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Herpetocetus Morrowi bs_bs_banner Zoological Journal of the Linnean Society, 2014, 170, 400–466. With 40 figures Herpetocetus morrowi (Cetacea: Mysticeti), a new species of diminutive baleen whale from the Upper Pliocene (Piacenzian) of California, USA, with observations on the evolution and relationships of the Cetotheriidae JOSEPH J. EL ADLI1,2*, THOMAS A. DEMÉRÉ1 and ROBERT W. BOESSENECKER3,4 1Department of Paleontology, P.O. Box 121390, San Diego Natural History Museum, San Diego, California, 92112, USA 2Department of Earth and Environmental Sciences, University of Michigan, 1109 Geddes Avenue, Ann Arbor, Michigan, 48109, USA 3Department of Geology, University of Otago, P.O. Box 56, Dunedin, 9054, New Zealand 4University of California Museum of Paleontology, University of California, 1101 Valley Life Sciences Building, Berkeley, California, 94720, USA Received 24 August 2013; revised 18 October 2013; accepted for publication 21 October 2013 The extinct edentulous mysticete family Cetotheriidae historically has been viewed as a notoriously paraphyletic group, and only recently have rigorous studies been executed to rectify this issue. These problems do not necessarily just stem from lack of phylogenetic analyses, but are in part because of a general lack of complete specimens, poor descriptions of taxa, and long-lived taxonomic instability issues. The fossil mysticete genus Herpetocetus is a poster child of these problems as it is primarily only known from a few relatively incomplete and poorly described specimens. A new species of Herpetocetus from the upper Pliocene of California, Herpetocetus morrowi sp. nov., provides an archetypal model for the genus based on a multitude of well-preserved specimens. These specimens reveal a diminutive mysticete characterized by an elongate rostrum and roughly quadrate cranium. A mosaic of primitive and derived features preserved in this new species underscores its potential value in helping to resolve a number of taxonomic and phylogenetic problems. The occurrence of specimens assignable to juvenile through to mature adult individuals provides a basis for investigating ontogenetic changes. Functional analysis of the unusual craniomandibular anatomy of H. morrowi suggests a limited degree of mandibular gape and an enhanced capacity for longitudinal rotation of the dentary, features that support a hypothesis of suction feeding convergent with that of living grey whales. A phylogenetic analysis provides support for recognition of a redefined and monophyletic Cetotheriidae and Herpetocetinae, and also serves as a basis for evaluating the recent proposal that the pygmy right whale (Caperea marginata) is a living cetothere. Morphological features of Herpetocetus morrowi, including features of the cranium and petrosal, suggest that a number of the purported synapomorphies supporting a Caperea−cetothere grouping are either symplesiomorphies, nonhomologous features, or are highly variable. © 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 170, 400–466. doi: 10.1111/zoj.12108 ADDITIONAL KEYWORDS: Caperea − functional morphology – palaeontology – phylogeny – systematics. INTRODUCTION taxa named by Van Beneden in the late 19th century, its status as a diagnosable taxon is questionable. The genus Herpetocetus has had a chequered nomen- Whitmore & Barnes (2008) provided the most recent clatural history, and like most of the fossil cetacean review of the nomenclatural history of Herpetocetus, and relying on a complex series of assumptions and *Corresponding author. E-mail: [email protected] referred specimens of uncertain provenance, these 400 © 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 170, 400–466 A NEW PLIOCENE-AGE CETOTHERIID 401 authors chose to retain the genus and assign to it isolated cranial and postcranial material from these several new species. Whitmore & Barnes (2008) also strata is unreasonable. Therefore, referred specimens recognized a group of closely related small-bodied of H. scaldiensis must be critically reassessed. The fossil mysticetes that they placed into a new subfam- authors do not, however, doubt that referred speci- ily, the Herpetocetinae. Unfortunately, as defined by mens of H. scaldiensis (IRSNB 405 and USNM these authors, herpetocetine membership was largely 336361) should be designated as herpetocetines based on authority and was not formulated in the based on similar morphological features documented context of a cladistic phylogenetic analysis. in more complete herpetocetine specimens that do As defined by Whitmore & Barnes (2008), the genus possess cranial material and associated dentaries Herpetocetus encompasses a relatively diverse and (i.e. UCMP 124950). However, given the dubious speciose group