Pelagornis, Lartet, 1857

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 : 138-141

Pelagornis sp.

EXAMINED MATERIAL. — FSAC Bouj-373, distal portion of maxillary rostrum bearing pseudo-teeth (two fragments).

MEASUREMENTS (in mm; pseudo-teeth are numbered consecutively from the most proximal to the most distal). — Preserved length of proximal portion of maxillary rostrum = 163.0; preserved length of distal portion of maxillary rostrum = 86.0; minimum length of maxillary rostrum anterior to narial openings = 243.0; length between transverse furrow and tip of maxillary rostrum = 44.0; distance between rostral end of longitudinal sulcus (left side) and tip of maxillary rostrum = 19.2; distance between distalmost rank 1 pseudo-tooth (PT6) and tip of maxillary rostrum = 32.6; length between TPT2 (left side) and tip of maxillary rostrum = 14.0; height of maxillary rostrum (apex to culmen) at the level of PT6 = 23.4; maximal width of bill tip = 18.6; PT1, anteroposterior length at base = 6.0; PT1, height = 4.5; PT2, anteroposterior length at base = 3.7; PT2, height = 1.3; PT4, anteroposterior length at base = 13.6; PT4, height = 10.6; PT6, anteroposterior length at base = 10.3; PT6, height = 8.8; TPT1, anteroposterior length at base = 4.2; TPT1, height = 2.4; distance between PT1 and PT4 = 47.4; distance between PT1 and PT2 = 19.2; distance between PT2 and PT3 = 12.2; distance between PT3 and PT4 = 16.0; distance between PT5 and PT6 = 10.7; distance between PT6 and TPT1 = 10.2.

DESCRIPTION

Anatomical terminology followsBaumel &Witmer (1993), with English equivalents of the Latin nomenclature.FSAC Bouj-373 consists of two fragments of maxillary rostrum that are almost contiguous ( Fig. 6 G-K). The posterior fragment consists of a large portion of maxillary rostrum located anterior to the narial openings ( Fig. 6G, K ). It is mediolaterally crushed and only preserves part of the right side of the maxillary rostrum. The poorly distorted anterior fragment mainly preserves the right side of the maxillary rostrum and the tip of the beak ( Fig.6 H-J).

As in other pseudo-toothed birds ( Pelagornithidae ), spikelike projections called pseudo-teeth are present along the tomial crest of the beak ( Louchart et al. 2018). The tips of preserved pseudo-teeth are eroded. In spite of the bad preservation, pseudo-teeth seem to be arranged in a regular pattern similar to that found in other species of Pelagornis ( Howard 1957; Stidham 2004; Mourer-Chauviré & Geraads 2008; Mayr & Rubilar-Rogers 2010; Ksepka 2014), with large rank 1 pseudo-teeth being separated by three smaller ones, the central rank 2 pseudo-tooth being larger than the adjacent rank 3 pseudo-teeth. In addition, rudimentary rank 4 pseudo-teeth occur in the middle of the space between rank 3 and rank 1-2 pseudo-teeth. In the Gueran specimen, the right tomial crest of the posterior fragment preserves four pseudo-teeth ( Fig. 6G ), including one medium-sized pseudo-tooth (PT1, rank 2) and one large pseudo-tooth (PT4, rank 1). A small pseudo-tooth (PT2, rank 3) and a tiny knob-like pseudo-tooth (PT3, rank 4) are located in the space between the larger pseudo-teeth (PT1 and PT4). The anterior portion of the maxillary rostrum preserves two pseudo-teeth on the right side ( Fig. 6H ), including one rudimentary knob-like pseudo-tooth (PT5, rank 4) and one large pseudo-tooth (PT6, rank 1). Rank 1 to rank 3 pseudo-teeth are conical in shape and stand vertically. On the left side ( Fig. 6J ), two tomial pseudo-teeth (TT1 and TT2) are located between the anterior tip of the rostrum and the first rank 1 pseudo-tooth. These tomial pseudo-teeth are sub-equal in size and more rounded than the other pseudoteeth. Only one tomial pseudo-tooth (TT1) is preserved on the right side, the anterior one (TT2) being broken.

