Noasaurus leali Bonaparte and Powell 1980

Species Noasaurus leali Bonaparte and Powell, 1980 Derivation of generic name: From NOA, the acronym for north-western Argentina (‘ Noroeste Argentino’ in Spanish), a geographic and historical region of Argentina composed of the provinces of Catamarca, Jujuy, La Rioja, Salta, Santiago del Estero, and Tucumán (NB—this is the first acronym to be used in the genus of a non-avian theropod; Molina-Pérez and Larramendi 2019), and sauros (σΑύΡΑ) meaning ‘lizard’ or ‘reptile’. Etymologically, Noasaurus translates to ‘reptile from north-western Argentina’. Derivation of specific name: From the family name ‘Leal’ to honour lab technician and discoverer of the El Brete fossil site Juan Carlos Leal (Fig. 1A). Holotype: PVL 4061, a left maxilla with five erupted crowns, a right quadrate, a mid-posterior cervical vertebral arch, a mid-cervical rib, a posterior cervical rib, an indeterminate postcervical vertebra, a manual phalanx of digit III, manual unguals possibly belonging to the left and right digit I, and a right metatarsal II (Figs 1E, 3A, B; Tables 2, 3). Occurrence and age: El Brete Estancia, Department of Candelaria, southern Salta Province, Northeastern Argentina (Fig. 2A, B); Lecho Formation, Balbuena Subgroup, Salta Group; early or mid Maastrichtian, Upper Cretaceous (Bonaparte et al. 1977, Bonaparte and Powell 1980, Marquillas et al. 2005, Montano et al. 2022; Fig. 2C). Diagnosis: Ceratosaur theropod with the following autapomorphies: (i) a concave alveolar margin of the maxilla; (ii) a diagonally oriented ridge along the dorsal portion of the maxillary fossa; (iii) a strongly arched quadrate body with a dorsoventrally low anterior margin of the pterygoid flange; (iv) maxillary crowns with minute mesial denticles and a low number (<30) of comparatively large distal denticles not diminishing in size basally; (v) a cervical neural arch with anterior epipophyseal prongs (modified from: Bonaparte and Powell 1980); (vi) a well-defined and acute middle longitudinal crest on the ventral surface and at midlength of the manual ungual blade (modified from: Agnolín and Chiarelli 2010); (vii) a strongly ventrally curved manual ungual forming an angle of about 90°; (viii) a manual ungual with a deep C-shaped articular surface in lateral view; and (ix) a deep subtriangular flexor fossa delimited distally by two ridges forming a V on the manual ungual (modified from: Bonaparte and Powell 1980, Agnolín and Chiarelli 2010). Body length, body mass, and age: As early as its first mention in the literature, Noasaurus was seen as a small theropod not exceeding 2 m (Bonaparte et al. 1977). The total length of this theropod was later estimated to be <1 m (Bonaparte 1996b, 2007), <1.5 m (Bonaparte 1996a), 1.5 m (Novas 2009, Paul 2010, 2016, 2024), 2.4 m (Lambert 1983, 1990, 1993, Holtz 2007), and 3 m (Benton 1984, Molina-Pérez and Larramendi 2019) in subsequent work. None of these authors, however, applied a formula to estimate the body length of Noasaurus. Using our dataset on skull, metatarsal, and body lengths in the most complete theropods (Supporting Information, S1.6), Noasaurus is estimated to be around 2 m in length using an estimated cranial length of 185 mm, and 1.6 m using the proximodistal height (115 mm) of metatarsal II. Our formula relies on metatarsal III, which is the tallest metatarsal of the foot and whose measurements are typically given in the literature. Because metatarsal II is slightly proximodistally shorter than metatarsal III in noasaurids (Noas aurinae + Elaphrosaurinae), the body length of Noasaurus probably ranged between 1.7 and 2 m (Fig. 3A, C). No femur or tibia is preserved to calculate the body mass of Noasaurus using Benson et al. ’s (2014), Campione et al.’s (2014), or Campione and Evans’ (2020) formulas. Noasaurus ’ body mass was estimated to be around 6 kg by Paul (2024), 15 kg by the same author (1988, 2010, 2016), and 38 kg by Molina-Pérez and Larramendi (2019). Likewise, the age of Noasaurus could not be assessed as histological analysis on the holotype is currently forbidden. Stiegler (2019), however, suggested that the Noasaurus material may belong to an immature individual based on the strongly arched quadrate, a condition restricted to immature individuals of Limusaurus. DESCRIPTION Cranium Preserved cranial elements The cranial elements of Noasaurus include a fairly complete left maxilla preserving five partially to almost complete erupted teeth, as well as a relatively complete right quadrate (Figs 3A, B, 4–6; Tables 2, 3). The squamosal described by Bonaparte and Powell (1980: fig. 7D, E; Fig. 1E) was later identified as a cervical rib by Novas (1989) in his Ph.D. dissertation (Bonaparte 1991) and is consequently described in the section ‘Axial skeleton’. Maxilla Most of the left maxilla is undistorted and only the posterior extremity of the jugal ramus is out of place (Fig. 4). Multiple fractures are, however, present throughout the bone, the two main ones