Ruedersdorfia berlinensis, Arratia & Schultze, 2024

Arratia, Gloria & Schultze, Hans-Peter, 2024, The oldest teleosts (Teleosteomorpha): their early taxonomic, phenotypic, and ecological diversification during the Triassic, Fossil Record 27 (1), pp. 29-53 : 29

Ruedersdorfia berlinensis sp. nov.

Fig. 11

Diagnosis.

(Based on a unique combination of characters among stem teleosts. Autapomorphies are identified with an asterisk [*].) The skull roof plate resulting from the fusion of parietal, postparietal, autosphenotic, and supratemporotabular is characteristic in that the orbital region is almost as long as the postorbital region, and the width of the midorbital region is about half the width of the postorbital region ([*]; Table 1 ). The length of nasal region is less than 10% of the cranial plate [*], being a small one among Triassic teleosteomorphs. Middle pitline short, not reaching the lateral margin of the supratemporotabular region [*]. Skull roof plate covered by a characteristic ornamentation (Fig. 11 ).

Derivatio nominis.

The genus name is dedicated to the place of origin ( Rüdersdorf) plus the ending “ichthys”, for fish. The species name refers to the town of Berlin, indicating the geographic position of the quarry, that is located 25 km east of the center of Berlin (Germany).

Type material.

Holotype. MB. f. 19910, a well-preserved skull roof including characteristic ornamentation.

Paratypes. MB. f. 14888, a skull roof plate preserved as impression. MB. f. 19911, a well-preserved skull roof including sensory canal system.

Provenience.

Opencast mine in Rüdersdorf, 25 km east of the center of Berlin, Germany.

Age.

Lower Middle Triassic, lower Anisian (middle Muschelkalk).

Description.

This taxon is represented by three nicely preserved skull roofs of ca. 18 mm length and 11 mm width at the postorbital region, with all skull dermal bones fused into a plate, with the exception of the rostral and nasal bones that are not preserved. The skull roof plate (Fig. 11 ) is narrow anteriorly at the so-called triangular nasal region and slightly expands posteriad, reaching its maximum width at the supratemporotabular [= dermopterotic] region; the skull roof plate ends in almost a straight line, with a small process that is exposed at the posterolateral corner of the supratemporotabulars in the paratypes. The skull roof differs from all other taxa studied here and other teleosteomorphs in that the orbital region is as long as the postorbital region (Table 1 ). The small triangular nasal region is short and its length is about 8% of the skull roof length. Considering the oblique position of both sutural surfaces for the nasal bones and the lateral exits of the supraorbital canal, it is assumed here that nasal bones were placed laterally to the median rostral bone. The orbital region is slightly narrower than the postorbital region, with the width at its mid-region ca. 33% of the postorbital region width (Table 1 ).

The skull roof (Fig. 11 ) does not show sutures or incomplete ones. The anteriormost, narrow orbital region is the smallest among the skull roofs studied here, and in addition, its anterior margin is slightly rounded, unlike other preorbital regions that commonly are triangular-shaped. This gives the skull roof characteristic proportions and shape (see Table 1 and section on Morphological comparisons and taxonomic assignments). There is no evidence of a supraoccipital bone. The exposed portion of the epiotics at the posteroventral region of the plate are well developed and conic in shape. The surface of the skull roof is covered by a layer of ganoine, characteristically ornamented (Fig. 11 ).

The supraorbital sensory canal is visible through the bone, with a characteristic trajectory, with few small pores, irregularly placed and opening directly on the surface. The supraorbital sensory canal extends posteriad, ending in the postparietal, just anterior to the middle pitline. Thus, the last section of the canal can be interpreted as its postparietal branch. The supraorbital canal, nicely preserved, shows that there is not a lateral connection with the infraorbital canal, neither with the otic canal whose trajectory (and pores) is not visible in the supratemporotabular region of the plate. Two pitlines are clearly visible on the postorbital region. One is the middle pitline that is placed posterior to the anterior pitline, and is short, not extending to the lateral surface of the supratemporotabular region. The short anterior pitline is placed in continuation with the postparietal branch of the supraorbital canal, and apparently it does not contact the middle pitline.

Figures

Figure 11. Ruedersdorfia berlinensis gen. et sp. nov. (holotype MB. f. 19910) from Ruedersdorf, near Berlin, Germany (central European Basin; Germanic Basin). Small arrrows point to the epiotics. A. Photograph of skull roof plate. B. Drawing illustrating details of ornamentation. Sensory canals and pit lines are not observed due to the thickness of the ornamentation. Abbreviation: lp. pr, latero-posterior process of the supratemporotabular area of the skull roof. Scale bar: 5 mm (A).