Images of a typical early paradoxidid trilobite from  the Tarhoucht area in the eastern Anti-Atlas.

Complete specimen of Acadoparadoxides levisettii, 13.2 cm long, with 18 thoracic segments, from the large excavations near Tarhia, 2 kilometres north of Tarhoucht ~

Tarhoucht and Tarhia are about 15 km south of the centre of the local town of Tinejdad, which is 50 km east of Tinerhir on Route N10 from Ouarzazate. Here is a Google Earth satellite image showing the metalled road from Tinejdad, suitable for all vehicles. You can download and print a copy in the short guide to the Tarhoucht area inserted below ~

Visitors can be sure of a warm welcome at Tarhia and Tarhoucht! Meet the locals ~

Sadly, Lahcen Baghi died in September, 2020, and his picture is retained among the images above as a tribute to his friendship and professional skill. He will be greatly missed.

For images of much of the Acadoparadoxides material and associated trilobites collected, charts and relevant documents, please click on this link ~

And here is a link to ResearchGate for a free download of the article by Gerd Geyer and Tony Vincent describing the new species of Acadoparadoxides and their stratigraphic context, entitled, "The Paradoxides puzzle resolved: the appearance of the oldest paradoxidines and its bearing on the Cambrian Series 3 lower boundary," which was published in 2015 in Paläontologische Zeitschrift 89, pages 335 - 98 ~

If you are planning a trip to Morocco, you will find that a visit to the Tarhoucht area in the south-east of the country is rewarding, not only for its Cambrian fossils, but for its attractive scenery and wildlife, too. So, here is a short guide to the area and its paradoxidid trilobites. You can download and print a copy for your own use by clicking on the tab at upper right ~

Here is a satellite image of the Tarhoucht area. Named jbels are outcrops of greenish silty mudstones of the Jbel Wawrmast Formation (uppermost "Lower Cambrian"), resting on hard sandstones of the unfossiliferous Tazlaft Formation. The lower part is the fossiliferous Brèche à Micmacca Member, containing five depositional cycles in this area, numbered 1 - 5 in reverse order of deposition. Thus, at Bou Tiouit in the south-east corner with a red flag, depositional cycle 5 is at its base. In the central area with green flags, deposition began with cycle 3, and in the northern and western jbels with yellow flags, the later sedimentation cycle 2 is at the base, marking the stepwise advance of a marine transgression. The broken white line shows the approximate position of the Cambrian coastline in depositional cycle 3, in which the earliest paradoxidid trilobites (genus Acadoparadoxides) made their appearance!

The following chart shows the stratigraphic ranges of the earliest species of Acadoparadoxides at Bou Tiouit, and of other important trilobites associated with them in the lowest 20 metres of depositional cycles (here called 'Colour Cycles') of the Brèche à Micmacca Member. Trilobite species which also occur in Spain are shown in red. This chart is also included in the short guide to the Tarhoucht area inserted above, where it can be downloaded and printed ~

The three colour images below are featured in Plates 36 - 38 of The Trilobite Book: A Visual Journey by the late Riccardo Levi-Setti of Chicago, USA, published in 2014 by University of Chicago Press, and they are reproduced here by kind permission of the author. All three trilobites were in his personal collection. Two can be identified with Acadoparadoxides pampalius and A. cf. mureroensis, while the large specimen of Acadoparadoxides levisettii is now in the trilobite "Hall of Fame" at the American Museum of Natural History in New York. The cranidia of all these specimens have been analysed in the files on the "Geometric analysis of cranidia" page of this website, where they can be studied in detail ~

Plate 39 of The Trilobite Book: A Visual Journey shows a complete carapace, 32.7 cm in length and with 18 thoracic segments, of the large species Acadoparadoxides briareus, excavated at higher levels on Bou Tiouit. It is also reproduced here by kind permission of the late Riccardo Levi-Setti. This species can be easily distinguished from the other species, not only by its greater ultimate size, but also by its large, transversely moderately oval pygidium ~

