Tetrapod Evolution

by

Michel Laurin

• LAST REVIEWED: 27 February 2019
• LAST MODIFIED: 27 February 2019
• DOI: 10.1093/obo/9780199941728-0027

Introduction

Tetrapods include all extant limbed vertebrates (and those that lost limbs, such as gymnophionans and snakes) and many or all extinct ones (depending on the adopted definition). This large clade is represented by over 21,000 extant species: more than 7,000 species of extant amphibians and more than 13,000 species of amniotes, which include mammals and reptiles, the latter also including birds in many recent taxonomies. The origin of tetrapods can be followed back into the Early Devonian (419–393 million years ago), shortly after tetrapodomorphs (as stem-tetrapods are called) diverged from dipnomorphs (the largest clade that includes lungfishes but not tetrapods). The first tetrapodomorphs retained paired fins, but by the Middle Devonian (393–383 million years ago), the first limbed vertebrates had appeared. The tetrapod crown (the smallest clade that includes lissamphibians and amniotes) first appears in the fossil record in the Early Carboniferous. The group subsequently diversified fairly quickly and occupied a diversity of habitats (saltwater, freshwater, and terrestrial) by the Early Carboniferous. Amniotes appeared no later than about 317 million years ago (Ma), although they remained a minor component of the terrestrial biota until the Early Permian. The origin of turtles remains contentious, but the first undisputed stem-turtle and lepidosauromorphs (squamates, Sphenodon, and extinct relatives) are known from the Triassic, whereas archosauromorphs (which include birds and crocodiles) can be traced back to the Late Permian. Much of what we know about early tetrapod evolution is based on the fossil record, but our understanding of the subsequent evolution of the group has progressed tremendously in recent years through molecular phylogenetics. This article is organized into thematic sections, such as tetrapod origins, biodiversity evolution, and mass extinction events, as well as systematic sections that deal with various clades, especially (but not only) extant ones. Throughout, the emphasis has been on recent papers because their bibliographies usually include references to older, influential publications, although some older, very important papers are covered too.

General Overviews

There are no textbooks on tetrapods specifically, probably because there are strong traditions to publish books on vertebrates as a whole, or about herpetology, ornithology, or mammalogy. Among books on vertebrates, Benton 2014 provides an accessible treatment of tetrapod history through the fossil record, while Carroll 1988 provides a more detailed but less up-to-date account. Pough, et al. 2004 discusses the ecology and evolution of all amphibians and reptiles, whereas Duellman and Trueb 1986 provides similar data on amphibians alone, with some emphasis on morphology. Wilson and Reeder 2005 is the most comprehensive and widely used reference about nomenclaturally valid mammalian taxa. The evolution of birds in the Mesozoic is covered in detail in Chiappe and Witmer 2002. Wolff 1991 provides a thorough overview of vertebrate anatomy and function, and evolution.

• Benton, Michael J. 2014. Vertebrate palaeontology. 4th ed. Chicester, UK: Wiley-Blackwell.

  Perhaps the most up-to-date vertebrate paleontology textbook currently available. Like most textbooks on vertebrate paleontology, it emphasizes tetrapods, especially their phylogeny, osteology, and evolution. First published in 1990 (London: Chapman & Hall).

• Carroll, Robert L. 1988. Vertebrate paleontology and evolution. New York: W. H. Freeman.

  Although less up to date than Benton 2014, this book gives more anatomical descriptions and illustrations. The book emphasizes the origins of extant taxa and covers both extinct and extant vertebrates.

• Chiappe, Luis M., and Lawrence M. Witmer, eds. 2002. Mesozoic birds: Above the heads of dinosaurs. Berkeley: Univ. of California Press.

  This edited book reviews the origin of birds and their early evolution, in the Mesozoic. Its chapters are written by specialists of early birds and cover a range of topics, such as the fossil record of footprints, feathers, and bone histology, but it emphasizes the anatomy, phylogeny, and paleobiology of Mesozoic birds. Available for purchase online.

• Duellman, William E., and Linda Trueb. 1986. Biology of amphibians. New York: McGraw-Hill.

  This textbook gives a wealth of morphological, ecological, behavioral, life history, and physiological data on all extant amphibians. Its evolution section also deals with presumed Paleozoic relatives of extant amphibians and with the phylogeny of extant amphibians, and it lists recognized taxa.

• Pough, F. Harvey, Robin M. Andrews, John E. Cadle, Martha L. Crump, Alan H. Savitzky, and Kentwood D. Wells. 2004. Herpetology. 3d ed. Upper Saddle River, NJ: Prentice Hall.

  Gives a thorough coverage of extant amphibians and reptiles (in the traditional sense; birds are excluded) and provides an extensive bibliography of all relevant topics. In addition to topics covered in Duellman and Trueb 1986, it includes a chapter on conservation (pp. 595–634), which has become a major research topic.

• Wilson, Don E., and DeeAnn M. Reeder, eds. 2005. Mammal species of the world: A taxonomic and geographic reference. 2 vols. 3d ed. Baltimore: Johns Hopkins Univ. Press.

  This book, along with the corresponding website, lists all valid extant mammalian taxa along with their authorship and synonymy. It also provides a simplified taxonomy (equivalent to a phylogeny with many fairly large polytomies), along with a history of the taxonomy of mammals.

• Wolff, Ronald G. 1991. Functional chordate anatomy. Lexington, MA: D. C. Heath.

  This book gives a detailed, abundantly illustrated account of vertebrate comparative anatomy. Its perspective is largely functional, with two consecutive chapters (pp. 225–318) devoted to locomotion, but the evolutionary aspects are pervasive because the adaptive value of structure is emphasized. Developmental, historical, and technical aspects are briefly covered.