Omomyidae

For an explanation of very similar terms, see Tarsiiformes.

Omomyidae
Temporal range: 56–34 Ma Late Paleocene – Oligocene[1]
The skull of Anaptomorphus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Suborder: Haplorhini
Clade: †Omomyiformes
Superfamily: †Omomyoidea
Family: †Omomyidae
Subgroups
Synonyms

Tarsiiformes

Omomyidae is a group of early primates that radiated during the Eocene epoch between about 55 to 34 million years ago (mya). Fossil omomyids are found in North America, Europe & Asia, making it 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 (56 mya) in North America, Europe, and Asia, and are the earliest known crown primates.

Characteristics

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Life restoration of Tetonius homunculus

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 evolved body masses in excess of 1 kg (2.2 lb) and frugivorous or folivorous diets. The largest omomyids were Macrotarsius and Ourayia, both at 1.5–2 kg (3.3–4.4 lb) in weight.[3] 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 primates alive today, omomyids had grasping hands and feet with digits tipped by nails instead of claws, although they possessed toilet claws like modern lemurs.[4] Features of their skeletons strongly indicate that omomyids lived in trees.[3] In at least one genus (Necrolemur), the lower leg bones, the tibia and fibula, were fused as in modern tarsiers. 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 lemurs.

Omomyid systematics and evolutionary relationships are controversial. Authors have suggested that omomyids are either:

  1. stem haplorhines [i.e., basal members of the group including living tarsiers and anthropoids].[5]
  2. stem tarsiiformes [i.e., basal offshoots of the tarsier lineage].[6]
  3. stem primates more closely related to adapids than to living primate taxa.

Recent research suggests the Omomyiformes are stem haplorhines, making them likely a paraphyletic grouping.[7]

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. These haplorhine adaptations - absent in omomyids - include:

  1. significant reduction of the canal for the stapedial branch of the internal carotid artery.
  2. route of the canal to house the promontory branch of the internal carotid artery through the auditory bulla of the temporal bone, i.e. "perbullar" (rather than across the promontory of tympanic cavity, "transpromontorial") .
  3. contact between the alisphenoid and zygomatic bones.
  4. 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 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 supra-meatal 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.

Among primates, omomyids have a uniquely derived characteristic. This is the presence of an aphaneric (not visible or readily distinguishable, due to its position), or "intrabullar" (within the bullae), ectotympanic bone, connected to the lateral wall of the auditory bulla by an unbroken annular bridge.

Classification

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References

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  1. ^ Savage, RJG, & Long, MR (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. p. 365. ISBN 978-0-8160-1194-0.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ^ Morse, Paul E.; Chester, Stephen G. B.; Boyer, Doug M.; Smith, Thierry; Smith, Richard; Gigase, Paul; Bloch, Jonathan I. (2019-03-01). "New fossils, systematics, and biogeography of the oldest known crown primate Teilhardina from the earliest Eocene of Asia, Europe, and North America". Journal of Human Evolution. 128: 103–131. doi:10.1016/j.jhevol.2018.08.005. ISSN 0047-2484. PMID 30497682. S2CID 54167483.
  3. ^ a b Rachel H. Dunn. "Additional postcranial remains of omomyid primates from the Uinta Formation, Utah and implications for the locomotor behavior of large-bodied omomyids". Journal of Human Evolution Volume 58, Issue 5, May 2010, pp. 406-417
  4. ^ "Early Primates Groomed with Claws".
  5. ^ Kay, Richard F.; Ross, Callum; Williams, Blythe A. (1997). "Anthropoid origins". Science. 275 (5301): 797–804. doi:10.1126/science.275.5301.797. PMID 9012340. S2CID 220087294.
  6. ^ Szalay, Frederick (1976). "Systematics of the Omomyidae (Tarsiiformes, Primates): Taxonomy, phylogeny, and adaptations". Bulletin of the American Museum of Natural History. 156 (3): 157–450.
  7. ^ Rossie, James B.; Smith, Timothy D.; Beard, K. Christopher; Godinot, Marc; Rowe, Timothy B. (2018). "Nasolacrimal anatomy and haplorhine origins". Journal of Human Evolution. 114: 176–183. doi:10.1016/j.jhevol.2017.11.004. ISSN 0047-2484. PMID 29447758.
  8. ^ a b Perry, J. M. G.; Dutchak, A. R.; Theodor, J. M. (2023). "New primates from the Eocene of Saskatchewan, Canada: Revision of the primates from the Cypress Hills Formation with description of new taxa". Palaeontologia Electronica. 26 (2). 26.2.20. doi:10.26879/1246.
  9. ^ a b c Amy L. Atwater; E. Christopher Kirk (2018). "New middle Eocene omomyines (Primates, Haplorhini) from San Diego County, California". Journal of Human Evolution. in press. doi:10.1016/j.jhevol.2018.04.010.
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