Port Kennedy Bone Cave

I'd gotten to thinking about some things I'd written at other venues, including some pieces I'd done as National Fossil Day monthly features a few years back, at the moment only accessible through Internet Archive but potentially to come back one day. One of these I thought I'd scoop up, given I'd written a companion piece for it here back in the day: a description of Port Kennedy Bone Cave. (Also, it fits in with other Eastern caves covered so far, all sharing the common thread of being investigated by Henry Mercer near the end of the 19th century). So, here it is, with the text edited to be more like the blog style, and inline citations included.

When the Continental Army spent the winter of 1777–1778 at Valley Forge in eastern Pennsylvania, they had no way of knowing they were practically on top of one of the richest fossil sites in eastern North America. Today, within the National Park Service’s Valley Forge National Historical Park, there is buried an ancient fissure, into which various mammals, birds, reptiles, insects, and plant fragments fell during the Middle Pleistocene. The site, known as Port Kennedy Bone Cave (or just Port Kennedy Cave), was found in the 1870s and explored through the 1890s, but became inaccessible and then buried and forgotten until relocated in the 2000s (Daeschler et al. 2005; Hojdila et al. 2005). Its fossils belong to one of the most significant Middle Pleistocene faunas in the United States (Daeschler et al. 1993, 2005).

A cross-section of the Port Kennedy site (Mercer 1899). The cross-hatched area (C) is where the 1894 to 1896 excavations were made. The dashed areas (D) are areas of bone deposits that were not excavated.

Port Kennedy Bone Cave, more precisely an old sinkhole, was discovered in 1870 during limestone quarrying in the Valley Forge area near the former town of Port Kennedy. The workers quarried into the feature, from the side, revealing the fossil-bearing fill. Several scientists from the area visited the site to describe the fossils (Daeschler et al. 1993). Charles M. Wheatley was the first (Wheatley 1871), followed by Edward Drinker Cope, both publishing preliminary findings in 1871 (Cope 1871). Port Kennedy Cave was in Cope's backyard, so to speak, and he returned to its fossils off and on throughout his career (Cope 1871, 1880, 1895, 1896, 1899; the last having been issued posthumously, almost the last publication attributed to him), naming a great number of vertebrate species, many of which have since been sunk. The mammal fossils of the site attracted the most attention, but other vertebrates, plant fossils, and insect fossils were also found. The insects were described by Horn (1876), with an additional name supplied by Scudder (1890) which Horn had intended to use; unfortunately the insect specimens have gone missing (Daeschler et al. 1993).

After the first excavation of the deposits, they were covered over. Later, in 1893, the sinkhole deposits were again exposed by quarrying activity, this time at a lower level. Additional fossil collections were made by Samuel G. Dixon and Henry C. Mercer from 1894 to 1896, when water made it impossible to continue at the time (Mercer 1899; Daeschler et al. 1993). Mercer (1899), incidentally, is well worth reading, both for the detailed description of the site and the practically modern approach Mercer used for excavating, documenting finds with a grid system. He went to such lengths because he was hoping to find evidence of humans and wanted to be sure that if there was any, it would be properly documented. The exact location of the site became forgotten over the years, and the quarry was used as a dump for industrial waste until it was filled (Daeschler et al. 1993, 2005). It was long rumored that a locomotive was crashed into the quarry for a now-lost 1915 silent film (“The Valley of Lost Hope”), but a magnetic survey in 2004 did not find any evidence of a large metal object (Hojdila et al. 2005). Eventually, the area filled in and was covered with vegetation.

Figure 2 from Mercer (1899) shows the gridwork used by the scientists to document where they found specific fossils. A ladder on the right shows the scale.

Port Kennedy Bone Cave is thought to have begun as an underground hole formed from the dissolution of the bedrock limestone (Cambrian-aged Ledger Formation), which became a sinkhole when the roof collapsed (Daeschler et al. 1993). Similar sinkholes appear today in certain parts of the country, such as Florida, where there is limestone bedrock saturated by groundwater. Over time, animals fell into the hole, died, and became buried by debris, which preserved their remains. Eventually the cave was filled with debris. These events took place several hundred thousand years ago, during the Middle Pleistocene; the exact age is not known for certain, but the fauna is regarded as Irvingtonian (Bell et al. 2004).

