Omomyid
Encyclopedia
Omomyids are a diverse group of early primates that radiated during the Eocene
epoch (34 to 59 mya) between about 55 and 34 million years ago (mya). Fossils of omomyids are found in North America, Europe, Asia, and possibly Africa. Omomyids are one of two groups of Eocene
primates with a geographic distribution spanning holarctic
continents, the other being the adapids (family Adapidae). Early representatives of the Omomyidae and Adapidae appear suddenly at the beginning of the Eocene (59 mya) in North America, Europe, and Asia, and are the earliest known crown primates.
Features that characterize many omomyids include large orbits (eye sockets), shortened rostra
and dental arcades, loss of anterior premolars, cheek teeth adapted for insectivorous or frugivorous diets, and relatively small body mass (i.e., less than 500 g). However, by the late middle Eocene (about 40 mya), some North American omomyids (e.g., Macrotarsius) evolved body masses in excess of 1 kg and frugivorous or folivorous diets. Large orbits in genera such as Tetonius, Shoshonius
, Necrolemur
, and Microchoerus indicate that these taxa were probably nocturnal. At least one omomyid genus from the late Eocene of Texas (Rooneyia
) had small orbits and was probably diurnal
.
Like primate
s alive today, omomyids had grasping hands and feet with digits tipped by nails instead of claws. Features of their skeletons strongly indicate that omomyids lived in trees. In at least one genus (Necrolemur), the lower leg bones, the tibia
and fibula, were fused as in modern tarsier
s. This feature may indicate that Necrolemur leaped frequently. Most other omomyid genera (e.g., Omomys) lack specializations for leaping, and their skeletons are more like those of living dwarf
and mouse lemur
s.
Omomyid systematics and evolutionary relationships are controversial. Various authors have suggested that omomyids are:
Attempts to link omomyids to living groups have been complicated by their primitive (plesiomorphic) skeletal anatomy. For example, omomyids lack the numerous skeletal specializations of living haplorhines, including:
Omomyids further demonstrate a gap between the upper central incisors, which presumably indicates the presence of a rhinarium
and philtrum
to channel fluids into the vomeronasal organ. Omomyids as a group also lack most of the derived specializations of living tarsiers, such as extremely enlarged orbits (Shoshonius
is a possible exception), a large suprameatal foramen
for an anastomosis
between the posterior auricular and middle meningeal circulation (again, Shoshonius is a possible exception, but the contents of the foramen in this extinct taxon are unknown), and extreme postcranial adaptations for leaping. In other respects (i.e., presence of an aphaneric, or intrabullar, ectotympanic
bone connected to the lateral bullar wall by an unbroken annular bridge), omomyids are uniquely derived among primates.
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 (34 to 59 mya) between about 55 and 34 million years ago (mya). Fossils of omomyids are found in North America, Europe, Asia, and possibly Africa. Omomyids are one of two groups of Eocene
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...
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 adapids (family Adapidae). Early representatives of the Omomyidae and Adapidae appear suddenly at the beginning of the Eocene (59 mya) in North America, Europe, and Asia, and are the earliest known crown primates.
Features that characterize many omomyids include large orbits (eye sockets), shortened rostra
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
and dental arcades, loss of anterior premolars, cheek teeth adapted for insectivorous or frugivorous diets, and relatively small body mass (i.e., less than 500 g). However, by the late middle Eocene (about 40 mya), some North American omomyids (e.g., Macrotarsius) evolved body masses in excess of 1 kg and frugivorous or folivorous diets. Large orbits in genera such as Tetonius, Shoshonius
Shoshonius
Shoshonius lived about 50 million years ago during the late early Eocene era, with specimens found in Central Wyoming. Shoshonius belongs to the extinct primate family Omomyidae, and shares many features with modern-day tarsiers. Due to its complexity, some have theorized that the Shoshonius may be...
, Necrolemur
Necrolemur
Necrolemur is an extinct genus of primate.The long creature closely resembled a tarsier; it was a nocturnal hunter with very large eyes and ears. Necrolemur had sharp teeth, which it probably used to bite through insect armor. Like modern tarsiers, it also possessed long fingers and toes, and a...
