Panbiogeographical analysis of the shark genus Rhizoprionodon (Chondrichthyes, Carcharhiniformes, Carcharhinidae).

The distributional patterns of the seven species of Rhizoprionodon were analysed using the panbiogeographical method of track analysis. The individual tracks of Rhizoprionodon suggest that the genus is mainly an Indian-Atlantic Ocean group. Five generalized tracks were found: (1) Caribbean, defined by R. porosus and R. terraenovae; (2) eastern coast of South America, defined by R. porosus and R. lalandei; (3) Indian Ocean, defined by R. acutus and R. oligolinx; (4) north-western Australia, defined by R. acutus, R. oligolinx and R. taylori; (5) north-north-eastern Australia, defined by R. acutus and R. taylori. Only R. longurio was not included in any generalized track, and its distribution is restricted to the eastern Pacific Ocean. Two biogeographical nodes were found at the intersection of the generalized tracks 1 and 2 (Caribbean Sea) and generalized tracks 4 and 5 (north Australia). The generalized tracks overlap with those found in several unrelated marine taxa. Overall, the generalized tracks are associated with warm currents. The biogeographical nodes found (Caribbean and Australian) are coincident with the global distribution of mangroves.

Comparative ontogenetic shape changes in the skull of Caiman species (Crocodylia, Alligatoridae).

Ontogenetic shape changes in the skull of three species of the genus Caiman (C. latirostris, C. sclerops, and C. yacare) are compared by geometric morphometrics for three-dimensional configurations (the least-squares analysis). The technique for obtaining the landmark coordinates is a simplification of the algorithm for multidimensional scaling. The ontogenetic nonlinear shape changes are similar in the three species but occur in a lesser extent in C. latirostris. These seem to be correlated with functional changes in the skull. The uniform shape change corresponds to an elongation of the skull, dorsoventral flattening, and lateral compression in C. sclerops and C. yacare. There is some lateral broadening in C. latirostris. Differences in the ontogenetic processes probably cause the differences in diet observed between C. latirostris and the other two species. Neotenic evolution seems to have acted in the skull of C. latirostris, and a posterior amplification of the early divergence led to a repatterning of the shape ontogenetic trajectory in this species. J. Morphol. 231:53-62, 1997. © 1997 Wiley-Liss, Inc.