Saturday, May 18, 2019

[PaleoMammalogy • 2019] Nehalaennia devossi • A New Balaenopterid Whale (Cetacea, Mysticeti) from the late Miocene of the Southern North Sea Basin and the Evolution of Balaenopterid Diversity


Nehalaennia devossi 
Bisconti​, Munsterman & Post, 2019  


Abstract 
Background:
Balaenopterid mysticetes represent the most successful family-rank group of this clade. Their evolutionary history is characterized by a rich fossil record but the origin of the living genera is still largely not understood. Recent discoveries in the southern border of the North Sea revealed a number of well preserved fossil balaenopterid whales that may help resolving this problem. In particular, skull NMR 14035 shares morphological characters with the living humpback whale, Megaptera novaeangliae and, for this reason, its characteristics are investigated here.

Methods:
The comparative anatomical analysis of the new specimen formed the basis of a new phylogenetic analysis of the Mysticeti based on a matrix including 350 morphological character states scored for 82 Operational Taxonomic Units. The stratigraphic age of the specimen was determined based on the analysis of the dinocyst assemblage recovered in the associated sediment. We assessed clade diversity in Balaenopteridae by counting the numbers of clades in given time intervals and then plotted the results.


Results: 
Nehalaennia devossi n. gen. et sp. is described for the first time from the late Tortonian (8.7–8.1 Ma) of the Westerschelde (The Netherlands). This new taxon belongs to Balaenopteridae and shows a surprisingly high number of advanced characters in the skull morphology. Nehalaennia devossi is compared to a large sample of balaenopterid mysticetes and a phylogenetic analysis placed it as the sister group of a clade including the genus Archaebalaenoptera. The inclusion of this fossil allowed to propose a phylogenetic hypothesis for Balaenopteridae in which (1) Eschrichtiidae (gray whales) represents a family of its own, (2) Balaenopteridae + Eschrichtiidae form a monophyletic group (superfamily Balaenopteroidea), (3) Cetotheriidae is the sister group of Balaenopteroidea, (4) living Balaenoptera species form a monophyletic group and (5) living M. novaeangliae is the sister group of Balaenoptera. Our work reveals a complex phylogenetic history of Balaenopteridae and N. devossi informs us about the early morphological transformations in this family. Over time, this family experienced a number of diversity pulses suggesting that true evolutionary radiations had taken place. The paleoecological drivers of these pulses are then investigated.

 Figure 3: Dorsal view of the holotype skull of Nehalaennia devossi (NMR 999100014035). (A) Photographic representation. (B) Interpretation. Scale bar equals 10 cm.

Systematic Paleontology

Mammalia Linneaus, 1758
Cetartiodactyla Montgelard, Caatzeflis & Douzery, 1997

Cetacea Brisson, 1762
Neoceti Fordyce & De Muizon, 2001

Mysticeti Flower, 1864
Chaeomysticeti Mitchell, 1989
Thalassotherii Bisconti, Lambert & Bosselaers, 2013

Balaenopteridae Gray, 1864

Nehalaennia new genus

Nehalaennia devossi new species
Holotype: Specimen 999100014035 of the collection of the Natuurhistorisch Museum Rotterdam.

Etymology: The genus name is one of the spellings of the name of the Keltic pagan goddess of the sea which was also accepted by Romans when they conquered what is now the most southern province of The Netherlands. The species name is given to honor Dr. John de Vos for his lifelong contribution to Dutch paleontology and his leading role in creating the unique bond and trust between Dutch professional and amateur paleontologists.
 
Differential diagnosis:
Nehalaennia devossi differs from Archaebalaenoptera castriarquati in having a rounded anterior border of the supraoccipital, anterior half of the supraoccipital not strongly compressed transversely, widely concave posterior border of the maxilla, shorter and wider ascending process of the maxilla, significantly shorter nasal bones and anterior border of the supraorbital process of the frontal anterolaterally concave. It differs from Plesiobalaenoptera quarantellii in showing a lower superior portion of the periotic, shorter and wider ascending process of the maxilla, more slender lateral process of the maxilla with deeper antorbital notch, posterior end of the posterior process of the periotic more robust and round. It differs from ‘Megaptera’ hubachi in having a ventrally concave glenoid fossa of the squamosal with the postglenoid process projecting ventrally and forming a c. 90° angle with the zygomatic process of the squamosal, in having a rounded anterior border of the supraoccipital, and in lacking exposure of the alisphenoid in the temporal fossa. It differs from ‘Balaenoptera’ bertae in having a wider and rounder anterior border of the supraoccipital, in having an anterolaterally concave anterior border of the supraorbital process of the frontal, in having a vertically-oriented postglenoid process of the squamosal making the glenoid fossa of the squamosal more concave in lateral view. It differs from Incakujira anillodefuego in having a rounder and wider anterior border of the supraoccipital, in having a comparatively shorter and slender supraorbital process of the frontal and a comparatively shorter zygomatic process of the squamosal, in having the premaxilla terminating anteriorly to the nasal. It differs from ‘Megaptera’ miocaena in having a narrower anterior border of the supraoccipital, comparatively longer ascending process of the maxilla with ‘primary dorsal infraorbital foramina’, more concave glenoid fossa of the squamosal. It differs from Fragilicetus velponi in lacking a squamosal bulging into the temporal fossa, in having a wider anterior border of the supraoccipital, in having a less strongly protruding posterolateral corner of the exoccipital, in having a rounded dorsal border of the periotic. It differs from Protororqualus cuvieri in having a wider and rounder anterior border of the supraoccipital, in having shorter zygomatic process of the squamosal, in having a wider space between the posterior border of the maxilla and the anterior border of the supraorbital process of the frontal, and in having an anterolaterally concave anterior border of the supraorbital process of the frontal. The same differences are observed when Nehalaennia devossi is compared against ‘Balaenoptera’ cortesi var. portisi. It differs from Parabalaenoptera baulinensis in having shorter and wider ascending process of the maxilla, rounded supraoccipital and shorter nasal bones.

Nehalaennia devossi
differs from the genus Balaenoptera in having a rounded anterior border of the supraoccipital, rounded posterior end of the ascending process of the maxilla, anterolaterally concave anterior border of the supraorbital process of the frontal, alisphenoid not exposed in the temporal fossa. It differs from Megaptera novaeangliae in having zygomatic process of the squamosal less diverging from the longitudinal axis of the skull, anterior border of the pars cochlearis of the periotic not strongly protruded, and more concave glenoid fossa of the squamosal in lateral view.

 Artistic reconstruction of Nehalaennia devossi shows two individuals during feeding upon schooling fishes. The leatherback turtle is used as a reference to show the hypothesized size of the rorqual. Credits for the illustration: Remie Bakker, Manimal Works, Rotterdam, The Netherlands.


Michelangelo Bisconti​, Dirk K. Munsterman and Klaas Post. 2019. A New Balaenopterid Whale from the late Miocene of the Southern North Sea Basin and the Evolution of Balaenopterid Diversity (Cetacea, Mysticeti). PeerJ. 7:e6915  DOI: 10.7717/peerj.6915

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