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Temnospondyl life cycles

From: Ben Creisler

A new online paper:

Rainer R. Schoch (2014)
Life cycles, plasticity and palaeoecology in temnospondyl amphibians.
Palaeontology (advance online publication)
DOI: 10.1111/pala.12100

In the largest early tetrapod clade, the temnospondyls, ontogenies
were diverse and quite distinct from the life cycles of extant
amphibians. Three well-studied clades exemplify the diversity of these
long-extinct ontogenies, here analysed with respect to their bearing
on developmental plasticity, reaction norms and evolution.
Sclerocephalus readily adjusted by means of developmental evolution to
different lake environments. In addition, plasticity (reaction norm)
played a significant role, apparent both morphologically and by
altered developmental traits. Size increase and extension of the
ontogenetic trajectory gave larger predators, a phenomenon also found
in the dissorophoid Micromelerpeton. Whereas Sclerocephalus was
throughout preying on the same fishes, Micromelerpeton was able to fit
into different trophic levels. In the branchiosaurid Apateon, a
biphasic life cycle was established, with metamorphosis producing a
terrestrial morph in some species; truncation of the ontogenetic
trajectory gave a sexually mature larva as an alternative morph
(neoteny). Plasticity was high in the larval morphs, permitting
neotenes to live as filter feeders or small carnivores. Fine-tuning of
development permitted Apateon populations to adjust to specific lake
properties and readily change from a filter-feeding to carnivorous
mode of life. In the nonmetamorphosing Triassic Gerrothorax,
morphology was extremely conserved, but histology reveals much
plasticity at the microscopical level, correlating with fluctuating
salinity and water energy. In responding to environmental fluctuations
by enhanced plasticity, the studied temnospondyls managed to populate
lakes inhabitable to other tetrapods and fishes.