A curious collection of pygidia.
The new early paradoxidid trilobite species of Acadoparadoxides described by Gerd Geyer and Tony Vincent in 2015 have stimulated a lively debate about their legitimacy. This page reviews evidence presented in an article by J. Javier Álvaro and Jorge Esteve, published in Geological Magazine in December 2020, in support of conclusions concerning Acadoparadoxides remains collected in the Tarhoucht area and near Assemame in Morocco, and considers the viability of that evidence. The articles referred to are listed at the end of the page, together with links to the articles themselves.
The Moroccan early species of Acadoparadoxides described in Geyer & Vincent (2015) were found to occur stratigraphically essentially in sequence through the interval referred to as 'Parasequence 3', between 6.0 - 19.3 m above the base of the Brèche à Micmacca Member of the late 'early Cambrian' Jbel Wawrmast Formation at the hill named Bou Tiouit, near Tarhoucht. This greatly facilitated separation and characterisation of the individual species, as outlined in this biostratigraphic chart from Geyer et al (2019) ~
In contrast, Álvaro & Esteve (2020), Fig. 1, illustrates a collection of seven Acadoparadoxides pygidia belonging to four species sensu Geyer & Vincent (2015), which the authors claim to have recovered from a single level at Bou Tiouit termed the "Cambropallas telesto acme level, worked by the fossil hunters of the area" (figure caption), and this figure is reproduced here for reference ~
Again, in its 'Concluding remarks,' the Álvaro team affirms, "Álvaro et al (2018) stated that the morphospecies Acadoparadoxides pampalius, A. ovatopyge, A. levisettii and A. mureroensis (including A. cf. mureroensis) co-occur within the Cambropallas telesto acme level of the Assemame quarry, eastern Anti-Atlas. After sampling in the Taroucht quarries, the source of Geyer & Vincent's (2015) fossil collection, we have confirmed that the morphotypes also co-occur in the same level of the Brèche à Micmacca Member." If this claim were correct, it would clearly lend support to the Álvaro team's proposal that most of the new species described in Geyer & Vincent (2015) are merely morphs of the Spanish species Acadoparadoxides mureroensis, which is said to be "characterised by a broad morphological variation" (Álvaro et al, 2018, p. 1567) and whose pygidium has a "variable outline, grading from subtriangular to subhexagonal and subovate"(!) (see emended diagnosis for the species in Álvaro et al, 2018, p. 1590 - 91). However, Álvaro and Esteve's article fails to identify where their collection level is located stratigraphically at Bou Tiouit, even though Fig. 1(a) of the article shows a view of the west side of the hill in which calcareous levels have been indicated. 'Parasequence 3' containing the Acadoparadoxides species referred to is the interval between the horizons labelled 'b' and 'c' in this figure. [Details of the collection of Acadoparadoxides remains made by the Álvaro team at its 'Level 4' at Assemame, and correlation with Bou Tiouit, can be found on the 'Correlation with Assemame' page of this website.]
Repeated enquiries made to the Álvaro team in the autumn of 2022 for further information on the level at which its collection was made at Bou Tiouit received no response. However, as the collections made by the Geyer team were limited to excavations on the north side of the hill, investigations have recently been undertaken by Tony Vincent on its west side to seek further data on this issue (May 2022, and May 2023). The following two images show Álvaro and Esteve's view of the west side (upper image) compared with a new, similar view in which parasequence data has been indicated (lower image) ~
In the Álvaro team's image, level 'a' is actually the line of a normal fault with a downthrow of about 6 metres toward the east, which conceals 'Parasequence 5' and all but the uppermost few centimetres of 'Parasequence 4', while calcareous level 'b' is the top of 'Parasequence 4' at 6.0 m above the base of the Brèche à Micmacca Member, and 'c' represents the top of 'Parasequence 3' at 19.3 m. An additional limestone at 10.8 m, labelled 'Parasequence 3(a)' in the new image has not been noted by Álvaro and Esteve.
