Eutrephoceras sp.
|
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 |
|
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
4
R. americanus R. shifieldensis
R
.
. corbaricus aethioparian 2
R
R
.
.
martinezi foncouvertensis PC 1
R. cretaceus this study R. sp. 0
R. tilli R R.. aturensis guanensis -1
-2 Modern
-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 |
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