Dryolestida

Dryolestida is an extinct order of mammals; most of the members are mostly known from the Jurassic to Paleogene, with one member, Necrolestes, surviving as late as the early Miocene.[1] They are considered members of the clade Cladotheria, close to the ancestry of therian mammals. It is also believed that they developed a fully mammalian jaw and also had the three middle ear bones. Other than that, not much is known about them, this is because their fossils are made up mostly of jaw and tooth remains.

Dryolestida
Temporal range: Bathonian-Santacrucian
164.7–17.5 Ma
Skeleton of Henkelotherium
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Clade: Cladotheria
Superorder: Dryolestoidea
Butler, 1939
Order: Dryolestida
Prothero, 1981
Families and genera

See text

Dryolestids were formerly considered part of Pantotheria and/or Eupantotheria. The clade Quirogatheria, erected by José Bonaparte in 1992, is often used as a synonym for Dryolestida. Originally, Quirogatheria was meant to include Brandoniidae, but this family is now included with the dryolestids.

Morphology

Dryolestids are mostly represented by teeth, fragmented dentaries and parts of the rostrum. The Jurassic forms retained a coronoid and splenial, but the Cretaceous forms lack these. Another primitive feature is the presence of a Meckelian groove (Meridiolestidans lost it altogether).[2] A fundamentally modern ear is known in at least Dryolestes and mesungulatids.[3][4]

Tooth enamel evolved differently in marsupials and eutherians. In a first phase, during the late Triassic and Jurassic, prisms separated from the interprismatic matrix, probably independently in several Mesozoic mammal lineages. More derived enamel types evolved in a second phase, during the Tertiary and Quaternary, but without replacing the old prismatic enamel, instead forming various combinations of three-dimensional structures (called schmelzmuster). Dryolestid dentition is thought to resemble the primitive mammalian dentition before the marsupial-eutherian differentiation and dryolestids are candidates to be the last common ancestor of the two mammalian subclasses.[5]

Two dryolestoids, Drescheratherium and Cronopio, have elongated upper canines.[6]

Distribution

Dryolestids are known from the Jurassic through Early Cretaceous of the northern hemisphere (North America, Eurasia, and North Africa) and from the Late Cretaceous through to the Miocene of South America.[7] Drylestoids are very rarely found in the Cenozoic, as are the few other Mesozoic mammals with later descendants, such as multituberculates, monotremes, and gondwanatheres.[8]

The oldest undisputed fossils of Dryolestidae were found in the Guimarota coal mine near Leiria, Portugal, the largest known deposit of Jurassic mammals. The tooth pattern of these fossils — 8–9 mesiodistally compressed molars with small, cusp-like talonids — distinguish them from tribosphenic mammals, and they form a sister group of the latter and Peramus together with Amphitherium, Paurodontidae, and Henkelotheriidae.[9]

The youngest fossil in the northern hemisphere is Crusafontia cuencana from early Cretaceous of Uña and Galve, Spain, though a fragmentary lower molar from the late Cretaceous Mesaverde Formation in Wyoming has been attributed to Dryolestidae. In South America, by contrast, dryolestoids thrived in the Late Cretaceous, diversifying in a myriad of forms such as the saber-toothed Cronopio or the herbivorous mesungulatids, becoming some of the most ecologically diverse Mesozoic South American mammals.[10] At least two major Late Cretaceous South American dryolestoid clades are known: Meridiolestida and a clade similar to Dryolestes itself, Groebertherium.[11]

With the advent of the Cenozoic, dryolestoids declined drastically in diversity, with only Peligrotherium being known from the Palaeocene. The exact reasons for this decline aren't clear; most likely they simply did not recover from the K-Pg event. Nonetheless, dryolestoids would continue to survive until the Miocene, from when Necrolestes is known; a gap of 50 million years exists between it and Peligrotherium.[12] A possible brandoniid tooth was described from the Eocene of Antarctica, although could rather represent a necrolestid.[13]

Classification

Classification modified after Rougier & Gaetano, 2011.[14]

