Biology:Palaeonictis

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Palaeonictis ("ancient weasel") is an extinct genus of placental mammals from extinct subfamily Palaeonictinae within extinct family Oxyaenidae, that lived in Europe and North America from the Late Paleocene to the Early Eocene.[1][2] Palaeonictines were a group of oxyaenids that consisted of omnivorous oxyaenids and were closely related to the hypercarnivorous macheroidines.[3][4][5][6] Palaeonictis was a small to medium sized oxyaenid, with the largest species, P. peloria, weighing 11.7 kg (26 lb).[7]

Taxonomy

Palaeonictis is classified as a Oxyaenidae, which was originally considered to be one of the two groups of Creodonta, with the other being Hyaenodontidae.[8][9][6] However, recent analysis have questioned the monophyletic nature of creodonts, finding it to be polyphyletic group of two unrelated clades.[10][11] Since then, Hyaenodontidae and Oxyaenidae, were ranked up to orders, Hyaenodonta and Oxyaenodonta respectively.[12][13][14]

Gunnell (1991) recovered palaeonictines were closely related to Tytthaena.[8] On the other hand, recent phylogenetic modeling performed by Zack et al. recovered palaeonictines as a sister clade to machaeroidines, a subfamily of sabertoothed oxyaenids.[4][5]

Cladogram of oxyaenids recovered by Gunnell (1991):[8]

Oxyaenidae
 
 
 

Tytthaena parrisi

 
 

Tytthaena lichna

 
 
 
 
 

Palaeonictis occidentalis

 
 

Palaeonictis peloria

 
 
 
 

Dipsalodon matthewi

 
 

Dipsalodon churchillorum

 
 
 
 
 
 
 

Dipsalidictis krausei

 
 
 

Dipsalidictis transiens

 
 
 

Dipsalidictis platypus

 
 

Dipsalidictis aequidens

 
 
 
 
 
 

Oxyaena gulo

 
 
 

Oxyaena intermedia

 
 

Oxyaena forcipata

 
 
 
 
 

Evolution

Oxyaenids were believed to have evolved in the Middle Paleocene, roughly 60 Ma.[12] However, they wouldn't appear in the fossil record until the Late Paleocene, with Tytthaena.[15] Palaeonictines first appeared Ti5 of the Tiffanian faunal stage,[2] with Palaeonictis first appearing during the latest Paleocene, with the oldest species P. peloria. This species was thought to have been ancestral to the other species of Palaeonictis, first giving rise to P. wingi and P. gigantea. The former would evolve into P. occidentalis following the PETM.[6]

Description

Life restoration of P. occidentalis

The biggest species, P. peloria, is known from an incomplete jaw that must have measured over 20 centimetres (7.9 in) in length.[6] Juhn et al. (2024) estimated that P. peloria weighed 11.7 kg (26 lb).[7] P. occidentalis was another large species within the genus weighing up to 6.33 kg (14.0 lb).[7] During the Paleocene-Eocene Thermal Maximum, the genus saw a decrease in size leading to the appearance of P. wingi and P. gigantea, the smallest species within the genus.[6]

Extinction

European oxyaenids, including P. gigantea, went extinct roughly 53 Ma during the Intra-Ypresian Mammal Turnover.[16] P. occidentalis was the last species to go extinct,[17] going extinct between the 4th and 6th biochron of the Wasatchian faunal stage.[8][18][19]

The extinction of Palaeonictis, as well as oxyaenids as a whole, has been debated by experts.[6][20] Gunnell (1998) and Chester et al. (2010) suggested the extinction of paleonictines, as well as other oxyaenids, was due to competition with carnivorans.[6] However, the excellent North American fossil record indicates oxyaenids were declining well before the appearance of the replacement taxa such as carnivorans.[9] Furthermore, Fischer et al. (2026) found a there was a notable temporal gap between similar sized European oxyaenids and carnivoramorphans suggesting competitive replacement likely wasn't responsible for the extinction of oxyaenids in Europe.[20]

