Cylindracanthus, Leidy, 1856

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 : 131

Cylindracanthus sp.

EXAMINED MATERIAL. — FSAC Bouj-141, 356 ( Fig. 5A ), 357, 358, 359, 360, 361, 362, fragments of rostra.

DESCRIPTION

The rostra are incomplete and cylindrical. The external surface is crossed by sub-parallel longitudinal ridges, sometimes convergent. The cross-section is circular, with a notched circumference owing to the longitudinal ridges. A unique median canal lies in the center of the cross-section.

REMARKS

These remains are very common in Boujdour. The notched circular cross-section showing a canal and the fluted external surface correspond to the rostrum of Cylindracanthus . This genus is only known by these peculiar rostra, sometimes showing two rows of minute teeth. They are retrieved in various localities from the Cretaceous to Eocene (and possibly Miocene and Pliocene, see Schultz 1987) in Africa, Asia, Europe, and North and South America ( Schultz 1987; Gallo et al. 2012; Averianov 2014; Grandstaff et al. 2017). Putative isolated vertebrae have also been reported but without anatomical connection with the rostrum, ( Leriche 1910; White 1926). The phylogenetic relationships of Cylindracanthus are still discussed and affinities with chimaeroids, billfishes, dercetids, acipenseriforms and beloniforms have been proposed ( Schultz 1987; Weems 1999; Parris et al. 2001; Monsch 2004; Friedman 2012; Bonde & Leal 2017) while Grandstaff et al. (2017) excluded structural resemblances with the billfish Makaira Lacepède, 1802 and the paddlefish Polyodon Lacepède, 1797 by analysing thin sections. In North Africa, Cylindracanthus occurs in the Ypresian beds of the Phosphate basins of Morocco and Algeria ( Arambourg 1952; Khalloufi et al. 2017), and in the Priabonian beds of Ad-Dakhla ( Adnet et al. 2010).

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.