POSTEMBRYONIC ONTOGENY OF THE SPADEFOOT TOAD, SCAPHIOPUS-INTERMONTANUS (ANURA, PELOBATIDAE) - SKELETAL MORPHOLOGY

Postembryonic skeletal ontogeny of the pelobatid frog Scaphiopus inter montanus is described based on a developmental series of cleared-and-s tained, whole-mount specimens. The focus is on laboratory-reared indiv iduals fed a herbivorous diet as larvae. Although there is variation i n the timing of ossification of individual skeletal elements relative to developmental stages based on external morphological criteria, the sequence of skeletal development generally is conservative. Compared w ith its close relative, S. bombifrons, ossifications that occur during prometamorphosis tend to be slightly delayed in S. intermontanus; how ever, cranial bones that ossify during late metamorphic climax in S. i ntermontanus are delayed until postmetamorphosis in S. bombifrons. The differences in timing between the two species are consistent, however , with differences observed between two developmental series of S. int ermontanus raised at two different temperatures. Noteworthy features o f skeletal development in S. intermontanus include: 1) presence of pal atine ossifications that form from independent centers of ossification and soon fuse with the postnarial portion of the vomers to form the c ompound vomeropalatine bones; 2) compound sphenethmoid that may arise from four or more endochondral centers of ossification and one dorsal, dermal center of ossification; and 3) presence of transverse processe s and vestigal prezygapophyses on the first postsacral vertebra. The m orphology of the larval orbitohyoideus and interhyoideus muscles is co mpared. The record of skeletal ontogeny and muscle morphology presente d herein for the herbivorous larval morph can serve as a baseline for comparisons with the ontogeny of the carnivorous larval morph of Scaph iopus. (C) 1998 Wiley-Liss, Inc.