A new small, mesorostrine inioid (Cetacea, Odontoceti, Delphinida) from four upper Miocene localities in the Pisco Basin, Peru

Abstract

The moderately rich past diversity of the superfamily Inioidea (Cetacea, Odontoceti) in both the Atlantic and Pacific oceans contrasts with the present survival of a single genus (Inia, Amazon river dolphin, family Iniidae) in freshwater deposits of South America and of a single species (Pontoporia blainvillei, franciscana, family Pontoporiidae) along the eastern coast of that continent. However, part of the late Miocene -Pliocene inioid fossil record consists of relatively fragmentarily known species, for which systematic affinities remain poorly understood. Based on a sample of six cranial specimens from lower upper Miocene (Tortonian, 9.5-8.6 Ma) marine deposits of the Pisco Formation exposed at four localities of the East Pisco Basin (southern coast of Peru), we describe a new genus and species of inioid, Samaydelphis chacaltanae. This mesorostrine, small-sized species is characterized by an upper tooth count of c. 30 teeth per row, a moderately elevated vertex of the cranium displaying a long anteromedial projection of the frontals and interparietal, and the plesiomorphic retention of a premaxilla-nasal contact. Recovered as a member of the family Pontoporiidae in our phylogenetic analysis, S. chacaltanae falls as sister group to Meherrinia isoni, from the upper Miocene of North Carolina (USA), which has previously been tentatively referred to the Iniidae or regarded as a stem Inioidea. Originating from the P1 allomember of the Pisco Formation, the mesorostrine S. chacaltanae was contemporaneous and sympatric with two other inioids, the brevirostrine pontoporiid Brachydelphis mazeasi and the longirostrine iniid Brujadelphis ankylorostris.

A new kentriodontid (Cetacea: Odontoceti) from the early to middle Miocene of the western North Pacific and a revision of kentriodontid phylogeny

“…Molecular phylogenetics is now widely accepted for reconstructing the phylogenetic relationships of organisms, but its results are sometimes different from analyses based only on morphological data. Although many of the aforementioned studies (e.g., Lambert et al, 2017 ; Peredo, Uhen & Nelson, 2018 ; Kimura & Hasegawa, 2019 ) chose the total evidence approach (parsimony analysis based both on molecular and morphological evidence) for their analyses, the resulting relationships they suggested are different from that of the analyses based on molecular data only in regard to the extant species ( McGowen, Spaulding & Gatesy, 2009 ; McGowen et al, 2011 ; McGowen et al, 2020 ; Geisler et al, 2011 ; Post, Louwye & Lambert, 2017 ; Lambert et al, 2018a ; Lambert et al, 2020 ).…”

A stem delphinidan from the Caribbean region of Venezuela

“…5 Phylogenetic relationships of the Caujarao delphinidan (MTT-V-558) within Odontoceti. Strict consensus resulting from a single tree with a CI of 0.159 and a RI of 0.565, resulting from a parsimony analysis with a molecular backbone enforced, based on Lambert et al ( 2020 ) ( a ). Strict consensus resulting from 27 trees with a CI of 0.162 and a RI of 0.603, resulting from the analysis omitting non-cranial characters, modified from Lambert et al ( 2020 ) ( b ).…”

“…In the case of Tagicetus and Hadrodelphis, their positions have greatly varied, being recovered in different positions across Delphinida. These taxa have been recovered independently either more closely related to Inioidea (Post et al 2017;Lambert et al 2020) or to Delphinoidea (Lambert et al 2018), or stem to both (Lambert et al 2017b;Post et al 2017;Peredo et al 2018).…”

“…Their affinities have also been disputed, as some analyses recovered them as distantly related (Lambert et al 2017b(Lambert et al , 2020Post et al 2017) and others hypothesized them as closely related (Lambert et al 2018). This variation among phylogenetic analyses can be attributed to the fragmentary state of several specimens, lacking either cranial regions, earbone material or mandibles; but also to the lack of coded postcranial material which could possess some phylogenetic signal (Boessenecker et al 2020).…”

“…5 ). The specimen was coded and included into an unmodified version of the matrix of Lambert et al ( 2020 ). Following previous analysis, a molecular backbone constrain based on McGowen et al ( 2019 ) was enforced, and nine fragmentary taxa were removed.…”