Bauersaurus, Čerňanský & Daza & Tabuce & Saxton & Vidalenc, 2023
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publication ID |
https://doi.org/ 10.4202/app.01083.2023 |
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publication LSID |
lsid:zoobank.org:pub:A660D450-F907-40F5-A602-610099AE70B3 |
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persistent identifier |
https://treatment.plazi.org/id/AB0EA06D-312C-FFD8-FC87-6FFDFC36FBD5 |
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treatment provided by |
Felipe |
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scientific name |
Bauersaurus |
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Genus Bauersaurus nov.
Zoobank LSID: urn:lsid:zoobank.org:act:94D1D3D6-2884-4B7E-BD55-868934FF9ACC
Type species: Bauersaurus cosensis sp. nov.; by monotypy; see below. Etymology: A combination of the last name of the North American herpetologist Aaron M. Bauer, to recognize his valuable contributions to squamate morphology, taxonomy, and systematics, especially on geckos, and the Greek saura (σαύρα), lizard. The name is masculine.
Diagnosis.—As for Bauersaurus cosensis gen. et sp. nov., by monotypy.
Bauersaurus cosensis sp. nov.
Figs. 1–4 View Fig View Fig View Fig View Fig .
Zoobank LSID: urn:lsid:zoobank.org:act:94D1D3D6-2884-4B7E-BD55-868934FF9ACC
Etymology: In reference to the locality of Cos in France.
Holotype: UM-COS-1012, right maxilla ( Figs. 1 View Fig , 3A View Fig , 4A View Fig , 5A View Fig , and Fig. 6 View Fig partly—the maxilla at the bottom).
Type locality: Cos , fissure-filling in the Quercy region (Southwest France). GPS coordinates: 44°13’11.20” N; 1°44’58.21” E GoogleMaps .
Type horizon: Uppermost lower Eocene ( MP 10–11).
Material.—The holotype and UM-COS-1013, right dentary, both from the type locality and horizon.
Diagnosis.—The new taxon differs from all fossil and extant taxa of Pan-Gekkota in the following combination of features from the maxilla: (i) posterior margin of facial process slopes down gradually dorsoventrally to the jugal facet, contra to all known gekkotans where the facial process ends more anteriorly, defining a well-developed posterior process with more or less parallel dorsal and ventral margins. In extant gekkotans the posterior margin of the facial process is highly variable, being mainly gradually sloped (diplodactylids), sometimes sinusoid (some carphodactylids and pygopodids), tall with a stepped posterior margin (eublepharids), mainly narrow and tall (sphaerodactylids), concave posteriorly (phyllodac- tylids), and combinations of the former (gekkonids); (ii) posterior margin of the facial process ends in a short, posteriorly oriented, and well defined process (posterior free terminus) vs. Eichstaettisaurus schroederi ( Broili, 1938) , Laonogekko lefevrei , Cadurcogekko piveteaui , Geiseleptes delfinoi , extant gekkotans. Compared with described fossils, the maxilla of L. lefevrei has a low sloping posterior margin, that is still more inclined relative to the Cos taxon; vs. a steep margin in Cadurcogekko piveteaui ; (iii) the facial process length is at least twice its height (although its tip is clearly broken) similar to Eichstaettisaurus schroederi , and? Cadurcogekko piveteaui , differing from L. lefevrei , Geiseleptes delfinoi , most extant gekkotans except long and depressed snouted forms like species of the gekkonid Uroplatus Duméril, 1806 ; (iv) the jugal facet is mostly dorsolateral in orientation, suggest- ing that the jugal was large and well braced to the maxilla, differing from extant gekkotans which have a very reduced jugal that contacts usually the dorsal surface of the maxilla; (v) the ventral surface of the maxillary medial shelf has a trough on the lateral side (as Aeluroscalabotes felinus ( Günther, 1864) ; vs. most other geckos). On the medial side, this fossa is bordered by a sharp low ridge, which is reduced in its anterior part. In the posterior region, however, the ridge of the maxillary medial shelf projects ventrally to form a vertical bony septum (almost vertical wall) which covers the tooth bases of the posterior teeth medially; (vi) the external surface of the facial process is smooth; as Geiseleptes delfinoi ; vs. Cadurcogekko piveteaui and Cadurcogekko verus , Laonogekko lefevrei (faintly sculptured), and similar to most gekkotans where the maxilla is smooth, except the rugose maxilla in Matoatoa brevipes ( Mocquard, 1900) , grooved maxilla of Hemidactylus turcicus ( Linnaeus, 1758) , and the pitted maxilla of Blaesodactylus antongilensis ( Böhme and Meier, 1980) and Chondrodactylus briboni ( Smith, 1846) ( Glynne et al. 2020) ; (vii) maxilla with six supralabial foramina that increase in diameter gradually and are located in the anterior two thirds of the bone, the posterior section lacks a foramen vs. Laonogekko lefevrei and Geiseleptes delfinoi these taxa have six as well, but the posteriormost one is located on the posteroventral process. Higher number of more posteriorly distributed foramina are present in Cadurcogekko piveteaui and Cadurcogekko verus , species of Gekko Laurenti, 1768 , Euleptes Fitzinger, 1843 , Eublepharis Gray, 1827 , Rhacodactylus Fitzinger, 1843 , and Saltuarius Couper, Covacevich, and Moritz, 1993 ; (viii) anterior margin of the maxilla with a free rounded and triangular tip (as in Laonogekko lefevrei , Cadurcogekko piveteaui , extant and extinct Euleptes , e.g., Euleptes europaea ( Gené, 1839) and Euleptes klembarai Čerňanský, Daza, and Bauer, 2018 ); (ix) transversally bicuspid teeth with labial and lingual cutting edge running mesiodistally and bent lingually (V-shaped in ventral view), separated by a concave sulcus (as in Eublepharis macularius [ Blyth, 1854], in Gonatodes albogularis , Coleonyx elegans Gray, 1845 , Oedura tryoni de Vis, 1884 , Aeluroscalabotes felinus , Geiseleptes delfinoi ; Gekkota indet 2. from Dormaal [ Čerňanský et al. 2022]; vs. Laonogekko lefevrei , Euleptes europaea , Gekko gecko [ Linnaeus, 1758], Rhacodactylus leachianus [ Cuvier, 1829]).
