Ecomorphological and Age-Related Adaptations in the Tongues of Phocoena dioptrica (Spectacled Porpoise) and Phocoena spinipinnis (Burmeister's Porpoise) (Phocoenidae: Cetacea).

Simple Summary: The tongues of vertebrates reflect their adaptations to various feeding strategies, the types of food they consume, and the environments they inhabit. In cetacean, the macro- and microanatomical aspects of the tongues of few species have been studied. Here, we analyzed, for the first time, the morphology of the tongues of two porpoise species (Spectacled and Burmeister's Porpoises; juvenile and adults), whose biology is little known. We describe a range of novel aspects related to ontogenetic morphological differences and document the finding of thermoregulatory structures and components of the immune system. Differences between juvenile and adult individuals of the same species, as well as between juveniles and adults of both species, may be related to their feeding types and/or geographical distribution. Additionally, we found a lingual vascular system, which has only been mentioned for baleen whales and the sperm whale (but never for smaller-toothed cetaceans), that may participate in the thermoregulation of these individuals. Both species have marginal papillae, but only in Burmeister's Porpoise were small taste buds, possibly vestigial, found. A better understanding of the biology of these two porpoise species will help to develop useful strategies that contribute to their protection in the near future. Vertebrates' tongues reflect part of their adaptations to diverse feeding strategies, the types of food items they eat, and the environments where they live. Our contribution was to analyze the macro- and microscopic morphology of the tongues of two porpoise species (Phocoena dioptrica and Phocoena spinipinnis; juveniles and adults), whose biology is little known. Macroscopic and microscopic studies (conventional histology, scanning electron microscopy, immunohistochemistry, and morphometry) were performed. Differences between juvenile and adult individuals of the same species, as well as between juveniles and adults of both species, were found, probably related to their feeding and/or geographical distribution. In addition, novel aspects related to ontogenetic morphological differences, thermoregulation, and immune system components were described. We found a lingual countercurrent vascular system (periarterial venous retia), only mentioned for mysticetes and Physeter macrocephalus (never for smaller odontocetes). In addition, we identified mechanoreceptors (lamellar corpuscles). Both species showed marginal papillae, but only in P. spinipinnis were small (probably vestigial) taste buds observed. Finally, lingual lymphoid aggregates were found. [ABSTRACT FROM AUTHOR]