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Dissacus

From Wikipedia, the free encyclopedia

Dissacus
Temporal range: Early Paleocene-Early Eocene (Danian to Ypresian), 63–52.4 Ma
Skull of Dissacus zanabazari
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Placentalia
Order: †Mesonychia
Family: †Mesonychidae
Genus: †Dissacus
Cope, 1881[1]
Type species
†Dissacus navajovius
Other Species
  • †D. argenteus O'Leary and Rose, 1995
  • †D. bohaiensis Tong and Wang, 2006
  • †D. europaeus Lemoine, 1891
  • †D. indigenus Dashzeveg, 1976
  • †D. magushanensis Yan and Tang, 1976
  • †D. praenuntius Matthew and Granger, 1915
  • †D. rotundus? Wang, 1975
  • †D. saurognathus? Wortman, 1897
  • †D. serior? O'Leary and Rose, 1995
  • †D. serratus Chow and Qi, 1978
  • †D. shanghoensis Chow et al., 1973
  • †D. zanabazari Geisler and McKenna, 2007
  • †D. zengi Ting, 2004

Dissacus is a paraphyletic genus of extinct carnivorous jackal to coyote-sized Mesonychidae, an early family of hoofed mammals that consisted of carnivore-omnivore. Their fossils in Early Paleocene to Middle Eocene aged strata in Eurasia and North America.[2][3] Dissacus europaeus may have evolved in North America migrated to Europe, and first appeared in European strata in the Thanetian (c. 58-57 MYA). A phylogenetic analysis of European mesonychids suggests that Dissacus was part of an early diversification of species in the Paleocene, and other genera diversified in a later episode in the early Eocene. D. europaeus survived the Paleocene-Eocene Thermal Maximum, a period of severe global warming, which suggests it had flexible habits.[2] Orientation patch analysis of the molar teeth of the North American D. praenuntius suggests its omnivorous with consisted diet consisting of meat, suggesting it wasn’t a hypercarnivore such a felid or weasel. It shared its environment with more omnivorous mammals of a similar body size.[4]

Originally, it was believed Dissacus was present in both Northwestern and Southwestern Europe,[2] however all European species, with the exception of D. europaeus, was reclassified as Hyaenodictis.[5] This reclassification restricted European Dissacus to Southernwestern Europe during the latest Paleocene to earliest Eocene.[2][5]

Taxonomy

[edit]

Phylogenetic modeling recovered Dissacus as a paraphyletic genus.[2][5][6][7][8] Spaulding et al. (2009) recovered D. praenuntius being more closely related to Pachyaena and Harpagolestes orientalis.[8]

Solé et al. (2018) recovered D. praenuntius, D. europaeus, and D. argenteus as basal mesonychids. D. serratus and D. zanabazari were recovered as members of the Asian Dissacus clade, with D. willwoodensis being recovered as close relative to the clade. The European Dissacus clade consisted of D. rougierae, D. raslanloubatieri, D. blayaci, and D. filholi. D. navajovius was recovered as a sister taxon to the monospecific Ankalagon, questioning the validity of the latter genus. Within the same analysis recovered D. serior within the Mesonyx clade.[2]

Solé et al. (2023) revived the genus Hyaenodictis finding it distinct from Dissacus, with D. filholi being its type species. In addition, they reclassified D. blayaci, D. progressus, D. rougierae and D. raslanloubatieri as European species and D. willwoodensis as the North American species of Hyaenodictis.[5]

Their phylogenetic analysis included D. rotundus, D. zengi, and D. magushanensis. D. rotundus was found to be closely related to D. navajovius and Ankalagon. The close relation between Ankalagon and D. navajovius suggests the former may be a species of Dissacus. D. zengi was recovered as a sister taxon to the Asian Dissacus clade and D. magushanensis was recovered as sister taxon to D. argenteus. Current Dissacus species also saw some revised positioning, with D. bohaiensis was moved to the Asian Dissacus clade.[5]

Description

[edit]
Size comparison between male and female D. saurognathus

D. navajovius was the smallest North American species, length and width regressions of m2 suggests the species weighed 9.92 kg (21.9 lb) on average, with the largest specimen, AMNH 3361 weighing 11.33 kg (25.0 lb). D. praenuntius was significantly larger than the afromentioned species, with Clarkforkian D. praenuntius averaging 18 kg (40 lb). During the PETM, D. praenuntius saw a decrease in size averaging at around 14.28 kg (31.5 lb).[9] Possible Dissacus species, D. saurognathus, was the largest species with a head length of 30 cm (12 in) and an estimated body mass of 46.9 kg (103 lb).[10][11] Including supplementary materials

D. europaeus was the smallest European mesonychid weighing 8–14 kg (18–31 lb) prior to the thermal maximum. During the thermal maximum, D. europaeus shrunk in size significantly with dwarfed sized specimens weighing 4–5 kg (8.8–11.0 lb).[2]

Paleobiology

[edit]
Life reconstruction of D. zanabazari

Locomotion

[edit]

A morphological study of limb bones of D. europaeus suggests this animal was digitigrade and more cursorial than is usually assumed for the genus.[12] Analysis of the elbow joint shows it was specialized for extra flexion and extension, an adaptation usually found in running species; the amount of specialization is unusual for a Paleocene mammal. This does not mean Dissacus species were swift runners by modern standards, but that D. europaeus was more adapted for running than other mammals of its time. It may be part of a trend among early Cenozoic mammals toward developing more specialized bodies to fill different ecological niches.[13]

Diet

[edit]

Prior to the Palaeocene-Eocene Thermal Maximum (PETM), D. praenuntius primarily ate meat. During and after the PETM, however, bone featured more prominently in its diet compared to before the hyperthermal event.[14]