Description. —The holotype UM-COS-1012 represents a nearly complete right maxilla ( Figs. 1 View Fig , 3A View Fig ). It is a long element, straight and lightly built. The anteroposterior maximum length is 10 mm. It consists of two major portions: the alveolar portion bearing the dentition and the dorsally extending facial process. An almost complete tooth row is preserved, excepting the anterior most region. The dental crest (labial wall) is deep, and the maxilla bears 36 tooth loci (the total number was probably slightly higher), preserving 12 complete teeth. The premaxillary process is damaged and the anterior opening of the superior alveolar canal is exposed. The lateral surface of the maxilla is pierced by six supralabial foramina, which slightly increase in size posteriorly. They are located along the ventral margin in the anterior two thirds of the bone, where the posteriormost one (also the largest) is located at the level of the 16th tooth position (counted from posterior). Posterior to this last foramen, there is a long section of the facial process without any foramen. Dorsal to this series (on the facial process), the surface is pierced by additional eleven, irregularly arranged small foramina. Some of them (those located in the posterodorsal region) are accompanied by short grooves running posterodorsally from the foramen. The facial process forms almost a vertical wall, being roughly trapezoidal in shape (notice that the posterodorsal margin of the facial process is missing). The dorsal margin is angled slightly medially, this section bears a narrow longitudinal facet for the nasal (and maybe frontal) visible in medial view. The process is markedly long anteroposteriorly. Its posterior margin gradually slopes ventrally at a sharp angle (28°) whereas the anterior margin is more ventrally sloped relative to the posterior one. The posterior margin of the facial process terminates in short, free, posterior process. This process is well separated from the alveolar margin by a small rounded notch. The anterior margin possesses a free terminus. It forms a blunt triangular tip ( Fig. 1A 1 View Fig ; this feature can be seen in extant and extinct species of the Euleptes but also in other taxa such as Hemidactylus Oken, 1817 , Tarentola Gray, 1825 , Dactylocnemis Steindachner, 1867 and Gekko ; see e.g., Čerňanský et al. 2018; Villa et al. 2018). In medial view, there is a fine ridge in the anterior region of the facial process that runs posterodorsally. This ridge originates from the maxillary medial (supradental) shelf at the level of the fourth preserved tooth position (counted from anterior). The internal side of the facial process posterior to this ridge is excavated, forming a cavity. The most prominent structure on the medial side is the maxillary medial shelf. It is relatively thin, but with a marked medial expansion. The maximal expansion is at the level of the large opening for the superior alveolar canal (and the level of the 16 th tooth position, counted from posterior); at this expansion, the maxilla would have join the palatine. The posterior section of the maxillary medial shelf protrudes ventrally to form a deep vertical bony septum (almost vertical wall) which covers the tooth bases of the posterior teeth medially. Counting from posterior to anterior, the septum starts to deepen ventrally at the level of the 13-tooth locus and reaches its maximal projection at the level of the ninth to fourth tooth positions. Further, the septum diminishes posteriorly. Thus, its ventral margin is roughly concave. It should be noted, however, that anterior to this vertical septum, there is a trough (sensu Grismer 1988) clearly visible in ventral view. This trough is bordered laterally by the dental crest supporting the teeth and medially by a distinct low ridge. Thus, the wall in the posterior region is only a continuation of this ridge running almost along the entire length of the maxillary medial shelf (although it is less distinct in the anterior region). The above-mentioned opening of the superior alveolar canal is located on the dorsal surface of the shelf approximately in its mediolateral mid-line. Laterally, this superior alveolar foramen is bordered by a sharp horizontal lip of bone. Posteriorly, a groove runs from the foramen. The groove turns and continues on the lateral surface, at the level of the posterior free terminus of the facial process. Here, the bottom of the groove is pierced by a small foramen. At this position, a large facet for jugal is visible, which suggests that the jugal had a strong connection with the maxilla including some extension onto the lateral surface of the maxilla.
