Terastiodontosaurus marcelosanchezi Georgalis & Smith 2024, sp. nov.
Year: 2024
Type: other
Abstract: Terastiodontosaurus marcelosanchezi Georgalis & Smith sp. nov. (Figs 2–17, 23A; Supporting Information, Figs S1–S 6) Zoobank registration: urn:lsid:zoobank.org:act: 881978AE-4954-4D2C-8D6E-12CD56CB4C20 Etymology: The species epithet is named after Professor Marcelo Sánchez-Villagra, director of the Palaeontological Institute of the University of Zurich, as an honour for his major contributions to palaeontology, zoology, and evolutionary biology, in addition to the kind friendship and his great support to the first author (G.L.G.) for many years. Holotype: A right maxilla (ONM CBI-1-645) (Figs 2, 3). Paratype: A left dentary (ONM CBI-1-646) (Figs 4, 5, 23A). Referred specimens: Four premaxillae (ONM CBI-1-658, ONM CBI-1-672, ONM CBI-1-711, and ONM CBI-1-1021), five right maxillae (ONM CBI-1-649, ONM CBI-1-651, ONM CBI-1-654, ONM CBI-1-667, and ONM CBI-1-1017), six left maxillae (ONM CBI-1-648, ONM CBI-1-653, ONM CBI-1- 1012, ONM CBI-1-1016, ONM CBI-1-1018, and ONM CBI-1-1022), one right maxilla fragment (ONM CBI-1-650), five right dentaries (ONM CBI-1-656, ONM CBI-1-660, ONM CBI-1-666, ONM CBI-1-1013, and ONM CBI-1-1020), 10 left dentaries (ONM CBI-1-647, ONM CBI-1-655, ONM CBI-1- 657, ONM CBI-1-659, ONM CBI-1-661, ONM CBI-1-662, ONM CBI-1-668, ONM CBI-1-670, ONM CBI-1-1014, and ONM CBI-1-1015), a fragment of the coronoid process of a left dentary (ONM CBI-1-664), and 17 tooth-bearing bone fragments (ONM CBI-1-652 and ONM CBI-1-671 [16 elements]). Tentatively also: numerous presacral vertebrae (ONM CBI-1- 673, ONM CBI-1-682, ONM CBI-1-685, ONM CBI-1-687, ONM CBI-1-691 [‘lot / batch’ with numerous vertebrae], ONM CBI-1-706 [‘lot / batch’ with numerous vertebrae], ONM CBI-1-820, ONM CBI-1-833, and ONM CBI-1-860) and two caudal vertebrae (ONM CBI-1-686 and ONM CBI-1-689). Diagnosis: Terastiodontosaurus marcelosanchezi can be referred to Amphisbaenia based on the prominent and enlarged median premaxillary tooth, the large anterior premaxillary foramina, the low tooth count on the maxilla and dentary, the ventral extension of the mandibular symphysis below Meckel’s groove, the broad insertion fossa for mandibular adductor muscles on the posterolateral surface of the dentary, and the strong and elevated coronoid process of the dentary. Terastiodontosaurus marcelosanchezi can be referred to Trogonophidae based on the presence of acrodont dentition, closely appressed (‘fused’) teeth, the interdigitating suture between the frontal and the facial process of the maxilla, and ectopterygoid abutting the posteromedial corner of the maxilla. Terastiodontosaurus marcelosanchezi is united with Trogonophis wiegmanni by: thick enamel on marginal teeth, and ‘twinning’ of paired premaxillary teeth, with median tooth separated by a diastema from paired teeth. Terastiodontosaurus marcelosanchezi is united with Todrasaurus gheerbranti by: thick enamel on marginal teeth, extremely enlarged (>60% longer than adjacent teeth) dentary tooth 3–4 positions from the rear, and small ‘hills’ on posterior dentary teeth. Terastiodontosaurus marcelosanchezi can be differentiated from all other amphisbaenians by the combination of the following features: very large size (with maximum known maxilla length> 16 mm and maximum dentary length of 17 mm), the flat apical surface of the cheek teeth, the position of the largest tooth on the maxilla, the number of maxillary teeth (usually three maxillary teeth), the ratio of the largest maxillary tooth length to the total maxillary tooth row length (between 0.5 and 0.7), and the position of the largest tooth on the dentary (fourth from posterior). Type locality and horizon: Chambi 1 (CBI-1), Djebel Chambi, Kassérine region, western part of Central Tunisia, Tunisia; late early to early middle Eocene (late Ypresian to early Lutetian). Geographical and stratigraphical range: Taxon known exclusively from its type locality. Nomenclatural remark on the new taxon: The authorship of this new genus and species should be referred to as Terastiodontosaurus Georgalis & Smith gen. nov. (for the new genus) and Terastiodontosaurus marcelosanchezi Georgalis & Smith gen. et sp. nov. (for the new species), following Article 50.1 and the ‘recommendation 50A concerning multiple authors’ of the International Code of Zoological Nomenclature (ICZN 1999). Description Holotype (Figs 2, 3) Theholotyperightmaxilla (ONMCBI-1-645)isalmostcomplete (Figs 2, 3). The premaxillary process curves up anterodorsally, forming part of the medial border of the external naris. The sharp rim weakens anteriorly, and the anterior portion of the process as a whole slopes ventrolaterally. The dorsal surface is slightly striated, probably where it was overlapped by the septomaxilla. The ventral surface of the premaxillary process curves upwards and is more coarsely striated where it overlaps the premaxilla. The superior alveolar canal opens anteriorly through two foramina: a dorsally directed foramen on the medial side of the facial process, and an anteriorly directed foramen immediately anterior to the facial process; between them the canal is roofed, but there appears to be a narrow groove, as if two growing folds of perichondral bone met over a channel but did not fuse fully. Anterior to the anterior opening of the superior alveolar