Evolution of Life Cycles in Early Amphibians

Abstract

Many modern amphibians have biphasic life cycles with aquatic larvae and terrestrial adults. The central questions are how and when this complicated ontogeny was established, and what is known about the lives of amphibians in the Paleozoic. Fossil evidence has accumulated that sheds light on the life histories of early amphibians, the origin of metamorphosis, and the transition to a fully terrestrial existence. The majority of early amphibians were aquatic or amphibious and underwent only gradual ontogenetic changes. Developmental plasticity played a major role in some taxa but was restricted to minor modification of ontogeny. In the Permo-Carboniferous dissorophoids, a condensation of crucial ontogenetic steps into a short phase (metamorphosis) is observed. It is likely that the origin of both metamorphosis and neoteny falls within these taxa. Fossil evidence also reveals the sequence of evolutionary changes: apparently, the ontogenetic change in feeding, not the transition to a terrestrial existence per se, made a drastic metamorphosis necessary.

New specimen of <i>Cacops woehri</i> indicates differences in the ontogenetic trajectories among cacopine dissorophids

“…The locality is considered to preserve an upland fauna, with the infills of the extensive cave system serving as natural traps for the vertebrate fauna inhabiting this upland environment (Reisz et al, 2009). The locality therefore complements data from wellknown Lower Permian lowland lacustrine localities (Reisz et al, 2009;Schoch, 2009). Within the Dolese fauna, members of the clade Dissorophoidea represent an important component of the tetrapod community with at least nine taxa known from this locality.…”

“…Amphibamids and branchiosaurids are represented by very small, miniaturized taxa which share a large number of characters with modern amphibians. While branchiosaurids were highly aquatic, amphibamids also include forms that were likely very terrestrial as metamorphosed adults (Schoch, 2009(Schoch, , 2010. Because of their central role in the controversial discussions surrounding the origin of modern amphibians, amphibamids and branchiosaurids have received much attention in the literature during the past 30 years, resulting in a quite detailed understanding of their diversity, biology, and phylogenetic relationships (Anderson and Bolt, 2013;Anderson et al, 2008a;Bourget and Anderson, 2011;Boy, 1972Boy, , 1986Boy, , 1987Boy and Sues, 2000;Fröbisch and Reisz, 2008;Fröbisch and Schoch, 2009;Huttenlocker et al, 2007;Schoch, 2004;Schoch and Milner, 2008;Schoch and Rubidge, 2005;Werneburg, 2001Werneburg, , 2002Werneburg, , 2003.…”

“…Unlike the small Xerodromes, olsoniforms are represented by rather large forms, some of which were heavily armored. They were likely highly terrestrial and predacious as post-metamorphic adults with an almost amniote-like ecology (Reisz et al, 2009;Schoch, 2009). Although they have been known from classic Permian deposits for over a century (Carroll, 1964;Demar, 1966Demar, , 1967Demar, , 1968Romer, 1947;Williston, 1910Williston, , 1911, they did not receive much attention for some decades, and many taxa remain in need of taxonomic revision.…”

“…For some Paleozoic amphibians, extensive ontogenetic series are preserved, providing important insights into their development and growth (Fröbisch et al, 2010;Schoch, 2004Schoch, , 2009Schoch, , 2014Witzmann and Pfretzschner, 2003;Witzmann and Schoch, 2006a, b). In particular, thanks to the excellent preservational conditions in the lakes that these taxa inhabited, micromelerpetontid and branchiosaurid dissorophoids have been studied extensively.…”

“…In particular, thanks to the excellent preservational conditions in the lakes that these taxa inhabited, micromelerpetontid and branchiosaurid dissorophoids have been studied extensively. Because of their phylogenetic significance amphibamid ontogeny (Schoch, 2009) has also attracted attention. However, much less is known about the ontogeny of the olsoniforms.…”