Pontogeneus brachyspondylus ( Müller, 1849 )

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 : 14

Pontogeneus brachyspondylus ( Müller, 1849)

Hydrarchos harlani Koch, 1846: 1-20 (in part).

Zeuglodon brachyspondylus Müller, 1849: 26-28 .

Zeuglodon brachyspondylum – Abel 1913: 203, 204 (unjustified emendation).

Pontogenus brachyspondylus – Kellogg 1936: 248-255.

LECTOTYPE. — A lumbar vertebra figured in Müller (1849: pl. XX) as “No. 6”.

PARALECTOTYPE. — MffNB, unknown number.All the other vertebrae regarded as Zeuglodon brachyspondylus byMüller (1849) and being part of the type specimen of Hydrarchos harlani ( Koch, 1846) . The syntype series includes 27 vertebrae of different individuals ( Kellogg 1936).

TYPE LOCALITY AND HORIZON. — Kellogg (1936) stated that the type series comes from the vicinity of Washington Old Court House, in Alabama, USA. The Upper Jackson Formation indicated in Kellogg (1936) is currently known as the Yazoo Clay Formation (upper unit of the Jackson Group) and is late Eocene in age.

DISCUSSION

Koch (1846) assembled the skeleton of several basilosaurid individuals to make a sea serpent chimera, which he named Hydrarchos harlani (synonym of H. sillimani ). After the discovery of the fake condition of H. harlani, Müller (1849) designated 27 vertebrae from Koch’s chimera as the type of Zeuglodon brachyspondylus . These 27 vertebrae constitute the syntype of the species. Kellogg (1936) combined Z. brachyspondylus Müller and Pontogeneus priscus Leidy into Pontogeneus brachyspondylus but did not designate a lectotype for the species. In fact, the type of P. priscus (cf. above) cannot be regarded as the neotype of Z. brachyspondylus (contra Uhen 1998) because a syntype was already designated by Müller (1849). Uhen (2005) considers the combination P. brachyspondylus as nomen nudum, but Gingerich (2007) designated a lumbar vertebra of the syntype (figured in Müller 1849: 26, pl. XX, series II, “No. 6”) as the lectotype of P. brachyspondylus . By this designation, Gingerich (2007) assumed that there were no other vertebrae of the syntype securely belonging to the same specimen as “No. 6”. However, Müller (1849) pointed out that the lumbars of the syntype belonged only to two different individuals (specimens “(1)” and “(2)” in Kellogg 1936: 248). Therefore, it is probable that other vertebrae of the syntype may belong to the lectotype (“No. 6” in Müller 1849), although they cannot be identified. Furthermore, the lectotype of P. brachyspondylus does not present any diagnostic feature that could differentiate it from Cynthiacetus or Masracetus (see below). Therefore, Pontogeneus brachyspondylus is regarded here as a Basilosauridae incerta sedis and its use is restrained to the lectotype and paralectotype series. Most of the specimens previously referred to P. brachyspondylus have been referred to Cynthiacetus maxwelli ( Uhen, 2005) or Masracetus markgrafi (cf. below and Gingerich 2007). Moreover, a third cervical referred to Zeuglodon brachyspondylus ( Dames 1894) bears a very large vertebrarterial foramen, a character observed only in Cynthiacetus ( Fig. 4 ). Currently housed in the Museum für Naturkunde in Berlin, this third cervical is associat- ed with an axis and the specimen is regarded here as cf. Cynthiacetus sp.

Figures

FIG. 4. — Comparison of the middle cervical vertebrae in large basilosaurids: A, MMNS VP455, third cervical vertebra of Cynthiacetus maxwelli; B, UM-WH74, third cervical vertebra of Basilosaurus isis; C, ANSP 13668, holotype of Pontogeneus priscus, probably a C3 or C4 (from Kellogg 1936); D, MffNB uncatalogued, third cervical vertebra of Cynthiacetus sp. (referred to Zeuglodon brachyspondylus by Dames [1894]). Note the large vertebrarterial foramina in C. maxwelli and P. priscus as compared to B. isis.