Gen. indet.

Zouhri, Samir, Gingerich, Philip D., Khalloufi, Bouziane, Bourdon, Estelle, Adnet, Sylvain, Jouve, Stéphane, Elboudali, Najia, Amane, Ayoub, Rage, Jean-Claude & Tabuce, Rodolphe, 2021, Middle Eocene vertebrate fauna from the Aridal Formation, Sabkha of Gueran, southwestern Morocco, Geodiversitas 43 (5), pp. 121-150 : 132-134

Gen. et sp. indet .

EXAMINED MATERIAL. — FSAC Bouj-109 ( Fig. 5H ), costal fragment; 352 ( Fig. 5I ), fragmentary hyoplastral process; 351 ( Fig. 5J ) fragmentary hypoplastron; 353 ( Fig. 5K ) and 354 ( Fig. 5L ), dermal plate fragments.

DESCRIPTION

FSAC Bouj-109 ( Fig. 5H ) is a fragment of costal of a largesized turtle, covered by three scute parts. The thoracic rib is visible, included in the dermal bone, lentoid in cross-section and roundly protruding along the ventral costal face. The direction of the rib and scutes indicate a medial fragment of costal, not far from the neural, covered by two successive vertebrals (medially) and the corresponding pleural scute (laterally). The ornamentation of the plate is formed by irregular dichotomic sulci on a rough and granulous surface, which are features found in the basic ornamentation of Cheloniidae ( Lapparent de Broin et al. 2014) .

FSAC Bouj-352 ( Fig 5I ), a fragmentary lateral process of right hyoplastron, and Bouj-351 ( Fig. 5J ) a subcomplete right hypoplastron, probably belong to the same individual. Both fragments show a granulous surface with protruding elongated polygones and dichotomic sulci, representing ornamentation features known in cheloniids. Digitations of hyoplastral and hypoplastral lateral processes are broken close to their base. However, they are much enveloped in the dermal callosity and seem to have shortly overtaken the callosity border. Between both lateral processes lies an important lateral fontanelle that was originally rectangular or square. The medial part of the hypoplastron, along with its counterpart, indicates a very short and narrow central fontanelle with a triangular posteromedial border, and posteriorly both hypoplastra were close and lacked digitations on their medial border. The main body of the hypoplastron is posteriorly broken anterior to the contact with the xiphiplastron, close to the area of the abdominofemoral sulcus. Anterior to the inguinal notch on the lateral hypoplastral process, an inguinal scute sulcus (i.e. the posterior inframarginal of the complete series that is present in cheloniids) joins the area of the femoroabdominal sulcus medially. The lateral hyo-hypoplastral processes are narrower than the main medial body of each hypoplastron, and consequently the lateral fontanelles are narrower than the main hypoplastral bodies and they are narrower than high. The base of each lateral, hyoplastral and hypoplastral process is also shorter than the length of the lateral fontanelles.

FSAC Bouj-353 ( Fig. 5K ) and Bouj-354 ( Fig. 5L ) are fragments of dermal plate which are not located on the shell. Bouj-354 shows a granular surface, not clearly polygonal, and probably corresponds to the same individual as Bouj-352 ( Fig. 5I ) and Bouj-351( Fig. 5J ). Bouj-353 shows a comparable ornamentation.

REMARKS

FSAC Bouj-352 ( Fig. 5I ), Bouj-351 ( Fig. 5J ) and possibly Bouj-354 ( Fig. 5L ) are parts of the same cheloniid individual, being found lying together in one piece ( Fig. 5P ), which also contained Bouj-350 ( Fig. 5M ), a dermochelyid remain. Bouj-353 ( Fig. 5K ) was probably collected near this piece and corresponds to the same cheloniid and possibly to the same individual.