Stratigraphy of the deposits (Figure 5 in Mercer 1899; Figure 9 in the same expands upon this to identify where specific taxa had been found). Subdivision 1 is a thin accumulation of plant-rich black sediment with fossils of small animals. Subdivision 2 is composed of reddish-yellow sandy clay, with bones of large mammals. Subdivision 3 is similar to Subdivision 1 except for being somewhat thicker. Subdivision 4 is composed of coarser yellow deposits with only mammal bones.

The fossils from the deposits were very soft, due to the groundwater. Mercer (1899: 273) described them as “wet and soft as over-ripe pears” when in the ground, and wrote with regret of the damages incurred during excavation: "But labor as we would the bones fell to pieces. In the interlaced tangle, the trowel destroyed more than it recovered. Not one-third of the skeletal remains found whole in the bank were saved or could be saved, while nine-tenths of the remaining number were crushed beyond recognition or reduced to masses of rotten splinters. Of the rescued specimens the majority were at best broken and distorted [Mercer 1899:274]." Complete skeletons were not found. Instead, the bones were disassociated (Mercer 1899). The fossils that were recovered show that the area around the sinkhole was forested and temperate to warm. Many but not all of the species found in the deposits are extinct today.

Figure 4 from Mercer (1899), showing a bear skull in preparation.

Seeds, leaves, twigs, and other plant fossils belong to about a dozen species. Most of the seeds represent hickory, beech, pine, and creeper. Most of the leaves belong to willow. Sphagnum moss was also found. Hickory also made up most of the identifiable wood, and oak was also present (Mercer 1899). A dozen species of beetles were found, but no other invertebrates were reported, or any fish. Amphibians and reptiles are represented by frogs, turtles, and snakes. The only bird appears to be a turkey. Many kinds of mammals were found, including: ground sloths, shrews, rodents, rabbits, pikas, bats, mustelids (including badgers, martens, otters, and wolverines), skunks, several varieties of felines (including bobcats, American cheetahs, and saber-toothed cats), dogs, foxes, short-faced bears, black bears, mastodons, horses, tapirs, deer, and peccaries (Mercer 1899; Daeschler et al. 1993). Common mammals of the late Pleistocene, such as the giant beaver and mammoth, were not found; bison has been reported doubtfully (Hay 1923), and not included in the most recent review (Daeschler et al. 1993). In approximate order, the most abundant mammals were sloths, rabbits, skunks, tapirs, short-faced bears, mastodons, and peccaries (Mercer 1899).

An assortment of seeds and nuts from Port Kennedy Cave (Mercer 1899: Figure 8). Mercer noted that several pine cones were found flattened but when removed from the deposit and brought into a warm room, expanded back to their natural form.

To date, at least 49 species of fossil animals have been named from fossils found at the site (see also Spamer and Daeschler 1995 and Spamer et al. 1995). They include 9 species of beetles, 2 turtles, a snake, 4 ground sloths, a shrew, 11 rodents, a pika, 2 mustelids, 6 skunks, 4 felines, a dog, a fox, a bear, a horse, a tapir, a peccary, a deer, and a poorly known ungulate. However, many of these species are now considered synonyms of other species, and only 15 or so of the reptile and mammal species are still in use. Among the most notable are the common Port Kennedy sloth Megalonyx wheatleyi; Smilodon gracilis, a saber-toothed cat; and an American cheetah, now known as Miracinonyx inexpectatus.

