Palaeogadus belli, Stringer & Sloan, 2023

Stringer, Gary L. & Sloan, James Carson, 2023, First Cretaceous teleostean otolith assemblage (Arkadelphia Formation, upper Maastrichtian) from Arkansas, USA, early Gadiformes, and the Western Interior Seaway, PaleoBios 40 (1994), pp. 1-39 : 14-16

PALAEOGADUS? BELLI SP. NOV.

FIG. 7B–H

Diagnosis— Moderately compressed, approximately oblong otoliths (sensu Smale et al. 1995) with a homosulcoid-type sulcus. The H/L ratio ranges from approximately 47%–62%, which is related to ontogenetic changes. Anterodorsal dome (predorsal expansion) evident on specimens greater than 2.0 mm. Ostium and cauda nearly equal in length. Narrow collum with ostial and caudal colliculi very near. Prominent ventral furrow that curves away from anteroventral and posteroventral margins.

Holotype — Palaeogadus? belli sp. nov., DMNH 2021- 09-22, 3.13 mm, Arkadelphia Formation ( Upper Cretaceous , upper Maastrichtian ), Cabot, Lonoke County, Arkansas, USA; coordinates: 34.941292, -92.044155.

Paratypes — Palaeogadus? belli sp. nov., DMNH 2021- 09-18, 1.25 mm. Palaeogadus? belli sp. nov., DMNH 2021-09-19, 1.78 mm. Palaeogadus? belli sp. nov., DMNH 2021-09-20, 2.21 mm. Palaeogadus? belli sp. nov., DMNH 2021-09-21, 2.34 mm. Same locality as holotype.

Occurrence— Type locality: Cabot , Lonoke County, Arkansas, USA; coordinates: 34.941292, -92.044155 ( Boring 5; Station 266; 22.86–23.32 m below ground elevation) , Arkadelphia Formation , Upper Cretaceous (upper Maastrichtian). The coordinates for the four other borings that yielded Palaeogadus? belli sp. nov. are as follows: B6 (34.941187, -92.043788), B8 (34.940683, -92.042295), B9 (34.940450, -92.041533), and B10 (34.940027, -92.040231) .

Etymology— Species named for retired Professor Dennis Bell (Monroe, Louisiana, USA) for his extensive assistance in paleontological vertebrate and invertebrate research, especially in the areas of photography of fossils and preparation of manuscript figures.

Description— Sagitta is moderately compressed. Shape is elongated and is best described as oblong (sensu Smale et al. 1995). Larger specimens tend to be more elongated and narrower posteriorly. Margins are crenulated, especially on the dorsal and ventral margins (all specimens were less than 3.5 mm in length). The dorsal margin tends to have more and deeper crenulations. Anterior margin is somewhat compressed but primarily rounded. Dorsal margin is more broadly rounded on smaller specimens, but a diagnostic anterodorsal (predorsal) dome becomes evident in specimens greater than 2.0 mm. Posterior margin is similar to anterior margin but tends to become more compressed and pointed in the larger specimens. The ventral margin is gently but unevenly curved and can be almost horizontal in the center.

The inner face is convex with a long, homosulcoid-type sulcus. The sulcus extends from almost the anterior to very near the posterior to the extent it could be classified as pseudo-ostiocaudal as defined by Smale et al. (1995). There is a fairly narrow collum between the ostium and the cauda. The ostium and cauda are both elongated, compressed ovals in shape and are similar in length. Colliculi are present in the ostium and cauda and approach very closely to the collum. The dorsal depression is found primarily above the collum. The dorsal depression is small, elongated but somewhat irregular, and best defined on its ventral margin. The ventral furrow is present and is very close to the ventral edge in the center. However, the ventral furrow curves strongly away from the anteroventral and posteroventral margins toward the sulcus. The outer face is irregular with a characteristic hollowing in the central dorsal area, especially in the larger of the specimens.

Remarks— Palaeogadus? belli sp. nov. has gadiform features that seem to place it into the family Merlucciidae . The species is similar to Palaeogadus weltoni Schwarzhans and Stringer (2020a) described from the Upper Cretaceous (upper Maastrichtian) Kemp Clay in northeast Texas ( Schwarzhans and Stringer 2020a). Morphological features similar to P. weltoni include the nearly equal length of the ostium and cauda, no pseudocolliculum in the collum, and the similar shape of the ventral furrow. However, there are some features that readily distinguish it from P. weltoni . These include the development of a fairly prominent anterodorsal dome by specimens greater than 2.0 mm and a narrow collum with the ostial and caudal colliculi situated very near the collum. Palaeogadus? belli also shows similarity to P.? bratishkoi Schwarzhans (2012) known from Paleocene (Thanetian) of Austria and is especially evident in the holotype (fig. 110a) and two of the paratypes (figs. 112 and 113) as illustrated in Schwarzhans (2012).

Palaeogadus? belli is one of the most common specimens in the Arkadelphia Formation comprising 7.02% of the total assemblage. It is only surpassed by the extremely abundant Vorhisia vulpes and Eutawichthys zideki . Unfortunately, all of the gadiform specimens from the Arkadelphia are small (around 3.1 mm in length for the best-preserved specimens), and some are poorly preserved. In spite of the size and preservation, there are features that indicate that the otoliths could belong to the merlucciid genus Palaeogadus to which it is tentatively assigned. However, it is important to note that there are many primitive features present in the Late Cretaceous P.? belli , and there is the distinct possibility that it represents an unknown fossil genus that may also include P. weltoni of Schwarzhans and Stringer (2020a) and possibly P.? bratishkoi of Schwarzhans (2012). The relatively large percentage of P.? belli , a putative cool-water form, in the Arkadelphia Formation at the Cabot site in Arkansas is certainly important in the determination and evaluation of the paleoenvironment and paleogeography in this portion of the Gulf Coastal Plain during the late Maastrichtian. This importance is addressed further and in greater detail in the “Paleoecology and Paleogeography” section.

Figures

Figure 7. Otoliths from the Cretaceous Arkadelphia Formation. All specimens unless otherwise noted are inner views of right sagittae. Length in mm. A. Apateodus crenellatus? Schwarzhans and Stringer (2020b), DMNH 2021-09-17, 1.78 mm. B. Palaeogadus? belli sp. nov., DMNH 2021-09-18, 1.25 mm (paratype). C. Palaeogadus? belli sp. nov., DMNH 2021-09-19, 1.78 mm (paratype). D. Palaeogadus? belli sp. nov., 2021-09-20, 2.21 mm (paratype). E. Palaeogadus? belli sp. nov., DMNH 2021-09-21, 2.34 mm (paratype). F. Palaeogadus? belli sp. nov., DMNH 2021-09-22, 3.13 mm (holotype). G. Palaeogadus? belli sp. nov., DMNH 2021-09-22, 3.13 mm (holotype, outer view). H Palaeogadus? belli sp. nov., DMNH 2021-09-22, 3.13 mm (holotype, dorsal view).