Belonostomus, Agassiz, 1843

Van Vranken, Nathan E., Fielitz, Christopher & Ebersole, Jun A., 2019, New occurrences of Belonostomus (Teleostomorpha: Aspidorhynchidae) from the Late Cretaceous of the North American Gulf Coastal Plain, USA, Palaeontologia Electronica 22 (3), pp. 1-11 : 3-7

Genus BELONOSTOMUS Agassiz, 1843

Belonostomus sp.

Referred material. SMU 77675 . Left and right premaxillae ( Figure 4 ). Collected f rom the contact between the Eagle Ford Shale and Austin Chalk in Collin County, Texas, USA, Upp er Cretaceous ( Figure 1 ) .

Description. The left and right premaxillae are slender bones that fuse, forming a ventral Vshaped trough. A thin bone that could be the vomer is preserved in the trough (Estes, 1964). Together, the premaxillae measure 179.80 mm in length. It closely resembles UTBEG 31051-39 and Belonostomus longirostris (Woodward, 1894; Bardack, 1968; Estes, 1964). The teeth on the specimen are small, slightly recurved, and increase in size posteriorly.

Referred material. SMU 77676 , partial predentary ( Figure 5 ). Collected from the Cenomanian Del Rio Formation in McLennan County, Texas, USA, Upper Cretaceous ( Figure 1 ) .

Description. The partially preserved predentary measures 46 mm and resembles FHSM VP 17431 (Everhart, 2009). The left and right dentaries are fused and form a predentary symphysis, which articulates with the predentary. In ventral aspect, the symphysis sits within a small recess, and the two dentaries interdigitate to form a crosshatched pattern with small bulbous ridges. This may be a new feature for Belonostomus . The teeth are consistent to descriptions found in Woodward (1894) and Estes (1964) and other specimens discussed in this report.

Referred material. SMU 77677 , a partial rostrum ( Figure 6 ). Collected from the contact between the Eagle Ford Shale and Austin Chalk in Collin County, Texas, USA, Upper Cretaceous ( Figure 1 ) .

Description. Measures 54.5 mm from anteriormost point to the base. In cross section the element looks like an inverted “U” with both sides fused medially, the fusion is mostly obscured by matrix. The overall morphology closely resembles Belonostomus longirostris (Brito and Suarez, 2003) . In ventral view, the teeth are closely spaced and are situated within a canal with a thin layer of bone, which covers at least one half of each tooth. Most of the teeth were not preserved.

Referred material. ALMNH 1994.24 .15, a partial premaxilla ( Figure 7 ). Collected from the upper Santonian Tombigbee Sand Member of the Eutaw Formation in Montgomery County, Alabama, USA, Upper Cretaceous .

Description. Measures 4.1 mm in greatest anteroposterior length and has a greatest width of 3 mm at its posterior end. Neither the anterior or posterior ends of ALMNH 1994.24.15 are preserved. In dorsal view, this premaxilla has straight lateral edges that have a slight medial taper anteriorly. The element is ornamented with a series of strong parallel striations that extend the length of the premaxilla and cover the dorsal and lateral edges. These striations occasionally intersect along the dorsal margin. In ventral view, a shallow sulcus extends medially along the entire length of the premaxilla. This sulcus is V-shaped in posterior view, and it becomes gradually shallower towards the anterior end. Positioned on each lateral side of this sulcus is a single row of minute, tightly packed, alveoli ( Figure 7.3 ). No teeth are preserved on this specimen, but the tooth rows extend the entire length of the element.

Referred material. MMNS 3152 , rostrum and premaxillae ( Figure 8 ). Collected from the Maastrichtian Prairie Bluff Chalk in Oktibbeha County, Mississippi, USA, Upper Cretaceous .

Description. The specimen represents the rostrum and premaxillae that are fused with no sutures to mark the boundaries between the elements. The specimen measures 176 mm long with the posterior 31 mm of the element possessing teeth. Ventrally, a suture marks the boundary between the left and right premaxilla. Each premaxilla has a single, large tooth positioned medially within a deep ventral excavation. Rows of smaller teeth reside on a ridge that flanks the medial tooth. Overall, the architecture of the teeth and premaxilla is similar to the other specimens and still consistent with most Belonostomus species except for B. helgandicus and “ Belonostomus sp. 3 ” (Brito. 1997). Small teeth are present between the gaps where larger teeth would have been and disappear at least onethird from the anterior tip of the element.

Referred material. ALMNH VP 1994.31.112, a partial dentary ( Figure 9 ). Collected from the upper Santonian Tombigbee Sand Member of the Eutaw Formation in Montgomery County, Alabama, USA, Upper Cretaceous.

PALAEO- ELECTRONICA.ORG

Description. The element measures 21 mm in greatest anteroposterior length, and nearly 4 mm in greatest labiolingual thickness. The oral surface of the dentary is covered with a dense tooth patch of irregularly placed sub-circular teeth of various diameters. The crown on the individual teeth is rounded and lacks a distinct cusp. A pronounced ridge extends medially across the length of the labial and lingual faces of the dentary. The ventral face is composed of a thin crest that also extends the length of the element and forms a distinct Tshaped outline in profile view.

Figures

FIGURE 1. A locality map showing the counties in Texas, USA where the three new Belonostomus fossils were collected.

FIGURE 4. Belonostomus sp. SMU 77675. Fused left and right premaxillae. 1, dorsal view; 2, ventral view; 3, left lateral view; 4, close up of the teeth in lateral view. Scale bars equal 10 mm.

FIGURE 5. Belonostomus sp. SMU 77676. Partial predentary. 1, ventral view; 2, dorsal view. Abbreviation: pds: predentary symphysis. Scale bars equal 10 mm.

FIGURE 6. Belonostomus sp. SMU 77677. 1, ventral view; 2, lateral view. Scale bars equal 10 mm.

FIGURE 7. Belonostomus sp. ALMNH 1994.24.15 1, dorsal view; 2, right lateral view; and 3, ventral view. Scale bars equal 5 mm.

FIGURE 8. Belonostomus sp. MMNS 3152. Rostrum and premaxillae. 1, left lateral view. Anterior to the left. 2, ventral view. Scale bar equal 10 mm.

FIGURE 9. Belonostomus sp. ALMNH 1994.31.112. 1, lateral view; 2, medial view; 3, dorsal view. Scale bars equal 5 mm.