Death of a Paradigm

For most of the 20th century, the palaeontological paradigm that olenellid trilobites define the upper part of the "Lower Cambrian", while paradoxidids define the "Middle Cambrian", with no obvious overlap, was largely accepted by the geological community. Olenellid trilobites, considered to be "primitive", have no suture lines, or lines of naturally occurring built-in weakness, along which the head or cephalon split during periodic moulting to allow the animals to grow. In contrast, paradoxidids were typical "advanced" trilobites with a full complement of such sutures. Eventually, though, it was discovered that in Morocco olenellids overlap with paradoxidids quite strongly, as exemplified by the description in 1993 by Gerd Geyer of the large olenellid Cambropallas telesto and the even larger paradoxidid Acadoparadoxides briareus, in an article entitled "The giant Cambrian trilobites of Morocco." These denizens of the Moroccan Cambrian sea were found to co-occur at the hill named Bou Tiouit, near Tarhoucht, in the eastern Anti-Atlas. At that time, the strong overlap of these trilobites in Morocco appeared to be due both to the delayed extinction of olenellids there, and the very early appearance of paradoxidids which then spread from Morocco to other regions. However, since writing these notes, evidence has been published which shows that an overlap of olenellids with paradoxidids is, in fact, the normal situation - see the intercontinental correlation chart below!

Here is an image of a slab from the silty mudstones of the uppermost "Lower Cambrian" Jbel Wawrmast Formation, collected at the large excavations near Tarhia, two kilometres to the north of Tarhoucht, by Moroccan collector Simo Oumouhou. It shows two beautifully preserved carapaces which illustrate appropriately the co-occurrence of olenellids with paradoxidids in Morocco. At upper left is a relatively small Cambropallas telesto which accompanies a complete Acadoparadoxides specimen at lower right. In the paradoxidid, the straight posterior margin of its wide, triangular pygidium, and the cranidium which appears to be wider across the anterior border than across its eye-lobes, identify it as Acadoparadoxides levisettii. The flat-lying Tarhia quarries, which are two metres or less in depth, correlate into the interval 13.0 - 15.0 metres above the base of the Formation at Bou Tiouit, an interval which consequently is now known as the 'Acadoparadoxides levisettii Subzone' ~

Many thanks are due to Simo Oumouhou of Erfoud, Morocco, for the loan of this image. His Instagram account simo.oumouhou contains images of many fine and unusual fossils, some of which may be for sale!

This intercontinental correlation chart is from an article by Sundberg, Webster and Geyer, published in the journal Lethaia in September 2022, which describes a new Cambrian trilobite fauna from the upper Harkless Formation at Clayton Ridge, Nevada, USA, from a single level. In the chart the blue line marks the base of the relatively recently established Miaolingian Series (the current "Middle Cambrian"), founded upon the first appearance of the small oryctocephalid trilobite Oryctocephalus indicus, which occurs quite widely. The red line defines the first occurrence level of another oryctocephalid, Ovatoryctocara granulata, and of closely related species of the same genus, which was the "runner-up" for definition of the new base of the "Middle Cambrian". The new collection from Nevada confirms that at least the last six olenellid biozones of the "Lower Cambrian" of western USA are stratigraphically higher than previously thought, and that they overlap strongly with the "Paradoxides" species of Siberia, and therefore also of other regions, such as Morocco where the large olenellid Cambropallas telesto overlaps early species of Acadoparadoxides. Radiometric dating and correlations indicate that paradoxidids were present by 509 million years ago, more than 2 million years before the extinction of the North American olenellids, creating a huge overlap and the death of the 20th century paradigm! On the chart I have highlighted the olenellid ranges in light green, and that of "Paradoxides" in Siberia in pink.

In Morocco, it is not yet possible to identify the base of the Miaolingian Series or new "Middle Cambrian", but the lower correlation level based upon Ovatoryctocara (red line) is probably represented in Morocco by a further oryctocephalid, Shergoldiella vincenti (Geyer 2006), which many palaeontologists now regard as really a regional species of Ovatoryctocara. In fact, the Lethaia article itself refers to Shergoldiella as "Ovatoryctocara vincenti", although the species has not yet been formally reassigned! At Bou Tiouit, Tarhoucht, the first occurrence of this species is 3 metres above the earliest appearance there of paradoxidids in the form of Acadoparadoxides pampalius, which suggests that the latter is roughly coeval with the earliest paradoxidids in Siberia, of the genus Anabaraspis.

Many thanks are due to Fred Sundberg of Show Low, Arizona, USA, for permission to use and slightly modify this correlation chart.

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Here is a short video following a journey from Tinejdad via Tarhia to Tarhoucht, stopping to visit the Tarhia excavations on the way, excavating at Bou Tiouit for Acadoparadoxides remains, then onward over Jbel Ougnate to Assemame on the south side of the Anti-Atlas ~

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