Geronticus olsoni, Mourer-Chauviré & Geraads, 2010

Mourer-Chauviré, Cécile & Geraads, Denis, 2010, The Upper Pliocene Avifauna of Ahl al Oughlam, Morocco. Systematics and Biogeography, Records of the Australian Museum 62 (1), pp. 157-184 : 165-167

Geronticus olsoni n.sp.

Fig. 4G–K

Holotype. Left coracoid, AaO-741.

Horizon and locality. Late Pliocene, age about 2.5 Ma, Ahl al Oughlam, southeast boundary of the city of Casablanca, Morocco.

Paratypes. Left coracoid, slightly incomplete, AaO-837.

Referred material. Right humeri, distal part and shaft, AaO-838, distal parts, AaO-736, 746; left humeri, proximal part, juv., AaO-4804, distal part, AaO-739; right ulna, shaft, AaO-2649; left ulna, proximal part, AaO-4802; right radius, distal part, AaO-2650; left radii, proximal part, AaO-3099, distal part, AaO-4798; right carpometacarpi, distal parts, juv., AaO-742, 848, 2651; left carpometacarpi, distal part, AaO-737, 745, 2662, distal part, juv., AaO-738; phalanges 1 of major digit of wing, AaO-740, 743, 744; right femur, incomplete, AaO-2652; left tibiotarsi, proximal parts, AaO-825, 2653, distal part, AaO-2654; right tarsometatarsus, two trochleae, AaO-752; left tarsometatarsus, almost complete, AaO-2655.

Diagnosis. Species belonging to the genus Geronticus and differing from the two Recent species, G. eremita , the Northern Bald Ibis , and Geronticus calvus , the Southern Bald Ibis , and from the extinct species G. apelex , by its larger size.

Measurements. See Table 4.

Etymology. To Storrs L. Olson, Senior Scientist at the Smithsonian Institution in recognition of his help during the time Cécile Mourer-Chauviré spent at the USNM, in Washington, and in recognition of Helen James’ and Storrs’ hospitality in their home, during the same period.

Curation of the material. The material will be deposited at the Institut National des Sciences de l’Archéologie et du Patrimoine (INSAP), in Rabat, Morocco.

Description and comparisons. Detailed osteological comparisons with the genera of Threskiornithidae present in the collections of USNM, UCBL, and Institut de Paléontologie Humaine, MNHN Paris, make it possible to refer this material to the genus Geronticus . Generally, in the genus Geronticus , the medial part of the sternal facet of the coracoid forms a projecting point, and the medial side of the shaft is concave. However this feature may be subject to a certain amount of variation as in the two skeletons of G. eremita from UCBL, one has a much more projecting point than the other one. The same variation can be observed in Olson’s paper on Pliocene ibises of South Africa ( Olson, 1985b). The coracoid of G. apelex has a point that projects only slightly ( Olson 1985b, fig. 5 A) while that of G. calvus has a slightly more projecting point ( Olson 1985b, fig. 5B). On the two coracoids from Ahl al Oughlam the point is not very projecting and the medial side of the shaft is straighter. However despite this one difference the coracoids of Ahl al Oughlam are similar in all other characteristics to those of Recent members of the genus Geronticus . The procoracoid is well developed medially and extends farther mediad than the acrocoracoid; the Foramen nervi supracoracoidei is situated at a similarly great distance in the sternal direction from the scapular facet; the sternal facet is oblique compared to the longitudinal axis of the bone and the Processus lateralis extends very far in the lateral direction; on the dorsal face, on the medial side, just proximally to the sternal facet, there is a small elongate and flattened surface, along the medial border. This surface is also present in the Recent specimens of G. eremita .

The distal humeri also share the characteristics of the genus Geronticus . They are not very elongated ventrad. The ectepicondylar prominence forms a elongated proximad and projecting dorsad ridge. The attachment of the anterior articular ligament is not very raised compared to the cranial face. The impression of M. brachialis is shallow. There are no particular morphological characteristics on the ulna. A few Papillae remigales caudales are visible.

