Bebej et al.—First remingtonocetid archaeocete from Egypt from Egypt
Sacrum.—The sacrum of Rayanistes afer includes four vertebrae, S1–S4 (Fig. 3.9–3.11). The ventral surface of the sacrum is heavily weathered, and much of it is not preserved. The auricular process is absent on the left side and poorly preserved on the right side. Dorsal sacral foramina are large (ranging from 1.9cm to 2.6 cm in diameter). The anterior and posterior epiphyses of S4 are circular in cross-section. As a whole, the sacrumofCGM42190 appears less robust than sacra known in specimens of Remingtonocetus domandaensis (Bebej et al., 2012), but this is partly because so much of the ventral surface has been eroded away. The overall length of S1–S4 and the size and thickness of the fused neural spines between S2 and S3 demonstrate that the sacrum of R. afer was a robust element. Like most other remingtonocetids, S1–S3 were fused
together whereas S4 remained free (Bebej et al., 2012); however, the pattern of fusion among S1–S3 in R. afer is unique. In R. domandaensis (GSP-UM 3408 and 3552), S1–S3 are solidly fused across centra, neural spines, zygapophyses, and pleurapophyses. In CGM 42190, the centrum of S1 is not fused to that of S2, although the centra of S2 and S3 are solidly fused together. The pleurapophyseal shelf appears continuous across S1–S4. There are pleurapophyseal articulations, but there is no pleurapophyseal fusion apparent between any of the sacral vertebrae. The neural spines of S2–S3 are fused together; however, the base of the incomplete neural spine of S1 is free from that of S2, suggesting a lack of fusion between these neural spines (at least near their bases). Zygapophyses between S1–S2 and S2–S3 are fused together, and those between S3–S4 may have been fused as well.
Caudal vertebra.—An additional almost complete vertebra is identified as Ca1 (Fig. 3.5–3.6). Anterior and posterior epiphyses are missing, but these were circular in cross-section. Robust transverse processes project laterally from the centrum, with a slight ventral curvature. Both left and right transverse processes are broken distally, but they appear to have been knob-like as in Ca1 of Remingtonocetus domandaensis (GSP-UM 3408; Fig. 3.7–3.8). The neural arch rises from the anterior part of the centrum and defines a semicircular neural canal. Pre- and postzygapophyses are not preserved. The neural spine is incomplete but appears to be mostly vertical in orientation. An additional fragmentary centrum might be that of Ca2, but it preserves little additional anatomical detail.
Innominate.—The left innominate of CGM 42190 preserves a virtually complete ilium, ischium, and acetabulum (Fig. 4.1). The acetabulum is large (4.0cm in diameter) and roughly circular. It is similar in size and shape to the acetabulum in Remingtonocetus domandaensis (GSP-UM 3408: 4.0cm on the right and 3.9cm on the left; GSP-UM 3552: 4.0 cm), and it is notably smaller than acetabular diameters typical for Dalanistes ahmedi (e.g., GSP-UM 3089: 4.6 cm; GSP-UM 3106: 4.5 cm; GSP-UM 3296: 4.4 cm). The lunate surface of CGM 42190 encompasses almost the entire circumference of the acetabulum, resulting in an acetabular notch that is very narrow (Fig. 5.1) like those seen in other remingtonocetids (Fig. 5.2–5.4), and unlike the broader acetabular notch seen in protocetids and other archaeocetes (Fig. 5.5–5.6).
889 The ilium is similar in size and overall shape to that of
R. domandaensis (GSP-UM 3552; Fig. 5.3). It is long, bears a broad auricular surface on the medial aspect of the ala for articulation with the sacrum, and exhibits a lateral flare away from the midline. The iliac body possesses a roughened area just anterior to the acetabulum that is approximately triangular in shape. This corresponds to the distinct triangular rugose depression for origin of the m. rectus femoris present in R. domandaensis (GSP-UM 3408 and 3552) and D. ahmedi (GSP-UM 3106 and 3296). The ilium of Rayanistes afer also has some notable differences compared to that of R. domandaensis. The ala of the ilium is slightly narrower dorsoventrally compared to that in R. domandaensis (GSP-UM 3552), yet the body and ala are both thicker mediolaterally, making the ilium of R. afer more robust. In addition, the distal-most tip of the ala in CGM 42190 comes to a prominent tuberosity that is not apparent in R. domandaensis (GSP- UM 3552). The ischium of R. afer is longer anteroposteriorly than the
ilium. The body of the ischium nearest to the acetabulum is narrower dorsoventrally, thicker mediolaterally, and rounder in cross-section than that of R. domandaensis (GSP-UM 3552). The dorsal margin of the ischium curves dorsally and medially, forming a complex, three-cornered ischial tuberosity that outlines a very broad and flat ischiatic table for attachment of muscles that served to retract the hind limb and flex the knee joint. The ischiatic table in CGM 42190 is more than twice as large as the comparable surface area preserved in R. domandaensis (GSP-UM 3552). The fragmentary innominate described for Kutchicetus minimus (IITR-SB 2647.32; Thewissen and Bajpai, 2009) suggests that it too may have had a similarly expanded ischiatic table. A piece of what appears to be the pubis was recovered with
CGM 42190. It is not attached to the rest of the innominate, but is similar in size and shape to the pubis of R. domandaensis (GSP-UM 3552).
Femur.—The femur of Rayanistes afer preserves the head, neck, greater trochanter, intertrochanteric fossa, base of the lesser trochanter, and shaft down to the distal epiphyseal plate (Fig. 6.1–6.2). This was found in two pieces, broken just distal to the lesser trochanter, but very little bone is missing. The cross-section visible at this point indicates that cortical bone is thick, and even the cancellous bone appears very dense. The proximal portion of the patellar groove is apparent, but the distal epiphysis and condyles are not preserved. The femur of R. afer is similar in size to the femur of Remingtonocetus domandaensis (GSP-UM 3054), which is also incomplete distally, but the femur of R. afer is more robust. The femoral head of R. afer is spherical and smooth,
lacking a distinct fovea capitis femoris. It is larger in diameter than that of R. domandaensis and is oriented more vertically on a much thicker neck. The greater trochanter in both species extends above the head to about the same degree, although both the greater and lesser trochanters of R. afer appear more substantial than those of R. domandaensis. Together the trochanters help define a large intertrochanteric fossa. The femoral shaft R. afer is more circular in cross-section and lacks
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