Souss Lagerstätte > Family Bigotinidae

 
Geyer, G. 2019: The earliest known West Gondwanan trilobites from the Anti-Atlas of Morocco, with a revision of the Family Bigotinidae Hupe, 1953. Fossils and Strata, No. 64, pp. 55–153.
 
 
The previously poorly investigated trilobite fauna of the upper Igoudine and lowest Amouslek formations in the western Anti-Atlas, Morocco, is critical for the understanding of the earliest trilobites on a global scale, is studied in detail and its taxonomic diversity and biostratigraphical characteristics reviewed. The key section at Tiout, particularly the Tiout Member, yields surprisingly diverse faunal associations with trilobites of the families Bigotinidae and Fallotaspididae, of which only Hupetina antiqua, Eofallotaspis prima, E. tioutensis and Fallotaspis cf. F. tazemmourtensis have been previously identified. New genera and species from the Tiout section comprise Bigotina kelleri n. sp., B. monningeri n. sp., Issendalenia grandispina n. gen., n. sp., Tioutella floccofavosa n. gen., n. sp., Pseudobigotina antiatlasensis n. gen., n. sp., Eladiolinania castor n. gen., n. sp., E. pollux n. gen., n. sp., Debrenella larvalis n. gen., n. sp. and Fallotaspis antecedens n. sp. Bigotinops chouberti n. sp. is a new species from below the known range of Fallotaspis tazemmourtensis in the Amouslek section. A revision of other bigotinid genera and species from the Iberian sector of West Gondwana, Cadomian France, the Siberian Platform and the Altay-Sayan Foldbelt leads to a recombination of Bigotina angulata Suvorova, 1960; Eladiolinania? palaciosi Lin~an et al., 2008; E.? gordaensis Lin~an et al., 2008; Suvorovaella priva (Suvorova, 1960) and Suvorovaella? patria (Suvorova, 1960) and a suggested new family Minusinellidae. The previously established Eofallotaspis and Fallotaspis tazemmourtensis zones in the Moroccan biostratigraphical scheme are revised to become the Hupetina antiqua, Eofallotaspis tioutensis and Fallotaspis plana zones.
 
 
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New contribution to solve the puzzle of the Moroccan Bigotinids. (Geyer, G. & Pais, M., March 2022).
 

Bigotinids belong to the earliest and least understood trilobite families. Their early occurrence “out of the nowhere” in Moroccan Anti-Atlas (and in Siberia!) is one of the biggest trilobite puzzles.


In 2019, Gerd Geyer revised the family, recognizing seven genera. The genus Bigotina, known originally from a species from western France, was shown to include four additional species (Geyer, 2019): Bigotina kelleri, Bigotina monningeri, Bigotina sp. A and Bigotina sp. B. The last two are new obvious different species but the scarce available complete specimens did not permit to base formal species on the available material. Around thirty new specimens have been found and analysed since then by the authors, most of them showing the characteristics of Bigotina sp. B (Geyer, 2019). Others are still difficult to attribute to any previous description and some evidence points to the existence of one more undescribed species (Bigotina sp. C).


Among the other genera of the family, Bigotinops is known only from Morocco. In addition to Bigotinops dangeardi (described in 1953 by Pierre Hupé), Bigotinops chouberti is a newly recognized species (Geyer, 2019) that seems to occur relatively frequently. Both species are present in the same early Cambrian strata, the Amouslek Formation, in the Amouslek, Tazemmourt and Tiout sections.


The oldest genus known so far is Hupetina, consisting of a single species, Hupetina antiqua, which was first described by Sdzuy in 1978 from the Tazemmourt section.

The four other genera of the Bigotinidae recognized from the Anti-Atlas (Pseudobigotina, Issendalenia, Tioutella, Eladiolinania) are only found in the upper part of the Igoudine Formation, which is dominated by thick-bedded limestone. The tiny trilobites are extremely difficult to recover from the rocks and will not develop into collectors’ items!

 
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Bigotinops dangeardi (Hupé, 1953)

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Bigotinops chouberti n. sp. (Geyer, 2019)

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Bigotina kelleri n. sp. (Geyer, 2019)

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Bigotina monningeri n. sp. (Geyer, 2019)

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Bigotina sp. A (Geyer, 2019)

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Bigotina sp. B (Geyer, 2019)

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Three different species (n= 24 specimens) of Bigotinids have been collected since Septembre 2019 till date at the Tazemmourt Section and are object of this study:
 
a) Four (4) Hupetina antiqua (Sduzy, 1978) well preserved specimens, collected on the Igoudine Formation on the Tazemmourt Section, at the previously known horizons;
 
b) Fourteen (14) long glabella Bigotina sp. well preserved specimens in thirteen plates (left-side group of the red line; note - image not updated with recently collected specimens):
 
- Frontal lobe slightly narrower than the minute Bigotina also found,  giving the whole glabella an acute aspect;
- Interocular areas similar to a slightly extended quarter-segment of a circle;
- Elongated body with a mean ratio x:y (lenght/with; n = XX complete specimens where the pigidium is preserved and shown);
- Maximun size for adults is XX mm (n = XX);
- Tentativelly assigned to Bigotina monningeri Geyer 2019 or to Bigotina sp. B Geyer 2019.
 
b) A short glabella Bigotina sp., with an almost perfectly eliptical body shape (length/width mean ratio=xx; n=xx). The maximum length for the adults is XX mm. Here named Bigotina n. sp. C.
Seven specimens in six different plates (right-side group of the red line; note - image not updated with recently collected specimens) are shown above.
 
