Frogs give new insights into vertebrate novelties

Abstract

We recognize a frog largely because of its shape—short body, long legs, and absence of a tail. These features are modifications of the “vertebrate body plan,” a head, a body, four appendages, and a tail. However, evolving lineages of vertebrates have modified that theme in incredibly diverse ways. Research by Senevirathne et al. (1) shows that there are exciting ways to explore the origin of vertebrate novelties. The features that characterize vertebrates are innovations, new structures. The head is “new,” a product of the inception of neural crest cells streaming into the “head” region and forming new structures (e.g., jaws, gill bars, teeth, and the like) (2, 3); vertebrae—the fundamental postcranial segmental units for which the subphylum is named—are new, because bone is “new” and restricted to vertebrates, invented by the inception of mineralization in specific mesodermal sites (4). Modifying the body plan is the stuff of evolution and the great biodiversity of vertebrate animals. Concepts about developmental processes, adaptation, and many other features emerged as consequences of the study of body plan diversification. Vertebrate animals have been the foci of study for hundreds, if not thousands, of years. Aristotle (5, 6) referred to many vertebrates, including frogs, in his discussions of both animal structure and the essence of life, from which diversity arose. The evolution of the first terrestrial vertebrates (class Amphibia, subphylum Vertebrata) has therefore received considerable attention! The closest relatives to frogs (Anura, “no tail”) are salamanders (Caudata, “tailed”), which have followed more closely the ancestral vertebrate (tetrapod) plan of having a moderately long body, four relatively short limbs of nearly the same length, and a tail, and caecilians (Gymnophiona, “naked snake”), elongate, limbless, and usually tailless amphibians. The oldest known salamander, frog, and caecilian fossils are Jurassic (some 200 Ma) (7⇓–9 … [↵][1]1Email: mhwake{at}berkeley.edu. [1]: #xref-corresp-1-1