Alfred King’s Forgotten Fossil Footprints

The science of paleontology – the study of ancient life based on fossils – began in Western Europe about 1800. It soon cropped up in the United States, as the populace of a young and growing nation discovered many fossils. Among these early discoveries were those of fossil footprints, most famously found during the early 1800s in the Connecticut River Valley of Massachusetts and described by Edward Hitchcock (1793-1864). Indeed, Hitchcock is now regarded as one of the founders of a major branch of paleontology called ichnology, the study of trace fossils, such as footprints, trails and burrows.

The trace fossils Hitchcock studied are about 200 million years old, close in age to the boundary between the Triassic and Jurassic periods of the geological timescale. Much older trace fossils of Carboniferous age, about 300 million to 349 million years old, were discovered in North America in the 1840s. The first report came in 1841 from Nova Scotia in eastern Canada by geologist William E. Logan (1798-1875). Other discoveries soon followed from western Pennsylvania, reported in a series of articles published by Alfred T. King (1813-58) between 1844 and 1846. More famous discoveries by Isaac Lea (1792-1886) in eastern Pennsylvania first saw print in 1849 (see “Following in the Footsteps of Isaac Lea’s Historic Footprints,” Summer 2007). Today, the footprints documented by Logan and Lea figure prominently in the history of ichnology, but King and his discoveries have been largely forgotten.

Born October 22, 1813, in Galway, New York, Alfred King grew up in relative poverty. While still a boy, he was apprenticed to a doctor. He later studied medicine and then opened his first medical practice in Philadelphia but was not successful in what apparently was a very competitive setting. In about 1838, having read a newspaper article expressing a need for doctors in rural western Pennsylvania, he relocated to start a medical practice in Pleasant Unity in Westmoreland County. Later, he moved his practice to nearby Greensburg.

Beginning in 1840 King wrote various articles for the Greensburg papers about astronomy, botany, medical forensics, microscopy, paleontology and zoology. He was evidently self-taught in most of these fields, and in this way seems typical of the renaissance men of science from the early 1800s. King’s articles, however, also touched on social issues and included criticism of Mosaic geology and the religious intolerance of science. In one argumentative article he concluded that “the baneful consequences of the belief in supernatural agency in the direction and accomplishment of earthly events have been dissipated to the four winds of heaven.” Not surprisingly, the local clergy and its supporters were not amused, and the ensuing polemics were to continue throughout the remaining years of King’s relatively short life.

In the 1840s, supported by his medical practice, King found time as a naturalist to study the local flora, fauna and geology of Westmoreland County. In 1844 he discovered what he took to be fossil footprints in the Upper Carboniferous (Pennsylvanian, about 305 million years old) sandstones exposed in the area. Between 1844 and 1846 King published these discoveries in two of the premier American scientific journals of the time, Proceedings of the Academy of Natural Sciences of Philadelphia and The American Journal of Science and the Arts. The footprints King described came from three localities: a rocky outcrop about 1 mile from Derry, a stone quarry in Unity Township about 5 miles southeast of Greensburg, and the summit of Chestnut Ridge about 27 miles from Greensburg.

King’s drawing of the trackway surface near Derry that formed the basis for his scientific names Ornithichnites (the “bird footprints” numbered 4) and Spheropezium (the other “footprints” numbered 1, 2 and 3). None of these “tracks,” however, are authentic fossil footprints. From Proceedings of the Academy of Natural Sciences of Philadelphia 2, no. 6 (November-December 1844)

The outcrop near Derry produced the footprints that King first described from a sandstone surface measuring about 15 by 20 feet. King’s published drawing shows a substantial number of tracks on that surface, as well as large potholes – he called them “pots” – in the rock. He recognized some of the tracks as those of birds, and he used Hitchcock’s scientific name for them: Ornithichnites, based on Greek roots that mean “bird trace.” He assigned these bird tracks to two species he named O. gallinuloides (the larger tracks) and O. culbertsonii (the smaller tracks). King noted that “ordinary observers have uniformly compared these tracks to those made by wild turkeys,” but he stressed that the “fourth toes” (dewclaw impressions) of these tracks are too long to have been made by a turkey. One of the species names he coined, gallinuloides, refers to the common gallinule (Gallinula galeata), a bird that lives in western Pennsylvania. He named the other species culbertsonii for his friend Alexander Culbertson (1809-79), a naturalist who gained fame as a trader in the western territories that adjoin the Missouri River.

The other tracks on that rock surface near Derry, those with five toes and round “sole” impressions, received the name Thenaropus. King took the name from the Greek thenaros, for palm, and pes, for foot, which meant to him a “palm footed animal.” He thought these were the tracks “of an immense saurian reptile.” Some of these tracks – those with round toes – puzzled King, and he noted that “it is extremely improbable that these animals [the trackmakers] should be associated with aquatic birds and saurian reptiles, that they should even be represented at this early period of our planet, during its half finished condition . . . it may have been an animal in some respects allied to the Hippopotamus.” Clearly, King thought he had found Carboniferous-age footprints of reptiles, birds and mammals.