The combination of the nearly flat bridge (not an obliquely elevated bridge), surface ornamentation, and fenestration of the plastron matches the cheloniid pattern. Only few middle to late Eocene cheloniids are known from their plastron in the Old World. Among the various cheloniid clades, some cheloniid genera were grouped in the western- European “ Eochelyinae Moody, 1968 ”, now considered as a paraphyletic taxon representing an evolutionary grade ( Lapparent de Broin et al. 2014, 2018). The Gueran species, represented by Bouj-351 and Bouj-352, represents this grade. It differs from the defined species included in the group in the relative proportions of the hyo-hypoplastral main body, in relation to the lateral and central fontanelles. There are several species in the early Eocene of the London Clay basin (Ypresian of the Isle of Sheppey (Kent) and Harwich (Essex) ( UK), described by Owen & Bell (1849) and Owen (1849-1884). Boujdour species is similar to “ Chelone breviceps Owen, 1842 ” (see Owen & Bell 1849: pl. 2), i.e. a junior synonym of Argillochelys antiqua (König, 1825) , in the shape of the quadrangular lateral fontanelles, but it differs in the wider proportions of these lateral fontanelles correlated with a narrower hypoplastral main body, and it differs in the robustness of the plates. However, the central fontanelle was narrow and short in both species. By contrast and as A. antiqua , the Gueran species differs from “ Chelone convexa ” (undefined taxon, perhaps a junior synonym of Argillochelys cuneiceps Owen , in Owen & Bell, 1849, the shell of which is not defined), Eochelone brabantica Dollo, 1903 (Lutetian, middle Eocene of Brabant, Belgium) and Eochelone voltregana Lapparent de Broin, Murelaga , Pérez- García, Francesc Farrés & Altimiras, 2018 (Priabonian of Osona county, Spain) in the much narrower central fontanelle, the main body of each hypoplastron being wider, but it is similar in the quadrangular lateral fontanelle general proportions. And in the robustness of the plastral elements, it is similar to E. voltregana . The Gueran species also differs from Puppigerus camperi (Gray, 1831) (Ypresian of London Clay and Lutetian of Brabant) in the lateral fontanelle size and shape, this structure being much smaller and triangular in Puppigerus Cope, 1871 adults with much wider hypoplastra, in a much wider plastron as a whole (due to the more developed shell ossification characteristic of this taxon) ( Moody 1974; Lapparent de Broin et al. 2018).

Figures

FIG. 5. — Actinopterygii and Testudines from the Sabkha of Gueran: A-G, Actinopterygii: Cylindracanthus sp., FSAC Bouj-356, rostrum in (A1) lateral and (A2) transversal views; B-E, Percomorpha indet.: B, FSAC Bouj-369,vertebra in (B1) lateral and (B2) transversal views; C, FSAC Bouj-363, vertebra in (C1) lateral and (C2) transversal views; D, FSAC Bouj-370, basioccipital in left lateral view; E, FSAC Bouj-371, fin spine in anterior view; F, Scombridae indet., FSAC Bouj-358, incomplete jawbone in labial view; G, Siluriformes indet., FSAC Bouj-372, right pectoral spine in anterior view; H-P, Testudines: H-L, Cheloniidae indet., FSAC Bouj-109,fragmentary costal in (H1) lateral transection, (H2) ventral, (H3) dorsal and (H4) medial transection views; I, FSAC Bouj-352,fragmentary lateral process of right hyoplastron in (I1) ventral and (I2) dorsal views; J, FSAC Bouj-351, subcomplete right hypoplastron in (J1) ventral and (J2) dorsal views; K, FSAC Bouj- 353, fragment of dermal plate, unlocated on the carapace, in dorsal view; L, FSAC Bouj-354, fragment of dermal plate, unlocated on the shell in (L1, L2) both faces; M, Dermochelyidae indet., FSAC Bouj-350, lateral pubic process of right pubis in (M1) ventral and (M2) dorsal views; N,? Podocnemidoidea indet., FSAC Bouj-196, fragment of right hypoplastron in (N1) dorsal and (N2) ventral views; O, Indeterminata (? Podocnemidoidea indet.), FSAC Bouj-95, fragment of dermal plate of carapace in (O1) dorsal and (O2) ventral views; P, Gueran turtles, pieces of the four fragments of Figure 5I, J, L and M, as preserved in view of conjunction in situ. Scale bars: 20 mm.