Dolphins and porpoises have complex pigmentation patterns. A terminology is devised for the complicated pattern on Delphinus delphis, and is applied to related species. A Stenella–Delphinus species group is recognized, with species which can be segregated into four pigmentation pattern types: STRIPED, CRISSCROSS, SADDLED, and SPOTTED. Morphological derivations indicate that saddled is like simple countershading; could independently have given rise to striped, spotted, or crisscross patterns; and is thus inferred to be the most generalized pattern of the four. Crisscross pattern is the most complex, possibly the most specialized, and occurs only on Delphinus. Other morphological evidence from rostral grooves and cranial air sinuses likewise indicates that Delphinus is more specialized than Stenella. The saddled pattern on Stenella is thus generalized and probably also primitive within the Delphinidae.An overlook of other delphinid species confirms that the saddled pattern is generalized and probably primitive. The Lissodelphinae show a generalized pattern; that of the Orcininae can be related to it. Species of the genus Lagenorhynchus show a gradation in the extent and increasing complexity of the dorsal flank blaze from L. obscurus and L. australis through L. obliquidens, L. albirostris, and L. cruciger to L. acutus. The two allopatric species L. cruciger and L. acutus are both specialized in the subdivision of the flank patch. Selection for blazes dorsoanteriorly on the trunk resulted in extension of flank blazes in Lagenorhynchus, of thoracic blazes in Stenella. L. acutus and D. delphis, among the most specialized representatives of genera Lagenorhynchus and Delphinus, respectively, independently evolved a yellow-brown side patch—it is on the flank of the former, on the thorax of the latter. The Cephalorhynchinae show patterns related to saddled, and perhaps paralleled the Orcininae in pigmentation trends. Cephalorhynchus heavisidei appears to be a mimic of Orcinus orca. C. commersoni and the allopatric phocoenid Phocoenoides truei appear to be convergent—both are disruptively pigmented in the same way. Additional pigmentation types recognized are UNIFORM, LOBED, and DISRUPTIVE.In the Stenella–Delphinus species group: the saddled pattern is possibly for obliterative shading through counterlighting for concealment; the striped pattern is possibly for disguise through disruptive pigmentation and camouflage; the spotted pattern on a countershaded base is possibly for camouflage by resemblance to background; and the crisscross pattern is possibly for disguise through disruptive pigmentation, and camouflage by countershading and shadow mimicry. On most delphinids, eye patches, bridle stripes, and lip patches serve to mask eyes, blowhole, and mouth. The thoracic patch may be a false shadow to conceal young swimming in echelon formation.Striped or Euphrosyne dolphins of Pacific and Atlantic waters are conspecific. Distinct subspecies of Stenella caeruleoalba are disallowed as yet unproved.
Differentiable Patch Selection for Image Recognition
