A new balaenopterid species from the Southern North Sea Basin informs about phylogeny and taxonomy of Burtinopsis and Protororqualus (Cetacea, Mysticeti, Balaenopteridae)

Abstract

Background An extensive radiation can be inferred among balaenopterid mysticetes in the last 10 million years based on a rich fossil record. Many extinct genera and species have been established in the past by the study of fossil rorquals from northern and southern hemispheres. In many cases, the new fossils are used to create new genera. However, in very recent times, new species of known genera have been described that help our understanding of the speciation processes and the biogeography of these whales. Here, a new species of balaenopterid whales is described in order to better understand the past diversity of Balaenopteridae and to analyze its paleobiogeographical implications. As the new species closely resembles a taxon established in the 19th century (i.e., Burtinopsis), a detailed analysis of this taxon was necessary to support the new taxonomic statements of this article. Methods A new partial skeleton including skull and earbones is described and compared to an extended sample of living and fossil mysticete species. A phylogenetic analysis including 355 character states scored in 88 taxa was performed to understand its relationships within the genus Protororqualus, to allow paleobiogeographic inferences and to better understand the relationships of Protororqualus within Balaenopteridae. Maximum parsimony analyses of character evolution were performed to understand morphological transformations within Balaenopteridae. The revision of Burtinopsis was carried out based on detailed descriptions and comparisons of the type materials that were figured and measured. Results Protororqualus wilfriedneesi sp. nov. was established based on a comparative analysis of the skull and earbone morphology. The specimen is dated back to the Zanclean (Lower Pliocene, between c. 5.3 and 3.6 Ma). A taphonomical study of the holotype skeleton revealed evidence of interactions with sharks and fishes before the definitive burial of the carcass. Based on the phylogenetic analysis, the monophyly of the genus Protororqualus was confirmed. Protororqualus wilfriedneesi sp. nov. was more derived than Protororqualus cuvieri suggesting that it resulted from an invasion of the North Sea Basin (and the North Atlantic ocean) from the Mediterranean basin. Several specimens from western and eastern sides of the Atlantic Ocean are described that suggest that Protororqualus wilfriedneesi had a trans-Atlantic distribution in the Pliocene.

The tympanoperiotic complex of the blue whale, Balaenoptera musculus

“…Only a slight dorsal projection of the anterior process is observed in the Miocene periotic MuMAB 240508 (Bisconti et al, 2022) representing one of the largest fossil balaenopterid ever described. The lack of the median promontorial groove is typical of a group of extant and fossil balaenopterids including Balaenoptera , Megaptera , Marzanoptera tersillae (Bisconti, Pellegrino, & Carnevale, 2021), and Protororqualus wilfriedneesi (Bisconti & Bosselaers, 2020). Given the scattered positions of these species in the phylogenies of mysticetes provided in different articles (Boessenecker, 2013; Marx & Kohno, 2016), it is possible that the loss of the median promontorial groove occurred in different balaenopterid lineages and became fixed in the modern Balaenoptera clade.…”

“…Among extant balaenopterid species, the medially concave outline of the involucrum in dorsal view is shared by the blue whale and Balaenoptera borealis . Several fossil balaenopteroids show this character, for example, Protororqualus wilfriedneesi (Bisconti & Bosselaers, 2020), IRSNB M.795, and 797 (“ Balaenoptera ” rostratella ).…”

“…A raised dorsal surface of the periotic may correspond to the primitive condition in thalassotherian mysticetes, as it is observed in extinct genera of early diverging thalassotherians like Parietobalaena , Atlanticetus , and Isanacetus (see Kellogg, 1968a; Bisconti, Damarco, Pavia, et al, 2021; Kimura & Ozawa, 2002 for illustrations), but it is then lost in more advanced cetotheriids like Herpetocetus and Metopocetus (see El Adli et al, 2014; Kellogg, 1968b for illustrations). The distribution of the dorsal protrusion in periotics of early diverging balaenopterids is apparently irregular as it is seen in Plesiobalaenoptera quarantellii , but not in Protororqualus wilfriedneesi and Fragilicetus velponi (see Bisconti & Bosselaers, 2020, 2016 for illustrations). Putative fossil balaenopterid specimens published by Van Beneden (1882) show dorsal protrusions on the central portion of the periotic that could be compatible with the morphology described in the present paper.…”

“…The present phylogenetic analysis is based on the character descriptions and coding provided by Ekdale et al (2011), and represents an expansion of previous studies on mysticete earbone morphology and development published earlier (Bisconti, 2001; Geisler & Luo, 1996, 1998; Luo & Gingerich, 1999). Additional works dealing with mysticete tympanoperiotic morphology have been published in recent years (Bisconti et al, 2022; Park, Evans, et al, 2017) focusing on fossil specimens and demonstrating that, in paleontological works, periotics and tympanic bullae play major roles in deciphering the phylogenetic relationships of extant and extinct baleen whales (Bisconti et al, 2022; Bisconti & Bosselaers, 2020; Bisconti, Damarco, Pavia, et al, 2021; Bisconti, Pellegrino, & Carnevale, 2021; Park, Marx, et al, 2017; Tsai & Boessenecker, 2017; Tsai & Fordyce, 2016).…”