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Journal of Paleontology 89(5):882–893


(ratio of notch width to acetabulum diameter of 0.09); and a femur with dense cortical bone and lacking a distinct fovea capitis femoris. Rayanistes afer is distinctive among remingto- nocetids in having the neural spine on L6 angled posteriorly; an innominate with an ilium that is lower dorsally and an ischium that extends much higher dorsally; and in having a femur with a shorter neck, more vertically oriented head, and more circular diaphyseal cross-section with no distinct lateral flange. Rayanistes afer is closest to Remingtonocetus domandaensis


and Remingtonocetus harudiensis in size but differs (to the extent they can be compared) from Remingtonocetus and Dalanistes in orientation of the neural spine on the last lumbar vertebra (Fig. 3); relative development of the ilium and ischium on the innominate (Fig. 4); and orientation of the head, length of the neck, and robustness of the greater trochanter on the femur (Fig. 6). Rayanistes afer differs from Andrewsiphius sloani in being larger, and in the orientation and relative size of the femoral head. Rayanistes afer is closest in innominate morphology to Ambulocetus natans, but differs in having a larger acetabulum (Fig. 4), a narrower acetabular notch (Fig. 5), and a much shorter femur with a larger femoral head (Fig. 6).


Occurrence.—Rayanistes afer is known only from the type locality of middle to late Lutetian age (early middle Eocene) in Fayum Province, Egypt.


Description.—The preserved lumbar vertebra, sacrum, caudal vertebra, innominate, and femur of Rayanistes afer are described separately in detail below. Measurements are given in Table 1.


Etymology.—Species name ‘afer’ (L., ‘Africa’) refers to the provenance of the holotype and its significance as the first remingtonocetid known from the African continent.


Lumbar vertebrae.—CGM 42190 includes one well-preserved lumbar vertebra (Fig. 3.1–3.2), with fragments of others. This is identified as L6 because it has a transverse process with an anteroposteriorly shorter and more angled base, like that of L6 in Remingtonocetus (Bebej et al., 2012). Anterior and posterior epiphyses are reniform and come to slight corners laterally at the level of the transverse processes. A thin, short transverse process is preserved on the right side. It projects anteroventrally from the centrum, but extends very little laterally. The pedicles supporting the neural arch are thick (approximately 1.5cm mediolaterally) and outline a neural canal that is semicircular to triangular in shape. Slight depressions for attachment of ligamenta flava are present on the anterior laminae dorsal to the neural canal, but they are not nearly as prominent as the deep ligamentous pits present on lumbar vertebrae of R. domandaensis (GSP-UM3552). Prezygapophyses are gently curved and face dorsomedially. Metapophyses are present, but not as robust as those of R. domandaensis (GSP-UM 3552). Postzygapophyses are not preserved. The base is all that remains of the neural spine, and its angulation indicates that the neural spine was inclined posteriorly rather than anteriorly or vertically as in all other remingtonocetids. An additional partial lumbar centrum is tentatively identified as L5. Only the right dorsal-most portion of the


Table 1. Measurements of vertebrae and hind limb elements of Rayanistes afer n. gen. n. sp. compared to those of Remingtonocetus domandaensis


Measurement


Lumbar vertebrae L5 centrum length L6 centrum length


L6 centrum anterior width L6 centrum anterior height L6 centrum posterior width L6 centrum posterior height L6 neural canal width L6 neural canal height Sacrum


S1-S4 total length


Sacrum width over auricular processes S1 centrum length


S1 centrum anterior width S1 centrum anterior height S1 neural canal width S1 neural canal height S2 centrum length


S2 centrum anterior width S3 centrum anterior width


Rayanistes afer


Rem. domandaensis


CGM 42190 GSP-UM 3408 5.31 5.40 5.78 4.44 6.10 4.38 2.46 1.90


5.14 5.23 5.32 4.14 5.31 4.05 2.53 1.75


CGM 42190 GSP-UM 3408 22.20 9.40 5.54 4.23 —


20.20 9.80


2.76* 1.84 5.12


S2 centrum anterior height —— S3 centrum length


4.28* 5.23


S3 centrum anterior height —— S4 centrum length


3.66 5.54


S4 centrum anterior width S4 centrum anterior height Caudal vertebra Ca1 centrum length


Ca1 centrum anterior width Ca1 centrum anterior height Ca1 centrum posterior width Ca1 centrum posterior height Ca1 neural canal width Ca1 neural canal height Innominate Total length


Acetabulum diameter Acetabulum depth


Acetabular notch width Ilium length from center of acetabulum


Auricular surface (anteroposterior) Auricular surface (dorsoventral)


4.09 3.74


5.25* 5.52


3.85* 2.35 1.86 5.10 4.05


4.75* 3.70


5.14 3.88 3.23


CGM 42190 GSP-UM 3408 4.84 4.44 4.22 5.15 4.50 2.28 1.16


CGM 42190 GSP-UM 3552 33.20* 4.00


4.91 4.39 3.64 5.15 4.08 2.09 1.62


Ilium ramus height anterior to acetabulum 3.42 Ilium ala dorsoventral height


Ischium length from center of acetabulum


Ischial tuberosity height above obturator foramen


Obturator foramen (dorsoventral) —— Femur


Obturator foramen (anteroposterior)


Length (as preserved) Length (maximum) Head diameter Neck diameter


Height of greater trochanter (above head) Midshaft diameter (anteroposterior) Midshaft diameter (mediolateral)


Measurements are in centimeters. *Estimates.


centrum is preserved. It appears similar in length to L6, although its other proportions cannot be accurately estimated. A partial neural spine with a right postzygapophysis (possibly of L5) was also recovered. The postzygapophysis faces ventrolaterally with a strong lateral component, indicating that it must belong to a post-diaphragmatic thoracic or lumbar vertebra. The neural spine on this fragment appears to be inclined posteriorly, corroborating interpretation of the neural spine angle of L6.





Distal breadth (anteroposterior) —— Distal breadth (mediolateral)


22.00* 3.90 3.60 1.00 2.87 2.96


5.84*


Ischial ramus height posterior to acetabulum 2.87 9.04


15.67 9.90


17.50


1.78* 0.37*


8.82* 5.56*


30.00* 4.00 1.60 0.30


10.35


18.10 3.66


12.10* 3.56


7.78* 5.87*


5.70* 7.72


CGM 42190 GSP-UM 3054 19.80


18.70


19.60* 3.50 2.94 1.30 2.47 3.00


5.60*


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