Nasal compartmentalization in Kogiidae (Cetacea, Physeteroidea): insights from a new late Miocene dwarf sperm whale from the Pisco Formation

Abstract

Facial compartmentalization in the skull of extant pygmy whales (Kogiidae) is a unique feature among cetaceans that allows for the housing of a wide array of organs responsible for echolocation. Recent fossil findings indicate a remarkable disparity of the facial bone organization in Miocene kogiids, but the significance of such a rearrangement for the evolution of the clade has been barely explored. Here we describe Kogia danomurai sp. nov., a late Miocene (c. 5.8 Ma) taxon from the Pisco Formation (Peru), based on a partially preserved skull with a new facial bone pattern. Phylogenetic analysis recovers K. danomurai as the most basal representative of the extant genus Kogia, displaying a combination of derived (incipiently developed and excavated sagittal facial crest) and plesiomorphic features (high position of the temporal fossa, and antorbital notch not transformed into a narrow slit). Furthermore, when compared with the extant Kogia, the facial patterning found in K. danomurai indicates differential development among the facial organs, implying different capabilities of sound production relative to extant Kogia spp. Different facial bone patterns are particularly notable within the multi-species kogiid assemblage of the Pisco Formation, which suggests causal connections between different patterns and feeding ecologies (e.g. nekton piscivory and benthic foraging). At c. 5.8 Ma, K. danomurai was part of a cetacean community composed of clades typical of the late Miocene, and of other early representatives of extant taxa, a mixture probably representing an initial shift of the coastal faunas toward the ecosystem dynamics of the present-day south-eastern Pacific.

Late Neogene evolution of the Peruvian margin and its ecosystems: a synthesis from the Sacaco record

“…Delphinus, Lagenorhynchus, and the pygmy sperm whale Kogia (Fig. 8; Benites-Palomino et al 2021). Some marine birds (Spheniscus, Phalacrocorax) and the rorqual Balaenoptera occur since ~ 10 Ma (Figs.…”

Sperm whales (Physeteroidea) from the Pisco Formation, Peru, and their trophic role as fat sources for late Miocene sharks

“…However, in sperm whales, an additional large concentration of fats and lipids occurs in the hypertrophied nasal complex, thus improving the floatability of the carcass, constituting an easy source of nutrients for scavengers. In the case of Scaphokogia , due to its highly derived nasal anatomy [26,29], this would especially have been the case, and as such, explains the observed bite marks. Carcasses from these sperm whales would have constituted easily accessible fat sources for sharks scavenging near the ocean surface.…”

“…In Scaphokogia , the skull exhibits a highly derived cranial repatterning interpreted as due to the presence of the remarkably developed forehead organs (e.g. the melon and spermaceti; figure 2 a–c ), as indicated by the deeply enlarged supracranial basin [26,29]. As in other Kogiidae, the dorsal surface of the rostrum most likely received most of the melon organ [26,27], a fatty organ rich in lipids [30,46].…”

“…the melon and spermaceti) are rich in lipids and fatty oils, being heavily regulated by the surrounding facial muscles [33]. In the case of kogiids, the supracranial basin has undergone a secondary division or compartmentalization due to the presence of a sagittal facial crest, resulting in the reduction of some organs and the development of additional soft-tissue structures such as the 'vocal cap' on the right, the spermaceti and the left package of facial muscles [29,34,35].…”

The tempo of cetacean cranial evolution

“…Members of both families have heightened facial asymmetry in the premaxilla, maxilla, and where present, nasals. 17,47 Filter feeders, all of which are edentulous, baleen-bearing mysticetes, displayed the lowest evolutionary rates in individual cranial bones, with the exception of the maxilla and zygo-squamosal (Figure S6A). These bones endured a massive functional change from raptorial feeding in the early toothed mysticetes to filter feeding in the crownward mysticetes 48,49 with change concentrated on a few basal branches, followed by little change within the clade itself.…”