In 1836, Edward Hitchcock named several footprint morphologies from the Early Jurassic of Connecticut and Massachusetts, classifying these prints in 7 species within the ichnogenus Ornithichnites, and suggested they had been made by large extinct birds. In 1837, Hitchcock provided the name Sauroidichnites for material he thought more reptilian in nature; subsequently, manus prints were found associated with these morphologies. In 1845, Hitchcock changed methodology, renaming his previously-established ichnotaxa, erecting instead names for the animals that made the tracks. However, because valid names already existed, most of the replacement species names are invalid. Additional renaming was undertaken in 1848, 1858 and 1865; the result is a morass of objective and subjective synonyms, further confused by a change in cataloging system and the lack of catalog numbers prior to 1848. 

As early as 1843 Hitchcock had suggested there might be an as-yet-unknown group of saurians with feet similar to those of birds. The 1856 Massachusetts discovery of a bipedal tridactyl trackway with a tail drag reaffirmed the notion that there might have been a group of animals intermediate between birds and 'lower vertebrates' (i.e., reptiles); a suggestion also made in Britain in 1854 for Wealden material. Due to his  academic career and preoccupation with his assumed-imminent death, Hitchcock did not explore this further. In 1858, Hitchcock suggested that some of the more saurian-type tracks may have been made by reptiles such as those whose remains had been found in Connecticut and Massachusetts earlier in the 19^th century; animals now identified as prosauropods, and theropods. (Some of the prints to which Hitchcock was referring are currently attributed to crocodylomorphs; others to ornithischians.) Meanwhile, in 1862, British workers suggested that the 3-toed prints in the Wealden might have been made by Iguanodon, and while debate raged in Europe as to the affinity of the newly-discovered Archaeopteryx, in the US it was noted that the extremities were, in a general sense, consistent with the anatomy of the still-unidentified Connecticut Valley trackmakers. It was not until 1867 that Cope explicitly stated the still-current view that dinosaurs made most of the bipedal Connecticut Valley prints.