UM-COS-1013 represents the posterior portion of the right dentary ( Figs. 2 View Fig , 3B View Fig ). It has a robust appearance and preserves 19 tooth loci (with two teeth still attached). Based on this preserved portion it can be estimated that the dentary, when complete, was long and tubular, with a com- pletely enclosed Meckelian canal, as in crown gekkotans, contrary to the Cretaceous gekkonomorph Hoburogekko suchanovi , in which the borders of the Meckelian canal are partially fused ( Alifanov 1989; Daza et al. 2012). The posterior region has a wedge-shaped opening of the Meckelian canal. At first glance, it seems as though some remains of the splenial are ankylosed to the dentary, but what is visible is the anterior part of the facet of the splenial. This is consis- tent with observation in extant gekkotans where: (i) the splenial is recessed onto the dentary, creating a flush profile; (ii) the facet indicates clearly the splenial abutment with the anteromedial process of the coronoid, and the coronoid is certainly missing, and (iii) there is no clear indication of the anterior dental or the anterior mylohyoid foramina, which are usually in the anteromedial portion of the splenial. The preserved splenial facet indicates that the anterior portion has the characteristic triangular shape of crown gekkotans. The dental crest is tall, but its height does not exceed the height of the ventral portion of the dentary (the alveolar part of the dentary is less than half the total height of the dentary). The subdental shelf is well-developed, moderately expanded medially, forming a clearly visible surface in dorsal view. In the posterior region, it bears a partly preserved facet for the coronoid. The otherwise smooth external surface of the preserved portion is pierced by one elliptical labial foramen. The foramen is in the midline of the bone. The dentary is broken posteriorly, in the region where the facet for the anterolateral process of the coronoid would be visible, a coronoid clasping the dentary on both the lateral and medial sides of the dentary can be used to differentiate gekkotans from skinks ( Daza et al. 2015), although these facets, especially the one for the anteromedial process of the splenial can be found in the dentary of almost any lizard.
Dentition: The following description is of the maxillary and dentary teeth (both exhibit an identical morphology, although note that only two teeth are preserved in the dentary, Fig. 4 View Fig ). Tooth attachment is pleurodont and tooth replace- ment occurs lingually. The dental crest (labial wall) is high, and teeth exceed this structure only by one quarter of their length or less. The teeth are tall and conical, with rounded crowns. They are slender, being slightly more robust only in the posterior part of the tooth row. Their apices possess two cusps, labial and lingual, which are separated by a concave sulcus. Because both cusps are inclined medially, the sulcus is V-shaped ( Fig. 4A View Fig 2 View Fig , B 1 View Fig ).
Remarks.—Although it is very approximate to estimate the size of an animal using a few disarticulated bones, using the proportions of a comparable living species ( Pseudothecadactylus australis ), Bauersaurus cosensis gen. et sp. nov. would have been a medium-sized gecko with an estimated skull length 23 mm, and snout-vent length ( SVL) of 70 mm. This species is too incomplete to be included on a large scale morphological data set, but based on the overall morphology of the two bones preserved and the cylindrical/ conical teeth with transversally bicuspid tooth crowns, it is provisionally assigned to total clade Pan-Gekkota.
Stratigraphic and geographic range.— Type locality and horizon only.
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Mohonk Preserve, Inc. |
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