Diversity and Distribution of the Genus Platypeltoides (Nileidae) in Morocco

Recently two new species of the genus Platypeltoides (Nileidae, Trilobita) from the Anti-Atlas region of Morocco have been described. Because new material is still appearing in this area, we have considered to review this subject. The aim of this article is to describe all the species of the genus Platypeltoides appeared in the Lower Fezouata Formation (Tremadocian, Lower Ordovician) and distributed in three different locations of the Moroccan Anti-Atlas. Several specimens of this genus and kept in the Museo Geológico del Seminario (Barcelona, Spain), Museo Geominero (Madrid, Spain) and the Natural History Museum (London, UK) are here described and discussed. In this paper, all known species of the Platypeltoides genus of Morocco are presented. All them appear in the Zagora region and in the Guelmim area. Three species have already been described: P. magrebiensis?, P. hammondi and P. carmenae. We left two more in open nomenclature, Platypeltoides aff. carmenae and Platypeltoides sp. Finally, another species changes its genus: Asaphellus cuervoae = Platypeltoides cuervoae. Indeed, four species (but possibly two more) of the genus Platypeltoides are present in the Lower Ordovician of Morocco.


Introduction
In the last two years, we have described two new species of Platypeltoides from the Lower Ordovician (Tremadocian) of the Fezouata Shale of Morocco: P. hammondi Corbacho & López-Soriano, 2016 [1] and P. carmenae Corbacho et al., 2017 [2]. After obtaining two new species, we have decided to write this article, which is a part of the project that, since 2005, we have been developing on the study of the trilobites of the Ordovician of Morocco, supported by the Museo Geológico del Seminario de Barcelona (Spain) and the Department of Paleontology of the Associació de Perits i Taxadors de Catalunya (Spain), founded by one of the autors (JC).
Historical Background The first geological research done in Morocco was carried out by the French geologist Henri Coquand (1813-1881), who collected and described the first fossils [3]. The presence of Ordovician rocks in the Anti-Atlas zone was firstly mentioned by Neltner [4], specifically in the Tafilalt area. Similarly, it was established the existence of the Ordovician system both in the western (Jbel Tachilla, Tiznit area [5]) and central Anti-Atlas (Foum Zguid area; Bondon in [6]).

Origin of the Specimens
The specimens examined in this study originate from Anti-Atlas, Morocco and belong to the Lower Ordovician (Tremadocian), Lower Fezouata Formation. All the sites mentioned in this study have been visited by the first author (JC). The images of the holotypes of the different species from the cited publications are presented. Platypeltoides magrebiensis? is also represented by the paratype (MGM902X) conserved in the Museo Geominero of Madrid (Spain) and an authentic specimen (MGSB-JC224) conserved in the Museo Geológico del Seminario of Barcelona (Spain) and P. cuervoae two paratypes are also presented (MGSB-JC76 and MGSB-JC77) conserved in the Museo Geológico del Seminario of Barcelona (Spain) and one (NHMUK-it28945) conserved in the Natural History Museum of London (UK).

Preparation and Treatment of Specimens
All the specimens presented in this study, except the holotype and paratype of P. magrebiensis, have been obtained and worked by Moroccan specialists for the first author (JC).
All specimens, except P. magrebiensis?, have been treated with ammonium chloride to highlight their details (the quality of the figures of P. magrebiensis? has been improved through the PhotoScape software). A Canon digital camera, model EOS 1100 D, has been used to take the pictures. For the coordinates, a Garmin GPS Foretrex 401 model has been used.  TL = total exoskeleton length; EL = total eye lenght; CL = total cephalon length; DEC = distance between the posterior eye side and the posterior cephalon side; CW = total cephalon width; CW1 = maximun cranidium width (in posterior margin); GW = basal glabela width; FWG = frontal glabela width in the widest part; PW = máximum pygidium width; RW = anterior width of the pygidial rachis; RL = total length of pygidial rachis; PL = total pygidium length.

