Gaudryceras submurdochi Raffi and Olivero, 2019
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publication ID |
https://doi.org/ 10.4202/app.00560.2018 |
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persistent identifier |
https://treatment.plazi.org/id/03AF87EA-291D-594B-ED3C-FEAFFADBCC74 |
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treatment provided by |
Felipe |
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scientific name |
Gaudryceras submurdochi Raffi and Olivero |
| status |
sp. nov. |
Gaudryceras submurdochi Raffi and Olivero sp. nov.
Fig. 4 View Fig .
2018 Gaudryceras aff. murdochi ( Marshall,1926) View in CoL ; Olivero and Raffi
2018: 85.
ZooBank LSID: urn:lsid:zoobank.org:act:C48CBFAB-B76E-44F3-8FC9-9B85C682BCC8
Etymology: From Latin sub, somewhat; meaning that the new species is somewhat similar to Vertebrites murdochi , the type species of the genus Vertebrites .
Holotype: CADIC PI 415 , moderate shell (D 80 mm) with complete phragmocone and incomplete body chamber ( Fig. 4A View Fig ).
Type locality: Redonda Point locality, southeastern James Ross Island, Antarctica.
Type horizon: Informal Member II of the Rabot Formation, Ammonite Assemblage 6 Natalites spp. Group 2; Campanian (Cretaceous).
Material. — A total of 31 specimens that includes 28 small shells partly preserving the phragmocone and body chamber ( CADIC PI 418–445 ) and 3 mostly complete large shells ( CADIC PI 415–417 ). All from type locality and horizon except CADIC PI419 , CADIC PI423 , CADIC PI431 , which are from Brandy Bay locality, Santa Marta Formation and CADIC PI 417 from Hamilton Norte locality, Rabot Formation .
Diagnosis. —Moderate shell, early whorls similar to “ Vertebrites ” murdochi Marshall, 1926 in ribbing style and shell shape but with less depressed whorl section and denser and more marked constrictions and collars. Body chamber with compressed whorl section ornamented with single, slightly sinuous flat ribs, bearing numerous constrictions preceded by strong collars.
Description.—Early growth stages (D up to 40–45 mm): Neanoconch ornamented with more than 10 sharp, strong flares. The coiling is fairly evolute and serpenticone, the whorl section fairly depressed (Wb/Wh ~1.1–1.2; Table 2). The umbilicus is fairly wide to wide (U ~45–55%; Table 2), umbilical wall very short and convex, merging with a broadly rounded umbilical shoulder. Flank convex merging into a broadly rounded venter. Whorl section and coiling becoming progressively less depressed and more involute, respectively, through ontogeny. Ribs coarse and strongly prorsiradiate on main flank, just at or slightly below the whorl contact the ribs split into numerous fine lirae or subcostae, which are not preserved on the internal mold. In a half whorl, there are about 25–30 main ribs near the umbilical shoulder and more than 75–100 on the venter. Four to five deeply incised constrictions preceded by strong, very wide collars per whorl. The constrictions are best marked in the internal mold and the collars are only visible when the test is preserved. Suture line is typical for the genus.
Later growth stage (D up to 80 mm): The coiling is progressively more involute, with the umbilicus of the largest shell (D 80 mm) of moderate width (U 34%; Table 2). Whorl section nearly as high as broad to fairly compressed (Wb/ Wh ~1.02–0.81; Table 2). The dense splitting of the ribs is progressively suppressed and only single ribs are preserved in the last part of the phragmocone and body chamber. Single ribs are first prorsiradiate and then change to moderately sinuous on flank and slightly projected on venter. Body chamber with 6–7 sinuous, well-marked constrictions and collars per half whorl.
Remarks. —The ribbing style, coiling, and whorl sections of the early growth stages are very similar to that of Vertebrites murdochi from the Upper Cretaceous of New Zealand ( Marshall 1926) and possibly New Caledonia ( Henderson 1970), but Gaudryceras submurdochi Raffi and Olivero sp. nov. has less depressed whorl section at corresponding diameters (SOM: fig. 1), its adult body chamber is more involute (SOM: fig. 2) and is ornamented with single, slightly sinuous ribs, constrictions and collars. Vertebrites is doubtfully recognized as a separate gaudryceratid genus or subgenus ( Henderson and McNamara 1985) and this is based mainly on the assumption that Vertebrites murdochi may represent an adult specimen, preserving in its last whorl the typical wire-like ornament, depressed whorl section, and serpenticone coiling characterizing its early whorls. We concur with Henderson and McNamara (1985) that larger specimens of Vertebrites murdochi are needed to confirm its present generic status. In addition, independently of the validity of the genus Vertebrites , the change during ontogeny from evolute coiling and depressed whorl section to more involute coiling and compressed whorl section in G. submurdochi sp. nov. clearly indicate that this species correspond to the genus Gaudryceras (see Kennedy and Klinger 1979; Hoffmann 2010).
The inner whorls of Gaudryceras hamanakense Matsumoto and Yoshida, 1979 from the Maastrichtian of Hokkaido, Japan and Sakhalin, Russia ( Matsumoto and Yoshida 1979; Maeda et al. 2005) are similar to G. submurdochi sp. nov., but the former has finer ribs that continue into the body chamber. At corresponding diameters, G. hamanakense is also more depressed than G. submurdochi sp. nov.
Stratigraphic and geographic range.—Early Campanian of the Beta Member, Santa Marta Formation, and early Campanian (possible up to the earliest mid-Campanian) of the Rabot Formation, James Ross Island, Antarctica. Ammonite Assemblage 6 Natalites spp. Group 2.
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