Ontogeny of a new Palaeogene pipid frog from southern South America and xenopodinomorph evolution

摘要: Lacustrine interbeds of a volcaniclastic succession that crops out extensively in north-western Patagonia yielded impressions articulated, nearly complete, frogs different ontogenetic stages including tadpoles. The stratigraphic position the fossil bearing beds this sequence and evaluation palaeofloristic data against record climatic change southern high latitudes support middle Eocene – early Oligocene age for frogs. These are described as new genus species resembles late Palaeocene ‘Xenopus’ romeri from Brazil, differs S. pascuali Patagonia, relatively wide short braincase fused first two presacral vertebrae. However, unlike ‘X.’ romeri, nasals paired bear short, but distinct, rostral processes. A parsimony analysis based on 49 adult osteological characters demonstrates these South American pipids closely related to xenopodines, restricted African continent today, although their interrelationships remain poorly resolved. Interpretation exemplified by specimens suggests developmental pattern more similar extant xenopodines than ontogeny distant pipoid relatives. Moreover, similarity between larvae those Xenopus Silurana strongly habits. Many larval features may be considered caenogenetic, i.e. specializations tadpoles obligate, microphagous suspension feeders. © 2003 Linnean Society London, Zoological Journal Society, 2003, 139, 439-476.