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Leptictidans Temporal range: Late Cretaceous - Oligocene Possible descendant taxon Placentalia survives to present 70–33 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Fossil specimen of Leptictidium auderiense
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Clade:	Eutheria
Order:	†Leptictida McKenna, 1975
Subgroups
†Gypsonictopidae †Leptictidae †Pseudorhyncocyonidae

Leptictida (leptos iktis "small/slender weasel") is a possibly paraphyletic extinct order of eutherian mammals. Their classification is contentious: according to cladistic studies, they may be (distantly) related to Euarchontoglires (rodents, primates and their relatives), although they are more recently regarded as the first branch to split from basal eutherians. One recent large-scale cladistic analysis of eutherian mammals favored lepictidans as close to the placental crown-clade; and several other recent analyses that included data from Cretaceous non-eutherian mammals found Leptictis to belong to the superorder Afrotheria.

The most recent phylogenetic studies recover it as actually a paraphyletic assemblage leading to Placentalia.

Description

The leptictids are a characteristic example of the non-specialized placental mammals that took part in the late Cretaceous-Paleocene evolutionary radiation, originally bunched together in the order Insectivora. The leptictids became extinct during the Oligocene. Their archaic cranium and dentition make it difficult to determine their relationship to other groups. Leptictid postcranial anatomy has been studied from the well-preserved middle Eocene Leptictidium specimens found at Messel, Germany.

Judging from these specimens, lepticids were small placentals with a body length ranging from 60 to 90 cm (24 to 35 in). The head had a long and slender snout, probably featuring a short trunk, which may have been used for scratching the undergrowth in search of insects and worms. The mouth's archaic dentition included two or three incisors, a canine, and V-shaped cheek-teeth - four premolars and three molars.

Their forelegs were shortened, but their hind legs were elongated. While this anatomy is reminiscent of small kangaroos and jerboas, suggesting a jumping locomotion, the structure of the tarsal bones hints at a specialization for terrestrial running. Perhaps these animals were capable of both modes of locomotion; running slowly in search for food, and jumping quickly to avoid threats. Additionally, the Messel specimens feature a surprisingly long tail, unique among modern placental mammals, formed by 40 vertebrae and probably used for balance.

Classification

• Order Leptictida
  • Family Gypsonictopidae
    • Genus Gypsonictops
    • Genus Sikuomys
  • Family Leptictidae
    • Genus Amphigyion
    • Genus Gallolestes
    • Genus Labes
    • Genus Lainodon
    • Genus Leptonysson
    • Genus Palaeictops
    • Genus Praolestes
    • Genus Wania
    • Subfamily Leptictinae
      • Genus Blacktops
      • Genus Ictopidium
      • Genus Leptictis
      • Genus Myrmecoboides
      • Genus Ongghonia
      • Genus Prodiacodon
      • Genus Protictops
  • Family Pseudorhyncocyonidae
    • Genus Diaphyodectes
    • Genus Leptictidium
    • Genus Phakodon
    • Genus Pseudorhyncocyon

Notes

1. Hooker, J. J.; O'Regan, H. (2013-07-15). "Origin and evolution of the Pseudorhyncocyonidae, a European Paleogene family of insectivorous placental mammals". Palaeontology. 56 (4): 807–835. Bibcode:2013Palgy..56..807H. doi:10.1111/pala.12018.
2. Zack, S. P.; Penkrot, T. A.; Bloch, J. I.; Rose, K. D. (March 2005). "Affinities of 'Hyopsodontids' to elephant shrews and a Holarctic origin of Afrotheria" (PDF). Nature. 434 (7032): 497–501. Bibcode:2005Natur.434..497Z. doi:10.1038/nature03351. PMID 15791254. S2CID 4428738.
3. Wible, J. R.; Rougier, G. W.; Novacek, M. J.; Asher, R. J. (September 2009). "The eutherian mammal Maelestes gobiensis from the Late Cretaceous of Mongolia and the phylogeny of Cretaceous Eutheria". Bulletin of the American Museum of Natural History. 2009 (327): 1–123. doi:10.1206/623.1. hdl:2246/6001. S2CID 86337881.
4. O'Leary, Maureen A.; Bloch, Jonathan I.; Flynn, John J.; et al. (8 February 2013). "The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals". Science. 339 (6120): 662–667. Bibcode:2013Sci...339..662O. doi:10.1126/science.1229237. hdl:11336/7302. PMID 23393258. S2CID 206544776.
5. Halliday, Thomas J. D. (2015). "Resolving the relationships of Paleocene placental mammals" (PDF). Biological Reviews. 92 (1): 521–550. doi:10.1111/brv.12242. PMC 6849585. PMID 28075073.
6. ^ Augustí and Antón, 2002, p. 5

References

• Agustí, Jordi; Antón, Mauricio (2002). Mammoths, Sabertooths, and Hominids: 65 Millions Years of Mammalian Evolution in Europe. New York: Columbia University Press. ISBN 978-0-231-11640-4. OCLC 51534272.

