AMERICAN MUSEUM Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2904, pp. 1-27, figs. 1-20, 1 table December 30, 1987 The Affinities of Notocetus vanbenedeni, an Early Miocene Platanistoid (Cetacea, Mammalia) from Patagonia, Southern Argentina CHRISTIAN DE MUIZON' ABSTRACT The study of previously undescribed material the loss of the coracoid process and the acromion of the Early Miocene Odontocete Cetacean No- located on the anterior edge. These three families tocetus vanbenedeni allows a new interpretation of (Platanistidae, Squalodelphidae, and Squalodon- its relationships, and a reevaluation of the taxon tidae) constitute the Platanistoidea. The Squalo- Platanistoidea. The new specimen consists of a dontidae, however, may be poly- or paraphyletic well preserved auditory region (periotic, tympanic, as they are defined by symplesiomorphies only; malleus, stapes, squamosal, and partial occipital) they are not analyzed here and the group is ten- associated with several teeth and some postcranial tatively regarded as monophyletic. The phyloge- elements (scapula, vertebrae, and rib fragments). netic relationships ofthis family will be considered The presence of an articular rim on the periotic elsewhere. The ziphiid affinities ofNotocetus van- and the morphology ofthe tympanic demonstrate benedeni, assumed by some previous workers, are the close relationship of Notocetus with the Plat- rejected. The Ziphiidae could, however, have their anistidae. Notocetus is referable to the family origin in some squalodont-like odontocetes, a Squalodelphidae, which also includes the genera statement which favors a possible polyphyletism Squalodelphis and Phocageneus. This family is the of the Squalodontidae. sister-group ofthe Platanistidae, which consists of Notocetus is an Argentinian genus, but the oc- the genera Platanista, Zarachis, and Pomatodel- currence ofa periotic and a partial tympanic from phis. Platanistidae and Squalodelphidae are re- the Calvert Formation of Maryland extends the garded as the sister-groups of the Squalodontidae distribution of the genus to the Middle Miocene on the basis oftwo synapomorphies ofthe scapula: of North America. INTRODUCTION Notocetus vanbenedeni was first described specimen consisting of a nearly complete under that name by Moreno (1892) on the skull, mandible, some ribs, and vertebrae. basis ofa well preserved skull and associated Both skulls lack the periotics, while a tym- mandible. Later, True (19 10) described a new panic bone is associated with the specimen ' Curator, Institut de Paleontologie, UA 12 CNRS, Museum National d'Histoire Naturelle, 8 rue Buffon 75005, Paris, France. Copyright © American Museum of Natural History 1987 ISSN 0003-0082 / Price $3.70 2 AMERICAN MUSEUM NOVITATES NO. 2904 described by True. The collections of the CNRS (Centre National de la Recherche American Museum of Natural History in- Scientifique) and by the "Fondation de la Vo- clude a specimen (AMNH 29026) here re- cation." Photographs are by D. Serrette and ferred to Notocetus vanbenedeni that consists by the author, ink drawing by F. Pilard, and of a partial right squamosal and occipital, word processing was done by L. Da and E. complete tympanic, periotic and malleus, Molin. several teeth, a scapula, and some incomplete vertebrae and rib fragments. I here describe the most important parts 'of this specimen, ABBREVIATIONS which allows a new interpretation ofthe phy- Institutional logenetic relationships of Notocetus van- benedeni, a species here classified among the AMNH American Museum of Natural History, Platanistoidea (sensu de Muizon, 1984). New York, USA Ameghino (1894: 43) regarded the genus IGUP Instituto di Geologia del l'Universita di Padova, Italy Notocetus Moreno (1892) as preoccupied by MLP Museo de La Plata, Argentina Notiocetus Ameghino (1891) because the MNHN Museum National d'Histoire Naturelle, names differed by one letter only, and pro- Paris, France posed the new name Diochoticus. The same USNM Smithsonian Institution, United States year, apparently ignorant of Ameghino's National Museum of Natural History, (1894) study, Lydekker (1894: 12) proposed, Washington, D.C., USA for the same reason, the name Argyrodelphis. True (1910: 19), Kellogg (1928), and Colbert (1944) followed Ameghino's designation Abbreviations in illustrations which is two months older than Lydekker's. In fact, it is a recommendation of the Inter- ACR acromion national Code ofZoological Nomenclature to AES anteroexternal sulcus avoid the creation of names which differ by AFI articular facet for incus AFP articular facet for periotic only one letter and which may result in con- AFT articular facet for tympanic fusion to other workers, but once such names AHM articular head