A new Miocene baleen whale from the Peruvian desert

Abstract

The Pisco-Ica and Sacaco basins of southern Peru are renowned for their abundance of exceptionally preserved fossil cetaceans, several of which retain traces of soft tissue and occasionally even stomach contents. Previous work has mostly focused on odontocetes, with baleen whales currently being restricted to just three described taxa. Here, we report a new Late Miocene rorqual (family Balaenopteridae), Incakujira anillodefuego gen. et sp. nov., based on two exceptionally preserved specimens from the Pisco Formation exposed at Aguada de Lomas, Sacaco Basin, southern Peru. Incakujira overall closely resembles modern balaenopterids, but stands out for its unusually gracile ascending process of the maxilla, as well as a markedly twisted postglenoid process of the squamosal. The latter likely impeded lateral (omega) rotation of the mandible, in stark contrast with the highly flexible craniomandibular joint of extant lunge-feeding rorquals. Overall, Incakujira expands the still meagre Miocene record of balaenopterids and reveals a previously underappreciated degree of complexity in the evolution of their iconic lunge-feeding strategy.

How whales used to filter: exceptionally preserved baleen in a Miocene cetotheriid

“…perpendicular to the plate surface), but 1.8 plates cm À1 if measured parasagittally, with neither estimate being entirely reliable owing to dorsoventral compression of the rack. A conservative compromise, allowing for one extra millimetre per plate to account for decay, places plate density about 2 plates cm À1higher than in most living baleen whales, but comparable to Caperea, Miocaperea, the extant rorquals Balaenoptera acutorostrata and B. borealis and, possibly, certain fossil balaenopterids (Bisconti, 2012;Young, 2012;Gioncada et al 2016;Marx & Kohno, 2016). The plates themselves are well preserved ( Fig.…”

“…A conservative compromise, allowing for one extra millimetre per plate to account for decay, places plate density about 2 plates cm −1 – higher than in most living baleen whales, but comparable to Caperea , Miocaperea , the extant rorquals Balaenoptera acutorostrata and B. borealis and, possibly, certain fossil balaenopterids (Bisconti, ; Young, ; Gioncada et al. ; Marx & Kohno, ). The plates themselves are well preserved (Fig.…”

“…; Bisconti, ; Gioncada et al. ; Marx & Kohno, ). By contrast, little is known about baleen structure and function in extinct morphotypes that substantially differ from the living species in their overall anatomy, which presents a major obstacle to understanding the evolution of mysticete feeding ecology.…”

“…Descriptions of fossilised baleen are rare, and currently restricted to specimens (e.g. fossil rorquals) that closely resemble extant whales in their morphology and, presumably, lifestyle (Esperante et al 2008;Bisconti, 2012;Gioncada et al 2016;Marx & Kohno, 2016). By contrast, little is known about baleen structure and function in extinct morphotypes that substantially differ from the living species in their overall anatomy, which presents a major obstacle to understanding the evolution of mysticete feeding ecology.…”

<i>Koristocetus pescei</i> gen. et sp. nov., a diminutive sperm whale (Cetacea: Odontoceti: Kogiidae) from the late Miocene of Peru

“…Indeed, the fossil record of vertebrates from Pisco Formation stands out for the exceptional abundance of specimens, high diversity and disparity, and remarkable quality of preservation (e.g., Hoffstetter, 1968;de Muizon, 1981de Muizon, , 1984de Muizon, , 1988de Muizon, , 1993de Muizon and DeVries, 1985;Pilleri, 1989Pilleri, -1990de Muizon and McDonald, 1995;de Muizon et al, 1999de Muizon et al, , 2002de Muizon et al, , 2003de Muizon et al, , 2004aMcDonald and de Muizon, 2002;de Muizon and Domning, 2002;Brand et al, 2004Brand et al, , 2011Esperante et al, 2008Lambert et al, 2008Lambert et al, , 2009Lambert et al, , 2010aLambert et al, , b, 2015Lambert et al, , 2017Ehret et al, 2009Ehret et al, , 2012Bianucci et al, 2010Bianucci et al, , 2016aBisconti, 2012;Lambert and de Muizon, 2013;Amson et al, 2014Amson et al, , 2015aAmson et al, , b, 2016Collareta et al, 2015Collareta et al, , 2017bGariboldi et al, 2015;Stucchi et al, 2015Stucchi et al, , 2016Gioncada et al, 2016;Marx and Kohno, 2016;Di Celma et al, 2017; A kogiid sper...…”