Carcharhinus kasserinensis, Adnet & Marivaux & Cappetta & Charruault & Essid & Jiquel & Ammar & Marandat & Marzougui & Merzeraud & Temani & Vianey-Liaud & Tabuce, 2020

Adnet, Sylvain, Marivaux, Laurent, Cappetta, Henri, Charruault, Anne-Lise, Essid, El Mabrouk, Jiquel, Suzanne, Ammar, Hayet Khayati, Marandat, Bernard, Marzougui, Wissem, Merzeraud, Gilles, Temani, Rim, Vianey-Liaud, Monique & Tabuce, Rodolphe, 2020, Diversity and renewal of tropical elasmobranchs around the Middle Eocene Climatic Optimum (MECO) in North Africa: New data from the lagoonal deposits of Djebel el Kébar, Central Tunisia, Palaeontologia Electronica (a 38) 23 (2), pp. 1-62 : 6-11

Carcharhinus kasserinensis nov. sp.

Figures 3 , 4 A-B zoobank.org/ BBD87F04-3CC9-4B13-9C24-1F37A28DC5D4

2012 Carcharhinus sp. Underwood and Gunter, p.27- 28, fig. 2.

2016 Carcharhinus sp. Merzeraud et al., p. 14-15, tab. 1.

Etymology. Derived from the name of Kasserine region where the holotype comes from.

Type locality and stratum. KEB 1-087 ( Figure 3B ), from Souar-Fortuna Formations in Djebel el Kébar, Amamria hamlet near Soug-Jedid village (Sidi Bouzid Township), Tunisia: locality named KEB- 1 in Merzeraud et al.(2016) and previously dated (radiometric K-Ar datings) as middle Bartonian (38.7 ± 1.0 Ma to 40.7 ± 1.1 Ma, covering the NP17) in Marivaux et al. (2014a) .

Other material. Additional material, including figured KEB 1-086, KEB 1-088 to 1-099, KEB 1-226, 1-227 ( Figures 3A , C-N, 4A-B), mainly consists of several hundred broken upper and lower teeth from the KEB- 1 locality, Souar-Fortuna formations, Djebel el Kébar, Tunisia.

Diagnosis. Medium-sized carcharhinid species belonging to the “Bull-group” and only known by isolated teeth. Marked dignathic heterodonty with flat, blade-like cusps in upper teeth and weak erected, asymetrical cusps in lower teeth. Upper teeth display a triangular crown without distinct anterior heel when lateral heel is reduced to oblique cutting edge, partially notched from the principal cusp. Upper mesial edge of the cusp appears to be deflected distally and both cutting edges are fully but irregularly serrated. Root is large and tall, especially in the central part leading to a medially incurved crown-root boundary in labial view. Lower teeth have an erect cusp with irregularly serrated cutting edges from apex to asymmetrical heels, with one developed mesially or distally. Root is peculiarly massive medially with a deep and wide nutritive groove.

Description

Upper teeth. The specimens reach a maximum 13 mm in width even if some fragments suggest a larger size (up to 17 mm). This tooth size is comparable or larger than the other Middle Eocene representatives of requiem sharks and, thus, was considered as belonging to adults. These teeth, including the holotype ( Figure 3B ), are very labiolingually flattened with a triangular crown more or less slanted distally, in anterior ( Figure 3A ) to lateral files ( Figure 3 C-G), respectively. The mesial and distal cutting edges are fully serrated from the crown-root boundary to the apex of the cusp. The serrations are mainly simple (mono serrated) but particularly irregular and coarser in its lower part ( Figure 3B3 ). “Typical” double serration (e.g., replication of large serrae boarded by a pair of small serrae) appears locally on the cutting edge, but this pattern is never continuously replicated. This feature could be present on both cutting edges even if it is more strongly marked on the distal one of lateral to posterior upper teeth, near the notch distinguishing the cusp from the distal heel. In lingual and labial views, the mesial cutting edge appears straight in its lower part in more anterior files ( Figure 3 A-B) to slightly convex and deflected distally in more lateral files ( Figure 3 G-I). In the same view, the distal cutting edge is slightly concave to strongly angular in anterior to lateral files, respectively. The distal heel, well-marked by a notch and a coarser serration of its cutting edge, is present in antero-lateral to lateral files ( Figure 3 D-H). In labial view, the crown-root boundary is reduced in length and medially arched in both anterior and lateral files. The root is massive, tall, and greater in length than that of the crown, except in parasymphyseal files ( Figure 3A ). The shape of the basal crown border is often medially arched ( Figure 3 B-C) in anterior and lateral files to straight and disrupted by a median notch in posterior files ( Figure 3I ). Lateral extremities of the root are mainly rounded. The root lobes are well developed and separated in lingual view by a nutritive groove, widely open in lateral to posterior files ( Figure 3 C-I), and shallow in anterior and antero-lateral files ( Figure 3 A-C). The nutritive groove is often relatively reduced in the largest teeth ( Figure 3B ) and tends to be erased by abrasion. Some smaller teeth ( Figure 4 A-B), considered as representatives of younger specimens, display similar shapes with adults except for the size of serrations that appears even coarser compared to the tooth size.