King’s comments about “this early period of our planet” provide an important context to the significance of his discoveries. In the 1840s what was known about the history of life largely came from only a few decades of fossil collecting in Western Europe. That knowledge suggested that no birds or mammals (and, to many, not even land-living reptiles or amphibians) lived during the Carboniferous. The period was already known to be a time of extensive coal swamps (it was often called the “coal age”), and this world was thought by many to have an atmosphere inhospitable to land-living, air-breathing vertebrates. Indeed, legendary French paleontologist Alexandre Brongniart (1770-1847) had argued that the Carboniferous atmosphere contained so much carbon dioxide that no land-living vertebrate animals could tolerate it. The North American Carboniferous footprint discoveries of the 1840s challenged that conclusion, providing prima facie evidence of land-living vertebrates in the form of their footprints made on land.

When describing the footprints he found, King provided remarkably detailed geological data on the tracksite near Derry. He described the track-bearing layer as “a coarse-grained sandstone, about 150 feet beneath the largest of our coal seams, and near 800 feet beneath the topmost stratum of our coal formation.” To the geologists of his day, this confirmed the Carboniferous age of the track-bearing layer. King likened the potholes in the track-bearing layer to similar holes scoured in modern stream bottoms, particularly the nearby Youghiogheny River. He thus envisioned the track-bearing layer as a river deposit.

A representative collection of the footprints King described is housed at the Beneski Museum of Natural History, Amherst College, Amherst, Massachusetts. All of the objects shown here are carved petroglyphs in sandstone (upper left and lower right) or plaster casts of such carvings. No records apparently exist explaining how King’s tracks and replicas made it to Amherst, but he may have given or loaned them to Edward Hitchcock, whose trace fossil collection resides at the museum. Photo by Spencer G. Lucas

In the style of his day, however, King went much further, rhapsodizing about the trackmakers as they “basked on the oozy shore of a river or an ocean, and left the vivid imprint of their feet in its plastic mud,” even though the footprints near Derry are in sandstone. King went on to note that his “discovery evidently conflicts with an hypothesis long since thrown out, and still maintained by distinguished geologists, that the atmosphere during the carboniferous period was essentially different from what it is at present. . . . it contained a much larger amount of carbonic acid gas, which . . . caused the rapid and enormous growth of the coal plants.” But, as King noted, “this could not have been, since we now find that lung-breathing animals existed at the same epoch.”

In 1845 King published more fossil footprints, these from the stone quarry southeast of Greensburg. They were to be his most important paleontological discovery. Here the tracks were “on a slab of fine-grained micaceous sandstone, which was taken from a quarry about 50 feet lower than the tracks already described.” Thus these tracks were also from the “coal formation,” although, as King stressed, they were quite different from the tracks he had named Thenaropus in the previous year. In the stone quarry, King found trackways in convex relief, meaning they were filled in by the layer of sediment deposited above the original concave relief tracks, on a mudcracked surface about 5 by 3.5 feet, parts of which he illustrated. King noted the trackway pattern (closely spaced hands and feet) and the four-toed forefoot (manus) versus five-toed hind foot (pes) to conclude that these features “seem to indicate an alliance with the Batrachians.” This was a remarkable observation in 1845, given that the tracks King described are remarkably similar to, though much larger than, the footprints of living batrachians (salamanders). This kind of comparison, now referred to as actualism (“the present is the key to the past”), was cutting-edge thinking in the 1840s.

King’s first article in 1844 had introduced the name Thenaropus for three species of footprints he named, but in 1845 he felt that the name should be applied to the newly discovered tracks from the stone quarry. For the tracks he previously called Thenaropus, he proposed to change the name to something he deemed more appropriate, namely Spheropus, from the Greek spheros, for sphere, and pes, for foot. Such name changing, however, is frowned upon by scientists, and the journal editor advised that “we would suggest the propriety of his adopting some new name, as a new use of this word [Thenaropus] will only create increased confusion.” That said, the editor, Yale professor Benjamin Silliman (1779-1864), allowed it, although he did modify Spheropus to Spheropezium (from the Greek pezum, for sole).

This is apparently the only authentic Carboniferous fossil track slab studied by Alfred King still available to scientists. It is in the collection of the Beneski Museum of Natural History, Amherst College, and is the type specimen of Limnopus heterodactylus. Photo by Spencer G. Lucas

In 1846 King published on his third locality, Chestnut Ridge, where the tracks were also in a coarse-grained sandstone of the “coal formation.” He identified most of these tracks as from “cloven-hoofed ruminant mammals,” reaffirming his earlier identification of mammals of Carboniferous age. King also noted the presence of “four to six huge tracks [each about 13 inches long] of a different character, and possibly Batrachian.”

