Fig 1.
Phylogenetic relationships of early cetaceans showing the temporal ranges and general relationships of Pakicetidae, Ambulocetidae, Remingtonocetidae, Protocetidae, and Basilosauridae discussed here.
Table 1.
List of material analyzed in this study.
Fig 2.
Left femur of Remingtonocetus domandaensis, GSP-UM 3054, virtual diaphyseal cross section.
Section located just below the lesser trochanter, about one third of the length of the bone from the proximal end. MC: medullary cavity. The contrast between bone and the infilling sediment shows that the MC is open. Scale bar equals 5 mm.
Fig 3.
Left rib 9 of Rodhocetus kasranii GSP-UM 3012, in anterior view.
A-D, virtual transverse sections (left) and corresponding binary images (right; in black: bone; in white: cavities) following the positions labelled on the rib. Scale bars equal 1 mm.
Fig 4.
A, Rodhocetus kasranii GSP-UM 3012, transverse virtual section of thoracic vertebra T6. B, Qaisracetus arifi GSP-UM 3410, mid-sagittal section of centrum of thoracic vertebra T9. Scale bars equal: A, 10 mm; B, 5 mm.
Fig 5.
Left femur of Rodhocetus kasranii GSP-UM 3012.
A-B, partial longitudinal section in lateral view; proximal is at the top. Limits of the compact cortex (dotted lines), as well as the position of the growth center (GC), are indicated on B; C, transverse section cutting the growth center. Scale bars equal 5mm. Cavities are either filled by sediment (light grey) or by epoxy (black) resulting from bone preparation.
Fig 6.
Virtual transverse sections. A- Right humerus; B- Left femur. Scale bars equal 5mm.
Fig 7.
Left humerus of Qaisracetus arif.
GSP-UM 3318 in virtual longitudinal (A) and transverse (B) sections. The longitudinal section is in posterior view. Scale bars equal 5 mm. Arrows point to LAGs. GC: growth center.
Fig 8.
Left rib 4 of Dorudon atrox UM 101222 (WH-224).
A photo of the rib with scanned segments (1 to 5) and positions of the transverse sections (A to E) labelled is shown on the left in posterior view. Corresponding virtual transverse and longitudinal sections are shown on the right (in center and right columns, respectively). Scale bars equal: A-E, 5 mm; 1–5, 10 mm.
Fig 9.
Proximal portion of the left humerus of Dorudon atrox UM 101222 (WH-224) in virtual transverse section.
Scale bar equals 5mm.
Fig 10.
Dorudon atrox UM 101222 (WH-224).
Virtual transverse sections of the left ulna (A) and radius (B). Scale bar equals 5 mm.
Fig 11.
Basilosaurid femora virtual sections.
A, Proximal right femur of Dorudon atrox UM 97506 (WH-072), longitudinal section in lateral view. B, Distal left femur of female Basilosaurus isis UM 97527 (WH-152), in medial view; C, Proximal left femur of male Basilosaurus isis UM 93231 (WH-132), in medial view. For all sections, anterior is at the left and proximal at the top. In each panel there is a longitudinal partial section on the left and three transverse sections. Scale bars equal 10 mm for longitudinal and 5 mm for transverse sections.
Fig 12.
Virtual transverse section of the humerus of Cynthiacetus peruvianus MNHN.F.PRU 10.
Scale bar equals 5mm.
Fig 13.
Left rib 4 of Basilosaurus isis WH-074.
A-C, transverse sections from the proximal, middle, and distal portions of the rib; medial is at the left and posterior at the top. D, longitudinal section from the middle of the rib, in anterior view; medial is at the left and posterior at the top. Scale bars equal 1 cm.
Fig 14.
Scanned polished sections of lumbar or anterior caudal vertebrae of Basilosaurus cetoides.
A- USNM 510831a, transverse section figured in Fordyce & Watson, 1998; dorsal is at the top. B, USNM 510831b, longitudinal section. Scale bars equal 2 cm.
Fig 15.
Left humerus of Basilosaurus isis UM 94803 (WH-9).
A, Longitudinal section of the specimen in lateral view. B, transverse section. Arrows point to LAGs. Scale bar equals 10 mm.
Table 2.
Summary of the microanatomical features observed.