, and Microchoerus indicate that these taxa were probably nocturnal. At least one omomyid genus from the late Eocene of Texas (Rooneyia
Rooneyia
Rooneyia is an extinct genus of primate. The genus includes one species, Rooneyia viejaensis. It lived approximately 55 million years ago. Tim Ryan, at the Pennsylvania State University, has scanned the only known specimen....
) had small orbits and was probably diurnal
Diurnal animal
Diurnality is a plant or animal behavior characterized by activity during the day and sleeping at night.-In animals:Animals that are not diurnal might be nocturnal or crepuscular . Many animal species are diurnal, including many mammals, insects, reptiles and birds...
.
Like 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 alive today, omomyids had grasping hands and feet with digits tipped by nails instead of claws. Features of their skeletons strongly indicate that omomyids lived in trees. In at least one genus (Necrolemur), the lower leg bones, the tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
and fibula, were fused as in modern tarsier
Tarsier
Tarsiers are haplorrhine primates of the genus Tarsius, a genus in the family Tarsiidae, which is itself the lone extant family within the infraorder Tarsiiformes...
s. This feature may indicate that Necrolemur leaped frequently. Most other omomyid genera (e.g., Omomys) lack specializations for leaping, and their skeletons are more like those of living dwarf
Dwarf lemur
The dwarf lemurs are the lemurs of the genus Cheirogaleus. All of the species in this genus, like all other lemurs, are native to Madagascar.- Description :...
and mouse lemur
Mouse lemur
The mouse lemurs are nocturnal lemurs of the genus Microcebus. Like all lemurs, mouse lemurs are native to Madagascar.Mouse lemurs have a combined head, body and tail length of less than , making them the smallest primates ; however, their weight fluctuates in response to daylight duration.Mouse...
s.
Omomyid systematics and evolutionary relationships are controversial. Various authors have suggested that omomyids are:
- stem haplorhinesHaplorrhiniThe haplorhines, the "dry-nosed" primates , are members of the Haplorhini clade: the prosimian tarsiers and the anthropoids...
[i.e., basal members of the group including living tarsierTarsierTarsiers are haplorrhine primates of the genus Tarsius, a genus in the family Tarsiidae, which is itself the lone extant family within the infraorder Tarsiiformes...
s and anthropoids]. - stem tarsiiformesTarsierTarsiers are haplorrhine primates of the genus Tarsius, a genus in the family Tarsiidae, which is itself the lone extant family within the infraorder Tarsiiformes...
[i.e., basal offshoots of the tarsier lineage]. - stem primates more closely related to adapids than to living primate taxa.
Attempts to link omomyids to living groups have been complicated by their primitive (plesiomorphic) skeletal anatomy. For example, omomyids lack the numerous skeletal specializations of living haplorhines, including:
- significant reduction of the canal for the stapedial branch of the internal carotid arteryCarotid arteryCarotid artery can refer to:* Common carotid artery* External carotid artery* Internal carotid artery...
. - a "perbullar" (rather than "transpromontorial") route of the canal for the promontory branch of the internal carotid artery.
- contact between the alisphenoid and zygomaticZygomatic boneThe zygomatic bone is a paired bone of the human skull. It articulates with the maxilla, the temporal bone, the sphenoid bone and the frontal bone. The zygomatic is homologous to the jugal bone of other tetrapods...
bones. - presence of an anterior accessory cavity confluent with the tympanic cavity.
Omomyids further demonstrate a gap between the upper central incisors, which presumably indicates the presence of a rhinarium
Rhinarium
The rhinarium is the moist, naked surface around the nostrils of the nose in most mammals. In actual scientific usage it is typically called a "wet snout" or "wet nose" from its moist and shiny appearance...
and philtrum
Philtrum
The philtrum , is a medial cleft common to many mammals, extending from the nose to the upper lip, and, together with a glandular rhinarium and slit-like nostrils, is believed to constitute the primitive condition for mammals in general...
to channel fluids into the vomeronasal organ. Omomyids as a group also lack most of the derived specializations of living tarsiers, such as extremely enlarged orbits (Shoshonius
Shoshonius
Shoshonius lived about 50 million years ago during the late early Eocene era, with specimens found in Central Wyoming. Shoshonius belongs to the extinct primate family Omomyidae, and shares many features with modern-day tarsiers. Due to its complexity, some have theorized that the Shoshonius may be...