By the time of this last of King’s publications on fossil footprints, his work clearly had received global attention. One keen observer was Charles Lyell (1797-1875), a British scientist widely regarded as one of the founders of geology. Indeed, Lyell was so interested that he wanted to check on the authenticity of King’s “coal age” tracks on a visit to North America. Lyell did so on the second of four visits he made to North America between 1845 and 1846, accompanied by his wife Mary.

In spring 1846 the Lyells, after touring the southern United States, traveled up the Mississippi River, then up the Ohio River, arriving in Pittsburgh on April 16. From there, they traveled by coach via East Liberty, Wilkinsburg and Adamsburg to Greensburg, then a town of about 1,000 inhabitants. Here they met King and an unusual associate, given King’s relationship to the church, a young Presbyterian clergyman, the Reverend Mr. Hackney. The first stop was the stone quarry in Unity Township, where Lyell examined the footprints King had named Thenaropus heterodactylus. Lyell was impressed. He agreed that these were authentic “coal age” footprints of a “saurian,” and the British geologist likened them to Chirotherium, a well-known kind of reptile footprint first described in the 1830s from German Triassic rocks and soon thereafter discovered in England. Lyell evidently took a slab of the tracks with him, later illustrating it in a woodcut in his 1849 book.

A woodcut of some of the tracks found by King near Greensburg, published by Charles Lyell in his book documenting his 1845-46 visit to North America. These are authentic footprints of a relatively large Carboniferous amphibian intersected by mudcracks.  From Charles Lyell, A Second Visit to the United States (John Murray, 1849)

Lyell had reached a very different conclusion upon examination of the other footprints that King had described, namely that they were “artificially cut,” or in other words “sculptured by Indians” – petroglyphs made by Native Americans. To wit, near Derry and at Chestnut Ridge, the tracks in coarse sandstone troubled Lyell: “I find it quite impossible to imagine the layers of sand when in a soft state or capable of receiving footprints, to have been ever so placed, to admit of such an impression being made.” Lyell also drew attention to the sharp, not-at-all-weathered edges of the track impressions and to the uneven nature of the track surface, with tracks on different layers, but none registered on multiple layers (no undertracks). Furthermore, he made an analogy to petroglyphs he had seen in Missouri and recalled the then-infamous record of supposed human footprints in limestone found near St. Louis. These footprints had been first reported in 1822, and it was 20 years before David Dale Owen (1807-60), one of America’s first geologists, convincingly argued that these were Native American carvings.

Indeed, a comparison of local petroglyphs to most of King’s so-called footprints (now preserved as pieces of sandstone or plaster casts in the Beneski Museum of Natural History at Amherst College, Amherst, Massachusetts) confirms Lyell’s conclusion. Thus the classic monograph by Carnegie Museum archaeologist James Swauger (1913-2005) on rock art of the upper Ohio Valley illustrates petroglyphs remarkably similar to the “footprints” King described from the stone quarry and Chestnut Ridge. These were made, according to Swauger, by the Monongahela people between 1200 and 1750 AD and include carvings of bird, bear, human and other animal tracks that are very similar to the objects that King termed Ornithichnites and his original Thenaropus, renamed Spheropezium.

The Lyells left Greensburg by coach on April 19, arriving in Philadelphia a few days later. Quick to establish the priority of his conclusions, Lyell sent an article written in Philadelphia on April 26, 1846, to his good friend Benjamin Silliman for publication in the American Journal of Science. On April 27 he sent a letter of similar content to England to be read at the next meeting of the Geological Society in London and then published in their proceedings. The article and the letter affirmed the authenticity of the Unity Township quarry tracks as Carboniferous footprints of a “quadruped nearly allied to the Cheirotherium [sic] of Europe, if not the same.”

These drawings of Native American petroglyphs, published by archeologist James L. Swauger in his classic book on the rock art of the upper Ohio River Valley, bear a striking similarity to some of King’s “fossil footprints.” The upper and middle left are birds, the lower left is human, and the right are bears. From James I. Swauger, Rock Art of the Upper Ohio Valley (Akademisch Druck Und Verlagsanstalt, 1974)

Lyell wrote the first great English-language treatise on geology, Principles of Geology (1830). In it he had declared opposition to the idea that “saurians” did not live during the Carboniferous, but he was convinced that no birds or mammals were extant at that time. King’s publication of the footprints from western Pennsylvania had challenged Lyell, and he must have been pleased to confirm Carboniferous “saurian” tracks and discount the apparent bird and mammal tracks as manmade. Lyell concluded in his 1846 article that “here in Pennsylvania, for the first time we meet with evidence of air-breathing quadrupeds capable of roaming in those [Carboniferous] forests.” (Technically, Logan’s 1841 discovery of bona fide Carboniferous “saurian” tracks in Nova Scotia predated King’s.) In his article,Lyell also noted that King now agreed with his assessment of the tracks, and he praised the young Pennsylvania savant, stating that “his sole desire was to arrive at the truth, and to correct any mistakes into which he might have fallen.”

