Haptodus

Discovery and history

Haptodus baylei, the type species of Haptodus, is known only from a single, badly preserved specimen hosted in the Muséum National d'Histoire Naturelle of Paris. It was collected at Les Télots, near Autun of France, from a terrestrial horizon dating to the Asselian stage of the Cisuralian series, about 299-296.4 million years old.
H. garnettensis is the best known species of the genus. Its holotype is RM 14156, a partially articulated skeleton (cranial and postcranial) of immature individual. More than 16 well-preserved specimen of various ontological states were referred to this species. All specimens came from the Garnett Quarry, located in the Anderson County of Kansas. They were collected from the Rock Lake Member of the Stanton Formation (Lansing Group), dating to the late Kasimovian stage of the late Pennsylvanian series, about 305-303.9 million years old.
The taxonomy of many pelycosaurs was revised in details by Alfred Sherwood Romer & Llewellyn Price (1940). They synonymized many genera, including Callibrachion (from Margenne near Autun, France), Datheosaurus (from Nowa Ruda of Poland), Palaeohatteria and Pantelosaurus (both from Germany), with Haptodus, but retained these taxa as distinct species. After describing H. garnettensis in 1977, Currie (1979) synonymized all European haptodontines, as well as Cutleria wilmarthi, with the type of the genus, H. baylei. Later, Laurin (1993 and 1994) considered Haptodontinae to represent a polyphyletic grade of basal sphenacodonts, and revalidated Cutleria, Palaeohatteria and Pantelosaurus, while Callibrachion was considered to be a nomen dubium and Datheosaurus was not examined. Laurin also suggested that the type species of the genus H. baylei might be a nomen dubium, too, meaning that the only well preserved species, H. garnettensis, would have to be reassigned to its own genus. His revision has been accepted since.
In his dissertation revising basal Sphenacodontia, Spindler (2015) demonstrated that Haptodus garnettensis and H. grandis are not congeneric with the Haptodus type species to the exclusion of other basal sphenacodontians and instead representing distinct genera, while showing that some specimens referred to garnettensis belong to two different taxa distinct from garnettensis.