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884


Journal of Paleontology 89(5):882–893


and a femur lacking a distinct fovea capitis femoris (Gingerich et al., 1995a, 1998; Madar et al., 2002). Remingtonocetid sacra are relatively narrow and long, with a minimal biauricular breadth to sacral length ratio in the range of 0.38 to 0.49. The pakicetid Pakicetus is at the small end of this range (Madar, 2007), and the ambulocetid Ambulocetus is at the large end of this range (Madar et al., 2002). Protocetids, in contrast, have broader sacra, with a minimal biauricular breadth to sacral length ratio in the range of 0.47 to 0.76. Remingtonocetid innominates have bladelike ilia and


ischia rising sharply from the body anterior and posterior to the acetabulum. The acetabulum appears relatively large and deep due to its sharp rim, although measurements of relative size and depth do not show a clear difference from protocetids. The acetabular notch separating ends of the lunate surface within the acetabulum is narrow or closed entirely. Remingtonocetids have an acetabular notch to acetabulum diameter ratio ranging from 0.00 (closed) to 0.12, in contrast to protocetids, for which this ratio ranges from 0.28 to 0.38. Remingtonocetid femora differ from those of most other middle Eocene archaeocetes in lacking a distinct fovea capitis femoris. In addition, remingtonocetid femora have denser cortical bone than those of contemporary protocetids and consequently show less damage due to compression during burial.


Discussion.—Two species of non-basilosaurid archaeocetes (Protocetus atavus and Pappocetus lugardi) were known when the first remingtonocetid specimens were described. Sahni and Mishra (1972) described the first remingtonocetids from the middle Eocene of India, and named the new species Protocetus sloani from a fragmentary cranium and edentulous jaw pieces. Sahni and Mishra (1975) described four additional cetaceans from the Eocene of Kutch: Indocetus ramani and Protocetus harudiensis, which they considered to be protocetid archae- ocetes, and Andrewsiphius kutchensis and Andrewsiphius minor, which they placed in the odontocete family Agorophiidae. Better comparative material allowed Kumar and Sahni (1986) to recognize the distinctness of these taxa, leading them to combine P. sloani and P. harudiensis in the new genus Remingtonocetus, and to group Remingtonocetus and Andrewsiphius together in the new family Remingtonocetidae. Dalanistes ahmedi (Gingerich et al., 1995a), Attockicetus


praecursor (Thewissen and Hussain, 2000), Kutchicetus minimus (Bajpai and Thewissen, 2000), and Remingtonocetus domandaensis (Gingerich et al., 2001a) were placed in Remingtonocetidae mainly on the basis of cranial material with the diagnostically long narrow skulls and rostra of remingtono- cetids. The first specimens of Remingtonocetus with postcranial remains were initially misidentified as the protocetid Indocetus ramani (Gingerich et al., 1993). Discovery of Dalanistes ahmedi with associated skeletal elements enabled the error to be corrected (Gingerich et al., 1995a). Protocetids and remingtonocetids are much better known now than they were in the 1990s, and most of the known remingtonocetid postcranial elements are as distinctive as remingtonocetid cranial elements. Loss of the acetabular notch separating ends of the lunate surface within the acetabulum of the innominate in remingtonocetids means that the acetabular fossa is also greatly reduced or lost, a condition consistent with reduction and loss of


the fovea capitis femoris. Both features indicate reduction or loss of the round (or teres) ligament connecting the femoral head to the acetabulum, suggesting a hip joint with less weight- bearing capability in remingtonocetids compared to other early archaeocetes (see below). Gingerich et al. (1995a, 1998) reported that protocetids lack a distinct acetabular notch, but this was an error due to misidentification of a broken remingtonocetid innominate (GSP-UM 3015) as that of a protocetid.


Genus Rayanistes new genus


Type species.—Rayanistes afer, by monotypy. Diagnosis.—As for type species by monotypy.


Etymology.—A combination of ‘Rayan,’ from Wadi El Rayan, provenance of the holotype, and ‘istes’ (Gr., masc., ‘agent’). This construction parallels Platanista (the modern Indus and Ganges river dolphin) and Dalanistes (the large-bodied remingtonocetid known from Indo-Pakistan).


Occurrence.—Rayanistes is known only from the type locality (see below).


Remarks.—The species described here is placed in a new genus because its distinctive morphology indicates locomotor adaptations different from those of other remingtonocetids.


Rayanistes afer new species Figures 3.1–3.2, 3.5–3.6, 3.9–3.11, 4.1, 5.1, 6.1–6.2


Holotype.—CGM 42190, associated elements of one postcranial skeleton, including a well preserved lumbar vertebra; partially preserved sacrum; well preserved caudal vertebra; left innominate preserving the ilium, ischium, and acetabulum; and a nearly complete left femur. The holotype is the only known specimen. CGM 42190 was collected in the Western Desert of


Egypt near the southern bench of Qaret Qusur El-Arab, 8 km southwest of Minqar El-Rayan and 32km south-southeast of Wadi Al-Hitan. It was recovered from one of the higher terraces in the upper middle part of the Midawara Formation, which is the second formation in the Wadi El-Rayan series of Beadnell (1905). The Midawara Formation rests on the nummulitic limestone platform of the Muweilih Formation and is overlain by hard resistant limestones of the Sath El-Hadid Formation. The Midawara Formation is a multistory sedimentary


package in Wadi El-Rayan. A single sedimentary cycle consists of thick shales and dark green sandy glauconites topped by benches of thin coquinal limestone. The middle part of the Midawara Formation here is 30–40 meters thick and bears a rich middle Eocene assemblage of neoselachians (Underwood et al., 2011) and marine mammals (Gingerich et al., 2013). Based on regional lithological and paleontological correlation between Cairo et al., (2008) found that the Midawara Formation spans the fourth and fifth Mokattamian stages, making it middle to late Lutetian in age.


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