Lower teeth. The state of preservation of lower teeth is bad compared to the upper ones. When preserved, lower teeth have a protruding and central cusp, quite symmetrical, with uninterrupted cutting edges from the apex to the basal. If one lateral heel is weakly developed, the other seems always more developed in anterior and lateral files ( Figure 3 K-N). If the smallest one is oblique and continuous with cutting edges of cusp, the biggest is notched by a serration locally coarser, forming a kind of small cusplet. As in the upper teeth, irregular serrations are often more strongly developed in the lower part of the cutting edges (and especially on one heel) than near the apex. Labial and lingual faces are slightly sinuous ( Figure 3N3 ) in profile. The root is well developed with a thick medio-lingual protuberance in lateral view ( Figure 3N3 ). The root lobes, when conserved, have rounded lateral extremities and are separated by a median and nutritive groove ( Figure 3N 1 ), which appears deeper and wider than in upper teeth. An abnormal tooth ( Figure 3J ), possibly from the parasymphyseal file, displays a double cuspided crown and a double nutritive groove as resulting of the fusion of two teeth.

Remarks

Teeth of living species of Carcharhinus have long attracted attention of many scientists giving the extensive literature with well-done illustrations for comparisons (e.g., Compagno, 1988; Naylor, 1990; Naylor and Marcus, 1992; Voigt and Weber, 2011). Carcharhinus kasserinensis nov. sp. clearly differs from any living species in its diagnosis features and particularly in presence of cutting edges with a very irregular mono serration, announcing the beginnings of double serration, and the asymmetrical crown of the lower teeth. Some living Indonesian species (e.g., C. borneensis , C. dussumieri ) display a coarser serration on the distal heel of upper teeth, and asymmetrical lower teeth, but none have the massive aspect of them. Among the rare Paleogene Bull shark group (or whaler sharks) characterized by large serrated upper teeth, the new species C. kasserinensis differs from C. perseus Adnet et al., 2011 from the Early Oligocene of Pakistan in having a stronger dignathic heterodonty (triangular upper teeth and symmetrical lower teeth) with weaker lower and upper teeth. Given the latter trait, C. kasserinensis nov. sp. reminds those of the large C. balochensis Adnet et al., 2011 from the Late Eocene to Early Oligocene of Pakistan and Oman, the medium-sized C. marcinae Ebersole et al., 2019 from mid Bartonian of Alabama, USA, or C. underwoodi Samonds et al., 2019 from the Middle-Late Eocene of Madagascar. However, it differs from the two first in having an irregularly serrated cutting edge when C. balochensis and C. mancinae upper teeth share more regular and compound and/or double serration. It differs from the last one in having a clear dignathic heterodonty with unsymmetrical lower teeth, and irregular mono serration of upper teeth that does not decrease drastically in size near the apex of cusps. Samonds et al. (2019) described a Middle-Late Eocene species of Carcharhinus ( C. underwoodi ) from Madagascar considering that the youngest C. balochensis from the Indian Ocean was invalid and should be synonymized with Galeocerdo eaglesomei . However, as noticed by Ebersole et al. (2019), the latter statement is currently unsupported, eluding that C. balochensis shares classic dignathic heterodonty of Carcharhinus (contrary to Galeocerdo ), a compound serration (never doubly serrate in G. eaglesomei ) and does not show the V-shape root morphology (underlined with the concave labial crown-root boundary) of usual Galeocerdo eaglesomei . In fact, C. underwoodi (Samonds et al., 2019, Figure 3 G-R) probably displays a similar dignathic heterodonty with C. balochensis , if we consider the figured lower teeth finely serrated (Samonds et al., 2019, figure 2M-O) incorrectly attributed to Galeocerdo eaglesomei . Whatever, the median sized species C. underwoodi is easily distinct from the new species having smaller upper teeth with median and distal cutting edges finely serrated. In the Tethysian realm, the oldest fossil evidence of the “Bull-group” has long been reported from the marine Tertiary sediments of Birket-el-Qurun of Fayum, Egypt (Dames, 1883; Stromer, 1905a under the name C. egertoni ) and dated to the late Eocene (Case and Cappetta, 1990). Since then, numerous fossil remains were observed in several Late Eocene deposits of Egypt (BQ, QS and KM) and SW Morocco (Adnet et al., 2010), but the new species C. kasserinensis clearly differs in having a smaller size, irregular serrated cutting edges, and lower teeth with asymmetrical heels.

