition to woodland musk-ox and stilt legged deer (Sangamona fugitiva). Koch Spring was excavated in 1843, but most, if not all the fossils, were shipped to European museums and are now lost.
Jeffrey Saunders posing behind some mammoth bones found at Boney Spring, Missouri. He co-authored one of my most favorite scientific papers I’ve ever read. From data they analyzed that came from 6 springs on the Pomme de Terre river terrace, they were able to reconstruct what the environment was like during the mid to late Wisconsinian Ice Age in Missouri.
Fossils from Boney Spring date to the LGM. This spring hosted the greatest variety of animal fossils found in all the springs. Scientists even found seed shrimp and insect fossils in Boney Spring. One of the insect species (Ocophora) is a boreal rove beetle that no longer occurs this far south. Scientists catalogued the bones from 2 species of fish, 4 of amphibians, and 7 of reptiles. Many small mammals left fossil evidence at Boney Spring–fox squirrels, woodchucks, flying squirrels, chipmunks, gophers, and bog lemmings. Larger mammals such as giant beaver, Harlan’s ground sloth, horse, tapir, and white tail deer left bones here as well. The remains of at least 31 mastodons rested here until they were excavated prior to reservoir inundation. Pollen from one of the mastodon tusks contained 26%-30% spruce, but also substantial amounts of oak, willow, alder, elm, and tulip. This particular mastodon must have died during the latter stages of the Ice Age when hardwoods were recolonizing the land from spruce forests.
Truman Lake now covers those amazing springs where so much paleoecological information was gleaned.
References:
King, James; and Jeffrey Saunders
“Environmental Insularity and the Extinction of the American Mastodon”
Quaternary Extinctions: a prehistoric revolution edited by Paul Martin and Richard Klein University of Arizona Press 1984
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