References

  1. ↑ Stephen Jay Gould, John Barber & Peter Andrews (2001). The Book of Life. W. W. Norton & Company. ISBN 0-393-32156-8. https://archive.org/details/bookoflife00goul. 
  2. ↑ 2.0 2.1 F. Solé, E. Gheerbrant and M. Godinot (2011.) New Data on the Oxyaenidae from the Early Eocene of Europe; biostratigraphic, paleobiogeographic and paleoecologic implications Palaeontologia Electronica, Vol. 14, Issue 2; 13A: Pages 1-41
  3. ↑ Floréal Solé, Emmanuel Gheerbrant and Marc Godinot. "New data on the Oxyaenidae from the Early Eocene of Europe; biostratigraphic, paleobiogeographic and paleoecologic implications". https://www.researchgate.net/publication/251231346. 
  4. ↑ 4.0 4.1 Zack, Shawn P.; Rose, Kenneth D.; O'Leary, Maureen A. (2025-06-24). "New Cranial and Postcranial Remains of the Once Enigmatic Early Eocene Mammal Wyolestes (Mammalia, Ferae, Hyaenodonta) from North America, and Phylogenetic Evidence for its Interordinal Relationships". Bulletin of the American Museum of Natural History 2025 (475). doi:10.1206/0003-0090.475.1.1. ISSN 0003-0090. https://bioone.org/journals/bulletin-of-the-american-museum-of-natural-history/volume-2025/issue-475/0003-0090.475.1.1/New-Cranial-and-Postcranial-Remains-of-the-Once-Enigmatic-Early/10.1206/0003-0090.475.1.1.full. 
  5. ↑ 5.0 5.1 Zack, Shawn P. (2019). "A skeleton of a Uintan machaeroidine ‘creodont’ and the phylogeny of carnivorous eutherian mammals". Journal of Systematic Palaeontology 19 (8): 653-689. doi:10.1080/14772019.2018.1466374. https://www.tandfonline.com/doi/full/10.1080/14772019.2018.1466374. 
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Stephen G. B. Chester; Jonathan I. Bloch; Ross Secord; Doug M. Boyer (2010). "A new small bodied species of Palaeonictis (Creodonta, Oxyaenidae) from the Paleocene-Eocene thermal maximum". Journal of Mammalian Evolution 17 (4): 227–243. doi:10.1007/s10914-010-9141-y. https://digitalcommons.unl.edu/geosciencefacpub/298. 
  7. ↑ 7.0 7.1 7.2 Juhn, Mark S.; Balisi, Mairin A.; Doughty, Evan M.; Friscia, Anthony R.; Howenstine, Aidan O.; Jacquemetton, Christiane; Marcot, Jonathan; Nugen, Sarah et al. (2024). "Cenozoic climate change and the evolution of North American mammalian predator ecomorphology" (in en). Paleobiology 50 (3): 452–461. doi:10.1017/pab.2024.27. ISSN 0094-8373. https://www.cambridge.org/core/journals/paleobiology/article/cenozoic-climate-change-and-the-evolution-of-north-american-mammalian-predator-ecomorphology/CDF3786B3FA8A1DB57FF6CED340F33F3. 
  8. ↑ 8.0 8.1 8.2 8.3 Gunnel, Gregg F.; Gingerich, Philip D. (1991). "Systematics and evolution of late Paleocene and early Eocene Oxyaenidae (Mammalia, Creodonta) in the Clarks Fork Basin, Wyoming". Contributions from the Museum of Paleontology (The University of Michigan) 28 (7): 141–180. http://deepblue.lib.umich.edu/bitstream/2027.42/48543/2/ID397.pdf. 
  9. ↑ 9.0 9.1 Van, Valkenburgh B. (1999). "Major patterns in the history of carnivorous mammals". Annual Review of Earth and Planetary Sciences 27: 463–493. doi:10.1146/annurev.earth.27.1.463. Bibcode: 1999AREPS..27..463V. 
  10. ↑ Morlo, Michael; Gunnell, G.; Polly, P. D. (2009). "What, if not nothing, is a creodont? Phylogeny and classification of Hyaenodontida and other former creodonts". Journal of Vertebrate Paleontology 29 (Supplement 3): 152A. doi:10.1080/02724634.2009.10411818. 
  11. ↑ Polly, P. D. (1994). "What, if anything, is a creodont?". Journal of Vertebrate Paleontology 14 (Supplement 3): 42A. doi:10.1080/02724634.1994.10011592. 
  12. ↑ 12.0 12.1 Solé, Floréal & Smith, Thierry (2013). "Dispersals of placental carnivorous mammals (Carnivoramorpha, Oxyaenodonta & Hyaenodontida) near the Paleocene-Eocene boundary: a climatic and almost worldwide story" Geologica Belgica 16/4: 254–261
  13. ↑ Solé, Floréal; Ladevèze, Sandrine (2017). "Evolution of the hypercarnivorous dentition in mammals ( Metatheria , Eutheria ) and its bearing on the development of tribosphenic molars". Evolution & Development 19 (2): 56–68. doi:10.1111/ede.12219. https://onlinelibrary.wiley.com/doi/abs/10.1111/ede.12219. 
  14. ↑ Kort, Anne E.; Ahrens, Heather; David Polly, P.; Morlo, Michael (2021-10-01). "Postcrania and paleobiology of Patriofelis ulta (Mammalia, Oxyaenodonta) of the Bridgerian (lower–middle Eocene) of North America". Journal of Vertebrate Paleontology 41 (6). doi:10.1080/02724634.2021.2045491. ISSN 0272-4634. 
  15. ↑ P. D. Gingerich. (1980.) "Tytthaena parrisi, Oldest Known Oxyaenid (Mammalia, Creodonta) from the Late Paleocene of Western North America." Journal of Paleontology 54(3):570-576
  16. ↑ Solé, Floréal; Fischer, Valentin; Le Verger, Kévin; Mennecart, Bastien; Speijer, Robert P.; Peigné, Stéphane; Smith, Thierry (2022). "Evolution of European carnivorous mammal assemblages through the Paleogene". Biological Journal of the Linnean Society 135 (4): 734–753. doi:10.1093/biolinnean/blac002. https://academic.oup.com/biolinnean/article/135/4/734/6532007?login=false. 
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Chester2010
  18. ↑ F. Solé, E. Gheerbrant and M. Godinot (2011.) New Data on the Oxyaenidae from the Early Eocene of Europe; biostratigraphic, paleobiogeographic and paleoecologic implications Palaeontologia Electronica, Vol. 14, Issue 2; 13A: Pages 1-41
  19. ↑ Chew, Amy E. (2009). "Paleoecology of the Early Eocene Willwood Mammal Fauna from the Central Bighorn Basin, Wyoming". Paleobiology 35 (1): 13–31. doi:10.1666/07072.1. ISSN 0094-8373. Bibcode: 2009Pbio...35...13C. https://www.jstor.org/stable/20445619. 
  20. ↑ 20.0 20.1 Fischer, ValentinExpression error: Unrecognized word "et". (2026). "The rise of carnivoran mammals in Europe through the lens of body mass". Biology Letters 22 (8). doi:10.1098/rsbl.2026.0319. https://royalsocietypublishing.org/rsbl/article/22/8/20260319/482707/The-rise-of-carnivoran-mammals-in-Europe-through. 

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