Three years later, in 1849, Lyell published a book about his second trip to North America, a scientific travelogue of the journey. In it he repeated much of the content of his 1846 article and included a woodcut illustration of one of the slabs with authentic tracks from the stone quarry in Unity Township. In the 1846 article, Lyell had described King as “a young man, engaged in extensive medical practice in a remote town, acting under every discouragement which want of sympathy in those immediately around him, and of access to scientific books or museums could produce.” In the book, Lyell drew the significance of King’s footprint discoveries along very broad lines: “Never, certainly, in the history of science, were discoveries made more calculated to put us on guard for the future against hasty generalisations founded on mere negative evidence.” And Lyell went on to rail for several pages against those clergymen and other Pennsylvanians who had opposed King because his discoveries – indicative of early life on a very old planet Earth – ran contrary to Biblical writ.

After Lyell left Pennsylvania, King seems to not have worked on fossil footprints again. He continued to develop his medical practice and became a professor at the Medical College of Philadelphia. By the end of 1857, although only in his mid-forties, King was very ill from what was described as “inflammation of the stomach and intestines.” He died on January 2, 1858, at age 45.

Little scientific mention was made of King’s articles during the late 1800s. Nevertheless, in the early 1900s, George F. Matthew (1837-1923), one of the first great students of the Carboniferous footprints of Nova Scotia, was well aware of King’s work and named a new species of Thenaropus for tracks from the famous sea cliffs at Joggins. Subsequent scientific compilations listed the taxonomic names King had created for his footprints; however, no reappraisal of his work appeared, largely because nobody seemed to have known the location of the footprints.

True, Donald Baird (1926-2011), an eminent American student of fossil footprints, mentioned in a 1965 article that one of King’s specimens of Thenaropus heterodactylus was in the collection of Amherst College. But German paleontologist Oskar Kuhn (1908-90), who in 1963 compiled all of the named kinds of fossil footprints, regarded almost all of King’s tracks as genuine. And in 1971 another great German expert on fossil footprints, Hartmut Haubold (1941-), treated King’s Spheropezium as a valid name for a kind of reptilian footprint.

The tracks that King found at a stone quarry in Unity Township were made by an amphibian that looked something like this. New Mexico Museum of Natural History and Science/Artwork by Matt Celeskey

Alfred King was a pioneer in the study of fossil footprints. Unfortunately, most of the “footprints” he published are petroglyphs – an easy mistake made at a time when little was known about Carboniferous footprints and not much more was known about Native American petroglyphs. One of King’s discoveries, however, is a genuine fossil of Carboniferous amphibian tracks – among the first conclusive evidence of air-breathing vertebrates on land during that period, more than 300 million years ago. This was enough evidence to convince one of the giants of 19th century geology, Charles Lyell, and to thus change scientific understanding of life on land during the “coal age.” But, important as King’s discovery was, he only worked about three years on paleontology, and his published contributions are slim – five articles amounting to less than 20 printed pages. Furthermore, little was known of the collections he made for more than 150 years.

King made a significant contribution to knowledge of the Carboniferous world early in the study of geology. Nevertheless, like many whose contributions were not part of an extensive career in science, King and his research were largely forgotten. He should now be more widely recognized as one of Pennsylvania’s most gifted early scientists.

For Further Reading

An academic treatment of this subject was published as “Alfred King’s Pennsylvanian Tetrapod Footprints from Western Pennsylvania” by Spencer G. Lucas and Sebastian G. Dalman in The Carboniferous-Permian Transition (New Mexico Museum of Natural History and Science, 2013).

Alfred King’s articles were published in Proceedings of the Academy of Natural Sciences of Philadelphia 2, no. 6 (November-December 1844): 175-80; and 2, no. 12 (November-December 1845): 299-300 and in The American Journal of Science and the Arts 48 (April 1845): 343-52; 49 (October 1845): 216-17; and 2nd Series, 1 (1846): 268.

Charles Lyell’s classic work is Principles of Geology (John Murray, 1830). His remarks on King’s findings appear in “On Footmarks Dis-covered in the Coal Measures of Pennsylvania” in Quarterly Journal of the Geological Society of London 2 (1846): 417-20 and A Second Visit to the United States (John Murray, 1849).

Illustrations of petroglyphs similar to those King found were published in James L. Swauger’s Rock Art of the Upper Ohio Valley (Akademisch Druck und Verlagsanstalt, 1974).

Spencer G. Lucas is curator of geology and paleontology at the New Mexico Museum of Natural History and Science in Albuquerque.