Neurovascular foramina are visible on the bone surface. As in other pseudo-toothed birds, the lateral surface of the maxillary rostrum exhibits a deep longitudinal sulcus ( Fig. 6G, H ), which roughly parallels the culmen just above mid-height of the maxillary rostrum, and curves down at the level of the first rank 1 pseudo-tooth. The anterior end of the longitudinal sulcus lies between the two tomial pseudo-teeth. The anterior tip of the bill is downturned and broadly rounded. It is set apart from the rest of the maxillary rostrum by a transverse furrow ( Fig. 6H ), which is positioned just posterior to the first large pseudo-tooth, as in other species of Pelagornis ( Stidham 2004; Mayr & Rubilar-Rogers 2010; Ksepka 2014; Solórzano & Rincón 2015). The transverse furrow was originally complete across the dorsal surface of the rostrum. However, the specimen only preserves the right side of this structure. The transverse furrow turns anteroventrally near the point where it joins the longitudinal sulcus. As in other pseudo-toothed birds, the ventral surface of the maxillary rostrum bears two longitudinal sulci for reception of mandibular tomial crests and deep fossae for reception of mandibular pseudoteeth ( Fig. 6I ). A palatal ridge runs along the midline of the ventral surface and extends to the anterior tip of the beak. This palatal ridge is strongly convex and devoid of median sulcus, as in several fossils referable to Pelagornis ( Spulski 1910; Mayr & Rubilar-Rogers 2010; Solórzano & Rincón 2015).

The pseudo-toothed birds ( Pelagornithidae ) are an extinct group of large seabirds that included gigantic forms with wingspans above 5 m (Mayr & Rubilar-Rogers 2010; Ksepka 2014). Phylogenetic studies have shown that these highly specialized soaring birds are not part of the neoavian radiation ( Bourdon 2005; Mayr 2011; Mayr et al. 2019). Pelagornithids had a worldwide distribution and occur in late Paleocene to late Pliocene marine deposits ( Harrison 1985; Averianov et al. 1991; Mourer-Chauviré & Geraads 2008; Bourdon et al. 2010; Mayr & Rubilar-Rogers 2010; Boessenecker & Smith 2011; Fitzgerald et al. 2012; Cenizo et al. 2015; Mayr et al. 2019). Pseudo-toothed birds have an extensive stratigraphic range in Africa. Abundant pelagornithid remains assigned to the genus Dasornis Owen, 1870 are known from the late Paleocene (Thanetian)-early Eocene (Ypresian) phosphate deposits of the Oulad Abdoun Basin in Morocco ( Bourdon et al. 2010). A sternum assigned to Gigantornis Andrews, 1916 is known from the middle Eocene (Lutetian) Ameki Formation of Nigeria ( Andrews 1916). Fragmentary wing bones tentatively assigned to Gigantornis have been described from the middle Eocene (Lutetian) deposits of Kpogamé-Hahotoé, Togo ( Bourdon & Cappetta 2012). Indeterminate mandibular remains of pseudo-toothed birds are known from the late Eocene (Priabonian) deposits of the Samlat Formation in Morocco ( Zouhri et al. 2017). Cranial and postcranial remains assigned to Pelagornis Lartet, 1857 have been discovered in the late Pliocene deposits of Ahl Al Oughlam, Morocco (Mourer-Chauviré & Geraads 2008).

The Gueran specimen exhibits several diagnostic features of the Pelagornithidae : tomial crest bearing pseudo-teeth arranged in a regular pattern; presence of longitudinal sulcus on the lateral surface of the maxillary rostrum; ventral surface of maxillary rostrum bearing deep fossae for reception of mandibular pseudo-teeth and median palatal ridge (e.g., Bourdon et al. 2010; Mayr & Rubilar-Rogers 2010; Mayr & Zvonok 2012; Cenizo et al. 2015; Solórzano & Rincón 2015). The partial rostrum described here is from the upper middle Eocene (Bartonian), and constitute the second oldest record of the pseudo-toothed birds in North Africa.

