The 20th century in ichnology refers to advances made between the years 1900 and 1999 in the scientific study of trace fossils, the preserved record of the behavior and physiological processes of ancient life forms, especially fossil footprints. Significant fossil trackway discoveries began almost immediately after the start of the 20th century with the 1900 discovery at Ipolytarnoc, Hungary of a wide variety of bird and mammal footprints left behind during the early Miocene. Not long after, fossil Iguanodon footprints were discovered in Sussex, England, a discovery that probably served as the inspiration for Sir Arthur Conan Doyle's The Lost World.
Several enduring mysteries from the 19th century continued to vex ichnologists, like the identity of the Chirotherium trackmaker. Renowned paleontologist Franz von Nopcsa attributed the ichnogenus to the prosauropod dinosaur Plateosaurus, despite an apparent mismatch between its number of toes (4) and the preserved digit traces of Chirotherium (5). Von Nopcsa explained the discrepancy by arguing that one of the impressions in the Chirotherium tracks was left by a soft tissue structure that did not fossilize. However, it was Wolfgang Soergel who correctly hypothesized that Chirotherium was produced by a distant relative of modern crocodilians. Using only its footprints as a guide he reconstructed the life appearance of the Chirotherium trackmaker. Decades later paleontologists described an animal named Ticinosuchus which precisely fulfilled Soergel's predictions. Ticinosuchus or a close relative seems to have been the true Chirotherium trackmaker.
During the 20th century, many significant fossil trackway discoveries were made in the western United States. In the 1930s and 1940s, Roland T. Bird discovered the tracks of large sauropod and theropod dinosaurs in Texas. He excavated a major section of the track ways on behalf of the American Museum of Natural History. This was the first large scale excavation of fossil footprints in history. In the 1950s Lee Stokes reported unusual footprints he interpreted as the first known pterosaur tracks. This attribution would be controversial much of the rest of the century but has since been vindicated. The dinosaur footprints of Dinosaur Ridge in Colorado were also discovered and studied in the 20th century.
The advent of the dinosaur renaissance and the publication by R. McNeil Alexander of a formula which could reconstruct their running speed based on data from fossil trackways brought renewed interest and prestige to ichnology during the late 20th century. This led to several symposia on the subject of vertebrate trace fossils. In 1986 such a conference dedicated to dinosaur footprints was held in New Mexico. Roughly a decade later renowned German ichnologist Heinrich Haubold organized a conference dedicated to the more ancient footprints of the Paleozoic Era. This gathering has been regarded as a turning point in the study of tracks of that age.
1900s
1900 A major Lower Miocene fossil footprint site was discovered at Ipolytarnoc, Hungary. The site preserves more than 1600 individual footprints from a variety of birds and mammals. Avian ichnogenera at the site include Aviadactyla, Ornithotarnocia, Passeripeda and Tetraornithopedia. Mammalian ichnogenera include Bestiopeda, Carnivoripeda, Megapecoripeda, Mustelipeda, Pecoripeda, Rhinoceripeda. These mammal tracks were left by creatures like carnivorans, peccaries and rhinoceros. Mastodon tracks have also been reported, but may represent misidentifications.
1902 Dinosaur footprints were discovered at Fisher's Quarry, near Graterford, Pennsylvania. These tracks are now classified in the ichnogenus Atreipus.
1903 John Bell Hatcher reported probable crocodilian footprints from the Morrison Formation near Canon City, Colorado.
1904 Richard Swann Lull began studying the Connecticut Valley footprints. He described the new ichnogenus Anchisauripus, named such because he attributed it to the early sauropod-precursor Anchisaurus.
1905 Luis Dollo matched the foot of Iguanodon bernissartensis with a purported Iguanodon footprint in "the first attempt to match these tracks with a particular species of the genus".
1906 Pleistocene human footprints were discovered in the Niaux cave complex of France.
1908 Paleocene fossil amphibian footprints were discovered in the Fort Union Formation of Montana.
1909 Harold Broderick described the three-toed Middle Jurassic dinosaur footprints that had first been discovered during the 1890s at England's Yorkshire coast. Fossil Iguanodon footprints were discovered in the rocks of the Wealden Beds at Crowborough, Sussex. These tracks may have inspired Sir Arthur Conan Doyle to write The Lost World.
1910s
1910 Traces in the genus Octopodichnus were discovered in the Permian Lyons Sandstone of Colorado.
1913 Joviano Pacheco discovered the first dinosaur footprints in Brazil.
1914 Barnum Brown discovered the Centrosaurus apertus specimen AMNH 5351. Randy Moore has described the skeleton as the most complete Brown ever discovered. 90 million year old Cretaceous dinosaur footprints were discovered in New Jersey but were accidentally destroyed during an attempt at excavating them.
1915 Charles Schuchert discovered Carboniferous-aged fossil footprints in the rocks of the Wescogame Formation near the Grand Canyon.
1915-1916 Gomes first described the large Late Jurassic theropod footprints from Cabo Mondego, Portugal.
1918 Lull described the ichnogenus Laoporus.
1920s
Charles Whitney Gilmore began collecting and studying the Carboniferous and Permian-aged footprint fossils of the Grand Canyon area on behalf of the Smithsonian. He also constructed an outdoor exhibit about the tracks at Hermit Trail. William Peterson reported the discovery of large three-toed dinosaur tracks preserved in what is now the ceiling of a Carbon County, Utah coal mine. William Diller Matthew attributed these tracks to tyrannosaurs.
