Ctenochasmatidae Nopcsa, 1928

Alarcón Muñoz, Jhonatan, Buldrini Oviedo, Karina, Bajor, Dániel & Rubilar Rogers, David, 2022, Note On New Pterosaur Remains (Archosauria: Pterodactyloidea) From Cerro La Isla, Atacama Region, Northern Chile, Boletín del Museo Nacional de Historia Natural, Chile 71 (2), pp. 1-8 : 3-5

Ctenochasmatidae Nopcsa, 1928

Ctenochasmatidae indet. ( Figs. 2 and 3 )

Material. A fragmentary tooth bearing element that most likely represents part of a rostrum exposed in ventral view, with broken teeth (SGO.PV.347-c), the caudal portion of a mid-cervical vertebra (SGO. PV.22910).

DESCRIPTION

Jaw fragment. Specimen SGO.PV.347-c corresponds to a fragmentary tooth bearing element with broken teeth ( Fig. 2 ). Its preserved length is 5.3 cm. The teeth are closely-spaced (~ 6 teeth/cm), and the preserved dental bases suggest that they were gracile and obliquely orientated with respect to the longitudinal axis of the element. Although due to its fragmentarY nature, it is difficult to determine with certaintY whether it was part of the upper- or lower jaw; SGO.PV.347-c is tentatively interpreted here as part of a rostrum exposed in ventral view.

SGO.PV.347-c shows several similarities with other previously published fragments of toothbearing elements. SGO.PV.377 was also discovered at Cerro La Isla and interpreted as a post-symphyseal dentary fragment by Alarcón-Muñoz et al. (2020). It has subparallel margins; its medial wall is thinner than the lateral and it bears approximately 9 teeth/cm. In addition, SGO.PV.378 is also a dentary fragment from the same locality, which shows the same morphology and dental density as SGO.PV.377. By contrast, SGO.PV.347-c shows a mediallY wide osseous surface (identified as medial based on the orientation of the preserved tooth bases), making it more consistent with either a symphyseal mandibular portion, or a rostrum. Given that dental density tends to diminish posteriorly rather than anteriorly (9 teeth/cm in SGO. PV.377 and 378, as opposed to 6 teeth/cm), SGO.PV.347-c is most likely a rostral fragment from the medial or posterior region of the snout, making the tooth bearing element the right maxilla. Therefore, the overall morphology and dental features of SGO.PV.347-c agree with those observed in other remains from the same fossil-bearing layer exposed at Cerro La Isla, which were assigned to the Ctenochasmatidae in previous studies ( Martill et al. 2006, Alarcón-Muñoz et al. 2020 b).

Vertebra. Specimen SGO.PV.22910 corresponds to the posterior portion of a mid-cervical vertebra ( Fig. 3 ). The preserved anteroposterior length is 3.2 cm. The fragment is quite eroded. This portion of the vertebra is dorsoventrally high and mediolaterally compressed. Only part of the right postzygapophysis is preserved, which is dorsoventrally tall and dorsolaterally oriented. The posterior condyle is quite eroded but robust, with concave lateral surfaces, as in two other mid-cervical vertebrae from the same site (SGO.PV.350 and SGO.PV.351) assigned to the Ctenochasmatidae ( Alarcón-Muñoz et al. 2020) . The postexapophyses are not preserved. The ventral surface is markedly concave, which is another shared feature with previously reported ctenochasmatid vertebrae from Cerro La Isla ( Alarcón-Muñoz et al. 2020).

Figures

Figure 2. Ctenochasmatidae indet. (SGO.PV.347-c), mandibular fragment in occlusal view (A), and detail of the teeth (B). Schematic interpretations are shown.Abbreviations: to, tooth. Scale bars: 10 mm.

Figure 3. Ctenochasmatidae indet. (SGO.PV.22910), caudal portion of a mid-cervical vertebra in right lateral (A), dorsal (B) and ventral (C) views. Abbreviations: dep, depression; co: condyle; poz, postzygapophysis. Scale bar: 10 mm.