Adapis is the type genus of the Adapidae, an extinct family of primates from the Palaeogene within the extinct infraorder Adapiformes. It was endemic to western Europe and lived from the Middle to Late Eocene. Adapis was first named in 1822 by the French palaeontologist Georges Cuvier, who studied incomplete jaws from Montmartre and thought it to have been a "pachyderm" similar to the artiodactyl Anoplotherium. Adapis parisiensis was recognized by Cuvier in 1824; several other species of Adapis were named in the late 19th and 20th centuries. In the 1870s, Adapis was recognized formally as a primate rather than a "pachyderm", with later researchers noting that Adapis was therefore the first fossil primate to have ever been taxonomically described. Palaeolemur and Leptadapis of the subfamily Adapinae, an endemic European primate subfamily, were previously reclassified as synonyms or subgenera of Adapis but were eventually recognized again as distinct genera from Adapis. As a result, there are six total species of Adapis, with A. parisiensis being the type species.
Adapis was a medium-sized adapid with weight estimates approximately ranging from to and notably has varying degrees of shared anatomical traits with the clade Lemuriformes (lemurs and lorisoids), which is generally classified into the suborder Strepsirrhini along with Adapiformes. Adapis differs from lemuriformes due to a more prominent facial skeleton, high sagittal crests, large zygomatic arches, robust mandibles, and relatively small orbits among various other traits. In contrast to its close relative Leptadapis, Adapis has smaller orbits with stronger degrees of frontation and orbital convergence; the degrees of frontation and orbital convergence are not as well-pronounced as in Palaeolemur. In terms of dentition, Adapis has reduced and incisor-like canine teeth and premolars that progressively increase in size and become molarized from the front to back premolars of the dental row. Its dental morphology could have allowed for a primarily folivorous (leaf-eating) diet with probably some degree of fruit-eating, although it does not show a large degree of specializations. Adapis also has postcranial similarities to contemporaneous adapiforms and extant strepsirrhines such as the degree of limb robustness but lacks close analogues. It had the shortest hand of all Eocene-aged adapiforms with small digits but longer metacarpal bones. Like in other adapids, its forelimbs and hindlimbs were about as equally long; its hand posture allows for the body to be parallel to the ground when walking. Typical of strepsirrhines, it was an arboreal quaduped; hypotheses of the locomotion of Adapis range from slow climber to a walker-runner, with some researchers expressing with uncertainty that different species could have had different forms of arboreal locomotion.
The unambiguous fossil range of adapines like Adapis is limited to the Middle to Late Eocene of western Europe, coinciding with geographical separation of the landmass from others as an archipelago. This was in contrast to the other adapid subfamily Caenopithecinae, which was also present in Africa and Asia but only had one genus present in Europe. Adapis coexisted with both other primates, namely fellow adapids and omomyids of the subfamily Microchoerinae. Climates in western Europe were tropical to subtropical up to the Late Eocene, although the end of the Middle Eocene had significant climactic and faunal shifts.
Taxonomy Research history 19th century taxonomy
In 1812, French palaeontologist Georges Cuvier provided the first illustration and description of fossils of what he in later years assigned to Adapis. In 1822, Cuvier wrote about what he thought to have been a pachyderm based on fossilized jaws (upper and lower) from the gypsum quarries of Montmartre, assigning them to the provisional genus name Adapis. He described the skull as being roughly similar to that of a hedgehog but a third larger. He observed that the jaw had four incisors (two top and bottom each) that were sharp and slightly oblique like those of Anoplotherium, conical canine teeth, and seven upper molars that he also noted to be somewhat similar to those of Anoplotherium. Cuvier also said that the name Adapis had before been applied to hyraxes and was first used in a 1551 work by Swiss naturalist Conrad Gesner as a genus name for hares. Adapis means "no carpet" and is a compound of the Ancient Greek words (, 'not') and (, 'carpet'). The genus name may have been based on the idea that the taxon, then thought to have been a pachyderm, may have had rough or thorny skin. Because of its early taxonomic history, Adapis was the first fossil primate to have ever been taxonomically described.
In a later source volume dated at 1824, Cuvier created the name Adapis parisiensis for the species from Montmartre that he previously described. In 1829, German naturalist Johann Baptist Fischer listed Adapis as a valid species, creating the species name A. cuvieri in reference to the fossil material previously written about by Cuvier. The French naturalist Henri Marie Ducrotay de Blainville in an 1839–1864 osteography and French palaeontologist Paul Gervais in 1848 both treated A. parisiensis as the valid species name.