1920 Renovations to Oak Hill, the historical home of US President James Monroe, led to the discovery of fossil dinosaur footprints when workers repaved the properties walkways with Lower Jurassic stone. The preserved tracks included Grallator and Eubrontes prints ranging in length from . Other local footprints included the tracks of a crocodilian-like animal, Batrachopus. The tracks originated in the Midland Formation.
1923 Baron Franz von Nopsca published a "seminal" work on fossil amphibian and reptile tracks. He hypothesized that Plateosaurus was the Chirotherium trackmaker. Although Plateosaurus has only four hind toes and Chirotherium tracks have five impressions, Nopsca followed Willruth's argument that the "thumb" of Chirotherium was composed only of soft tissue and would have left no skeletal record. He also named the large Late Jurassic theropod fossils discovered at Cabo Mondego, Portugal Eutynichnium lusitanicum. However, this name lacks validity because Nopsca did not formally describe it or designate a type specimen.~154~
1924 J. Henderson reported the first known Paleozoic footprint fossils from Colorado.
1925 Wolfgang Soergel interpreted the Chirotherium trackmaker as a pseudosuchian related to, but much larger than, Euparkeria. He noted that the bulk of the animal's weight was born by its hindlimbs. German geologist Adolf Bachofen-Echt reported the first scientifically recognized dinosaur tracks from Croatia. These three-toed tracks were preserved on the Brioni Islands and Bachofen-Echt thought they were made by Iguanodon.~218~
1926 Charles Whitney Gilmore published his first report on fossil footprints from the Grand Canyon area.
1927 Comte Begouen reported the presence of an adult human's tracks in the Grotte de Cabarets cave in France. These tracks are accompanied by impressions left by the human's walking stick.
1928 Charles Gilmore described the Paleocene amphibian tracks from the Fort Union Formation of Montana. He named the new ichnospecies Ammobatrachus montanensis for the tracks. He observed that these were the first Paleocene fossil footprints to be documented in the scientific literature. Potential Paleocene mammal footprints were reported from Alberta.
1929 Hernandez-Pacheco described an Oligocene-aged fossil bird track site at Peralta de la Sal, Spain. 90 million year old Cretaceous carnivorous dinosaur footprints were discovered at the Hampton Cutter Clay Works quarry at Woodbridge, New Jersey. Teilhard de Chardin and C. C. Young reported the discovery of dinosaur footprints in Shanxi Province, China. These were the first scientifically documented dinosaur footprints in the country's history.
1930s
* Bradford Willard discovered a new ichnogenus Devonian-aged trace fossils in Pennsylvania that he named Paramphibius because he thought the trackmaker was a transitional form between fishes and tetrapods. He named a new taxon, the Ichthyopoda to classify this creature. Permian-aged fossil footprints were reported from the Abo Formation near Las Cruces, New Mexico. The University of Michigan Museum of Paleontology bought several slabs of Late Triassic fossil footprints collected near Mesa Redonda, New Mexico. Among the preserved tracks were three-toed reptile footprints and the four-toed ichnogenus Pseudotetrasauropus that may have been left by a primitive sauropodomorph. Roland T. Bird discovered a new Early Jurassic dinosaur tracksite in the Moenave Formation of northwestern Arizona. Although the site's location would be lost, Bird's photographs would help Dinosaur National Monument paleontologist Scott Madsen, and friend Keith Becker, relocate the site decades later. Dinosaur tracks were excavated from the Dakota Group near Lamar, Colorado. These tracks are now exhibited by the Denver Museum of Natural History. Late: An expansion of the Nevada State Prison was built over the Pleistocene fossil footprints that had been discovered there. However, some specimens had been collected before and are now curated by the Nevada State Museum.
1931 Fredrick von Huene reported the presence of Early Jurassic fossil footprints that were probably left by an evolutionary precursor to mammals in the Botucatu Sandstone of Brazil. Maurice Mehl erected the new ichnogenus Ignotornis for some bird tracks preserved in the Dakota Group near Golden, Colorado. These were the first scientifically documented Mesozoic bird footprints. The bird in question as interpreted as a "small shorebird or wader". The site would eventually be heavily collected and all of its tracks were presumed removed.
1932 Edward Branson and Maurice Mehl reported the presence of Carboniferous-aged fossil footprints of a new ichnospecies in the Tensleep Formation of Wyoming. They named the tracks Steganoposaurus belli and attributed them to an amphibian nearly three feet in length. Edward Branson and Maurice Mehl named a new kind of Late Triassic dinosaur footprint discovered in the Popo Agie Formation of western Wyoming. The new ichnogenus and species was named Agialopus wyomingensis.
1933 Late Triassic dinosaur footprints were discovered near Gettysburg, Pennsylvania. Carlton S. Nash found some more dinosaur footprints near the original location of Pliny Moody's track discovery in Massachusetts. The dinosaur footprints were reported in Australia for the first time.
1934 Roland Wilbur Brown described the ichnogenus Celliforma.
1936 Toepelman and Rodeck made the first report on fossil arthropod trackways in the Lyons Sandstone and fossil vertebrate footprints preserved in the Fountain Formation.
1937