Pachycormidae, Woodward, 1895

Maxwell, Erin E., Lambers, Paul H., López-Arbarello, Adriana & Schweigert, Günter, 2020, Re-evaluation of pachycormid fishes from the Late Jurassic of Southwestern Germany, Acta Palaeontologica Polonica 65 (3), pp. 429-453 : 448-450

publication ID	https://doi.org/ 10.4202/app.00749.2020
persistent identifier	https://treatment.plazi.org/id/E94C87EE-F34C-4828-FCD3-FE8987B3FB02
treatment provided by	Felipe
scientific name	Pachycormidae
status

Treatment

Pachycormidae gen. et sp. indet.

Material.— GPIT /OS/1301 ( Fig. 11 View Fig ), a caudal fin fragment figured by Quenstedt (1856 –1857: pl. 100: 6); GPIT /OS/1303, a partial skull consisting of both lower jaw rami and some poorly preserved cranial and visceral arch elements; both from the Late Jurassic of Nusplingen, Germany.

Description.— GPIT /OS/1301 is rather large fragment, ca. 9.5 cm in preserved length. The lepidotrichia are thin and the segments are relatively elongated, slightly expanded at the proximal and distal ends. The fin rays bifurcate distally. The anterior edge of the fin is damaged, making the morphology of the fringing fulcra impossible to determine. The posterior lepidotrichia are posteriorly curved and very slender. Based on the height to length of the fragment, it originates from a high aspect-ratio fin.

GPIT /OS/1303 ( Fig. 12 View Fig ) was described by Heineke (1906), but only a single element, the “suboperculum”, was figured. This element is in fact the articulated remains of the left so1 and so2. The right suborbitals are also present, but are not as well preserved. so2 is dorsally concave, and so1 is ventrally narrow, expanding dorsally and roughly triangular ( Fig. 12A View Fig 3 View Fig ). so2 is greatly enlarged and the anteriormost end of which is invaded by a sensory canal ( Fig. 12A View Fig 3 View Fig ). The presence of the sensory canal suggests that the ventralmost infraorbital is fused with the anterior end of so2. A small facet is present on the ventral edge of so2 for articulation with the supramaxilla. The surface of so2 is ornamented with tubercles, which are better-developed close to the ventral edge. Ventral to the suture with so1, the lateral surface of so2 is ornamented short lines radiating from its posterior margin, partially preserved as impressions on the matrix. These suggest a ridged ornamentation, more weakly developed than that of Simocormus macrolepidotus gen. et sp. nov. ( Figs. 2 View Fig , 3A View Fig 1 View Fig , A 2 View Fig ).

The lower jaws are 117 mm (right) and 120 mm (left) in length, indicating a fish of around 75 cm SL. The lateral surface of the dentary is smooth; the angular shows light tubercular ornamentation. The angular-dentary suture is clearly visible on the right. The mandibular sensory canal is visible, forming a 90° angle within the angular, continuing anteriorly parallel to the ventral edge of the angular and trending gradually dorsally once it enters the dentary.

The sharply pointed teeth appear to be conical in cross-section, and the cap enameloid is smooth. The collar enameloid is covered in fine striations ( Fig. 12A View Fig 4 View Fig ). Two dentary tooth rows are present, a tiny external row and a larger internal row. The dentary teeth in the larger tooth row are relatively small, but the anterior dentary bears two enlarged teeth, the anteriormost of which is procumbent.

The right anterior ceratohyal is preserved medial to the right mandibular ramus; the left is preserved under the left ramus and is only visible due to damage to the external surface of the latter. The left hypohyal with a foramen for the afferent hyoid artery remains in articulation with the corresponding anterior ceratohyal ( Fig. 12A View Fig 1 View Fig , A 2 View Fig ). Remarks.— GPIT /OS/1301 is not amenable to synapomorphy-based diagnosis, its large size, long, slender lepidotrichial segments, and the inferred high aspect-ratio shape of the fin are most consistent with Pachycormidae among the fishes reported from the Late Jurassic plattenkalks. Many of the filter-feeding pachycormids, including Asthenocormus , have unsegmented caudal fin rays ( Liston et al. 2013); however, lepidotrichial segmentation of the type observed in GPIT /OS/1301 is widely distributed among the toothed pachycormids.

GPIT /OS/1303 is referable to Pachycormidae based on the size, shape and arrangement of the suborbital elements (see argumentation in Lambers 1992). The well-developed mandibular dentition and procumbent dentary tooth place GPIT / OS/1303 within the toothed pachycormid clade. Generic referral is not possible due to the fragmentary nature of the specimen; however, the conical cross-section of the dentary teeth suggests that this specimen cannot be attributed to Orthocormus . The ridged ornamentation of so2 is shared with Simocormus macrolepidotus gen. et sp. nov. ( Woodward 1895; Lambers 1992), but is more weakly developed in GPIT / OS/1303. The small size, open sutures between the mandibular elements, and possibly also the lack of ornamentation on the lower jaw suggest that, despite the relatively large estimated size, GPIT /OS/1303 might represent a juvenile.