The fact that the higher Batrachia go on metamorphosing until several of their structures are so perfect as to require but the gentlest modification to make them fit for the Mammal, does not require one to suppose that the Toad and the Frog lie in the direct route from the Ichthyic to the Mammalian types. That such power of variation, such aptitude for transformation exists in these essential but metamorphic Fish, suggests the probability that some of the very earliest of the Amphibia, filial perhaps to forms far lower than the Lamprey, did not stop at the last metamorphic stage of anAnuran, but changed still further, and thus laid the foundation of the higher classes.
2001, George R. Zug, Laurie J. Vitt, Janalee P. Caldwell, “Thermoregulation, Performance, and Energetics”, inHerpetology: An Introductory Biology of Amphibians and Reptiles, 2nd edition, San Diego, Calif.; London:Academic Press,→ISBN,page191, column 1:
Inactivity may dominate ananuran’s life.Spea hammondii in the deserts of southwestern North America spend >90% of their life inactive; they appear explosively and breed with the first heavy summer rains, then feed for 2–3 weeks before becoming inactive for another year.
2006, Kevin M. Wright, “Overview of Amphibian Medicine”, in Douglas R. Mader, editor,Reptile Medicine and Surgery, 2nd edition, St. Louis, Mo.:SaundersElsevier,→ISBN,page947:
Often theanuran gives a release call, a signal to otheranurans that it is either not sexually receptive or is of the wrong sex to be amplexed. The release call may sound similar to a distress call, a vocalization emitted by ananuran in response to predation, but either call may serve to startle a clinician momentarily, by which time theanuran may escape.
As a further illustration, we may take the results of experiments in which a Urodele organiser (fromTriton alpestris) is grafted into anAnuran embryo (Bufo vulgaris).
1971, J. R. Tata, “Protein Synthesis during Amphibian Metamorphosis”, inA[ron] A[rthur] Moscona, Alberto Monroy, editors,Current Topics in Developmental Biology, volume 6, New York, N.Y.; London:Academic Press,→ISBN,page79:
It is well known that ananuran tadpole or an insect larva will never turn into its adult form if the respective endogenous metamorphic hormones, thyroxine and ecdysone, were withdrawn or prevented from reaching the target tissues.
[I]njection of urodele DNA into ananuran (frog) egg produces an extra "balancer" (i.e., protrusion on the chin of the embryo which may or may not be a real balancer), but so does injection of the DNA of this anuran into its own egg.
Anura (frog) on Wikipedia.Wikipedia