Muensteroceratidae Librovitch, 1957

Korn, Dieter, Bockwinkel, Jürgen, Ebbighausen, Volker & Klug, Christian, 2003, Palaeobiogeographic and evolutionary meaning of an early Late Tournaisian ammonoid fauna from the Tafilalt of Morocco, Acta Palaeontologica Polonica 48 (1), pp. 71-92 : 80-83

publication ID	https://doi.org/ 10.5281/zenodo.13272527
persistent identifier	https://treatment.plazi.org/id/03BE87DE-5A79-FFCB-FCF8-FC9D7724FE6B
treatment provided by	Felipe
scientific name	Muensteroceratidae Librovitch, 1957
status

Treatment

Family Muensteroceratidae Librovitch, 1957 View in CoL Muensteroceras Hyatt, 1884

Type species: Goniatites oweni parallela Hall, 1860 .

Muensteroceras quadriconstrictum sp. nov.

Figs. 16 View Fig , 17 View Fig , 18A–G View Fig .

Derivation of name: After the four constrictions in the steinkerns of the adult stage.

Holotype: Specimen MB.C.3922 (coll. Ebbighausen), Fig. 18A View Fig .

Type locality and horizon: Taouz, Jebel Ouaoufilal, locality A east of Ksar Bouhamed (Tafilalt, Morocco); Oued Znaïgui Formation, early Late Tournaisian.

Material.— 787 specimens between 3 and 26 mm conch diameter. Many are almost complete phragmocones. This is the most common species in the Ksar Bouhamed fauna.

Diagnosis.— Muensteroceras with pachyconic conch at 5 mm diameter (ww/dm 0.60 to 0.85), thickly discoidal to pachyconic conch at 10 mm diameter (ww/dm 0.50 to 0.75), and thickly discoidal at 20 mm diameter (ww/dm 0.45 to 0.60). Umbilicusinallstagesnarrow,rangingfrom7to20percentof the conch diameter. Steinkern often with four constrictions, at 90º intervals. Suture line with deep, parallel−sided external lobe, low median saddle, and asymmetrical adventive lobe.

Description.—As can be seen in the list of dimensions and the ratio plot ( Fig. 16 View Fig ), there is a wide population variability. The whorl width/ conch diameter ratio decreases during ontogeny; at 5 mm diameter it ranges from 0.62 to 0.84 (arithmetic mean 0.70;medianvalue0.71),at10mmdiameterfrom0.48to0.76 (mean 0.62; median 0.61), and at 20 mm diameter from 0.46 and 0.60 (mean 0.53; median 0.52). The variability in whorls width is greatest in juveniles. In contrast to the whorl section, thewidthoftheumbilicusshowsonlyminorchangesthroughout ontogeny, with larger specimens slightly more involute than juveniles. Within the sample, however the two morphologies are connected by a complete spectrum of intermediates, and separation is impossible ( Fig. 16 View Fig ).

The whorl expansion rate is as variable as the whorl width. Again, a correlation with the whorl width is notable, more pachyconic forms have a lower aperture (and thus WER of 1.90 to 2.00) than more discoidal specimens ( WER 2.00 to 2.30). Also, the whorl overlap rate (imprint zone rate, IZR) is higher in the more globose forms.

The constrictions have a slight forward projection over the flanks and a shallow external sinus. They begin in a short distance from the umbilicus and are deepest on the venter. In specimensover10mmdiameter,theconstrictionsareusually arranged 90º apart. These constrictions are already present at 5 mm conch diameter, but at this growth stage they are not as regularly distributed.

The suture line is typical for Muensteroceras ( Fig. 17 View Fig ) with narrow external lobe and low median saddle (0.20 of external lobe depth). The ventrolateral saddle is asymmetrical and broadly rounded, the adventive lobe is also asymmetric with steep ventral flank and sinuous dorsal flank.

Dimensions.—(in mm). Comparisons.—The new species differs in its conch proportions (whorl width/ conch diameter 0.50 to 0.70; uw/dm around 0.15) from most of the other species of the genus. More discoidal forms include M. parallelum ( Hall, 1860) (ww/dm 0.35), M. complanatum (de Koninck, 1880) (ww/dm 0.35), M. compressum Librovitch, 1940 (ww/dm 0.32), M. multiseptatum Librovitch, 1940 (ww/dm 0.35), M. perspectivum (de Koninck, 1880) (ww/dm 0.35), M. recticonstrictum Kusina, 1973 (ww/dm 0.40), M. (?) esbaughti ( Miller et al., 1949) (ww/dm 0.20), and M. (?) pfefferae ( Miller and Werner, 1942) (ww/dm 0.30).

Wider umbilici characterise the species M. barroisi ( Holzapfel, 1889) (uw/dm 0.20), M. collinsoni Gordon, 1965 (uw/dm 0.30), M. cordatum ( Crick, 1899) (uw/dm 0.20), M. delepinei Campbell et al., 1983 (uw/dm 0.24), M. frequens Kusina, 1973 (uw/dm 0.20), M. jenkinsi Campbell et al., 1983 (uw/dm 0.35), M. kazakhstanicum Librovitch, 1940 (uw/dm 0.20), M. kozhimense Kusina,1980 (uw/dm0.25), M. mitchelli Miller, 1935 (uw/dm 0.24), M. modestum Popov and Kusina, 1997 (uw/dm 0.24), M. oweni ( Hall, 1860) (uw/dm 0.28), M. pachydiscus Kusina, 1980 (uw/dm 0.34), M. parvulum Kusina, 1983 (uw/dm 0.40), M. pergibbosum Miller and Garner, 1955 (uw/dm 0.25), M. perspectivum (de Koninck, 1880) (uw/dm 0.25), M. recticonstrictum Kusina,1973 (uw/dm0.24), M. rotella (de Koninck, 1880) (uw/dm 0.20), and M. rowleyi Miller and Furnish, 1958 (uw/dm 0.20).

The remaining few species, which have similar conch ratios to M. quadriconstrictum sp. nov., differ in the following characters: M. medium Miller and Collinson, 1951 has an external lobe in which the flanks stand not as parallel as in M. quadriconstrictum sp. nov., and possesses an almost symmetrical ventrolateral saddle.

M. crassum ( Foord, 1903) and M. occidentale ( Foord, 1903) have similar suture lines, but do not possess steinkern constrictions. The latter is also the case for M. merlewoodense Campbell et al., 1983 and to M. stoliczkai ( Miller, 1931) .

Thus the combination of the characters: whorl thickness around half of the conch diameter, narrow umbilicus (uw/dm usually less than 0.15), and constrictions distinguish the new species from the others.

MB	Universidade de Lisboa, Museu Bocage

Copyright notice

No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.

Taxonomy

Kingdom	Animalia
Phylum	Mollusca
Class	Cephalopoda
Family	Muensteroceratidae