canal the dorsal surface of the premaxillary process is coarsely striated; here it was probably overlain by the septomaxilla, into which the neurovascular structure(s) of the superior alveolar nerve continued. It is unclear whether the division of the anterior opening of the superior alveolar canal marks a separation of the course of the subnarial artery and superior alveolar nerve, as in Iguanidae (Oelrich 1956, Smith 2009). On the medial side of the premaxillary process is a strong, dorsomedially facing facet for the vomer. Behind this the palatal shelf is restricted and its dorsal surface hollows out, where Jacobson’s organ sat; together with the vomer, here the maxilla formed the fenestra vomeronasalis externa. Posterior to the cavity for Jacobson’s organ the maxilla possesses a distinct medial process that contacts the horizontal wing of the vomer. The process continues laterally across the palatal shelf and extends posterodorsally as a weak ridge on the medial surface of the facial process of the maxilla. In other squamates, Smith and Gauthier (2013) identified this as the ‘nasolacrimal ridge’ after ascertaining a relationship with the lacrimal duct. Behind this process the palatal shelf is medially extensive. A distinct palatine process is absent, but an extensive, striated facet for the palatine articulation is present. The (posterior) superior alveolar foramen opens at the level of the anterior end of the palatine facet. A distinct facet for the ectopterygoid cannot be discerned, but it must have been an abutting one, and it might be confluent with the palatine facet. The posterior process of the maxilla is broad and flares sharply outwards (or laterad fide Gans and Montero 2008). Although striated surfaces of this maxilla commonly show tiny holes, the entire posterior surface of the posterior process is heavily porous and coarsely striated. Dorsally, the posterior process is thick and also coarsely longitudinally striated; there is no evidence that a distinct element articulated on this suborbital part of the maxilla. The facial process is thick. A rough facet for the nasal bone is found on the anterior margin of the facial process and turns posterodorsally as it ascends the process. There is a distinct change in angulation below the peak of the facial process, and the facet behind it (now more on the medial than the anterior surface of the facial process) is smoother; probably, the change marks the boundary between the nasal and part of the frontal facet. Immediately behind its apex the facial process is deeply notched, almost certainly to receive a tongue-like process of the frontal bone. Additionally, there is a number of rough, anteroventrally trending ridges and grooves posterior to the frontal notch, which possibly indicate a more extensive overlap of the maxilla on the prefrontal (like in lizards) than is observed today in Trogonophis wiegmanni. The lateral surface of the maxilla is porous and weakly rugose in its dorsal part, with some longitudinal grooves and ridges on the posterior process. There are three distinct labial foramina, all of them more or less above the level of the largest tooth. The two anterior ones are more closely spaced, while there is a considerable distance between the middle and posterior one, the latter also being the largest. These foramina communicate internally, as expected, with the superior alveolar canal, which runs longitudinally through the maxilla immediately above the tooth row. It conveys the superior alveolar nerve, which passes from the orbit into the maxillary canal through the superior alveolar foramen, in addition to the maxillary artery (Oelrich 1956). The dentition is acrodont. The maxilla possesses only three teeth, of which the second is by far the largest (some 75% longer than the next-largest tooth) and, in fact, covers much of the ventral portion of the bone; this tooth is followed in size by the anteriormost tooth, while the posteriormost tooth is considerably tiny. The teeth are closely appressed, with no interdental gaps between them. All three teeth are much flattened, particularly the two largest ones: their dorsoventral height is extremely low. Moreover, the μCT scan reveals that the enamel is extremely thick (Supporting Information, Fig. S1A). Several nutritive foramina are present at the base of the teeth. Paratype (Figs 4, 5) The paratype left dentary (ONM CBI-1-646) is relatively complete (Figs 4, 5). It is referred to the same species on the basis of co-occurrence and the following derived morphological features: great enamel thickness, reduced tooth row length and tooth count, presence of a greatly enlarged tooth, the ‘hill’ on the small, poster
Authors: Georgalis, Georgios L, Smith, Krister T, Marivaux, Laurent, Herrel, Anthony, Essid, El Mabrouk, Khayati Ammar, Hayet, Marzougui, Wissem, Temani, Rim, Tabuce, Rodolphe
Institutions: Centre National de la Recherche Scientifique, École Pratique des Hautes Études, Université de Montpellier, Institut des Sciences de l'Evolution de Montpellier, Institut de Recherche pour le Développement, University of Antwerp, Ghent University, Natural History Museum of Bern, Muséum national d'Histoire naturelle, Mécanismes Adaptatifs et Evolution, National Office of Mines
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W6949608438
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