If we exclude Carcharhinus mancinae from the Bartonian (see Ebersole et al., 2019) and Carcharhinus underwoodi dated with uncertainty to the Middle or Late Eocene (see Samonds et al., 2019), Middle Eocene records of Carcharhinus with serrated upper teeth have been sometimes reported but the material remains extremely scarce and often, have been either incorrectly dated or based on misidentification of other genera (Underwood and Gunter, 2012). Among them, a tooth from the GE (upper middle Eocene) was figured under the name Carcharhinus sp.1 by Case and Cappetta (1990, pl. 7, figures 164–165) and resembles those of C. balochensis , differing substantially from the latter in showing an important difference in size, a compound serration on the basal part of cutting edges (Adnet et al., 2011). Even if Underwood and Gunter (2012) suspected an error, it may represent a possible variant of C. kasserinensis nov. sp. Underwood et al. (2011, p. 57) revised the elasmobranch record of Wadi al Hitan and signaled that requiem sharks of the genus Carcharhinus (e.g., Underwood et al., 2011, Figure 4N from QS) are only abundant within the upper part of the succession (e.g., BQ, QS), where two species are present, including a large form showing strong serration and thus, affinities with C. perseus . However, they noted that rare and often poorly preserved specimens (provisionally referred to the same species in Underwood et al., 2011) were present within all of the underlying units (e.g., MI, GE). Some of them possibly belong to new species C. kasserinensis . More interesting, a large unique upper tooth from the Middle Eocene of Jamaica (Underwood and Gunter, 2012, Figure 2 ), assumed to come from the Chapleton Fm. (Donovan and Gunter, 2001) dated to uppermost Lutetian/lowermost Bartonian (Mitchell, 2016), is similar to the new species in overall shape. Not named, the upper tooth shows similar size and similar irregular serrations with new species. Coming from contemporaneous deposit (unverified), this tooth could represent a western record of these fossil great requiem sharks in the Tethys seaway, when those of Egypt would be the eastern representatives. Adnet et al. (2010) and Underwood and Gunter (2012) suspected that the great Carcharhinus and related genera arose as a dominant tropical marine clade during the Middle-Late Eocene.The new species and the coeval C. mancinae recently described by Ebersole et al. (2019) in contemporaneous deposits of Alabama, USA, confirm and precisely date the rise of the requiem sharks to Bartonian in Western Central Atlantic (Alabama) - Western Tethys seaway ( Tunisia) with a sufficient and well-dated material.

As in the great White Shark lineage (see Nyberg et al., 2006; Ehret et al., 2009, 2012), the emergence of the serration on upper teeth observed between the oldest pool (unserrated teeth in Cosmopolitodus hastalis ) and living form was quite progressive, from irregular (e.g., Carcharodon hubbeli ) to well-developed and regular serration (e.g., living Ca. carcharias ). Moreover, Ehret et al. (2012) confirmed that the serrated tooth of pacific Ca. hubbelli was probably adapted for taking marine mammals as prey, compared to the coeval piscivorous Co. hastalis (e.g., Collareta et al., 2017). Even if the comparison is not as robust, the serrations of C. kasserinensis nov. sp. are well marked and enlarged basally compared to coeval large carcharhinid sharing unserrated tooth (e.g., Negaprion , other Carcharhinus , Sphyrna ) but weaker overall and more irregular than those of coeval C. mancinae (characterized by a compound and/or double serrations) and younger taxa from the Late Eocene/Early Oligocene like C. underwoodi , C. balochensis or C. perseus , and all the extant species recovered since the Neogene. As the evolution of serrations or crenulations in shark would be advantageous for competition with coeval piscivorous taxa in exploring new prey (e.g., marine mammals and/or prey that needs to be sliced up and cannot be swallowed whole), it is not surprising that more than one taxa (e.g., among Carcharhinus , Hemipristis , Galeocerdo , and Otodus / Carcharocles ) would acquire serrations during the Middle Eocene along the tropical coasts where several marine mammals (e.g., archaeocetes, sea cows) raised, too.

