Panochthus sp.

Zamorano, Martín, 2020, Exceptional preservation of tracheal rings in a glyptodont mammal from the Late Pleistocene of Argentina, Acta Palaeontologica Polonica 65 (1), pp. 29-34 : 30-31

Panochthus sp.

Material.— MHM-P 87, twenty-three fragments of tracheal rings, including fragments that probably belong to the crioid cartilage. The specimen consists of part of the skull (badly preserved), mandibular rami, postcranial bones (both humeri, radii-ulnae, both femurs, tibiae-fibulae, several elements of the carpus and tarsus, thoracic and lumbar vertebrae, cervical ribs) and the almost complete dorsal carapace. Because of the exceptional preservation of this material, fragments of tracheal rings, the crycoid cartilage and, some elements of the hyoid apparatus could be identified and were published by Zamorano et al. (2018). Late Pleistocene of General Belgrano, Buenos Aires, Argentina (35°45’5.52” S, 58°37’35.96” W) ( Fig. 1). The remains were collected in sediments of the Luján Formation dated between ca 14 and 12 ky .

Description.—Tracheal cartilages are mostly small and fragile fragments; their thickness does not exceed 3 mm. Twenty-three fragments of these tracheal rings were found, twelve of them belong exclusively to lateral sectors 19–54 mm in length and 6–8 mm in width. The three longest of these last fragments are fully curved (none of them cover the lateral sector completely), whereas the other nine are almost straight ( Fig. 2A 1). Eight fragments belong to ventral portions of the rings; in this category are also included fragments of fused ventral and lateral portions ( Fig. 2A 2 ), three of them, the largest ones, probably belong to the cricoid cartilage (this latter is similar in shape to a tracheal ring, although larger; Drake et al. 2010) ( Fig. 2A 3 ). A tracheal ring was reconstructed; it is 80 mm high and 60 mm wide. Its diameter occupies approximately 15% of the skull height (without the mandible) (see Fig. 3B ). The tracheal rings of Panochthus sp. would belong to a cylindrical trachea, slightly flattened on the dorsal and ventral sides, the free ends of each ring (that is, on its dorsal side) overlap, the left one above the right one ( Fig. 3C ).

Remarks.—Among domestic mammals, it is similar to those of Sus scrofa domestica ( Fig. 3E ), whereas among wild mammals it is similar to those of Zalophus californianus ( Fig. 3D ). Tracheal rings of Sus scrofa scrofa , a wild subspecies similar to its conspecific, are also similar, but those of Zalophus californianus resemble even more those of Panochthus sp. , since these rings are flattened dorsally and ventrally, and not as in cross section as those of S. scrofa scrofa . Noteworthy, in S. scrofa domestica and Z. californianus the shape of the rings is constant along the entire trachea, as well as the overlapping of their free ends ( Moreto et al. 2017). It has to be taken into account that the free ends of the tracheal cartilage of living mammals (in this case S. scrofa domestica and Z. californianus ) are practically in contact, because the tracheal muscle holds them together, whereas in the fossils of Panochthus sp. these free ends are more widely separated.

Figures

Fig. 2. Tracheal cartilages of glyptodont mammal Panochthus sp. (MHM-P 87) from the Late Pleistocene of General Belgrano, Argentina, in ventral views. Lateral (A1), ventral and ventro-lateral (A2) portions, fragment of cricoid cartilage (A3) in ventral views.

Fig. 3. Cartilages present in the neck of glyptodont mammal Panochthus sp. compared with Recent California sea lion and domestic pig. A. Thyroid, cricoid, and tracheal cartilages in ventral view; generalized mammal (A 1), Panochthus sp. (A 2). B. Explanatory drawing of the Panochthus sp. skull in lateral view, with hyoid apparatus and tracheal rings. C–E. Tracheal rings in anterior view. C. Panochthus sp. (MHM-P 87). D. California sea lion Zalophus californianus Lesson, 1828. E. Domestic pig Sus scrofa domestica Linnaeus, 1758. A, modified from Martínez and Turpín 2015; D, E, modified from Moore et al. 2014. Abbreviations: cc, cricoid cartilage; hy, hyoid apparatus; mr, mandibular rami; sk, skull; tc, thyroid cartilage; tr, tracheal rings.