Interspecific variation of ontogeny and skull shape among porpoises (Phocoenidae)

Abstract

All extant members of Phocoenidae (porpoises) have been characterized as pedomorphic based on skeletal characters. To investigate the ontogenetic background for pedomorphosis and assess interspecific differences in ontogeny among phocoenids, samples of the six extant species were compared in terms of development of both epiphyseal and cranial suture fusion. Across all species, full maturity of the vertebral column was rare. Vertebral epiphyseal development did not progress so far in most Phocoena phocoena as in Phocoenoides dalli and Phocoena dioptrica. P. phocoena, Phocoena spinipinnis, Ph. dalli, and P. dioptrica, for which large series were available, were further compared in terms of ontogeny of cranial shape by three-dimensional geometric morphometrics. Ph. dalli and P. dioptrica generally showed further development of cranial sutures than the other species. Postnatal skull shape development was similar for all species studied; the majority of interspecific shape differences are present at parturition. Smaller species had a higher rate of shape development relative to growth in size than Ph. dalli and P. dioptrica, but they still showed less allometric development due to less postnatal growth. Interspecific shape differences indicate phylogenetic relationships similar to that proposed based on morphology or convergent evolution of the two pelagic species, Ph. dalli and P. dioptrica, under the scenarios suggested by recent molecular studies. A shape trend coinciding with habitat preference was detected; in species with pelagic preference the position and orientation of the foramen magnum aligned the skull with the vertebral column; the rostrum showed less ventral inclination, and the facial region was larger and more concave in lateral aspect.

Patterns and implications of extensive heterochrony in carnivoran cranial suture closure

“…Despite not sharing any specific heterochronic shifts, three of the four pinnipeds in this study (all except for O. rosmarus ) showed the lowest overall suture closure scores across carnivorans. Whether this pattern applies across the rest of Pinnipedia remains to be tested, but it raises the possibility that the transition to an aquatic lifestyle involves paedomorphosis of skeletal development, in this case manifested as low levels of suture closure, in pinnipeds, as has been previously suggested for some cetaceans (Mellor et al ., ; Galatius, ; Galatius et al ., ).…”

Sexual dimorphism of Dall's porpoise and harbor porpoise skulls

“…In this study we use geometric morphometrics to examine sexual dimorphism of skull shape in the sister species pair (Rosel et al 1995;Fajardo-Mellor et al 2006;May-Collado and Agnarsson 2006) harbor porpoise (Phocoena phocoena) and Dall's porpoise (Phocoenoides dalli). The two species occupy different habitats (Read 2002), which is also reflected in their skull morphology (Galatius et al 2011) and there are indications of different mating systems.…”

Echolocation by the harbour porpoise: life in coastal waters

“…23% in a comparison of both sexes of Californian Phocoenoides dalli and Phocoena phocoena from the inner Danish waters. In the same comparison, the skeletal structures surrounding the sound producing apparatus were relatively larger in Phocoenoides dalli (Galatius et al, 2011). Thus, judging from skull morphometrics the peak frequencies of Dall’s porpoise biosonar clicks should differ significantly from those of harbor porpoises, but they do not.…”

“…Support for the above can be derived from the diversity of species using NBHF biosonar and cranial morphometrics (Galatius et al, 2011). Dall’s porpoise has a substantially larger skull than that of the harbor porpoise; larger by ca.…”