Baleen’ Whale Rsos.Royalsocietypublishing.Org (Mysticeti: Aetiocetidae)
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A new Early Oligocene toothed ‘baleen’ whale rsos.royalsocietypublishing.org (Mysticeti: Aetiocetidae) Research from western North Cite this article: Marx FG, Tsai C-H, Fordyce America: one of the oldest RE. 2015 A new Early Oligocene toothed ‘baleen’ whale (Mysticeti: Aetiocetidae) from western North America: one of the oldest and and the smallest the smallest. R. Soc. open sci. 2: 150476. 1,2 2 http://dx.doi.org/10.1098/rsos.150476 Felix G. Marx , Cheng-Hsiu Tsai and R. Ewan Fordyce2,3 1Department of Geology and Palaeontology, National Museum of Nature and Science, Received: 11 September 2015 Tsukuba, Japan Accepted: 30 October 2015 2Department of Geology, University of Otago, Dunedin, New Zealand Published: 2 December 2015 3Departments of Paleobiology and Vertebrate Zoology, National Museum of Natural History, Washington DC, USA Subject Category: Archaic toothed mysticetes represent the evolutionary Biology (whole organism) transition from raptorial to bulk filter feeding in baleen whales. Aetiocetids, in particular, preserve an intermediate Subject Areas: morphological stage in which teeth functioned alongside a precursor of baleen, the hallmark of all modern mysticetes. evolution/palaeontology/taxonomy To date, however, aetiocetids are almost exclusively Late and systematics Oligocene and coeval with both other toothed mysticetes and fully fledged filter feeders. By contrast, reports of cetaceans Keywords: from the Early Oligocene remain rare, leaving the origins Mysticeti, baleen whale, Aetiocetidae, of aetiocetids, and thus of baleen, largely in the dark. Here, suction feeding, filter feeding, baleen we report a new aetiocetid, Fucaia buelli, from the earliest Oligocene (ca 33–31 Ma) of western North America. The new material narrows the temporal gap between aetiocetids and the oldest known mysticete, Llanocetus (ca 34 Ma). The Author for correspondence: specimen preserves abundant morphological detail relating Felix G. Marx to the phylogenetically informative ear bones (otherwise e-mail: [email protected] poorly documented in this family), the hyoid apparatus and much of the (heterodont) dentition. Fucaia comprises some of the smallest known mysticetes, comparable in size with the smallest odontocetes. Based on their phylogenetic relationships and dental and mandibular morphology, including tooth wear Electronic supplementary material is available at http://dx.doi.org/10.1098/rsos.150476 or via http://rsos.royalsocietypublishing.org. 2015 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited. patterns, we propose that aetiocetids were suction-assisted raptorial feeders and interpret this 2 strategy as a crucial, intermediary step, enabling the transition from raptorial to filter feeding. rsos.royalsocietypublishing.org Following this line of argument, a combination of raptorial and suction feeding would have been ................................................ ancestral to all toothed mysticetes, and possibly even baleen whales as a whole. 1. Introduction Aetiocetids are a clade of archaic toothed mysticetes known exclusively from the Oligocene [1], although recent, as yet unpublished, reports may hint at a possible survival until the late Early Miocene [2]. Originally regarded as archaeocetes [3], aetiocetids were subsequently recognized as basal mysticetes R. Soc. open sci. [4] and recently gained prominence as potential morphological intermediates between modern baleen- bearing mysticetes (Chaeomysticeti) and their toothed ancestors [5,6]. At present, Aetiocetidae comprise eight species in four genera—Aetiocetus, Ashorocetus, Chonecetus and Morawanocetus—from both sides of the North Pacific basin [1]. Willungacetus aldingensis from the Early Oligocene of Australia has also 2 been referred to this family [7], but the material is too poorly preserved to allow confident identification : 150476 [8]. In stark contrast, other toothed mysticetes, including mammalodontids and llanocetids, are only known from the Southern Hemisphere [8–10], with the possible exception of a potential, fragmentary mammalodontid from Malta [11]. Apart from Willungacetus and a referred Early Oligocene specimen of Aetiocetus cotylalveus (USNM 256593 [6]), all reported aetiocetids date from the Late Oligocene. Considering their intermediate morphology, this temporal distribution is rather striking, given that (i) the earliest toothed mysticete, Llanocetus denticrenatus, is known from the latest Eocene (ca 34 Ma [12]); and (ii) even chaeomysticetes are attested from the late Early Oligocene onwards [13]. Nevertheless, it is likely that the apparent lack of Early Oligocene aetiocetids