The distal part of the tibiotarsus is similar to Geronticus due to its strong elongation mediad, the medial condyle is much narrower than the lateral condyle and the Incisura intercondylaris is wide. The tubercle that is found on the lateral side of the distal opening of the Canalis extensorius is not strongly developed in the genus Geronticus , while it is much more developed in the genus Threskiornis . Both Tuberositates retinaculi extensoris are not strongly projecting in the genus Geronticus , while they are more developed in the closely related and potentially confusing genus Pseudibis .

The tarsometatarsus is short and robust as in the genus Geronticus . The Sulcus extensorius is deep proximally, and edged by two ridges. The hypotarsus presents two main ridges. The Crista medialis hypotarsi is incompletely preserved but the Crista lateralis is preserved and has a flattened plantar surface. The two ridges are separated by an open groove. The hypotarsus does not project far plantarly. It is separated from the Cotylae lateralis and medialis by a flattened Sulcus ligamentosus. The Cotyla lateralis has a rounded outline. On the plantar face, the Fossa parahypotarsalis medialis is deep. The lateral face of the shaft is much thicker than the medial face. The Fossa metatarsi I is situated entirely on the plantar face. The opening of the Foramen vasculare distale, on the plantar side, is situated just proximally to the Incisura intertrochlearis lateralis. In all these characteristics the Ahl al Oughlam tarsometatarsus fits the genus Geronticus . It differs from members of the genus Pseudibis which have a Cotyla lateralis with a proximally projecting tubercle in the latero-plantar corner, giving a subquadrangular shape, where the canal which separates the two hypotarsal ridges is roofed, and where the plantar opening of the Foramen vasculare distale is situated further proximally compared to the Incisura intertrochlearis lateralis.

Geronticus olsoni is, on average, 13% larger than the mean of two specimens of Recent G. eremita . According to the measurements given by Olson (1985b) for the main long bones of the two Recent species of bald ibises, the coracoid has the same size, but the wing bones (humerus, ulna, carpometacarpus) are distinctly shorter, the tarsometatarsus is slightly shorter, and the femur is slightly longer in G. calvu s than in G. eremita . Using the measurements given by Olson (1985b) the main long bones of G. olsoni are, on average, 12% larger than those of Recent G. eremita (n = 4) and 16% larger than those of G. calvus (n = 3). The only extinct species described so far in the genus Geronticus is G. apelex from the lower Pliocene of Langebaanweg, in South Africa ( Olson, 1985b). On average G. olsoni is 28% larger than G. apelex .

The area of Casablanca where Ahl al Oughlam is situated is close to the region where Geronticus eremita , an endangered species (del Hoyo et al., 1992), is still breeding. At the present time the Northern Bald Ibis nests on cliff ledges and among boulders on steep slopes, by the sea or inland (Cramp & Simmons, 1977). Although there are no immature elements, it is likely that G. olsoni also nested in the Ahl al Oughlam area.

Order Anseriformes

Figures

Figure 4. (A) Phoebastria sp. cf. P. nigripes, left humerus, distal part, AaO-718, cranial view. Morus peninsularis, B–D: (B) left coracoid, AaO-2108, ventral view; (C) right carpometacarpus, AaO-2643, ventral view; (D) left femur, AaO-724, caudal view. Morus sp. cf. M. bassanus, E–F: (E) right humerus, distal part, AaO-4801, cranial view; (F) left ulna, proximal part and shaft, AaO-2640, craniodorsal view.Geronticus olsoni n.sp., G–K: (G) right humerus, distal part and shaft,AaO-838, cranial view; (H) left coracoid,AaO-741, holotype, dorsal view; (I) idem, ventral view; (J) left tibiotarsus, distal part, AaO-2654, cranial view; … [caption continued on facing page]