is a possible exception), a large suprameatal foramen
Foramen
In anatomy, a foramen is any opening. Foramina inside the body of humans and other animals typically allow muscles, nerves, arteries, veins, or other structures to connect one part of the body with another.-Skull:...
for an anastomosis
Anastomosis
An anastomosis is the reconnection of two streams that previously branched out, such as blood vessels or leaf veins. The term is used in medicine, biology, mycology and geology....
between the posterior auricular and middle meningeal circulation (again, Shoshonius is a possible exception, but the contents of the foramen in this extinct taxon are unknown), and extreme postcranial adaptations for leaping. In other respects (i.e., presence of an aphaneric, or intrabullar, ectotympanic
Ectotympanic
The ectomtympanic is a bone that suspends the eardrum in mammals. It is homologus with the angular....
bone connected to the lateral bullar wall by an unbroken annular bridge), omomyids are uniquely derived among primates.
Classification
- Family Omomyidae
- EkgmowechashalaEkgmowechashalaEkgmowechashala is an extinct genus of primate. With a weight of approximately five pounds, around a foot tall and resembling a lemur, it is the only known North American primate of its time; it lived during the late Oligocene and early Miocene...
(possibly an adapiform) - AltaniusAltaniusAltanius is a genus of extinct primates found in the early Eocene of Mongolia. Though its phylogenetic relationship is questionable, many have placed it as either a primitive omomyid or as a member of the sister group to both adapoids and omomyids...
- AltiatlasiusAltiatlasiusAltiatlasius was a primate from the Paleocene. Its true taxonomic position remains controversial, it has been suggested that it should belong to the family Toliapinidae, the order Plesiadapiformes or that it should be recognized as a euprimate...
- Kohatius
- Subfamily Anaptomorphinae
- Tribe Trogolemurini
- Trogolemur
- Sphacorhysis
- Tribe Anaptomorphini
- Arapahovius
- Tatmanius
- TeilhardinaTeilhardinaTeilhardina was an early marmoset-like primate that lived in Europe, North America and Asia during in the Early Eocene epoch, about 56-47 million years ago. The paleontologist George Gaylord Simpson is credited with naming it after Jesuit paleontologist and philosopher Teilhard de Chardin...
- Anemorhysis
- Chlororhysis
- Tetonius
- Pseudotetonius
- Absarokius
- Anaptomorphus
- Aycrossia
- Strigorhysis
- Mckennamorphus
- Gazinius
- Tribe Trogolemurini
- Subfamily Microchoerinae
- Indusius
- Nannopithex
- Pseudoloris
- NecrolemurNecrolemurNecrolemur is an extinct genus of primate.The long creature closely resembled a tarsier; it was a nocturnal hunter with very large eyes and ears. Necrolemur had sharp teeth, which it probably used to bite through insect armor. Like modern tarsiers, it also possessed long fingers and toes, and a...
- Microchoerus
- Subfamily Omomyinae
- Huerfanius
- Mytonius
- Palaeacodon
- Tribe Rooneyini
- RooneyiaRooneyiaRooneyia is an extinct genus of primate. The genus includes one species, Rooneyia viejaensis. It lived approximately 55 million years ago. Tim Ryan, at the Pennsylvania State University, has scanned the only known specimen....
- Rooneyia
- Tribe Steiniini
- Steinius
- Tribe Uintaniini
- Jemezius
- Uintanius
- Tribe Hemiacodontini
- Hemiacodon
- Tribe Omomyini
- Chumachius
- Omomys
- Tribe Microtarsiini
- Yaquius
- Macrotarsius
- Tribe Washakiini
- Loveina
- ShoshoniusShoshoniusShoshonius lived about 50 million years ago during the late early Eocene era, with specimens found in Central Wyoming. Shoshonius belongs to the extinct primate family Omomyidae, and shares many features with modern-day tarsiers. Due to its complexity, some have theorized that the Shoshonius may be...
- Washakius
- Dyseolemur
- Tribe Utahiini
- Asiomomys
- Utahia
- Stockia
- Chipataia
- Ourayia
- Wyomomys
- Ageitodendron
- Ekgmowechashala