reflects a patchy fossil record, as shown by the mere handful of cetacean specimens from this period, rather than a genuine biological phenomenon. Here, we reduce this temporal gap by describing a new species and genus from the Early Oligocene Makah Formation of the Olympic Peninsula, WA, USA. The new material represents the oldest reported aetiocetid, and, crucially, preserves details of the otherwise poorly known dental, ear bone, hyoid and vertebral morphology characterizing this family. In particular, our specimen stands out from other reported aetiocetids in including an almost entirely preserved, extracted periotic, some well-preserved tooth crowns showing details of wear, and all of the cervical vertebrae. The new species represents one of the smallest mysticetes yet described and thus highlights the rather humble origins of the giants that plough the modern oceans. 2. Material and methods Most of the preparation of the new material was done mechanically and carried out at the Burke Museum of Natural History and Culture, University of Washington, USA. Additional preparation, including the extraction of the right periotic and details of the tooth crowns, was carried out at the Geology Museum of the University of Otago (Dunedin, New Zealand) using dilute acetic acid and pneumatic air scribes under a Zeiss binocular microscope. Morphological nomenclature and tympanoperiotic orientation follow Mead & Fordyce [14], unless indicated. We repeated the dated total evidence phylogenetic analysis of Marx & Fordyce [13, fig. 2], which already included the material described here under the label UWBM 84024. We retained all the taxa, scorings and analysis settings of the previous analysis, but made four alterations to the data matrix. First, we modified character 33 (fusion of the posterior premolar and molar roots) so that it now includes three ordered states: (0) roots separate along their entire length; (1) roots fused proximally, but separate distally; (2) roots fused or closely apposed along their entire length. This change was made to reflect the disparate morphology of Morawanocetus and mammalodontids (partially fused roots) and Aetiocetus and Fucaia (completely fused or apposed roots) in this regard. Second, we changed the coding of character 29 (enamel ornament on premolars) for Morawanocetus, from state 0, ‘vertical enamel ridges present on lingual surface only’, to state 1, ‘enamel ridges present on both lingual and labial surfaces’. Finally, we changed the codings of characters 191 (in situ orientation of main axes of tympanic bullae in ventral view) and 243 (parapophysis on seventh cervical vertebra) for Fucaia, from state 0, ‘diverging posteriorly’ to ‘?’, and from state 0, ‘present’ to state 1, ‘absent’, respectively. The latter three changes were made to correct previous coding errors (see discussion of phylogeny below). Our new morphological codings and the full matrix are available from MorphoBank, project 2238 3 (full matrix stored in the ‘Documents’ section). The analysis of the amended data matrix was run in rsos.royalsocietypublishing.org MRBAYES v. 3.2.6 [15], on the Cyberinfrastructure for Phylogenetic Research (CIPRES) Science Gateway ................................................ [16]. In addition, we analysed the morphological partition of our data using the traditional search option of TNT (v.1.1) [17,18], based on 5000 random stepwise-addition replicates and tree bisection reconnection branch swapping, saving 10 trees per replicate. Parsimony analyses were run assuming both equal and implied weighting (k = 3), with branch support estimated through symmetric resampling (2000 replicates), recorded as GC values [19]. 2.1. Institutional abbreviations R. Soc. open sci. AMP, Ashoro Museum of Paleontology, Ashoro, Hokkaido Japan; ChM, Charleston Museum, Charleston, South Carolina, USA; CMN, Canadian Museum of Nature, Ottawa, Canada; LACM, Natural History Museum of Los Angeles County, Los Angeles, CA, USA; NMV, Museum Victoria, Melbourne, Australia; OCPC, John D. Cooper Archaeological and Paleontological Center, Santa Ana, CA, USA; OU, 2 University of Otago Geology Museum, Dunedin, New Zealand; USNM, National Museum of Natural : 150476 History, Smithsonian Institution, Washington, DC, USA; UWBM, Burke Museum of Natural History and Culture, University of Washington, Seattle, WA, USA. 3. Systematic palaeontology Cetacea Brisson, 1762 Mysticeti Gray, 1864 Aetiocetidae Emlong, 1966 Fucaia,gen.nov. LSID. urn:lsid:zoobank.org:act:FDBB95FF-5D4F-4DD2-95F7-C834D07442FA Type species. Fucaia buelli,sp.nov. Etymology. After the Strait of Juan de Fuca, the area surrounding which yielded both F. buelli and its sister species F. goedertorum. Diagnosis. Small-sized mysticetes (approx. 2