Extinction

[edit]
Mandible of Pachyaena gigantea, one of the mesonychids that replaced Dissacus in Northwestern Europe

D. europaeus would go extinct roughly 55.5 million years ago contemporary with the appearance of Pachyaena and Palaeonictis in Northwestern Europe. However, it was unlikely Pachyaena ecologically replaced Dissacus, due to the former's much larger body size. Palaeonictis occupied a different niche than Dissacus,[2] with the latter having a greater preference for meat.[15] D. praenuntius, would go extinct in or shortly after Wa-2,[9][14][16] which dates to 54.7-54.4 million years ago.[17] Its extinction coincided with the diversification of Pachyaena and Hyaenodictis willwoodensis. Schwartz et al. (2025) suggested the possible chance of competitive replacement, however dental microwear on the two mesonychids is required.[14] The last North America species, represented by D. serior was found within Wa-6,[9] which dates to 53.0-52.4 million years ago.[17]

References

[edit]
  1. ↑ PaleoBiology Database: Dissacus, basic info
  2. 1 2 3 4 5 6 7 8 Solé, Floréal; Godinot, Marc; Laurent, Yves; Galoyer, Alain; Smith, Thierry (2018-09-01). "The European Mesonychid Mammals: Phylogeny, Ecology, Biogeography, and Biochronology". Journal of Mammalian Evolution. 25 (3): 339–379. doi:10.1007/s10914-016-9371-8. ISSN 1573-7055. S2CID 254701971.
  3. ↑ 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.
  4. ↑ 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. S2CID 15058311 – via U. of Nebraska digital commons.
  5. 1 2 3 4 5 Solé, Floréal; Fournier, Morgane; Ladevèze, Sandrine; et al. (2023). "New postcranial elements of mesonychid mammals from the Ypresian of France: New hypotheses for the radiation and evolution of the mesonychids in Europe". Journal of Mammalian Evolution. 30 (2): 371–401. doi:10.1007/s10914-023-09651-x.
  6. ↑ Solé, Floréal; Bast, Eric De; Yang, Jian; Li, Cheng-Sen; Smith, Thierry (2017). "The first species of Hapalodectes (Mesonychia, Mammalia) from the middle Paleocene of China (Qianshan Basin, Anhui Province) sheds light on the initial radiation of hapalodectids". Palaeontology. 60 (3): 433–449. doi:10.1111/pala.12293.
  7. ↑ Geisler, Jonathan H.; McKenna, Malcolm C. (2007). "A new species of mesonychian mammal from the lower Eocene of Mongolia and its phylogenetic relationships" (PDF). Acta Palaeontologica Polonica. 52 (1): 189–212.
  8. 1 2 Spaulding, Michelle; O'Leary, Maureen A.; Gatesy, John (2009-09-23). "Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution". PLOS ONE. 4 (9) e7062. Bibcode:2009PLoSO...4.7062S. doi:10.1371/journal.pone.0007062. ISSN 1932-6203. PMC 2740860. PMID 19774069.
  9. 1 2 3 Solé, Floréal; Morse, Paul E.; Bloch, Jonathan I.; Gingerich, Philip D.; Smith, Thierry (July 2021). "New specimens of the mesonychid Dissacus praenuntius from the early Eocene of Wyoming and evaluation of body size through the PETM in North America". Geobios. 66–67: 103–118. doi:10.1016/j.geobios.2021.02.005.
  10. ↑ Ross, Kenneth D. (October 31, 2006). The Beginning of the Age of Mammals. Johns Hopkins University. p. 274. ISBN 9780801884726.
  11. ↑ Saarinen, Juha J.; Boyer, Alison G.; Brown, James H.; Costa, Daniel P.; et al. (2014). "Patterns of maximum body size evolution in Cenozoic land mammals: eco-evolutionary processes and abiotic forcing". Proceedings of the Royal Society B: Biological Sciences. 281 (1784): 1–10. doi:10.1098/rspb.2013.2049. PMID 24741007.
  12. ↑ Agusti, Jordi; Anton, Mauricio (2002). Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe. Columbia University Press. pp. 13, 14. ISBN 0-231-11640-3.
  13. ↑ Thewissen, J.G.M. (1991). "Limb Osteology and function of the primitive Paleocene ungulate Pleuraspidotherium with notes on Tricuspiodon and Dissacus (Mammalia)". Geobios. 24 (4): 483–495. Bibcode:1991Geobi..24..483T. doi:10.1016/S0016-6995(06)80249-4.
  14. 1 2 3 Schwartz, Andrew; DeSantis, Larisa R.G.; Scott, Rob S. (1 October 2025). "Dietary change across the Paleocene-Eocene Thermal Maximum in the mesonychid Dissacus praenuntius" (PDF). Palaeogeography, Palaeoclimatology, Palaeoecology. 675 113089. doi:10.1016/j.palaeo.2025.113089. Retrieved 29 June 2025 – via Elsevier Science Direct.
  15. ↑ 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. S2CID 15058311.
  16. ↑ Clyde, W.C. (January 1997). Stratigraphy and mammalian paleontology of the McCullough Peaks, Northern Bighorn Basin, Wyoming: implications for biochronology, basin development, and community reorganization across the Paleocene-Eocene boundary (Doctor of Philosophy thesis).
  17. 1 2 Hodnett, John-Paul M.; Welsh, Edward T.; Santucci, Vincent L.; Tweet, Justin S. (2022). "A Middle Eocene brontothere (Mammalia; Perissodactyla; Brontotheriidae) from Yellowstone National Park, Wyoming". FOSSIL RECORD 8. New Mexico Museum of Natural History and Science. p. 211.


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