Eutrephoceras sp.

Tajika, Amane, Landman, Neil H., Koyasu, Hiromichi, Broussard, Amy, Anderson, Lian, Ikuno, Kenji & Ikuno, Kenji, 2023, New discovery of rhyncholites and conchorhynchs (cephalopod jaw elements) from the Upper Cretaceous Mount Laurel Formation of Delaware, American Museum Novitates 2023 (3998), pp. 1-20 : 11-17

publication ID

https://doi.org/ 10.1206/3998.1

persistent identifier

https://treatment.plazi.org/id/03966F4F-226A-FFF1-FDD3-0BFECB39357B

treatment provided by

Felipe

scientific name

Eutrephoceras sp.
status

 

Eutrephoceras sp.

Figure 8 View FIGURE 8

MATERIAL: Three broken phragmocones from the Mount Laurel Formation of Delaware ( AMNH 137092–137094).

DESCRIPTION: Our specimens are subspheroconic with a rounded flank, nearly closed umbilicus, and slightly sinuous suture. No trace of ribs is visible. These features characterize Eutrephoceras . The specimens range from 14.6 to 20.7 mm in maximum preserved conch diameter, but are broken phragmocones. Therefore, the actual diameter/ontogenetic stage of these individuals is not determinable. The whorl section is slightly depressed (ww/wh = 1.3–1.4; ww/ dm = 0.82–0.84). The number of septa per half whorl is nine (AMNH 137092). The siphuncle is not preserved. Measurements of all specimens are available in the online supplement.

DISCUSSION: Eutrephoceras dekayi ( Morton, 1834) is an Upper Cretaceous nautilid that has been widely reported from the Atlantic Coastal Plain including Delaware ( Landman et al., 2004). The conch parameters of our specimens are similar to those of E. dekayi reported by Landman et al. (2018) and Tajika et al. (2020). However, a recent study on modern nautilus suggests that the juvenile specimens of closely related nautilid species may not be morphologically distinct ( Tajika et al., 2021). Indeed, Landman et al. (2018) showed that the juveniles of E. dekayi and E. montanaensis exhibit a similar whorl section (ww/wh). Considering the small size (i.e., presumably representing the ontogenetic stage slightly after hatching; dm = 14.6–20.7 mm), we refrain from assigning the specimens to a species.

Height (H) Length of shaft (Ls)

20

15

)

15

mm

(

mm)

Height 10

(Ls 10

5 5

0 0

51015202530 51015202530

Length (mm) Length (mm)

Width (W) Length of hood (Lh)

30 20

)

mm) 15

(20 mm

Width Lh (10

10

5

0 0

010203040 51015202530

Length (mm) Length (mm)

Width of shaft (Ws) Cretaceous Paleogene 15 R. minimus R. donetzsensis R. dutemplei R. vilcassinus R. debeyi R. sagittarius R. lhommei ) R. americanus mm (10 R. simplex R R.. shifieldensis aethioparian R. karakaschi Ws R. solus R R.. corbaricus foncouvertensis R. grayensis R. martinezi R. marcellae 5 R. cretaceus R. sp. R. guanensis this study R. aturensis R. tilli R. turonicus R. erroitegiensis R. danicus 0 R. voitesti 5 10 15 20 25 30 Modern R. albestii Length (mm) N. belauensis R. oppenhemi

α 70

) 60 ° (alpha 50

40

30 5 10 15 20 25 30 Length (mm) β

100) ° (beta

80

60

5 10 15 20 25 30 Length (mm) δ

150) ° (delta 100

5 10 15 20 25 30 Length (mm)

Riegraf and Schmitt-Riegraf, 1995; Komarov, 2005a, 2005b; Košťák et al., 2010; Weaver et al., 2012). Height, width, Ws, Ls, Lh, α, β, and δ are plotted against length, respectively.

Cretaceous Paleogene PC1 vs. PC2

R. minimus R. vilcassinus

4

R. dutemplei R. sagittarius

R. debeyi R. lhommei 3

R. americanus R. shifieldensis

R. simplex R

R

.

. corbaricus aethioparian 2

R. grayensis 2

R. marcellae

R

R

.

.

martinezi foncouvertensis PC 1

R. cretaceus this study R. sp. 0

R. tilli R R.. aturensis guanensis -1

R. erroitegiensis

-2 Modern

N. belauensis -3

-4 -2 0 2 4 6 8

PC1

Length vs. PC1 Length vs. PC2

4 8

3 6

2 1 4 2 PC 2 PC 1

0 0

-1 -2 -2 -4 -3

5 1015202530 5 1015202530

Length (mm) Length (mm)

AMNH

American Museum of Natural History

Kingdom

Animalia

Phylum

Mollusca

Class

Cephalopoda

Order

Nautilida

Family

Nautilidae

Genus

Eutrephoceras

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