In an 1848–1852 osteography, Gervais erected the genus and species name Aphelotherium Duvernoyi based on a jaw with three molars from the limestone deposits of Barthelemy at the hill of Perreal in the French commune of Apt. In 1863, the French naturalist Jean-Baptiste Noulet wrote about a lower jaw with four molars from a locality called Sagnes in a fossil collection from Castres, assigning it to the erected name Aphelotherium Rouxi. Noulet stated that the fossil, which was initially studied by his late friend and colleague Léonce Roux as belonging to Mustela, was described by him as being half the size of A. Duvernoyi and barely larger than the jaw of a squirrel. In 1869, Swiss palaeontologists François Jules Pictet de la Rive and Aloïs Humbert wrote about a fossil collection of Swiss physician Philippe de La Harpe, in particular a small jaw that was studied by Swiss palaeontologist Ludwig Rütimeyer; Rütimeyer designated to the fossil the species name Lophiotherium Laharpi. Pictet suggested that the species name be retained in his article going forward.
In 1873, French palaeontologist Eugene Edmond Delfortrie wrote about a nearly complete fossil skull unearthed by Mr. Bétille from the calcium phosphates at his property of Sainte-Néboule de Bédour at the department of Lot. Delfortrie considered the fossil to be one that could help to fill the fossil gap for lemurs for the first time ever, considering the skull to have belonged to a lemur and therefore a primate. In light of the primate skull, he erected the genus Palæolemur, also establishing the species name Palæolemur Betillei. The same year, Gervais argued that Palaeolemur (also spelled by him as "Paléolémur") was not closely related to the lemurs of Madagascar because of the different dental formulas and the differences in the shapes of the teeth. He noted his and French palaeontologist Jean Albert Gaudry's observations that Palaeolemur and Aphelotherium were not well-distinguished from each other and Adapis to the point where the former two genera and their species should be synonymized with the latter genus and its species. He had additionally wrote about Adapis and Aphelotherium previously having been thought to have been pachyderms grouped in with Anoplotherium whereas Palaeolemur was grouped in with the lemurs based on a complete skull. He also mentioned that Caenopithecus lemuroides should probably also be reassigned to Adapis.
In 1874, French palaeontologist Henri Filhol reviewed the anatomy of Palaeolemur, describing its skull as being similar to those of lemurs but with key differences like a high sagittal crest that do not demonstrate as close of an affinity with them as previously thought. The reported species had multiple known jaws including that long held by Filhol himself, who long thought that it belonged to a pachyderm related to Anoplotherium and resembled that of Adapis. Filhol elaborated that it was only because of more complete skull evidence rather than dental evidence alone that he considered it to be a primate and not a pachyderm. He then hypothesized that the primate taxon would have belonged to the "Pachylemur" group but also agreed with the synonymization of both Palaeolemur and Aphelotherium with Adapis on the basis of similar dentitions and the latter genus name being the oldest. Using another skull from the commune of Saint-Antonin-Noble-Val, he named another species A. magnus. In 1876, Gervais erected the genus Leptadapis, where the species A. magnus was reclassified to.
In 1877, Filhol erected A. minor, having observed that remains assigned to it had been found in various deposits with A. parisiensis. He expressed being unsure of whether A. minor was a descendant of A. parisiensis and/or a distinct species. In 1878, Gaudry supported the synonymization of Aphelotherium with Adapis along with affinities of the latter with lemurs, albeit with significant anatomical differences like a more developed sagittal crest and smaller eye sockets. However, he supported the validity of Adapis duvernoyi, viewing it as distinct from A. parisiensis. He also expressed being unsure as to whether or not "A." magnus was a distinct species from A. parisiensis. In 1883, Filhol documented complete skulls and postcranial fossils (limb bones like the humeri and femora) of A. parisiensis and additional dental and postcranial material he determined belonged to A. magnus, all of which came from fossil collections from Quercy. The palaeontologist created the taxon A. parisiensis var. angustidens (or A. angustidens) using a lower jaw. Filhol recognized multiple other new variations of A. parisiensis, namely A. parisiensis var. crassa, A. parisiensis var. curvirostris, A. parisiensis var. mutans, and A. parisiensis var. mutata. He also listed Caenopithecus as a distinct genus from Adapis. In 1885, British palaeontologist Richard Lydekker reaffirmed the synonymizations of Aphelotherium duvernoyi (or "Adapis duvernoyi") and Palæolemur betillei with Adapis parisiensis. In 1888, Filhol communicated about a partial lower jaw with several premolars and molars that was provided to him by Mr. Rossignol. The fossil in question came from the phosphate deposits of Quercy and was assigned by him to the newly named A. angustidens.
20th- and 21st-century taxonomy