Anuran

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 an Anuran, but changed still further, and thus laid the foundation of the higher classes.

Inactivity may dominate an anuran’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.

Often the anuran gives a release call, a signal to other anurans 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 an anuran in response to predation, but either call may serve to startle a clinician momentarily, by which time the anuran may escape.

As a further illustration, we may take the results of experiments in which a Urodele organiser (from Triton alpestris) is grafted into an Anuran embryo (Bufo vulgaris).

It is well known that an anuran 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will never turn into its adult form if the respective endogenous metamorphic hormones, thyroxine and ecdysone, were withdrawn or prevented from reaching the target tissues.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 an anuran (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.