After the quarry filled with water, the site was forgotten and its exact location was lost until a series of technical surveys were made in 2004 and 2005 (Daeschler et al. 2005; Hojdila et al. 2005). Several different ground-penetrating techniques were used to map the subsurface of the approximate area of the quarry and sinkhole, based on differences between the sinkhole fill (sand, mud, and clay) and the surrounding limestone. Slight differences in gravity and electrical conductivity were able to show the probable location of the site (Daeschler et al. 2005; Hojdila et al. 2005). The deposits were not fully excavated in the 19th century, but it is unlikely that there will be any excavations anytime soon because of the hazardous waste and the water problems that interfered with the original excavations. Today, most of the fossils are in the collections of the Academy of Natural Sciences of Drexel University in Philadelphia and the American Museum of Natural History in New York. The Visitor Center of Valley Forge National Historical Park also displays some of the fossils.

References

Bell, C. J., E. L. Lundelius, A. D. Barnosky, R. W. Graham, E. H. Lindsay, D. R. Ruez, H. A. Semken, S. D. Webb, and R. J. Zakrzewski. 2004. The Blancan, Irvingtonian, and Rancholabrean Mammal Ages. Pages 232–314 in M. O. Woodburne, editor. Late Cretaceous and Cenozoic mammals of North America. Columbia University Press, New York, New York.

Cope, E. D. 1871. Preliminary report on the vertebrata discovered in the Port Kennedy Bone Cave. Proceedings of the American Philosophical Society 12:73–102.

Cope, E. D. 1880. On the extinct cats of America. American Naturalist 14(12):833–858.

Cope, E. D. 1895. The fossil Vertebrata from the fissure at Port Kennedy. Proceedings of the Academy of Natural Sciences of Philadelphia 47:446–450.

Cope, E. D. 1896. New and little known Mammalia from the Port Kennedy bone deposit. Proceedings of the Academy of Natural Sciences of Philadelphia 48:378–394.

Cope, E. D. 1899. Vertebrate remains from Port Kennedy bone deposit. Journal of the Academy of Natural Sciences of Philadelphia, 2nd series, 11(3):193–286.

Daeschler, E. B., M. C. Lamanna, and M. Carfioli. 2005. On the trail of an important Ice Age fossil deposit. Park Science 23(2):31–34.

Daeschler, E., E. E. Spamer, and D. C. Parris. 1993. Review and new data on the Port Kennedy local fauna and flora (Late Irvingtonian), Valley Forge National Historical Park, Montgomery County, Pennsylvania. The Mosasaur 5:23–41.

Hay, O. P. 1923. The Pleistocene of North America and its vertebrated animals from the states east of the Mississippi River and from the Canadian provinces east of longitude 95°. Carnegie Institution of Washington Publication 322.

Hojdila, J., T. DeMayo, S. Baughman, T. Bechtel, and M. Carfioli. 2005. The long-lost cave has been found! Park Science 23(2):35.

Horn, G. H. 1876. Notes on some coleopterous remains from the bone cave at Port Kennedy, Penna. Transactions of the American Entomological Society 5:241–245.

Mercer, H. C. 1899. The bone cave at Port Kennedy, Pennsylvania, and its partial excavation in 1894, 1895, and 1896. Journal of the Academy of Natural Sciences of Philadelphia 11:269–286.

Scudder, S. H. 1890. The Tertiary insects of North America. Report of the United States Geological Survey of the Territories 13:1–734.

Spamer, E. E., and E. Daeschler. 1995. Previously unfigured type specimens of fossil fish, reptiles, and mammals in the Academy of Natural Sciences of Philadelphia. Proceedings of the Academy of Natural Sciences of Philadelphia 146:429–458.

Spamer, E. E., E. Daeschler, and L. G. Vostreys-Shapiro. 1995. A study of fossil vertebrate types in the Academy of Natural Sciences of Philadelphia: taxonomic, systematic, and historical perspectives. The Academy of Natural Sciences of Philadelphia Special Publication 16.

Wheatley, C. M. 1871. Notice of the discovery of a cave in eastern Pennsylvania containing remains of post-Pliocene fossils, including those of Mastodon, Tapir, Megalonyx, Mylodon, etc. American Journal of Science and Arts, series 3, 1:235–237.