BASILOSAURIDAE Cope, 1868

Martínez-Cáceres, Manuel, Lambert, Olivier & Muizon, Christian de, 2017, The anatomy and phylogenetic affinities of Cynthiacetus peruvianus, a large Dorudon-like basilosaurid (Cetacea, Mammalia) from the late Eocene of Peru, Geodiversitas 39 (1), pp. 7-163 : 11-13

Family BASILOSAURIDAE Cope, 1868

Zeuglodontidae Bonaparte, 1849: 618 .

Hydrarchidae Bonaparte, 1850: 1 .

Basilosauridae Cope, 1868: 144 .

Stegorhinidae Brandt, 1873: 334 .

Prozeuglodontidae Moustafa, 1954: 87 .

Basilosauridae Barnes & Mitchell, 1978: 587 .

TYPE GENUS. — Basilosaurus Gibbes, 1847 .

INCLUDED GENERA. — Ancalecetus Gingerich & Uhen, 1996 ; Basilosaurus Gibbes, 1847 ; Basiloterus Gingerich Arif, Bhatti, Anwar & Sanders, 1997 ; Basilotritus Gol’din & Zvonok, 2013; Chrysocetus Uhen & Gingerich, 2001 ; Cynthiacetus Uhen, 2005 ; Dorudon Gibbes, 1845 ; Masracetus Gingerich, 2007 ; Ocucajea Uhen, Pyenson, DeVries, Urbina & Renne, 2011 ; Saghacetus Gingerich, 1992 ; Stromerius Gingerich, 2007 ; Supayacetus Uhen Pyenson, DeVries, Urbina & Renne, 2011 ; Zygorhiza True, 1908 .

EMENDED DIAGNOSIS. — Basilosaurids are medium-to-large sized archaeocetes characterized principally by: 1) a flat palate narrowing at the level of P4; 2) absence of M3; 3) anterior edge of the orbit dorsal to the level of P4 or P4/M1 diastema; 4) anterior process of the periotic strongly elliptical in cross-section; 5) triangular expansion on the posterolateral corner of the pars cochlearis; and 6) well developed ventrolateral tuberosity of the periotic.

AGE AND DISTRIBUTION. — Earliest described specimens are from the middle to late Bartonian beds of Pakistan ( Basilosaurus drazindai and Basiloterus hussaini ; Gingerich et al. 1997) and from Hampshire ( Basilosauridae indet.; Seeley 1876). On the other hand, latest basilosaurid specimens are the holotypes of Saghacetus osiris ( Dames, 1894) (Priabonian El-Sagha Formation, Egypt; Dames 1894) and Cynthiacetus peruvianus (Priabonian Otuma Formation, Peru; Martínez-Cáceres & Muizon 2011). Recently, several new basilosaurid specimens have been collected from the beds of the Eocene La Meseta Formation, in the Antarctic Peninsula ( Buono et al. 2011, 2016). The age of one of these specimens, including a partially preserved dentary with associated teeth, has been reassessed to the middle Lutetian-early Bartonian (46-40 Ma); if the geochronological attribution is confirmed, it should be the earliest known basilosaurid ( Buono et al. 2016).

DISCUSSION

When Harlan (1834) created the genus Basilosaurus based on a single vertebra, he did not designate a type species nor did he propose a binominal name for the taxon (which should invalidate Basilosaurus as a genus name). However, according to the Article 67.2.2 of the International Code of Zoological Nomenclature – ICZN ( International Commission on Zoological Nomenclature 1999), Basilosaurus is considered as a valid name since it was created before 1931. Therefore, the first species referred to the genus, B. cetoides (= Zeuglodon cetoides Owen, 1839 ) is considered as the type species. Besides, the type series of B. cetoides includes the specimens described by Owen (1839) and not the single vertebra described by Harlan (1834) and indicated as the holotype of B. cetoides by Kellogg (1936). The type series was first referred to Basilosaurus by Harlan (1835). Similarly, the name Zeuglodontidae Bonaparte, 1849 precedes that of Basilosauridae Cope, 1868 and should be retained as the senior name of the family (Article 40.1 of the ICZN). However, Basilosauridae replaced Zeuglodontidae before 1961 ( Cope 1868; Kellogg 1936) and is currently in prevailing usage (e.g. Barnes & Mitchell 1978; Uhen 1998; Luo & Gingerich 1999). According to the Article 40.2 of the ICZN, Basilosauridae should be maintained, as well as Basilosaurus , the type genus of the family.

TAXA EXCLUDED FROM THE BASILOSAURIDAE

In the present work, the New-Zealandian taxon Kekenodon onomata ( Hector 1881) is not included in the Basilosauridae following Fordyce (2004). The holotype of the species includes isolated teeth with mesial and distal accessory denticles, periotic and tympanic bulla ( Hector 1881). Moreover, the teeth of K. onomata differ from the typical basilosaurid dental morphology in being proportionally shorter mesiodistally and having a more rounded outline in labial or lingual views. The tympanic bulla of K. onomata is not entirely preserved but seems to be proportionally longer than in any basilosaurid and apparently has a pointed anterior edge, as observed in some toothed mysticetes (ChM PV5720; Fitzgerald 2010).

Another enigmatic taxon is Phococetus vasconum . Initially described as a basilosaurid from a single molariform tooth ( Delfortrie 1873), P. vasconum has been referred to both Odontoceti ( Gervais 1876; Van Beneden & Gervais 1880) and Mysticeti ( Mitchell 1989) . Mitchell (1989) placed together both K. onomata and P. vasconum in the mysticete sub-family Kekenodontinae. Until the description of better-preserved material, these taxa should be regarded as Pelagiceti incertae sedis (see also Clementz et al. 2012 for a discussion of the phylogenetic affinities of Kekenodontidae)

Similarly, the Oligocene specimens referred to the Basilosauridae by Fordyce (2002) might belong to a basal neocete rather than to a basilosaurid.

BASILOSAURIDAE incertae sedis

Some taxa that have been referred to the Basilosauridae have been originally described on the basis of fragmentary holotype regarded as irrelevant to diagnose a basilosaurid. Although their names are valid, Pontogeneus priscus Leidy, 1852 , P. brachyspondylus ( Müller, 1849) , and Masracetus markgrafi Gingerich, 2007 cannot be referred to any known species of the family nor any specimen can be reasonably referred to their holotype. They are discussed below.