Adapids (members of the taxon
Adapidae) are a diverse group of extinct primates that primarily radiated during the
EoceneThe Eocene epoch, lasting from 55.8 ± 0.2 to 33.9 ± 0.1 Ma , is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era. The Eocene spans the time from the end of the Paleocene epoch to the beginning of the Oligocene epoch. The start of the...
epoch between about 55 and 34 million years ago. However, one specialized endemic Asian group (sivaladapines) survived into the Miocene. Fossils of adapids are known from North America, Europe, Asia, and Africa. Adapids are one of two groups of Eocene primates with a geographic distribution spanning
holarcticThe Holarctic ecozone refers to the habitats found throughout the northern continents of the world as a whole. This region is divided into the Palearctic, consisting of Northern Africa and all of Eurasia, with the exception of Southeast Asia and the Indian subcontinent, and the Nearctic,...
continents, the other being the omomyids (Omomyidae).
Adapids (members of the taxon
Adapidae) are a diverse group of extinct primates that primarily radiated during the
EoceneThe Eocene epoch, lasting from 55.8 ± 0.2 to 33.9 ± 0.1 Ma , is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era. The Eocene spans the time from the end of the Paleocene epoch to the beginning of the Oligocene epoch. The start of the...
epoch between about 55 and 34 million years ago. However, one specialized endemic Asian group (sivaladapines) survived into the Miocene. Fossils of adapids are known from North America, Europe, Asia, and Africa. Adapids are one of two groups of Eocene primates with a geographic distribution spanning
holarcticThe Holarctic ecozone refers to the habitats found throughout the northern continents of the world as a whole. This region is divided into the Palearctic, consisting of Northern Africa and all of Eurasia, with the exception of Southeast Asia and the Indian subcontinent, and the Nearctic,...
continents, the other being the omomyids (Omomyidae). Early representatives of the Adapidae (e.g.,
Cantius and
Donrussellia) and Omomyidae (e.g.,
Teilhardina and
Melanerimia) are some of the earliest known
crown primatesA crown group is the smallest monophyletic group, or "clade", to contain the last common ancestor of all members, and all of that ancestor's descendants...
.
Features that characterize many adapids include small orbits (eye sockets), elongate rostra, cheek teeth adapted for folivorous or frugivorous diets, and relatively large body mass (i.e., greater than 1 kg). However, the endemic radiation of adapids in the early and middle Eocene of Europe included a number of taxa (e.g.,
Anchomomys) that were very small (about 250 g or less) and partly insectivorous. Small orbits in genera such as
Notharctus,
Smilodectes,
Adapis,
Leptadapis, and
Mahgarita indicate that these taxa were probably diurnal. At least one adapid genus from the late Eocene of Europe (
Pronycticebus) had large orbits and was probably nocturnal.
Like living
primateA primate is a member of the biological order Primates , the group that contains lemurs, lorisids, galagos, tarsiers, monkeys, and apes, with the last category including great apes. With the exception of humans, who inhabit every continent on Earth, most primates live in tropical or subtropical...
s, adapids had grasping hands and feet with digits tipped by nails instead of claws. Other features of the skeleton suggest that most adapids lived in trees. North American endemic adapids (notharctines) like
Notharctus had extremely long digits and skeletal proportions that superficially resemble those of living lemurs. In contrast, some authors have suggested that one group of late Eocene European adapids (adapines) had adaptations for suspension and slow climbing.
Adapid systematics and evolutionary relationships are controversial, but there is fairly good evidence from the postcranial skeleton (everything but the skull, or cranium) that adapids were stem strepsirrhines (members of the group including the living lemurs, lorises, and bushbabies). In particular, the anatomy of the adapid wrist and ankle (e.g., position of the groove for the flexor fibularis tendon on the talus, the presence of a sloping talo-fibular facet) show derived similarities with those of living strepsirrhines. However, ancient adapids lacked many of the anatomical specializations characteristic of living strepsirrhines, such as a tooth comb, a grooming claw on the second pedal digit, and a reduction in the size of the promontory branch of the internal carotid artery.