A phylogenetic analysis conducted by Rougier et al. (2012) indicated that meridiolestidans might not be members of Dryolestida but instead slightly more closely related to the placental mammals, marsupials and amphitheriids. Paurodontids were also recovered as not belonging to Dryolestida, but instead as a sister group of Meridiolestida in this analysis.[1] An analysis conducted by Averianov, Martin and Lopatin (2013) did not recover meridiolestidans as members of Dryolestida as well, but it found them to be the sister group of spalacotheriid "symmetrodonts" instead. However, paurodontids were recovered as members of Dryolestida in this analysis.[15] On the other hand, an analysis conducted by Chimento, Agnolin and Novas (2012) did recover meridiolestidans as members of Dryolestida.[16]

References

  1. Guillermo W. Rougier, John R. Wible, Robin M. D. Beck and Sebastian Apesteguía (2012). "The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America". Proceedings of the National Academy of Sciences of the United States of America. 109 (49): 20053–20058. Bibcode:2012PNAS..10920053R. doi:10.1073/pnas.1212997109. PMC 3523863. PMID 23169652.CS1 maint: uses authors parameter (link)
  2. Kielan-Jaworowska, Cifelli & Luo 2004, pp. 14, 375, 379–380
  3. Rougier, Guillermo W. (2009). "Mammals from the Allen Formation, Late Cretaceous, Argentina". Cretaceous Research. 30: 223–238. doi:10.1016/j.cretres.2008.07.006.
  4. ZHE-XI, LUO; RUF; Irina; Martin, Thomas (2012). "The petrosal and inner ear of the Late Jurassic cladotherian mammal Dryolestes leiriensis and implications for ear evolution in therian mammals". Zoological Journal of the Linnean Society. 166: 433–463. doi:10.1111/j.1096-3642.2012.00852.x.
  5. von Koenigswald 2000, p. 107
  6. Rougier, Guillermo W.; Apesteguía, Sebastián; Gaetano, Leandro C. (2011). "Highly specialized mammalian skulls from the Late Cretaceous of South America". Nature. 479: 98–102. doi:10.1038/nature10591. PMID 22051679.
  7. Kielan-Jaworowska, Cifelli & Luo 2004, pp. 14, 375, 379–380
  8. Rose 2006, pp. 335–6
  9. Martin 1997, Introduction
  10. Rougier et al. 2009, p. 208.
  11. Harper T, Parras A, Rougier GW. 2018. Reigitherium (Meridiolestida, Mesungulatoidea) an enigmatic Late Cretaceous mammal from Patagonia, Argentina: morphology, affinities, and dental evolution. Journal of Mammalian Evolution.
  12. Florentino Ameghino (1891). "Nuevos restos de mamíferos fósiles descubiertos por Carlos Ameghino en el Eoceno inferior de la Patagonia austral. Especies nuevas, adiciones y correciones". Revista Argentina de Historia Natural. 1: 289–328.
  13. Gelfo, J. N.; Bausza, N.; Reguero, M. (2019). "The fossil record of Antarctic land mammals: commented review and hypotheses for future research". Advances in Polar Science: 274–292.
  14. Guillermo W. Rougier, Sebastián Apesteguía and Leandro C. Gaetano (2011). "Highly specialized mammalian skulls from the Late Cretaceous of South America". Nature. 479 (7371): 98–102. Bibcode:2011Natur.479...98R. doi:10.1038/nature10591. PMID 22051679.CS1 maint: uses authors parameter (link) Supplementary information
  15. Alexander O. Averianov, Thomas Martin and Alexey V. Lopatin (2013). "A new phylogeny for basal Trechnotheria and Cladotheria and affinities of South American endemic Late Cretaceous mammals". Naturwissenschaften. 100 (4): 311–326. Bibcode:2013NW....100..311A. doi:10.1007/s00114-013-1028-3. PMID 23494201.CS1 maint: uses authors parameter (link)
  16. Nicolás R. Chimento, Federico L. Agnolin and Fernando E. Novas (2012). "The Patagonian fossil mammal Necrolestes: a Neogene survivor of Dryolestoidea" (PDF). Revista del Museo Argentino de Ciencias Naturales, Nueva Serie. 14 (2): 261–306. Archived from the original (PDF) on 2013-11-04. Retrieved 2013-03-21.

Further reading

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