Development of the cranium and paired fins in Betta splendens (Teleostei: Percomorpha): Intraspecific variation and interspecific comparisons.

The development of the chondrocranium and the relative timing of ossification of the osteocranium is described in the teleost fish Betta splendens from a large series of cleared and differentially stained specimens. General trends in ossification patterns are examined from developmental, phylogenetic, and functional contexts. As in many other vertebrates, dermal bones form before cartilage bones. Ossification sequence conforms to functional need in a very general way, but there are many inconsistencies in the details of order. For example, some bones that are directly involved in feeding ossify no earlier than bones more indirectly involved. Comparisons of ossification sequence within specific cranial regions are made among Betta splendens, Oryzias latipes (Atherinomorpha), and Barbus barbus (Ostariophysi) within a phylogenetic framework. Many evolutionary changes in relative sequence of ossification are evident within regions among these taxa, yet many other sequences are conserved. The logistic difficulty of comparing entire cranial ossification sequences (vs. regional sequences) makes evident the need for new methods for identifying and quantifying sequence changes. Intraspecific variation in order of ossification is described for the first time in teleost fishes. To the extent that ossification sequence varies intraspecifically, conclusions drawn from previous interspecific comparisons are compromised. Understanding the importance of changes in ossification order within and among taxa will require experimental, functional, and evolutionary work. © 1996 Wiley-Liss, Inc.