Fig 10. Proportional maps of centrum size and shape comparing lumbar vertebrae of Moroccan Basilosauridae with European Pachycetus paulsonii and its synonyms.

A, lumbar size and shape in the three common basilosaurids from Gueran and El Briej. All are Bartonian late middle Eocene in age. Dorudontine Chrysocetus fouadassii is the smallest, with lumbars approximately equal in length and width (based on 27 vertebrae of 8 individual specimens). Basilosaurine Eocetus schweinfurthi is the largest, with lumbars longer than they are wide (13 vertebrae of 7 individuals). Pachycetine Antaecetus aithai is intermediate in size, with lumbars longer than they are wide (17 vertebrae of 9 individuals). B, posterior thoracic and lumbar size and shape for 19 centrum lengths and widths listed in Table 6. These are Bartonian late middle Eocene in age. Lumbar type specimens of Zeuglodon paulsonii Brandt, 1873 [25], and Platyosphys einori Gritsenko, 2001 [41], are shown with solid red lines. Slightly smaller posterior thoracic type specimens of Pachycetus robustus Van Beneden, 1883 [28], and Basilotritus uheni Gol’din and Zvonok, 2013 [50], are shown with dashed red lines. All appear to represent a single species, Pachycetus paulsonii. C, lumbar size and shape in male and female Dorudon atrox (CGM 42813 and UM 97512; N = 35) and female Basilosaurus isis (CGM 42195; N = 19) from Wadi Al Hitan in Egypt are shown for comparison. These are Priabonian late Eocene in age. D. atrox is smaller, with shorter and relatively wider lumbars [8]. B. isis is larger, with longer and relatively narrower lumbars (Gingerich et al., in preparation). The variability of the Moroccan taxa is slightly greater than that of Egyptian taxa because more specimens are involved, and measurements of Moroccan taxa were recorded in the field with less measurement precision.