PelodytidaeEuropean Spadefoot Toads

Last updated:

Pelodytids are smooth-skinned frogs with fossorial habits whose fossil species outnumber its extant ones. There are but two extant species in a single genus. Two or three genera are known from fossils. Distribution is disjunct, with extant species known from western Europe and the Caucasus mountains.

The commonly cited synapomorphy that characterizes the parsley frogs is the complete fusion of the astragalus and calcaneum along their entire length (this is otherwise found only in the centrolenids). Pelodytids also have a parahyoid bone in the hyoid apparatus, a character otherwise known in the Pipanura only in rhinophrynids and palaeobatrachids. Parsley frogs are further distinguished from the other pelobatoids by having presacrals I and II fused, a parahyoid bone, and three (as opposed to two) tarsalia. Characters that unite Pelodytidae with the other pelobatoids include the lack of ribs, broadly expanded sacral diapophyses, eight stegochordal presacral vertebrae with imbricate neural arches, dentate premaxillae and maxillae, inguinal amplexus, and indirect development with type IV tadpoles bearing beaks and denticles. Diploid number is 24.

The common name for pelodytids, "parsley frogs," arises from the green skin coloration of Pelodytes punctatus, which causes it to look as if it is garnished with parsley. This small (40 mm snout-vent length) European frog is agile and gracile, with large eyes. It is primarily terrestrial and nocturnal, but during the breeding season is active during the day, when males apparently call from under water. Both species of Pelodytes are fossorial. Reproductive mode is primitive, with long strings of pigmented aquatic eggs deposited in lentic water, where they hatch into feeding tadpoles.

Pelodytids have traditionally been considered archaeobatrachians, members of the paraphyletic group of primitive frogs out of which the neobatrachians evolved. Traditionally, the superfamily Pelobatoidea, to which pelodytids belong, has been considered sister to the neobatrachians. Some authors propose the use of the term Mesobatrachia to refer to the clade containing Pelobatoidea and Pipoidea, suggesting a sister relationship not between pelobatoids and neobatrachians, but between pelobatoids and pipoids. Together, the mesobatrachians and neobatrachians form a large clade referred to as Pipanura. The superfamily Pelobatoidea is widely recognized as a monophyletic group containing Pelobatidae, Pelodytidae, and Megophryidae. Synapomorphies of the Pelobatoidea include the presence of a palatine process of the maxilla, and the ossification of the sternum into a bony style. The genus Pelodytes was given family status distinct from pelobatids and megophryids because of the fused astragalus and calcaneum. Pelodytidae tenuously includes the extinct genus Propelodytes, which throws the monophyly of Pelodytidae into doubt.

Several fossils attributed to Pelodytidae are known. The extinct genus Miopelodytes, as well as the extinct species Pelodytes arevacus, both have a fused astragalus and calcaneum, while the extinct genus Propelodytes does not. Fossils are known from the Eocene through Pleistocene in Europe, and from the Miocene in North America.

Cannatella, D. 1996. Pelodytidae: Tree of Life. (Website.) http://tolweb.org/tree?group=Pelodytidae&contgroup=Salientia

Cannatella, D., L. Ford, and L. Bockstanz. 1996. Salientia: Tree of Life. (Website.) http://tolweb.org/tree?group=Salientia&contgroup=Living_amphibians

Duellman, W. E., and L. Trueb. 1986. Biology of Amphibians. Johns Hopkins University Press, Baltimore, MD.

Ford, L. S., and D. Cannatella. 1993. The major clades of frogs. Herpetological Monographs 7:94-117.

Pough, F. H., R. M. Andrews, J. E. Cadle, M. L. Crump, A. H. Savitzky, and K. D. Wells. 1998. Herpetology. Prentice-Hall, Inc., Upper Saddle River, NJ.

Zug, G. R. 1993. Herpetology: an introductory biology of amphibians and reptiles. Academic Press, San Diego.

Contributors

Heather Heying (author).

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.