Mesozoic Mammals

Abstract

Mesozoic mammals are those mammals that lived during the Mesozoic era, from 245 to 65 million years before the present. The lineage leading to mammals, Synapsida, is truly ancient; it branched off the trunk leading to reptiles at least 350 million years ago.

Keywords: mammals; Mesozoic; fossils; evolution; phylogeny

Figure 1.

Phylogenetic relationships of the major groups of Mesozoic mammals and their minimal geological ages. Different possible definitions of Mammalia are indicated.

Figure 2.

The origin of the mammalian ear and jaw articulation. (a) A generalized vertebrate. The dentary is one of many jaw bones; the articulation between the skull and jaw is formed by the quadrate (dark blue) and the articular (yellow). The tympanum, or eardrum (light blue), is behind the quadrate. (b) An early member of the mammalian lineage. The dentary is large, but the articulation between jaw and skull is still formed by the quadrate and articular. The tympanum is in the lower jaw, behind the dentary. (c) A mammal. The dentary is the only bone of the lower jaw. Bones of the old articulation between skull and jaw are now much smaller, free from the jaw and, with the exception of the stapes (green), have different names. The stapes, arranged at about 90° from the other ear ossicles, transmits the sound vibrations picked up by the eardrum and ossicles into the inner ear, where they are transduced into electrical impulses on their way to the brain.

Figure 3.

Diversity of Mesozoic mammals and early relatives. (a) Pachygenelus, a member of the putative group from which mammals originated. (b) and (c) Sinoconodon and Morganucodon, respectively, members of the early radiation of mammals. (d), (e) and (f) Monotreme, Multituberculate and Vincelestes respectively, members of the middle radiation of Mesozoic mammals. Monotremes are the only survivors of these groups. (g) and (h) An early marsupial and placental relative, respectively. The roots of both, marsupials and placentals, seem to originate in the Mesozoic, but the living groups and their direct ancestors appeared later during the Tertiary. Figures (a–c) and (e) are adapted, with permission, from Hopson JA (1994) Synapsid evolution and the radiation of non‐eutherian mammals. In: Prothero DR and Schoch RM (eds). Major Features of Vertebrate Evolution. Short Courses in Paleontology7: 190–219. Chicago: The Paleontological Society.

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Further Reading

Allin EF and Hopson JA (1992) Evolution of the auditory system in Synapsida. In: Webster DB, Fay RR and Popper AN (eds). The Evolutionary Biology of Hearing, pp. 587–614. New York: Springer‐Verlag.

Hopson JA and Crompton AW (1969) Origin of mammals. Evolutionary Biology 3: 15–72.

Hu Y, Wang Y, Luo Z and Li C (1997) A new symmetrodont mammal from China and its implications for mammalian evolution. Nature 390: 137–142.

Kermack DM and Kermack KA (eds) (1971) Early mammals. Zoological Journal of the Linnean Society 50 (Supplement 1).

Kermack KA, Mussett F and Rigney HW (1981) The skull of Morganucodon. Zoological Journal of the Linnean Society 71: 1–158.

Kielan‐Jaworowska Z and Gambaryan PP (1994) Postcranial anatomy and habits of Asian multituberculate mammals. Fossils & Strata 36 [whole issue].

Lillegraven JA, Kielan‐Jaworowska Z and Clemens WA (eds) (1979) Mesozoic Mammals: The First Two‐thirds of Mammalian History. Berkeley, CA: University of California Press.

Lillegraven JA and Krusat G (1991) Cranio‐mandibular anatomy of Haldanodon exspectatus (Docodonta; Mammalia) from the late Jurassic of Portugal. Contributions to Geology, University of Wyoming, Special Papers 28: 39–138.

Rougier GW, Wible JR and Novacek MJ (1996) Middle‐ear ossicles of Kryptobaatar dashzevegi (Mammalia, Multituberculata): implications for mammaliamorph relationships and the evolution of the auditory apparatus. American Museum Novitates 3187 [whole issue].

Szalay FS, Novacek MJ and McKenna MC (eds) (1993) Mammal Phylogeny: Mesozoic Differentiation, Multituberculates, Monotremes, Early Therians, and Marsupials. New York: Springer‐Verlag.

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How to Cite close
Rougier, Guillermo W(May 2001) Mesozoic Mammals. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001571]