DOI: 10.5061/dryad.stqjq2c15
title: Data from: The earliest baleen whale of the mediterranean: Large-scale implications of an early miocene thalassotherian mysticete from Piedmont, Italy

description: The discovery of an Early Miocene chaeomysticete from the Pietra da
 Cantoni Group in Piedmont (north-western Italy) allowed for the creation
 of Atlanticetus n. gen. and Atlanticetus lavei n. sp. The new species is
 represented by a partial skeleton including the earbones and shows
 anatomical resemblance with Atlanticetus patulus (new combination) from
 the western North Atlantic. The Early Miocene age of the new specimen
 supports the view that it represents the oldest record of Chaeomysticeti
 from the Mediterranean. A new phylogenetic analysis showed that both A.
 patulus and A. lavei belong to a radiation of basal thalassotherian taxa.
 The basal thalassotherians are found being monophyletic to the exclusion
 of Cetotheriidae and Balaenopteroidea. The reconstruction of ancestral
 characters at selected nodes informs that the group including Atlanticetus
 and living balaenopterid taxa independently evolved rostra wide at base,
 anterolateral expansion in the tympanic bulla and a peculiar arrangement
 of the endocranial foramina of the periotic exhibiting a noteworthy
 phenomenon of convergent evolution in feeding and hearing functions with
 Balaenopteridae. The paleobiogeographic analysis showed that the North
 Pacific was the center of origin of Balaenomorpha (crown mysticetes),
 Thalassotherii and Balaenoidea. The recurrent invasion of the
 Mediterranean by balaenomorph mysticetes occurred from both the North
 Atlantic and North Pacific.
description: <i>Anatomy,
 photography and measurements.</i> The specimen studied is in the
 collection of the Museo Paleontologico Territoriale Astigiano  (MPTA),
 Asti, Piedmont (north-west Italy) with the accession number 13301. The
 specimen includes a partially complete skeleton that was mechanically
 prepared and fixed using Paraloid. Measurements were taken with digital
 calipers Sourcingmap (300 mm) and Tacklife D02 (150 mm) both with error
 margin to the nearest 0.01 mm. Photography was made by using a Nikon D750
 full frame DLSR with Tamron 90 mm f/2.8 Di VC macro lens. Light was
 provided by a Speedlight flash Nikon D700 with softbox mounted on the
 DSLR. Anatomical terms follow Mead & Fordyce (2009), Ekdale
 <i>et al.</i> (2011), and Martìnez-Cáceres <i>et
 al.</i> (2017). The comparative analysis included all the mysticete
 taxa listed in the Supplementary Information file that comprise most of
 the described species of living and fossil mysticetes belonging to all the
 baleen whale radiations. <i>Anatomical
 abbreviations.</i><b> </b>Anatomical abbreviations as
 follows:<b> </b>aam, area for articulation with malleus; aat,
 anterior attachment site for tympanic bulla; al, anterolateral lobe; apmx,
 ascending process of maxilla; ap, attachment pedicle of the compound
 posterior process of the tympanoperiotic; app, anterior process of
 periotic; atc, anterodorsal crest; atl, atlas; cp, conical process; ct,
 crista transversa; elf, endolymphatic foramen; Eo, Eustachian outlet; eof,
 endocranial opening of facial canal; fi, fossa incudis; fnp, facial nerve
 path on posterior process of periotic; fms, fossa for stapedial muscle;
 fo, foramen ovale; fpsq, falciform process of squamosal; hppt, hamular
 process of pterygoid; hye, hiatus epytympanicus; iam, internal acoustic
 meatus; inr, involucral ridge; inv, involucrum; ipp, inner posterior
 prominence; ipn, interoprominential notch; ir, involucral ridge; lf,
 lateral furrow; lof, lateral opening of the facial canal; lt, lateral
 tuberosity; mr, main ridge; opp, outer posterior prominence; ow, oval
 window; pch, pars cochlearis; per, periotic; plf, perilymphatic foramen;
 pllf, fossa for perilymphatic foramen; ppp, posterior process of periotic;
 prg, promontorial groove; rw, round window; sma, suprameatal area of
 periotic; sp, sigmoid process; stm, stylomastoid fossa; ttg, tensor
 tympani groove; tyb, tympanic bulla; tyc, tympanic cavity; vg, vascular
 groove. <i>Institutional
 abbreviations</i>. MGB, Museo Geopaleontologico ‘Giovanni
 Capellini’, Università degli Studi di Bologna, Bologna, Italia; MPTA,
 Museo Paleontologico Territoriale Astigiano, Asti, Italia; RBINS, Royal
 Belgian Institute of Natural Sciences, Brussels, Belgium; USNM, National
 Museum of Natural History, Smithsonian Institution, Washington DC,
 USA. <i>Phylogenetic analysis.</i> The
 phylogenetic analysis was performed based on the morphological dataset
 available from the Supplementary Information file that includes 355
 characters scored in 88 taxa. Inference of phylogenetic trees was made by
 using TNT 1.5 software (Goloboff & Catalano 2016) by 2000
 replications of Tree Bisection Reconnection algorithm (TNT command mult
 2000=tbr) retaining 10 trees each. A treespace of 20000 potential
 cladograms was allowed in the tree buffer. Protocetidae was set as
 outgroup. An analysis using implied weights (default parameters: function
 <i>k </i>= 3.0) was also performed by using all the new
 technology algorithms as implemented in TNT and hitting the shortest trees
 10 times at least. Then a traditional search was done based on the trees
 stored in the RAM. The available RAM was 16 MB with 6% occupied by the
 buffer. The total memory required for the data was 0.56 MB. Node support
 was calculated in TNT by bootstrap (1000 replicates, traditional search
 with default parameters), symmetric resampling (1000 replicates, absolute
 frequencies) and Bremer support (suboptimal value set to 10). Character
 mappings onto the preferred cladograms were performed through MESQUITE 3.6
 (Maddison & Maddison, 2019).  The agreement between the
 phylogenetic pattern and the stratigraphic ages of the taxa was calculated
 by the Stratigraphic Consistency Index (SCI; Huelsenbeck 1994). The
 reconstruction of the biogeographic states at the nodes of the
 phylogenetic tree was made by MESQUITE 3.61 (Maddison & Maddison
 2019) using  maximum likelihood algorithms with default Mk1 model as
 implemented in the software. The geographic occurrences and the
 stratigraphic ages of the specimens used in the analysis are available in
 the Supplementary Information of this paper.