Ptychitid Ammonoids appear at the lower-middle Anisian boundary (246.36 million years ago) with Malletoptychites, although this date is well constrained only in the Tethys Himalaya, and are a typical component of the open-marine ammonoid assemblages during Anisian and partially Ladinian times. The family fills the gap after a minor Ammonoid extinction event when almost all Grambergiids disappeared. The type genus itself, Ptychites, is one of the most characteristic Ammonoids in the fossil record, and was erected by the Austro-Hungarian geologist and palaeontologist Johann August Georg Edmund Mojsisovics von Mojsvar in 1875, based on material from the Tethys Realm. Only a limited number of species was known in the early years after erecting the genus, but Mojsisovics’ 1882 monograph, Die Cephalopoden der mediterranen Triasprovinz, boosted its importance. This work is regarded as a milestone in the history of Triassic Ammonoids and chronostratigraphy. Mojsisovics enlarged the number of species of Ptychites, and advanced the organisation of this genus in several groups. After the group featured prominently in Mojsisovics' monograph it became one of the guide fossils for Triassic correlations. Its iconic statuswas also reflected by being a part of Ernst Haeckel’s Ammonoid selection in his influential book, Kunstformen der Natur, a trendsetting issue, connecting science and art more than a century ago. Ptychites has now been described from almost all over the world, including Nevada, British Columbia, Spitsbergen, the Himalayas, the Northern Alps, the Balaton Highlands, and the Dinarids and Hellenids. In the Triassic of Spitsbergen and the Western Tethys, namely the wider Alpine and the Himalayan regions, the genus Ptychites is especially characteristic. Therefore, scientists introduced the terms 'Ptychitenkalke' (Ptychites limestone) and 'Ptychites beds'. Ptychites were well adapted to quite a large number of different palaeoenvironments. Despite this fact, the genus shows a low morphological disparity.
In a paper published in the Journal of Paleontology on 11 May 2020, Eva Bischof and Jens Lehmann of the Geowissenschaftliche Sammlung at Universität Bremen, describe a new species of Ptychites from the Fossil Hill Member of the Favret Formation, which outcrops in Muller Canyon in the Augusta Mountains of Pershing County, Nevada, as part of a study of the Ptychitid Ammonoids from the middle and late Anisian of Nevada.
The study area in north-western Nevada, belongs to the world’s most complete low-palaeolatitude sequences, revealing late Anisian Ammonoid faunas. The continuous sequences, which include a very diverse and abundant Ammonoid fauna, provide a good basis for ontogenetic studies on a high-resolution scale. Due to their distinctive ontogenetic trajectories (model curves), Ptychitids will act as an important cornerstone in future quantification of ontogenetic analyses.
Because Ptychites is found all over the world, Bichof and Lehmann's study also contributes to the worldwide correlation of Middle Triassic sediments. Representatives of this group have been described from many different localities all over the world. However, most of these records originate from condensed facies, with significant uncertainty regarding the number and age of the faunas, and the composition of the populations. This makes correlative work particularly challenging.
The bulk of the fossil material used by Bichof and Lehmann was collected by members of the Geosciences Collection of the University of Bremen (Germany). It derives from the Muller and Favret Canyon of the Augusta Mountains (Pershing County), north-western Nevada, USA. A complete section of the upper portion of the late Anisian Fossil Hill Member of the Favret Formation and the lowermost part of the early Ladinian Home Station Member of the Augusta Mountain Formation was meticulously documented and measured. Furthermore, James Jenks collected additional material in Rieber Gulch and Favret Canyon of the Augusta Mountains in Pershing County, and the Wildhorse-McCoy Mine area in Churchill County. Since the fossil material of James Jenkswas loosely collected, nomeasured sections are associated with this material. However, the sites where the fossil material was found are thoroughly documented and the biostratigraphic framework is well known.
(1) Middle Triassic paleogeographical setting. Nevada as well as other important localities of Ptychites spp. are marked. (2), (3) Location of the study area in northwest Nevada, USA. The most important localities of Fossil Hill Member outcrops are marked. Bichof & Lehmann (2020).
Biostratigraphically, Ptychites spp. from Nevada that are the focus of Bichof and Lehmann's study were collected in the Balatonites shoshonensis and the Gymnotoceras mimetus–Gymnotoceras rotelliformis biozones of the Fossil Hill Member (middle and late Anisian). The Fossil Hill Member consists of alternating layers of calcareous siltstone and mudstone with lenticular limestone. The rich fauna of the succession primarily consists of Halobiid Bivalves and Ammonoids. Ceratitids are quite abundant and diverse throughout the member. The Anisian faunas of the Humboldt Range were previously described in the 19th and early 20th centuries.
Measured lithostratigraphic sections in the Muller and Favret canyons of the Augusta Mountains, Pershing County, NW Nevada, USA from where the specimens were collected. Black dots: Beds within Bichof & Lehmann's measured sections; Gray dots: JJ-localities documented by James Jenks, Salt Lake City, Utah, USA; Gray triangle: HB-locality, documented by Hugo Bucher, Zurich, Switzerland. Bichof & Lehmann (2020).
The new species is named Ptychites embreei, in honour of geologist Patrick Embree of Orangevale, California, for his contributions and broad support of the research on the Triassic of Nevada. In total, Bichof and Lehmann collected 38 specimens of Ptychites embreei in Muller Canyon. Two specimens: GSUB C9642, C9643, from bed No. MUC1818; 10 specimens: GSUB C9453, C9455–C9462, C8564, from bed No. MUC2175; one specimen: GSUB C8423, from bed No. MUC2870; 19 specimens: GSUB C8254, C8265, C8267, C8269, C8270, C8272–C8280, C8285–C8287, C8290, from bed No. MUC2980; and six specimens: GSUB C9619, C9621–C9624, C10313; from bed No. MUC3239.
Ptychites embreei from Muller Canyon, Augusta Mountains, Pershing County. (1)–(3) GSUB C8272, (4)–(6) GSUB C10313, (7)–(9) GSUB C8289 (paratype). Bichof & Lehmann (2020).
The holotype of Ptychites embreei (GSUB C9453) is a complete specimen with a maximum diameter of 29.77 mm. Because of its large size, compared to other representatives of this new species, it is interpreted as an adult specimen; there are no other criteria for maturity. The pachyconicshell is subevolute and reveals a deeply incised umbilicus with a steep umbilical wall and a distinctive umbilical shoulder. The surface of the shell is smooth and bears a very fine ornament of striae. The venter is perfectly rounded and smooth.
Holotype GSUB C9453 of Ptychites embreei from Muller Canyon, Augusta Mountains, Pershing County. Bichof & Lehmann (2020).
Among the Ptychitids of Nevada, Ptychites embreei covers by far the largest time span. It remains to be clarified whether this is due to biological processes or reflects a bias caused by more intensive sampling associated with this study relative to prior work.
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