of fossil mysticetes that have been history regarding the lectotype specimen it is unrea- described from upper Miocene and Pliocene marine sonable to assume that these referred specimens facies exposed on the east and west coasts of both are assignable to H. scaldiensis. This study will con- the north Pacific and north Atlantic oceans. In 1872, sider specimens referred to H. scaldiensis by other Pierre-Joseph Van Beneden described the type workers (i.e. IRSNB 405 and USNM 336361 by species of Herpetocetus, Herpetocetus scaldiensis Van Whitmore & Barnes, 2008) as not belonging to Beneden, 1872, based on a series of unassociated H. scaldiensis, and therefore will discuss them, mysticete fossil remains from Antwerp, Belgium. and their position within Herpetocetinae, indepen- These specimens, commissioned for collection by dently from IRSNB M.379. This approach was fol- Bernard du Bus, were excavated by soldiers during lowed in order to allow for comparison with other construction of fortifications at Antwerp years before herpetocetines, which merits consideration even if it Van Beneden began work on the collections (Deméré, is possible that referral of these specimens to Berta & McGowen, 2005: 104). Several of the fossil H. scaldiensis is inaccurate. specimens originally assigned to H. scaldiensis by The type locality of H. scaldiensis is equivocal and Van Beneden have been found to actually represent its ultimate designation has major implications for different undescribed mysticete taxa (Deméré et al., the age of the specimen. The marine sedimentary 2005). facies in the vicinity of Antwerp, Belgium, and from Unfortunately, Van Beneden did not select a type which IRSNB M.379 may have been collected, are of specimen for Herpetocetus either in his original manu- the obsolete Diestian and Scaldisian stages. These script or in his subsequent, beautifully illustrated stages correspond to the Late Tortonian to Messinian monograph series published in 1882. It was not until (Louwye & Laga, 1998) and Zanclean to Early Abel (1938) that IRSNB M.379 (formerly catalogued as Piacenzian, respectively. Dollo (1909: 116) listed IRSNB 14; O. Lambert pers. comm., February 2013), a H. scaldiensis in the fauna recovered from marine left dentary included by Van Beneden in his original sandstones of the local Bolderian Stage, assumed at description of H. scaldiensis, was designated as the the time to be Late Miocene in age but now assigned lectotype of H. scaldiensis. Whitmore & Barnes (2008) to the lower to middle Miocene (Louwye et al., 2000; recently provided an extensive historical account of the Laga, Louwye & Geets, 2001), whereas Abel (1938: specimens assigned by various authors to this species 22) indicated that the lectotype dentary was collected and noted that three specimens studied by Van from Upper Miocene deposits (Anversian). Whitmore Beneden (1882), a partial squamosal, a partial dentary, & Barnes (2008) concluded that the locality of the and an atlas, are possibly from the same individual lectotype for H. scaldiensis was most likely Scaldisian and could serve as cotypes of H. scaldiensis. If correct, in age based on Van Beneden’s reference to the these specimens (IRSNB 405, 137, and 355, respec- ‘sable gris’ (Van Beneden, 1882) as the locality for tively) would make it possible to associate the unique H. scaldiensis. In their paper, Whitmore & Barnes mandibular morphology of the lectotype dentary with interpreted the ‘sable gris’ to be the sables à Isocardia portions of the cranium and axial skeleton. However, cor (Scaldisian in age), but dismissed, without because of the poorly documented and apparently evidence, the possibility that IRSNB M.379 may haphazard method of collection of all of these speci- have originated from another layer of grey sands mens, it does not seem likely that they belong to the described by de Heinzelin (1955) that correspond same individual and it is just as scientifically erro- to the latest Diestian Stage. Van Beneden (in neous now, as it was in the original description by Van Mourlon, 1876) expressed that Herpetocetus was Beneden, to assign them to the same taxon in the recovered from Diestian age rock units based on asso- absence of clear association. ciation with other macrofauna. Referred specimens of Owing to the current lack of specimens of H. H. scaldiensis (e.g. USNM 336361) collected by Paul scaldiensis from Belgium possessing clearly associ- L. Gigase and discussed by Whitmore & Barnes ated cranial and mandibular material, referral of (2008) have been found in Pliocene age deposits, the © 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 170, 400–466 402 J. J. EL ADLI ET AL. Kattendijk sands (Zanclean) and Ooederen sands left petrosal, distal
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