Above is a compilation of all species of Bigotina and Bigotinops, showing characteristic details of the cranidia. Most of the specimens described in the original article of Geyer (2019) were collected from the Tiout Member of the Igoudine Formation at Tiout and Amouslek, but they are believed to occur in the Tazemmourt section as well. The typical species of the Tazemmourt section is Hupetina antiqua, which occurs at the top of the Igoudine Formation south of Tazemmourt. Bigotinops dangeardi, by contrast, is a typical species from the Tazemmourt section, which comes from the Amouslek Formation.


The three different genera are distinguished as follows:


a) Bigotinops has a long glabella with its frontal lobe distinctly narrower than the ones behind so that the glabella has an acute aspect. The glabella and the anterior border are connected by a slight raise (“plectrum”) on the sagittal axis. The interocular areas are similar to a slightly extended quarter segment of a circle. The anterior border is more or less evenly curved. The body is relatively long. 


b) Bigotina has an apparently shorter glabella. Its frontal lobe does not extend beyond the eye ridges. As in Bigotinops, the anterior border is more or less evenly curved. Bigotina lacks a plectrum, and the furrow behind the anterior border is of equal depth throughout. The maximum length for the adults is XX mm.


c) Hupetina is characterized by a tapering glabella with a subacute front. Its frontal lobe reaches almost to the anterior border, and this relatively narrow anterior border shows a relatively distinct “kink” on the sagittal axis so that the margin appears to be almost acute. 

 

The number of available specimens is small as these are extremely rare species, but certain taxa can be positively identified:

 
1- Bigotinops dangeardi Hupé, 1953: Plectrum in front of the glabella distinct, palpebral lobes relatively short, their posterior tips not reaching to posterior border furrow (Geyer, 2019). Only one specimen is known from Hupé’s original publications. None of the collected specimens shows these characteristics. See the photo (from Geyer 2019).
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2- Bigotinops chouberti Geyer, 2019: Occipital ring relatively broad (sag.), extended into a short to moderately long terminal spine; mostly indistinct swelling in front of the glabella of nearly equal width as the frontal lobe of glabella. This species was collected from the Amouslek section. None of the collected specimens from Tazemmourt shows these characters. See the photo (from Geyer 2019).

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3- Bigotina kelleri Geyer, 2019: Anterior cephalic margin considerably curved; eye ridges and palpebral lobes form a homogenous lobe with relatively strong curvature; parafrontal band fused with glabellar frontal lobe; external surface of carapace covered with densely spaced granules of varying size. None of the Tazemmourt specimens shows these characters. See the photo (from Geyer 2019). 

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4- Bigotina monningeri Geyer, 2019: Anterior cephalic margin moderately curved; glabella slightly tapering, with faintly curved lateral margins; frontal lobe laterally constricted; occipital ring without occipital spine; palpebral lobes long; parafrontal band fused with glabellar frontal lobe; intraocular areas slightly longitudinally extended, with small bacculae; anterior border relatively narrow, distinctly convex in tr. profile, of subequal breath (sag.) with preglabellar field. Some of the specimens collected in the Tazemmourt section show these characters (left-side group of the red line). See the photo (from Geyer 2019).

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5- Bigotina sp. A (Geyer, 2019): Glabella in adult individuals of ca. 80% cephalic length (including occipital ring), subparallel from occipital ring to L3 or slightly tapering forward, with straight or faintly constricted lateral margins. Frontal lobe slightly less elevated than rest of the glabella, slightly narrower (tr.) than L3, its anterior margin with gentle curvature in dorsal view, confluent with posterior half of adaxial ends of eye ridges. Occipital ring with considerably curved posterior margin, with small terminal node or short spine-like termination. Interocular areas similar to a slightly extended quarter-segment of a circle, of about half max. width of glabella, ca. 30–35% max. cephalic length adjacent to axial furrow, without baccula-type swelling. Eye ridge moderately prominent and well elevated, almost straight, oblique to axis; longitudinal subdivision recognizable for at least the adaxial half of its extension.

None of the specimens collected at Tazemmourt shows these characters. See the photo (from Geyer 2019).

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6- Bigotina sp. B (Geyer, 2019): Glabella in adult individuals of ca. 82–87% cephalic length (including occipital ring), subparallel from occipital ring to L3 and with slightly curved lateral margins. Frontal lobe slightly less elevated than rest of the glabella, clearly narrower (tr.) than L3, its anterior margin with parabolic curvature in dorsal view, confluent with posterior half of adaxial ends of eye ridges; max. tr. width of frontal lobe near its posterior end two-thirds to three-quarters of max. cranidial width across L1. Occipital ring with considerably curved posterior margin, without occipital spine, but apparently with small subterminal node; Palpebral lobe moderately long, exsag. length in adult individuals ca. 33–37% max. cephalic length, distinctly oblique to axis, anterior end of ocular suture opposite mid-length of L2, the posterior end opposite mid-length or posterior part of L1; crescentic with low curvature along the ocular suture. Interocular areas are similar to a slightly extended quarter-segment of a circle, of about half max. width of glabella, up to ca. 35% max. cephalic length adjacent to axial furrow; weakly elevated, without postocular wing or strip.

 

Some of the newly collected specimens appear to show these characteristics, except that a genal spine seems to be lacking (left-side group from the red line). See the photo (from Geyer 2019). 

   
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Preliminary conclusions:


The left-side (red line) group of specimens, with elongated body and glabella, are tentatively assigned to Bigotina monningeri Geyer, 2019 or, with a higher degree of confidence, to Bigotina sp. B. Further measures, photos and specimens are needed to extend the sample and allow a confident determination.


The specimens on the right-hand side (red line) with their elliptical bodies, short glabella and minute adults sizes, is possibly a unique species from the Tazemmourt section (named here Bigotina sp. C). This also requires further studies.


The present approach helps to better understand the Bigotinids fauna of the Tazemmourt Section and to direct further studies.

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