August 31 , 2016

Anurans are characterized by a biphasic lifecyle, consisting of radically different larval (“tadpole”) and adult (“frog”) morphs. Although the fossil record for tadpoles is more limited compared to the record for frogs, it is more extensive and informative than generally appreciated. The tadpole fossil record consists exclusively of body fossils, often in the form of skeletons with associated soft tissues. Tadpole fossils are known from more than 40 localities of Early Cretaceous (late Berriasian – early Valanginian) to late Miocene age: 24 localities (Early Cretaceous and Cenozoic) in Europe, mostly from deposits of middle Eocene – Miocene age in central and southern Germany and northern Czech Republic; four or five localities (Miocene) in Asia; five localities (latest Cretaceous – Miocene) in continental Africa; and three localities each on the Arabian Plate (Early Cretaceous and Oligocene) and in North America (Eocene) and South America (Campanian and Paleogene). Fossil tadpoles are assignable to at least 16 species belonging to 13 genera and five (possibly as many as seven) families. The tadpole fossil record is dominated by pipoids (Pipidae, Palaeobatrachidae, Rhinophrynidae, and basal pipimorphs), but also includes representatives of Pelobatidae and Ranidae, and possibly Pelodytidae and ?Discoglossidae sensu lato. The tadpole fossil record is limited to lacustrine deposits, yet a significant number of localities in those deposits have yielded size series of tadpole body fossils that have proven informative for examining ontogenetic patterns. Other body fossils suggested at various times to be tadpoles are reviewed: the enigmatic Middle Devonian Palaeospondylus is a fish; the unique holotype specimen of the basal Triassic proto-frog Triadobatrachus is a fully transformed individual, not a metamorphic tadpole; a fossil from the Middle or Late Jurassic of China originally described as a tadpole is an insect; a small skeleton from the Early Cretaceous of Israel originally reported as a tadpole likely is not; and the identity of a fossil preserved within a piece of Miocene Dominican amber and said to be a tadpole hatching from an egg cannot be verified. Extant tadpoles are known to excavate shallow depressions (so-called tadpole nests or holes) in finegrained sediments at the bottom of shallow, low energy water bodies; however, there is no convincing evidence for those structures or any other traces attributable to the activities of tadpoles in the fossil record.

James Gardner (2016)
The fossil record of tadpoles.
Fossil Imprint 72(1-2): 17–44