Pachydiscus (Pachydiscus) epiplectus Redtenbacher 1873 from: Ward, P.D..Kennedy, W.J.. (1993): Maastrichtian Ammonites from the Biscay Region (France, Spain) . Memoir (The Paleontological Society), Journal of Paleontology34 (Supplement to Vol. 67)(5) p. 1-58 | . |
Notice: This catalogue page may contain unedited data.
|
Species Pachydiscus (Pachydiscus) epiplectus Redtenbacher 1873 |
|
|
|
| Alternative name: |
|
| Diagnosis / Definition: |
Ward & Kennedy (1993):
Description. -
"The whorl section varies from compressed to
depressed, sometimes on the same specimen, due to post-mortem
crushing, with a small deep umbilicus, the umbilical wall
and shoulder rounded. The inner flanks are inflated, the outer
flanks flattened and convergent, with a broadly rounded venter.
The greatest breadth is below mid-flank. Primary ribs arise at
the umbilical shoulder, singly or in pairs, from feeble bullae or
not and are narrow, sharp and prorsiradiate, separated by wide
interspaces. They sweep forwards across the inner flank, while
intercalated ribs are inserted at various points high or low on
the flank to give an estimated 20-22 bullae at the umbilical
shoulder and a total of 50-55 ribs per whorl at a diameter of
100-1 50 mm. The ribs appear slightly flexuous in some specimens
(due to post-mortem distortion?) but all sweep forwards
over the ventrolateral shoulders where they are markedly concave,
and pass across the venter in a broad convexity. The bestpreserved
of the larger specimens . . . is distorted, with a major
diameter of 220 mm. It shows the same style of ornament persisting
to around 170 mm, beyond which it is poorly preserved,
although flank ribs persist and there is strong ventral ribbing,
the rib density being an estimated 60 per whorl. In the largest
specimen . . . the ribbing appears to be effaced on the mid-flank
region." (Kennedy and Summesberger, 1986, p. 192.)
The Biscay specimens are crushed flat, a less misleading deformation
than that shown by the Austrian material (e.g., Figure
23.4, 23.5). A typical juvenile is shown in Figure 30.5, and
illustrates the ornament at this stage. There are an estimated
total of 55-60 ribs per whorl, long primaries arising at umbilical
shoulder, and variably bullate, with one or two intercalated ribs
arising low on flank. These juveniles co-occur with much larger
specimens that show weakening flank, but persistent ventral
ornament to diameters of at least 250 mm. |
| Discussion / Comments: |
Ward & Kennedy (1993):
Type. -
Lectotype, by subsequent designation by Kennedy and
Summesberger, 1986, p. 192, is No. 1868.X. 14, in the collections
of the Institute of Geology of Vienna University, the original
of Redtenbacher, 1873, p. 121, P1. 28, fig. la, b, from
Muthmannsdorf in the Neue Welt Basin, Austria.
Discussion.-
This has been a poorly known species, recently
revised by Kennedy and Summesberger (1 986). It is easily distinguished
from other Biscay species, such as Pachydiscus (P.)
neubergicus, P. (P.) gollevillensis and P. (P.) armenicus, by the
much more involute, massive, relatively high-whorled Nautilus-like
shell. This gross shell mo~hologiys matched by Anapachydiscus
terminus n. so., to be described below. Juveniles are easily
separated by the pronounced umbilical bullae and much fine;,
denser ribs of terminus, which commonly arise in pairs from
bullae at the umbilical shoulder, while adults have weak or no
flank ribbing. Differences from other P. (Pachydiscus) species
are discussed by Kennedy and Summesberger (1 986). The other
common pachydiscid in the Biscay faunas is Anapachydiscus
fresvillensis (Seunes, 1 890a) (Figure 36.1,36.2). This has a similarly
massive shell, but juveniles can be distinguished, when
well preserved, by the presence of strong umbilical spines corresponding
to prominent flat-topped umbilical bullae on molds.
There are generally only around 1 1-12 such spines/bullae per
whorl, and around 30 ribs. Bullae weaken from 60 mm diameter
or so, and migrate out to an inner flank position, thereafter
declining, as does flank ribbing, leaving an adult shell ornamented
by coarse rounded ventrolateral and ventral ribs, numbering
40 per whorl.
Occurrence. -
In the Biscay sections this taxon is found low
in Member I (lower Maastrichtian). The types are from the lower
Maastrichtian of the Neue Welt Basin in Austria, and the species
is also known from the lower Maastrichtian of Neuberg, Steiermark,
Austria, the former USSR, and Bulgaria. It may also be
present at Tercis, Landes, France, and in Madagascar. |
| Systematics: |
38
Ordo Ammonoidea
Subordo Ammonitina
Superfamilia Desmocerataceae
Familia Pachydiscidae
Genus Pachydiscus
Subgenus Pachydiscus
Species Pachydiscus (Pachydiscus) epiplectus
|
| Synonym list: |
Ward & Kennedy (1993):
1986 Pachydiscus (Pachydiscus) epiplectus Redtenbacher. - Kennedy & Summesberger : p.192 pl.6, fig. 3,4;
pl. 7, figs. 1,2;
pl. 8, fig. 1, 2;
pl. 9;
pl. 10, fig. 1-3;
pl. 11, fig. 14;
pl. 12;
pl. 13, fig. 1-3 (with full synonymy)
|
| Stratigraphy - relative ages: |
lower Maastrichtian: Ward & Kennedy (1993)
|
| Specimen: |
Collections of the Institute of Geology of Vienna University, Inventory number: No. 1868.X.14
|
| References: |
Redtenbacher,A.. (1873):
Die Cephalopodenfauna der Gosauschichten in den nordöstlichen Alpen: . Abhandlungen der königlich-kaiserlichen geologischen Reichsanstalt Vol. 5 p. 91-140
Kennedy,W.J.. and Summesberger,H.. (1986):
Lower Maastrichtian ammonites from Neuberg, Steirmark, Austria: . Beiträge zur Paläontologie von Österreich Vol. 12 p. 181–242
Ward,P.D.. and Kennedy,W.J.. (1993):
Maastrichtian Ammonites from the Biscay Region (France, Spain) . Memoir (The Paleontological Society), Journal of Paleontology34 (Supplement to Vol. 67)(5) p. 1-58
|
This work is licensed under a Creative Commons Attribution 2.5 License.
|
|
Taxon Concept provided by