Mapes and Doguzhaeva—New Pennsylvanian coleoids from Nebraska and Iowa
the length of the camerae. The terminal septum is slightly displaced because of the crushing of the specimen.
Etymology.—After the Stark Shale that yielded the holotype. Occurrence.—Same as the genus.
Discussion.—One unusual aspect of this holotype is the pre- sence of preserved mantle tissue in the body chamber. Similar material has been observed in other coleoids from the Paleozoic and Mesozoic (Kear et al., 1995; Doguzhaeva and Mutvei, 2003; Doguzhaeva et al., 2007), and all of these taxa are presumed to have been good swimmers. This same conclusion can also be applied to this Stark specimen. Additionally, the presence of fossil ink in the shape of the original organ is unusual. This ink is comparable to the ink of both fossil and modern coleoids (Doguzhaeva et al., 2004).
Genus Donovaniconus Doguzhaeva, Mapes, and Mutvei, 2003 Figure 3.4–3.8
Type species.—Donovaniconus oklahomensis Doguzhaeva, Mapes, and Mutvei, 2003.
Type locality.—Wewoka Formation (Pennsylvanian, Desmoinesian=Moscovian) at the Deep Fork River Bridge east of Okmulgee, Oklahoma (see Mapes, 1979, locality P-6, p. 9,10).
Description.—Laterally crushed, weakly mineralized body chamber 37.9mm long with essentially parallel sides, partly complete breviconic phragmocone 14.3mm long, overall speci- men length 51.8mm; estimated phragmocone apical angle ~25°; body chamber aperture width 14.1mm, width at terminal septum 11.0mm, because the body chamber expands slightly just orad of terminal septum 13.0mm wide; three closely spaced septa are preserved, mural part of each septum extends about one-half cameral length; mineralization of the conch very weak with thickest shell traces at posterior end of body chamber and around the three septa; shell is a thin bluish (phosphate replaced arago- nite), semitransparent covering at orad end of body chamber and on ink sac upper surface; ink sac has cylindrical shape with rounded base that tapers to a flat, blunt point on orad end, cylindrical part ~8mmlong and then for 5mmgradually tapers to narrowly tapered duct ~8.0mm long, ink sac total length is 21.0mm and is approximately two-thirds of body chamber length; apical end of ink sac is 14.0mmorad of terminal septum, which places the ink sac in forward two-thirds of body chamber; on body chamber surface there are branching grooves that probably represent the original pathways of the blood supply for muscles that controlled expulsion of ink from the ink sac. On
an ink-filled sac (is) in the body chamber (bc) and the partly complete breviconic phragomocone (ph) with aligned circular septal necks; (2) enlargement of a striated brown layer on the surface of the shell that is interpreted as the remains of the mantle tissue; (3) enlargement of the septal necks (is) that form a ring probably because of deposits around the cyrtochonanitic septal necks. Donovaniconus sp. (4, 5) Specimen UMSN 62497A (part) and diagram of the specimen, respectively; (4) overall view showing the impression of the animal’s relatively long, parallel-sided body chamber (bc) with a three-dimensional, ink-filled sac (is), and a partly complete phragmocone with remains of several closely spaced septa including the terminal septum (ts); (5) diagram of the faint body chamber impression and the partly complete breviconic phragmocone, the latter of which has the upper (dorsal?) edge preserved as a faint impression, and on the lower (ventral?) side as a thin strip of shell material; the earliest part of the shell is not preserved; (6) specimen UMSN 62497B (counterpart) showing the impression of the parallel-sided body chamber (bc) with an ink-filled sac (is) impression and a partly complete phragmocone (ph); the apical end of the ink-filled sac has a greater diameter than the restricted orad end; also note that the ink sac is placed about midway in the body chamber. Scale bars are 5mm.
Figure 3. (1–3) Pabianoconus starkensis n. gen. and n. sp. (1) Overall view of holotype UNSM 16568A showing body chamber with external shell containing
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impressed shale surface that was in contact with thinly miner- alized body chamber, there are fine, longitudinal lirae indicating that body chamber external surface was ornamented.
Occurrence.—Specimen SUI 62497 (part and counterpart) was collected by J.P. Pope at the Howe Quarry, Adair County, Iowa (NW1/4 sec. 1, T.76 N., R.30 W.) from the Stark Shale (Pennsylvanian, Missourian = Kasimovian). See Pope et al. (2002) for additional information of the geology of the region and of the quarry.
Discussion.—The specimen of Donovaniconus is unique in the Stark Shale coleoid collection with its relatively long, parallel- sided body chamber and breviconic phragmocone with closely spaced septa. However, the eight fragmented coleoid specimens described, but not named, herein (see Figure 3.1–3.6) may represent this or a closely related genus based on the long pieces of body chamber and the septal spacing observed on phragmo- cone segments.
Unnamed coleoids Figure 4.1–4.6
Description.—Eight debris cluster specimens (UNSM 16563, 16564-6 pieces, 16565, 1656A, B, 16569A, B, 16570, 16571, 16572) are included in the Stark coleoid collection. All of the specimens are similar in preservation with replacement of the aragonitic shell by phosphate and the degree of fragmentation of the cephalopod conchs. The shell replacement ranges from good to poor, with some shell fragments being well preserved with two layers of shell and other segments being preserved as “ghosts” with only a thin film on the shale surface. The shell debris is confined to a single bedding plane on shale slabs, as are the named coleoids described elsewhere in this report. Some specimens differ slightly in being shell dedris without sig- nificant other material in the cluster and other specimens having unidentifiable, finely macerated debris mixed with the shell fragments. The debris clusters are irregular in size ranging from 55mm to 115mm in maximum length. Only one specimen (UNSM 16564) appeared to have ink fragments dispersed among the shell debris. Four specimens (UNSM 16565–16567 and 16571) have scattered arm hooks associated with the debris clusters; all the hooks are moderately to poorly preserved and are<1mmin length. The siphuncle is present on four specimens (UNSM 16562, 16564, 16566, and 16570) and is preserved by relatively thick circular structures that contain the cyrtochoanitic septal necks. The thickness of the structures compared to the relative thinness of the shell probably represents cameral deposits around the septal necks, which allowed greater pre- servation potential. The circular structures range in diameter
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