Adapid
Encyclopedia
Adapids are a diverse group of extinct primates that primarily radiated during the Eocene
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 holarctic
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 primates
.
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 primate
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 toothcomb
, a toilet-claw
on the second pedal digit, and a reduction in the size of the promontory branch of the internal carotid artery.
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene 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 holarctic
Holarctic
The 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 primates
Crown group
A crown group is a group consisting of living representatives, their ancestors back to the most recent common ancestor of that group, and all of that ancestor's descendants. The name was given by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms...
.
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 primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
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 toothcomb
Toothcomb
A toothcomb is an anatomical structure found in strepsirrhine primates, which includes lemurs, lorises and galagos. A toothcomb consists of long, flat forward-angled teeth, and includes the lower incisors and the canine teeth...
, a toilet-claw
Toilet-claw
A toilet-claw is the specialized claw or nail on the foot of certain primates, used for personal grooming. All prosimians have a toilet claw, but the digit that is specialized in this manner varies. Tarsiers have a toilet claw on toe two and toe three...
on the second pedal digit, and a reduction in the size of the promontory branch of the internal carotid artery.