crossing the middle parts of the ascending and jugal rami horizontally and vertically, respectively. A small piece of bone directly ventral to the ascending ramus was also glued back. The maxilla has been damaged since 2012 (when it was examined the first time by one of us), with an additional fracture at the base of the ascending ramus, while the first maxillary tooth is now loose and kept separately (Fig. 6O, P). The distalmost portion of the ascending ramus illustrated by Bonaparte and Powell (1980) is also missing and most likely lost. A photo of the maxilla provided by Candeiro (2007) shows that this portion of the ascending ramus was already missing before 2007. However, an illustration of the Noasaurus material published by Bonaparte (2007), as well as a movie showing some of the specimens shortly after their preparation (Fig. 1D; Supporting Information, S1.2), confirm that the missing part was originally present. The maxillary bone is fairly complete, missing the dorsal part of the ascending ramus, the anterior portion of the anteromedial process, the medial wall from the posterior extremity of the jugal ramus, small pieces of the alveolar margin and the antorbital ridge, as well as several maxillary teeth (Fig. 4). In lateral view, the maxilla consists of a subtriangular bone with a dorsoventrally tall maxilla body, a short ascending ramus, an anteroposteriorly short pre-antorbital body and long jugal ramus (Fig. 4A). The preserved maxilla is dorsoventrally lower than anteroposteriorly long and the complete bone (Fig. 1E) was longer than tall. The anterior body occupies two-fifths of the maxillary length and is shorter than the jugal ramus. Its anteriormost part is particularly short and dorsoventrally lower than the jugal ramus (Fig. 4A). The anterior margin of the anterior body is weakly concave and posterodorsally inclined at an angle of 53° from the long axis of the alveolar margin. Both the anterior ramus and pre-antorbital body of the maxilla are roughly subtriangular in outline and the angles of the anterior corner of the anterior ramus and pre-antorbital body are approximately 43° and 48°, respectively (Fig. 4A). The anterior ramus occupies one-half of the anterior body and three-fourths of the antorbital body. The anterior margin of the maxilla is weakly sigmoid, with the margin of the anterior body and the ventral one-third of the preserved ascending ramus being slightly concave while the dorsal two-thirds of the remaining ascending ramus is weakly convex. The alveolar margin of the maxilla is gently concave, with the apex of the concavity located around half the length of the bone (Fig. 4A). The jugal ramus, which accounts for ~67% of the maxillary body, corresponds to an elongated subtriangular projection pointing posteriorly and delimited by two weakly sigmoid, almost straight ventral and dorsal margins. The jugal contact at the posterior end of the jugal ramus forms an almost right-angled isosceles triangle pointing anteriorly in lateral view. Based on Bonaparte and Powell (1980: fig. 7A, B; Fig. 1E), the ventral two-thirds of the ascending ramus mainly projects dorsally, perpendicular to the alveolar margin of the maxilla, whereas the dorsal third curves posterodorsally at an angle of ~45° from the long axis of the alveolar margin. The dorsal extremity of the ascending ramus was forked, with the two short dorsal and ventral subtriangular extremities projecting posterodorsally and posteriorly, respectively, as revealed by Bonaparte and Powell’s (1980) figure 7A, B (Fig. 1E; NB—the oldest available photo of the maxilla provided by Bonaparte (2007) reveals that the posteriormost extremity of the ascending ramus was already missing before 2007; Supporting Information, S1.1, Fig. SA3). The forked extremity of the ascending ramus was probably articulating with the anterior process of the lacrimal. If we cannot exclude the fact that the ascending ramus illustrated byBonaparte and Powell (1980) was incomplete and the articulation with the lacrimal, which may have then occurred more posteriorly, had a different shape, a posterior U-shaped fork of the ascending process is the typical morphology for the lacrimal contact of the maxilla in theropods (Rauhut, pers. comm. January 2024), supporting the fact that the ascending ramus figured by Bonaparte and Powell (1980) was complete. A row of maxillary alveolar foramina is present, directly dorsal to the alveolar margin, parallel to the latter. The foramina are difficult to discern as most of them are obscured by matrix or correspond to a very shallow depression, but they can be seen with razing light. A second row of foramina, the maxillary circumfenestra foramina, is present directly ventral to the antorbital ridge and the most visible foramina are present at the level of mx6-8 (Fig. 4A). A well-delimited antorbital fossa is present laterally, extending over the posterior one-third of the anterior body, the dorsal one-third of the jugal ramus, and the anterodorsal two-thi