Specimens repositories. Holotype and Paratypes are deposited in the paleontological collections of the museum of the “ Office National des Mines ” of Tunis , 24 rue 8601, 2035 La Charguia, 1080 Tunis, Tunisia

Temporal range.?Early Bartonian ( Jamaica) to middle Bartonian ( Tunisia).

cf. “ Carcharhinus” frequens (Dames, 1883)

Figure 4 C-G

1883 Carcharias (Aprionodon) frequens Dames ; Dames, p143-144, tab.3, figs. 7a-p

1905a Carcharias sp. ; Stromer, p. 176-177, tab. 16(14), figs. 16-19, 21, 23-17, 28

1908 Carcharias (Aprionodon) aff. frequens Dames ; Priem, p. 414, pl. 15, figs. 6,7

1971 Aprionodon frequens Dames ; Casier, p. 2, pl.1, fig. 6.

1990 Carcharhinus frequens (Dames) ; Case and Cappetta, p. 12-13, pl. 5, figs. 102-107, pl. 7, fig. 143-148, 151-159.

2010 Carcharhinus frequens (Dames) ; Adnet et al., p. 863-864, tab. 1.

2011 Carcharhinus aff. frequens (Dames) ; Adnet et al., p. 32, fig. 3G–H.

2011 Negaprion sp. ; Underwood et al., p. 52-62, tab. 1, fig. 5T–U.

2012 Negaprion frequens (Dames) ; Zalmout et al., p.80, fig. 5A-D.

2017 Negaprion frequens (Dames) ; Van Vliet et al., p. 10, fig. 12G.

2019 cf. “ Carcharhinus” frequens (Dames) ; Sweydan et al., p. 198, fig. 3IJ

Material. Material consists of a fifty broken upper and lower teeth from KEB- 1 locality, Souar-Fortuna formations, Djebel el Kébar, Tunisia, and including the figured material KEB 1-100 to 1- 104 (Figure

4C-G).

Description

With rather moderate dignathic heterodonty, teeth of this carcharhinid species are somewhat gracile and of small size (up to 1 cm). There is no serration on both mesial and distal cutting edge as well as on the heels of upper and lower teeth.

Cutting edges are continuous from heels to top of cusps and never notched, including in the more posterior files. For both upper and lower jaws, the labial face of the tooth crowns is flat, whereas the lingual face is convex. Upper teeth ( Figure 4 C-D), have a cusp rather large at its base, triangular, and more or less slanted distally depending on their position on the jaw. Lower teeth ( Figure 4 E-G) have a higher cusp, straight and slender compared to the previous ones. Crown heels are lesser marked in anterior lower files. The root is developed, low, and separated into two distinct lobes by a shallow nutritive groove. The root lobes in lower teeth are shorter than those of the upper teeth and always separated by a nutritive groove.

Remarks

Frequently attributed to the genus Negaprion (see synonyms list), Sweden et al. (2019) summarized the discussions around the unresolved generic status of this taxa. Material from Tunisia, too scarce, does not allow improvement. Despite a general size twice or three times smaller compared to the Late Eocene representatives from Egypt where this species was formally described (e.g., Dames, 1883; Case and Cappetta, 1990), there is no real difference in tooth morphology. Often misidentified (see also Sweyden et al., 2019), this species was previously known in EG (Strougo et al., 2007) and since then in GE (A-C), Fayum - Egypt (Underwood et al., 2011; see Sweydan et al., 2019 for a review). Relatively rare in GE, this species is considered as the most abundant carcharhinid in the younger fossil assemblages of BQ, Fayum (Dames, 1883; Case and Cappetta, 1990). Subsequently reported from many other Late Eocene localities, cf. “ Carcharhinus” frequens seems to have been a frequent medium-sized carcharhinid that frequented all the western Tethys seaway, from Southwestern Morocco to Qatar (Dames, 1883; Strömer, 1905a; Casier, 1971; Case and Cappetta, 1990; Murray et al., 2010; Adnet et al., 2011; Underwood et al., 2011; Zalmout et al., 2012; Sweyden et al., 2019) until its disappearance after the Rupelian in Egypt (Murray et al., 2014; Van Vliet et al., 2017). Here we report the oldest well-dated occurrence of that taxon, which demonstrate that this common Late Eocene tropical carcharhinid actually occurs since the middle Bartonian. Clearly different from C. kasserinensis nov. sp. in having slender upper teeth, cf. “ C.” frequens possibly represents the ancestral pool of piscivore Carcharhinus that now includes the living finetooth shark C. isodon (Müller and Henle, 1839) and the smoothtooth blacktip shark C. leiodon Garrick, 1985 .

