Mapes and Doguzhaeva—New Pennsylvanian coleoids from Nebraska and Iowa
having a mineralized body chamber (as does Pabianiconus starkensis n. gen. n. sp.). Donovaniconus differs in having a long, parallel-sided body chamber and longitudinal lirae as ornament on the body chamber.
Nebraskaconus whitei new species Figure 2.1–2.4
Types.—Holotype (UNSM 1918).
Diagnosis.—Short, breviconic phragmocone with ink sac extending beyond the end of the mineralized part of the body chamber, septa closely spaced, mural part of septum about half the cameral length, apical end of ink sac located near, but not at, the terminal septum.
Description.—Shell length ~67mm; crushed breviconic phrag- mocone 36.1mm long and 17.4mm wide at terminal septum; phragmocone apicad from terminal septum has partly miner- alized shell wall and septa for ~17.5mm, apicad of septa for 18.6mm, only faint shell traces to the presumed conch apex; estimated phragmocone and body chamber apical angle ~10°; body chamber length from terminal septum to orad tip of ink sac is 30.9mm; approximately eight closely spaced septa are pre- sent with mural part of septum extending approximately half a camera length; orad end of phragmocone and posterior part of dorsum of body chamber preserve numerous fine, transverse wrinkles between the septa, which sometimes are impressions on shale matrix; on presumed ventral phragmocone surface are eight hollow ovals that probably are septal foramen with thin siphuncular deposits on the septal surfaces; ink sac is 27.7mmlong and 8.4mm wide at widest point, with rounded apical end ~7.0mm orad of terminal septum on presumed venter, ink sac base is flatly oval for ~12.1mm and then narrows in 15.6mm to a flat, blunt point.
Etymology.—After Mr. W.D. “Ted” White, who collected the holotype.
Occurrence.—Same as the genus.
Discussion.—Based on the length of the body chamber from the terminal septum (30.9mm), the body of the animal was at least 30mm long. There is no sign of arm hooks orad of the aperture or on the shale surface, and it is possible that the animal did not have hooks on the arms. The meaning of the “wrinkles” located at the base of the body chamber and near the terminal septum of the phragmocone is unclear at this time; however, as a speculation, these “wrinkles” could be the remnants of the “wrinkle layer” seen in bactritoid-like coleoids (Mutvei et al., 2012). The orientation of the specimen when it came to rest on the sea floor is uncertain; however, the position of the siphuncular elements in the crushed phragmocone, which are typically on the presumed ventral side of coleoids, supports an interpretation that the animal was on its side when it came to rest. The ink sac is the only trace of the soft body of the animal, and there is no evidence that there was a pro-ostracum or pro-ostracum-like structure or rostrum on the phragmocone.
Genus Starkites new genus Type species.—Starkites compressus new genus new species.
Description.—Crushed breviconic phragmocone 21.0mm long and 16.1mm wide at terminal aperture; phragmocone 6.9mm wide with incomplete apex and with approximately nine closely spaced septa with nine hollow ovals that represent the siphuncle foramen with cyrtochoanitic septal necks with thin siphuncular deposits around the septal necks that aided in their preservation; numerous wrinkles between the septa on orad phragmocone end on presumed dorsum may represent a “wrinkle layer”; ink sac 19.9mm long and 5.0mm wide at its rounded apical end, which is adjacent to terminal septum on the presumed ventral side of the animal, is nearly cylindrical for ~8.0mm and then narrows in a length of 11.9mm to a blunt point that is buried in the shale; body chamber, pro-ostracum, and rostrum are absent.
Etymology.—Named after the shape of the shell after diagenetic crushing.
Occurrence.—From the Stark Shale at the LaPlatte Quarry south of Bellevue, Nebraska. No other information is available.
Diagnosis.—As for the type species.
Etymology.—Named after the Stark Shale that yielded the holotype.
Occurrence.—From the Stark Shale (Pennsylvanian, Missourian = Kasimovian) at the Old Public Works (WPA) Quarry near Bellevue, Nebraska. No other information is available.
Discussion.—All other coleoid taxa from the Stark Shale retain traces of a body chamber. Because this taxon lacks this condi- tion, it is unique. The ink sac being adjacent to the terminal septum is seen in both Starkites n. gen. and Pabianiconus n. gen., however, the later genus has a well-mineralized body chamber.
Evidence that the body of the animal was present when the specimen came to rest on the sea floor bottom can be
deduced because of the presence of a complete ink sac that is filled with ink, which is in front of the last septum of the phragmocone. That position is the logical place where an ink sac would be expected. It also seems reasonable that if the body had a shell that formed a body chamber, which had been removed by diagenetic processes, the mineralized phragmocone also would have been removed. Thus, the conclusion that can be made is that there was never a mineralized shell for the main body of the animal and only the internal phragmocone was mineralized.
Starkites compressus new species Figure 2.5–2.8
Diagnosis.—Mineralized breviconic phragmocone with closely spaced septa. Body chamber, rostrum, and pro-ostracum absent. Apical angle of the phragmocone ~10°, ink sac abuts the terminal septum.
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