Skull shapes of the Lissodelphininae: radiation, adaptation and asymmetry

Abstract

Within Delphinidae, the sub-family Lissodelphininae consists of 8 Southern Ocean species and 2 North Pacific species. Lissodelphininae is a result of recent phylogenetic revisions based on molecular methods. Thus, morphological radiation within the taxon has not been investigated previously. The sub-family consists of ecologically diverse groups such as (1) the Cephalorhynchus genus of 4 small species inhabiting coastal and shelf waters, (2) the robust species in the Lagenorhynchus genus with the coastal La. australis, the offshore La. cruciger, the pelagic species La. obscurus and La. obliquidens, and (3) the morphologically aberrant genus Lissodelphis. Here, the shapes of 164 skulls from adults of all 10 species were compared using 3-dimensional geometric morphometrics. The Lissodelphininae skulls were supplemented by samples of Lagenorhynchus albirostris and Delphinus delphis to obtain a context for the variation found within the subfamily. Principal components analysis was used to map the most important components of shape variation on phylogeny. The first component of shape variation described an elongation of the rostrum, lateral and dorsoventral compression of the neurocranium and smaller temporal fossa. The two Lissodelphis species were on the high extreme of this spectrum, while Lagenorhynchus australis, La. cruciger and Cephalorhynchus heavisidii were at the low extreme. Along the second component, La. cruciger was isolated from the other species by its expanded neurocranium and concave facial profile. Shape variation supports the gross phylogenetic relationships proposed by recent molecular studies. However, despite the great diversity of ecology and external morphology within the subfamily, shape variation of the feeding apparatus was modest, indicating a similar mode of feeding across the subfamily. All 10 species were similar in their pattern of skull asymmetry, but interestingly, two species using narrowband high frequency clicks (La. cruciger and C. hectori) were among the most asymmetric species, contradicting previous interpretations of odontocete skull asymmetry. J. Morphol. 277:776-785, 2016. © 2016 Wiley Periodicals, Inc.

Skull ontogeny and modularity in two species of Lagenorhynchus: Morphological and ecological implications

“…The premaxillary sac fossa displayed a stronger concavity in L. obscurus and also the temporal fossa had a more dorsal position. Some of these differences, such as those regarding rostrum length and inclination, and concavity of premaxillary sac fossa were also noted by Galatius and Goodall ().…”

“…The premaxillary sac fossa displayed a stronger concavity in L. obscurus and also the temporal fossa had a more dorsal position. Some of these differences, such as those regarding rostrum length and inclination, and concavity of premaxillary sac fossa were also noted by Galatius and Goodall (2016). Regarding the feeding apparatus, Perrin (1975) proposed that robust feeding apparatuses are advantageous in coastal waters, where available prey may be larger, more irregularly and heavily constructed than offshore.…”

Asymmetry of the nasofacial skull in toothed whales (Odontoceti)

“…As a whole, there does not seem to be a strict functional correlation between click type and skull asymmetry. This is in accordance with the findings of Galatius & Goodall () who could neither correlate the skull asymmetry of Lissodelphininae (a subfamily of the Delphinidae) unambiguously with one of the echolocator types mentioned above. One reason for this may be that the degree of asymmetry seen in the nasofacial skull of odontocetes does not exclusively reflect the anatomy of the related soft sound generator structures.…”

Vertebral Morphology in Partially Sympatric Dolphins: A 3D Approach

“…One group consisting of sister species, the Pacific white-side dolphin (Lagenorhynchus obliquidens) and the dusky dolphin, is well distinguished from the clade formed by Cephalorhynchus spp., Peale's dolphin, and the hourglass dolphin; these latter being sister species (Figure 1). Lissodelphininae species are thought to have undergone a rapid adaptive radiation during the Late Miocene/Pliocene (∼5-3.5 Ma) in the South Atlantic Ocean, mostly attributed to differential adaptation to local habitats and to dispersal processes (Banguera-Hinestroza et al, 2014;Galatius and Goodall, 2016;McGowen et al, 2020). In this study, we suggest that morphological differences in the vertebral column of these closely related and partially sympatric species might be accordingly related to selective pressures arising from differential foraging strategies and preferred habitats, yielding a direct impact on each species biomechanical properties and behavioral performance.…”