Masracetus markgrafi Gingerich 2007

Zeuglodon isis Stromer, 1908: 128 (in part).

Zeuglodon cf. brachyspondylus Müller, 1849:26-28. — Stromer 1908: 136. — Kellogg 1936: 262. — Slijper 1936: 319.

Cynthiacetus maxwelli Uhen, 2005: 160 (in part).

HOLOTYPE. — SMNS 11414, vertebral column, part of specimen ‘St. 8’ in Stromer (1908: 129). The associated skull is catalogued as SMNS 11413.

TYPE LOCALITY AND HORIZON. — Uhen (2005) pointed out that SMNS 11414 and SMNS 11413 could come from the Gehannam Formation (Bartonian) of the Fayum Province, Egypt. However, Gingerich (2007) follows Kellogg (1936) and indicates that the holotype of M. markgrafi comes from the Birket Qarun Formation, in the vicinity of Dimeh, also in the Fayum Province. This formation is regarded as early Priabonian in age by Gingerich (1992).

DIAGNOSIS. — Large basilosaurid lacking the vertebral elongation observed in Basilosaurus. Masracetus is slightly larger than Cynthiacetus with a lower lumbar length-to-width ratio Llum / Wlum (Gingerich 2007). DISCUSSION

The holotype of Masracetus markgrafi was initially referred to Z. brachyspondylus (Stromer 1908) and more recently to C. maxwelli (Uhen 2005). Gingerich (2007) pointed out that Masracetus differs from other basilosaurids in the size and proportions of its lumbar vertebrae. Based on this feature, Gingerich (2007) hypothesizes that Pontogeneus brachyspondylus could be referred to Masracetus. Because a comparison of lumbar ratios in a large sampling of basilosaurid specimens (Table 2) does not clearly distinguish Cynthiacetus from Masracetus, the differences between the two genera could very well represent intra-specific variation (when compared to the variation observed in D. atrox and Z. kochii). Until study of the most complete specimen of M. markgrafi (collected in 2006: Gingerich 2007) clarifies the validity of both Masracetus and M. markgrafi, we follow Gingerich (2007) and regard M. markragi as a different species from Cynthiacetus spp.