Further reading

• Meehan, T. J.; Martin, Larry D. (2010). "New leptictids (Mammalia: Insectivora) from the Early Oligocene of Nebraska, USA". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 256 (1): 99–107. doi:10.1127/0077-7749/2010/0035.
• Novacek, Michael J (1977). "A review of Paleocene and Eocene Leptictidae (Eutheria, Mammalia) from North America" (PDF). PaleoBios. 1: 24.

External links

• Insectivore-like mammals: Tiny teeth and their enigmatic owners

v t e Eutheria
Kingdom: Animalia Phylum: Chordata Class: Mammalia Subclass: Theria Synapsida see Synapsida Cynodontia see Cynodontia Mammalia see Mammalia Eutheria see below↓ Eutheria
Eutheria †Acristatherium? †Ambolestes? †Bayshinoryctes †Bobolestes? †Cokotherium? †Durlstodon †Durlstotherium †Endotherium †Eomaia? †Hovurlestes †Hyotheridium? †Indoclemensia †Juramaia? †Microtherulum? †Montanalestes? †Murtoilestes? †Prokennalestes? †Sinodelphys? †Adapisoriculidae Adapisoriculus Afrodon Bustylus Deccanolestes? Garatherium Namibiodon Remiculus? Sahnitherium? Wyonycteris? †Asioryctitheria Asioryctes Bulaklestes Daulestes Kennalestes Sasayamamylos Uchkudukodon Ukhaatherium †Cimolestidae Aboletylestes Acmeodon Alveugena Ambilestes Avunculus Bagalestes Batodon? Betonnia Chacopterygus Cimolestes Didelphodus Gelastops Ilerdoryctes Maelestes? Naranius Paleotomus Pararyctes Procerberus Protentomodon Puercolestes Scollardius Tsaganius †Didymoconidae Archaeoryctes Ardynictis Didymoconus Hunanictis Kennatherium Zeuctherium †Horolodectidae Ferrequitherium Horolodectes †Leptictida Gypsonictopidae Gypsonictops Sikuomys Pseudorhyncocyonidae Diaphyodectes Leptictidium Phakodon Pseudorhyncocyon Leptictidae Amphigyion Blacktops Gallolestes Ictopidium Labes Lainodon Leptictis Leptonysson Megaleptictis Myrmecoboides Ongghonia Palaeictops Praolestes Prodiacodon Protictops Wania †Palaeoryctidae Aaptoryctes Aceroryctes Eoryctes Lainoryctes Nuryctes Ottoryctes Palaeoryctes Pinoryctes †Pantolesta Paroxyclaenidae Dulcidon Euhookeria Fratrodon Kiinkerishella Kopidodon Merialus Paraspaniella Paroxyclaenus Pugiodens Sororodon Spaniella Vulpavoides Pantolestidae Amaramnis Aphronorus Bessoecetor Bisonalveus Bogdia Bouffinomus Buxolestes Chadronia Coriphagus Cryptopithecus Dyspterna Galethylax Gobipithecus Kochictis Oboia Pagonomus Palaeosinopa Pantolestes Pentacodon Thelysia Todralestes †Taeniodonta Schowalteria Conoryctidae Conoryctella Conoryctes Huerfanodon Onychodectidae Onychodectes Stylinodontidae Ectoganus Psittacotherium Stylinodon Wortmania †Tillodontia Adapidium Azygonyx Basalina Benaius Chungchienia Dysnoetodon Esthonyx Franchaius Higotherium Interogale Kuanchuanius Lofochaius Megalesthonyx Meiostylodon Plesiesthonyx Plethorodon Simplodon Tillodon Trogosus Yuesthonyx †Zalambdalestidae Alymlestes Anchilestes Barunlestes Beleutinus Kulbeckia Prozalambdalestes Zalambdalestes Zhangolestes Zofialestes †Zhelestidae Alostera? Aspanlestes Avitotherium Azilestes? Borisodon Eoungulatum Eozhelestes Gallolestes Kharmerungulatum Khuduklestes? Lainodon Mistralestes? Oxlestes? Paranyctoides? Parazhelestes Sheikhdzheilia Sorlestes Valentinella? Zhalmousia Zhelestes †Pantodonta see Pantodonta Placentalia Afrotheria Boreoeutheria Xenarthra

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