Most of the extensive excavations on the west side of Bou Tiouit (shown below) are below 10.0 m above the base of the Brèche à Micmacca Member, and are located entirely within the A. pampalius Subzone, as defined in the figure following from Geyer et al (2019) outlining the zonation of 'Parasequence 3' ~
The local excavators confirmed that, during their visit, the Álvaro team was much engaged in quarrying at these excavations, from which only the pygidium of A. pampalius in Fig. 1(d) of Álvaro & Esteve (2020) could have been recovered. The only other quarry in 'Parasequence 3' on the west side of Bou Tiouit is a small excavation between 18.0 - 18.6 m, near the top of the parasequence and in the lower half of the A. ovatopyge/A. nobilis Subzone (see zonation figure above), but whether this is the origin of the A. ovatopyge pygidium in Fig. 1(e) of their article, or not, is unknown. Here is a view of this small excavation ~
There are no excavations on the west side in the A. levisettii and A. cf. mureroensis Subzones, and consequently the actual origin of the four well-articulated pygidia of A. levisettii in Álvaro & Esteve (2020), Fig. 1(f - i) and of A. cf. mureroensis in Fig. 1(j), is problematic. The claim that all the figured pygidia were collected from a single level coinciding with the Cambropallas telesto 'acme' level is also problematic. Although occasional remains of the olenellid trilobite Cambropallas telesto are encountered by local excavators through 'Parasequence 3' where the paradoxidids under discussion are located, the trilobite is not actively sought for in that interval but at a mass-mortality level well above it in 'Parasequence 2', a level which is exploited not only at Tarhoucht but also at other locations in the eastern Anti-Atlas of Morocco. This, therefore, is the Cambropallas telesto 'acme' level referred to by Álvaro and Esteve. At Bou Tiouit, contemporary excavations for Cambropallas are on the north side of the hill, but there is, indeed, an older excavation for this trilobite on the west side (confirmed by local excavators) which is no longer worked and somewhat degraded, and within the view of the hill in Álvaro & Esteve (2020), Fig.1(a). The stratigraphic interval between the purple band at the top of 'Parasequence 3' (essentially the level marked 'c' in this figure) and the approximate centre of the excavated level was measured as about 7 metres, so the 'acme' level lies at about 26.0 m above the base of the Brèche à Micmacca at Bou Tiouit, as indicated in these two images ~
As this 'acme' level of Cambropallas is well above the known biostratigraphic ranges of the Acadoparadoxides species collected by Álvaro and Esteve, the actual origin of their figured collection of pygidia remains enigmatic and unsupported by reliable stratigraphic data. Therefore, their claim of a single-level origin cannot be considered seriously. A similar situation probably prevails at the excavations near Assemame referred to by the authors, where they made a collection of Acadoparadoxides remains at 'Level 4', which was also said to coincide with the Cambropallas telesto 'acme' level (see details in Álvaro et al, 2018). Here, the true stratigraphic location of 'Level 4' has now been established, and where only paradoxidid remains of A. levisettii and A. cf. mureroensis could be identified by the Geyer team (see the 'Correlation with Assemame' page of this website), but a vast mound of excavated debris adjacent to the 'Level 4' excavations has evidently accumulated mostly from quarrying above the top of 'Parasequence 3', in the lower part of 'Parasequence 2' and well above the 'Level 4' excavations. Álvaro and Esteve may have misunderstood local information on the stratigraphic position of excavations for Cambropallas, confusing them with the lower 'Level 4' excavations. The following image is a view of the excavations near Assemame, showing the vast mound of debris reaching almost to the top of 'Parasequence 3', and originating mainly from well above the 'Level 4' excavations for paradoxidid remains ~
Completing this page is a slab from the Cambropallas telesto mass-mortality level in the eastern Anti-Atlas, which illustrates the distinctive nature of this notable horizon ~
References
ÁLVARO, J. J., ESTEVE, J. & ZAMORA, S., 2018. Morphological assessment of the earliest paradoxidid trilobites (Cambrian Series 3) from Morocco and Spain. Geological Magazine 115, 1566 - 1595.
ÁLVARO, J. J. & ESTEVE, J., 2020. Reply to Comment on: Álvaro, J. J., Esteve, J. & Zamora, S., 2018. Morphological assessment of the earliest paradoxidid trilobites (Cambrian Series 3 from Morocco and Spain [Geological Magazine] by Geyer, G., Nowicki J., Zylinska A. & Landing E. Geological Magazine 157, 1971 - 82.
GEYER, G. & VINCENT, T., 2015. The Paradoxides puzzle resolved: the appearance of the earliest paradoxidines and its bearing on the Cambrian Series 3 lower boundary. Paläontologische Zeitschrift 89, (3), 335 - 98.
GEYER, G., NOWICKI, J., ZYLINSKA, A., & LANDING, E., 2019. Comment on: Álvaro, J. J., Esteve, J., & Zamora, S. 2019. Morphological assessment of the earliest paradoxidid trilobites (Cambrian Series 3) from Morocco and Spain [Geological Magazine]. Geological Magazine 156, 1691 - 1707.