Figures

FIGURE 1. Paleotemperatures (ice-free deep-ocean T°/ tropical sea surface T°) and Thermic events during the “doubthouse” conditions of Eocene period (from Cramwinckel et al., 2018 modified with events dating from Hollis et al., 2019). Stratigraphically and geographical locations of the main deposits with Elasmobranch associations along the southwestern Tethys. Abbreviations: DAK: Dakhla (Adnet et al., 2010), GEN: Genam (Zouhri et al., 2017, in press); AZ: Aznag (Tabuce et al., 2005) PM: Phosphate ores (see Noubhani and Cappetta, 1997), Morocco; GAF: Gafsa basin (see Arambourg, 1952); KEBAR: Kébar (this work and Adnet et al., 2019); MBK: Mabrouk (see Sweydan et al., 2019), Tunisia; EG: ElGedida (see Strougo et al., 2007); KM: KM11 (see Adnet et al., 2011) MT: Minqar Tabaghbagh (see Zalmout et al., 2012); BQ: Birquet Qarun QS: Quar et Sa; GE: Genahamm Fm.; MI: Midawara FM. from Wadi al Hitan, see Underwood et al., 2011), Egypt; QD: Qa Faydat al Dahikya, Jordania, see Mustafat and Zalmout, 2002).

FIGURE 2. Locality of KEB-1, Djebel el Kébar, Kasserine region, Tunisia. A, Simplified topographic map of Tunisia locating the Djebel el Kébar in central Tunisia; B, simplified stratigraphical position of fossiliferous level having yielded the fossil-bearing KEB-1 locality; C, photograph showing the typical badlands of variegated clays from the early Tertiary sequence of Djebel el Kébar. See Merzeraud et al. (2016) for precise details about geological settings.

FIGURE 3. A-N: Carcharhinus kasserinensis nov. sp. A. Parasymphyseal upper tooth KEB 1-086, A1. labial view, A2. Lingual view; B. HOLOTYPE Anterior upper tooth KEB 1-087, B1. Labial view, B2. Lingual view, B3. Magnificence of mesial cutting edge; C. Antero-lateral upper tooth KEB 1-088, C1. Labial view, C2. Lingual view; D. Antero-lateral upper tooth KEB 1-089, D1. Labial view, D2. Lingual view; E. Antero-lateral upper tooth KEB 1-226, E1 Lingual view, E2. Labial view; F. Antero-lateral upper tooth KEB 1-227; G. Antero-lateral upper tooth KEB 1-090, G1. Labial view, G2. Lingual view; H. Lateral upper tooth KEB 1-091, labial view; I Posterior upper tooth KEB 1-092, lingual view; J. Symphyseal abnormal lower tooth KEB 1-093, J1. Labial view, J2. Lingual view; K. Anterior lower tooth KEB 1-094, labial view; L. Anterior lower tooth KEB 1-095, L1. Labial view, L2. Lingual view; M. Antero-lateral lower tooth KEB 1- 096, M1. Labial view, M2. Lingual view; N. Antero-lateral lower tooth KEB 1-097, N1. Lingual view, N2. Labial view, N3. Profile.

FIGURE 4. A-B: Carcharhinus kasserinensis nov. sp., A. Antero-lateral upper tooth of young specimen KEB 1-098, A1. Lingual view, A2. Labial view; B. Antero-lateral upper tooth of young specimen KEB 1-099, labial view. C-G: Carcharhinus frequens. C. Lateral upper tooth KEB 1-100, C1. Labial view, C2. Lingual view; D. Lateral upper tooth KEB 1-101, D1. Labial view, D2. Lingual view; E. Anterior lower tooth KEB 1-102, E1. Labial view, E2. Lingual view; F. Lateral lower tooth KEB 1-103, F1. Labial view, F2. Lingual view; G. Posterior lower tooth KEB 1-104, lingual view; H- K: Misrichtys sp. H. Anterior lower tooth KEB 1-105, lingual view; I. Lateral upper tooth KEB 1-106, labial view; J. Posterior lower tooth KEB 1-107, j1. Labial view, J2. Lingual view; K. Lateral upper tooth KEB 1-108, labial view; L-R: Rhizoprionodon sp. L. Anterior upper tooth KEB 1-126, labial view; M. lateral upper tooth KEB 1-127, labial view; N. Lateral upper tooth KEB 1-128, labial view; O. Anterior lower tooth KEB 1-129, labial view; P. Lateral lower tooth KEB 1-130, P1. Labial view, P2. Lingual view; Q. Posterior lower tooth KEB 1-131, labial view; R. Antero-lateral lower tooth KEB 1-132, R1. Labial view, R2. Lingual view.