of malleus are established they must strictly follow the ALCT anterolateral convexity of tympanic law of priority. It is for this reason that Ca- ALNT anterolateral notch of tympanic brera (1926), Simpson (1945), and Romer APP anterior process of periotic (1969) recognized the genus name Notocetus ARP articular rim of periotic as valid and regarded the name Diochotichus AST anterior spine of tympanic Ameghino (1894), used by True (1910), as a AZS articular zone for squamosal junior synonym of Notocetus. This opinion AZT articular zone for tympanic is followed here. CGL glenoid cavity of the squamosal COP coracoid process CPT conical process of tympanic ACKNOWLEDGMENTS DOCA dorsal opening of cochlear aqueduct DOFA dorsal opening of Fallopian aqueduct Special thanks are due to Drs. M. Novacek DOVA dorsal opening of vestibular aqueduct and R. H. Tedford (American Museum of DTPP dorsal tuberosity of posterior process Natural History), Drs. C. E. Ray and F. C. of periotic Whitmore (U.S. National Museum), and EAM external auditory meatus Professor G. B. Dal Piaz and Dr. L. Altichieri ETF epitubarian fossa (Instituto di Geologia dell'Universita di Pa- EXO exoccipital un- FCM fossa capitis mallei dova) for permission to study specimens FMS fossa for medium sinus der their care. I also thank Dr. L. G. Marshall FPOS fossa for posterior sinus (Geochronology Center at the Institute of FPS falcate process of squamosal Human Origins, Berkeley), R. H. Tedford, FSG foramen singulare M. Novacek, and an anonymous reviewer for HAPP hooklike articular process of periotic helpful comments on the manuscript. Partial IAM internal auditory meatus funding for this research was provided by the IAW internal auditory window 1987 DE MUIZON: NOTOCETUS VANBENEDENI 3 IV involucrum 11) stated that Frenguelli's Patagonian land LFT lateral furrow of tympanic mammals probably come from his bed e and, LLT lateral lobe of tympanic if they are actually from marine beds, this MLT medial lobe of tympanic author sees no MNM manubrium of malleus evidence against the possibil- MPM processus muscularis of malleus ity of an intermediate age between Colhue- MX maxillary Huapi and Santa Cruz. Since no land mam- PA palatine mals have been found in beds right above the PCP pars cochlearis of periotic Patagonian, it may be assumed, pending fur- PEO periotic ther discoveries, that the Patagonian marine PGP postglenoid process mammals have a Colhue-Huapi to Santa Cruz PMP postmeatal process age, i.e., Early Miocene (Marshall et al., 1983, POP paroccipital process 1986; MacFadden et al., 1985). PPP posterior process of periotic PPT posterior process of tympanic DESCRIPTION OF THE SPECIMEN PTT processus tubarius of tympanic PT pterygoid The dentition of Notocetus vanbenedeni RAP relictual articular pit shows slight but obvious heterodonty. The RW round window teeth are all single-rooted, differing from the SPP superior process of periotic posterior teeth ofthe Squalodontidae and the SPS spiny process of squamosal Agorophiidae which are double-rooted (fig. SPT sigmoid process of tympanic 1). The anterior teeth ofN. vanbenedeni have ST stapes a conical and elevated crown which is slightly STF fossa for stapedial' muscle recurved posteriorly and lingually. In shape STMF sternomastoid fossa they resemble typical delphinoid teeth. They TBM tuberculum of malleus UPN notch for unciform process of tympanic show a slight anterior keel, the bases ofwhich UPT unciform process of tympanic sometimes bear one or two tiny cingular cusps. VGT ventral groove of tympanic A posterior keel is hardly discernible and often VOFA ventral opening of Fallopian aqueduct absent. No distinct cingulum can be observed VTP ventral tuberosity of periotic at the base ofthe crown. The enamel is rough- ZPS zygomatic process of squamosal ly rugose, approaching in this respect the morphology observed in Steno and Inia. The LOCALITY AND AGE OF THE SPECIMEN posterior teeth have a low triangular crown; they are approximately triangular in cross The specimen AMNH 29026 was collected section, and the posteriormost teeth are gen- in 1933 by the J. H. Scarritt Expedition, near erally as long as high. Their crown possesses Cerro Castillo opposite Trelew in Patagonia. well marked anterior and posterior keels; the It was discovered in bed g of Simpson's sec- posterior keel bears one, two, or three notable tion of the south wall of the Chubut Valley accessory cusps, the highest sometimes (Simpson, 1935: fig. 1). The sediment is a reaching the apical third of the keel. A chain "thick bedded, pale, yellowish tuff," with Os- of small cingular cusps rise at approximately trea hatcheri, numerous sharks, rays, ceta- half the height of the anterior keel obliquely ceans, and penguins.