The first appearance of Pelagornis comes from the late Oligocene of North America ( Mayr et al. 2013; Ksepka 2014), and its latest record is in the late Pliocene of North America and Africa (Mourer-Chauviré & Geraads 2008; Boessenecker & Smith 2011). With the exception of Antarctica, Pelagornis achieved a global distribution during the Neogene ( Lartet 1857; Howard & Warter 1969; Olson 1985; Ono 1989; Matsuoka et al. 1998; Stidham 2004; Mourer- Chauviré & Geraads 2008; Mayr & Rubilar-Rogers 2010; Boessenecker & Smith 2011; Fitzgerald et al. 2012; Mayr et al. 2013; Solórzano & Rincón 2015).

The taxonomic assignment of the Gueran specimen to Pelagornis is based on the presence of a transverse furrow positioned just posterior to the first large pseudo-tooth, which is a diagnostic feature of the genus (Mayr & Rubilar- Rogers 2010). Such a transverse furrow is absent in the early Paleocene Protodontopteryx ruthae Mayr, Pietri, Love, Mannering & Scofield, 2019 ( Mayr et al. 2019), the late Paleocene/early Eocene Dasornis toliapicus (Owen, 1873) ( Bourdon et al. 2010) , and the middle Eocene Lutetodontopteryx tethyensis Mayr & Zvonok, 2021 ( Mayr & Zvonok 2012). In addition, in FSAC Bouj-373, several features including pseudo-tooth pattern, presence of tomial pseudoteeth, down-curved bill and convex median palatal ridge, match well with species of Pelagornis ( Spulski 1910; Stidham 2004; Mourer-Chauviré & Geraads 2008; Mayr & Rubilar- Rogers 2010; Ksepka 2014; Solórzano & Rincón 2015). The earliest ascertained record of the genus Pelagornis is late Oligocene (Chattian) in age ( Ksepka 2014). The specimen from Gueran is upper middle Eocene (Bartonian) in age and extends the fossil record of Pelagornis back by at least 10 million years.

The anterior hook of the beak is longer in FSAC Bouj- 373 than in Pelagornis orri ( Howard, 1957) ( Howard 1957; Stidham 2004) and Pelagornis sandersi Ksepka, 2014 ( Ksepka 2014) . Moreover, the presence of two tomial pseudo-teeth on either side of the anterior end of the longitudinal sulcus is similar to the condition found in P. orri ( Stidham 2004) and Pelagornis chilensis Mayr & Rubilar-Rogers, 2010 (Mayr & Rubilar-Rogers 2010). In contrast, in P. sandersi , there is only one tomial pseudo-tooth between the tip of the beak and the first large pseudo-tooth ( Ksepka 2014). However, the fragmentary nature of FSAC Bouj-373 precludes assignment to the species level.

Figures

FIG. 6. — Serpentes and Aves from Sabkha of Gueran: A-F, Serpentes, vertebrae: A-E, FSAC Bouj-317, in anterior (A), right lateral (B), dorsal (C), posterior (D) and ventral (E) views; F, FSAC Bouj-300 in anterior view; G-K, Aves from Sabkha of Gueran, Pelagornis sp. (Pelagornithidae), FSAC Bouj-373, two fragments of maxillary rostrum: G, K, posterior fragment in right lateral (G) and left lateral (K) views; H-J, tip of maxillary rostrum in right lateral (H), ventral (I) and left lateral (J) views. Abbreviations: c, culmen; fos, fossae for reception of mandibular pseudo-teeth; ls, longitudinal sulcus; plr, palatal ridge; r1-r4, rank 1-rank 4 pseudoteeth; tc, tomial crest; tf, transverse furrow. Pseudo-teeth (PT1-PT6) and tomial pseudo-teeth (TT1-TT2) are numbered consecutively from the most proximal to the most distal. Scale bar: 10 mm.