Systematic Paleontology
The
Material -Three specimens are presented. The holotype nº MGM901X (holaspis) has a total carapace length of 53 mm and the paratype nº MGM902X (false specimen) has a total carapace length of 277 mm; they were used for the description of the species and are kept in the Museo Geominero de Madrid (Spain) [15]. The third specimen, with a total carapace length of 235 mm, belongs to the collection of Joan Corbacho kept in Museo Geológico del Seminario de Barcelona (Spain) under the entry MGSB-JC224 (authentic specimen).
Geographical distribution -Upper part of the Lower Fezouata Formation. The studied locality exposes blue green argillites from the Upper Tremadocian, Lower Ordovician ( Figure 1, locality nº1). The locality yielding the new trilobite is located approximately 32 km of the SE of Agdz and 14 km of the south of Tansikht, Dra Valley, Morocco. The coordinates of the excavation were 30º 33' 58" N -6º 9' 55" W -Altitude 860 m.
Material -Only a single individual (holotype) is presented. This is a moderately well-preserved individual which is kept in the collections of the Museo Geológico del Seminario de Barcelona (Spain), under the entry MGSB82122. Its total carapace length is 165 mm.
Geographical distribution -Upper part of the Lower Fezouata Formation. The studied locality exposes blue green argillites from the Upper Tremadocian. The locality yielding the trilobite is located approximately 32 km of the SE of Agdz and 14 km of the south of Tansikht, Dra Valley, Morocco ( Figure 1, locality nº1). The coordinates of the excavation were 30º 33' 58" N -6º 9' 55" W -Altitude 860 m.

Platypeltoides carmenae Corbacho et al., 2017
2017 Platypeltoides carmenae Corbacho et al.,pag. 21, Diagnosis -Platypeltoides of large size, with a slightly subtriangular-shaped cephalon and medium-sized genal spines, large eyes located in the transverse median line of the cranidium, a thin anterior border and a slightly subtriangular pygidium with three axial rings and a terminal axial piece [2].
Material -Only a single individual (holotype) is presented. Total carapace length of 220 mm, is kept in the collections of the Natural History Museum of London (UK), under the entry NHMUK-it29220.   Discussion -When this species was first described, the extremely long genal spines and other particular characteristics caused us to underestimate the importance of the number of segments, and for this reason it was assigned to the genus Asaphellus. With the study of new complete and well-preserved specimens, it has been proven that they only have 7 thoracic segments, so they should be assigned to the genus Platypeltoides. Diagnosis -Platypeltoides of large size, with a slightly subtriangular-shaped cephalon and medium-sized genal spines, large eyes located in the transverse median line of the cranidium, a narrow border and a subtriangular pygidium with three axial rings and a terminal axial piece [2].

Platypeltoides cuervoae (Corbacho
Material -A single specimen with a total carapace length of 155 mm is included. It is kept in the collection of Keith Hammond in the Museo Geológico del Seminario de Barcelona (Spain), under the annotation MGSB-KH2b.
Geographical distribution -Upper part of the Lower Fezouata Formation. The studied locality exposes blue green argillites from the Upper Tremadocian. The locality yielding the new trilobite is located approximately 21 km al N de Zagora, Dra Valley, Morocco (Figure 1, locality nº2). The coordinates of the site are N 30º30'54'' -W 5º45'24'' -Altitude 804 m.
The following trilobite species also appear in this outcrop: See figure 6.
Discusion -Because only one specimen is available, it is left in open nomenclature.

Platypeltoides sp.
Material -A single specimen with a total carapace length of 56 mm is included. It is kept in the collection of Joan Corbacho in the Museo Geológico del Seminario de Barcelona (Spain), under the annotation MGSB-JC561.
Geographical distribution -Upper part of the Lower Fezouata Formation. The studied locality exposes blue green argillites from the Upper Tremadocian. The locality yielding the new trilobite is located approximately 21 km al N de Zagora, Dra Valley, Morocco (Figure 1, locality nº2)  Discussion -Only one specimen is available. Here we propose that it could be a juvenile specimen because of the large size of its eyes, as it also occurs with the holotype of P. magrebiensis?, which is a holaspis (Plate 1, fig. b) since the length of their carapaces are almost equal. The small spines that it presents are normal in the juvenile specimens of some species of Platypeltoides, that are subsequently lost when arriving at the adult phase of development. For these reasons, it is left in open nomenclature.

Conclusion
Regarding the diversity of the genus Platypeltoides, four described species and two possible new species to be described are included in this report. In Morocco, until 2016, only Platypeltoides magrebiensis? was recorded in the Zagora region, but this study shows that the distribution of Platypeltoides is concentrated both in the Zagora region and in the Guelmim area. All them appear in the Lower Fezouata Formation (Tremadocian), Lower Ordovician. The presence of well developed genal spines in adult specimens is a very particular characteristic of the species P. hammondi, P. cuervoae and P. carmenae; they are the only three species in which this characteristic has been observed in this genus.