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First African oryctocephalid trilobites from the Lower–Middle Cambrian boundary interval
Palaeoworld 15 (2006) 348–359
Research paper
First African oryctocephalid trilobites from the Lower–Middle Cambrian boundary interval Gerd Geyer Institut f¨ur Pal¨aontologie, Bayerische Julius-Maximilians-Universit¨at W¨urzburg, Pleicherwall 1, 97070 W¨urzburg, Germany Received 14 February 2006; received in revised form 9 May 2006; accepted 16 October 2006
Abstract Oryctocephalid trilobites from Lower Middle Cambrian strata of the eastern Anti-Atlas, Morocco, are the first described Oryctocephalidae known from Africa. They represent the new genus and species Shergoldiella vincenti. However, a similar species was earlier described as Tonkinella sequei Li˜na´ n et Gozalo, 1999, from coeval lower Middle Cambrian strata of the Iberian Chains, northern Spain. This Iberian species is imperfectly preserved and assigned herein to Shergoldiella with reservations. If this assignment is correct, it would reinforce earlier suggested correlations between Morocco and Spain. Nevertheless, Shergoldiella suggests a morphocline from a typical oryctocephalid-type morphology towards the Tonkinella-type morphology. Close similarity with Ovatoryctocara ovata suggests a similar stratigraphic position in accordance with earlier suggested intercontinental correlations. © 2006 Nanjing Institute of Geology and Palaeontology, CAS. Published by Elsevier Ltd. All rights reserved. Keywords: Trilobita; Middle Cambrian; Biostratigraphy; West Gondwana
1. Introduction Oryctocephalid trilobites are among the most distinctive and short-lived trilobites in the Lower–Middle Cambrian boundary interval and thus play a major role in the discussion, at which stratigraphic level the base of the Cambrian Series 3 (replacing the traditional Lower–Middle Cambrian boundary) and Stage 5 should be placed (Sundberg et al., 1999; Fletcher, 2003; Zhao et al., 2004, 2005; Geyer, 2005). At the moment, most scientists favor the placement of a GSSP for the base of this series and stage at the FAD of Oryctocephalus indicus (Reed, 1910) although additional concepts may be suitable. Other oryctocephalid trilobites, such as Arthricocephaus chauveaui Bergeron, 1899, Ovatoryctocara granulata (Chernysheva, 1962), and, less clearly, Lancastria spp., Oryctocephalites spp. and Microryctocara
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spp. also play key roles in this discussion (see Geyer, 2005, for comprehensive discussion). A major disadvantage of a GSSP based on the FAD of Oryctocephalus indicus is that this level cannot be identified with sufficient precision in Baltica and West Gondwana at this moment (Geyer, 2005) so that additional biostratigraphic data are needed for an improved intercontinental correlation. Shergoldiella vincenti n. gen., n. sp. is the first discovered oryctocephalid trilobite from Africa, found in the traditional Lower–Middle Cambrian boundary interval. Its affinities and potential for correlation is discussed in this article with reference to the few other known West Gondwanan Oryctocephalidae. 2. Material, stratigraphic occurrence and preservation The material described herein as Shergoldiella vincenti n. gen., n. sp. comes from the Jbel Wawrmast
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G. Geyer / Palaeoworld 15 (2006) 348–359
Formation of the well-known Tarhoucht area in the eastern Anti-Atlas of Morocco. The Jbel Wawrmast Formation largely consists of yellowish-weathering, fine-grained sandstones and green and blue-green siltstones. The lower part of the formation, from which the material was recovered, is characterized by thin, lithologically variable limestones which are rhythmically intercalated into the sandstones.
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This part of the formation is termed the Br`eche a` Micmacca Member. The formation has a thickness of ca. 150 m in the Tarhoucht area, but all the specimens found so far are apparently coming from the basal meters (Fig. 1). The small village of Tarhoucht has gained international reputation because of an extensive quarrying for fossils, particularly trilobites, with most of the inhab-
Fig. 1. Profile of the Jbel Wawrmast Formation at the Tarhoucht-Bou Tiouit section, illustrating graing-size profile, color changes, sedimentologic features, paleoenvironmental interpretation, and biostratigraphic sequence. Thickness (left margin) in meters from the base of the formation. Asterisk indicates strata with Shergoldiella vincenti n. gen., n. sp. Color legend: p/r, purple or red; bl, blue; bl gr, bluish green; y, yellow; y gr, yellowish green; l gr, light green, m gr, medium green; d gr, dark green; gy, grey; b, black, w, white. Modified from Geyer et al. (1995, fig. 25).
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itants being involved in the fossil trade. Cambropallas telesto Geyer, 1993, the youngest known olenelloid trilobite, Paradoxides (Acadoparadoxides) briareus Geyer, 1993, Protolenus (P.) interscriptus Geyer, 1990, and Hamatolenus (H.) vincenti Geyer et Landing, 2004 are examples for nicely preserved trilobites from the area which occur frequently on the international fossil market. The locality and its stratigraphy have been described in detail by Geyer (1993), Geyer et al. (1995), and Heldmaier (1997). Two sections in this area yielded the material of Shergoldiella vincenti described herein. 2.1. Bou Tiouit section The classical outcrops are in the lower part of the Jbel Wawrmast Formation on the northern slope of Bou Tiouit, a mountain just south of the village, where Cambopallas telesto and Paradoxides (Acadoparadoxides) briareus were obtained from low quarries in two stratigraphic levels, which are exploited by the local people by comparatively primitive techniques. Both levels fall into the lower (but not lowest) Middle Cambrian Cephalopyge notabilis Zone, Agdzian Stage, which represents all but the lowermost stratum of the Jbel Wawrmast Formation (Fig. 2). As described earlier (Geyer et al., 1995, pp. 112–117), there exist fairly diverse assemblages, mostly composed of different species of trilobites, plus a few brachiopods, hyoliths, helcionellids, pelagiellids, echinoderms, and trace fossils, dependent on the particular lithofacies.
2.2. Tarhia Track localities A second area for exploration of fossil material was opened by the local fossil dealers in 2001. This area, termed Tarhia Track localities, is situated west of the road from Tarhoucht to Tarhia about one kilometer to the north of the village of Tarhoucht (31◦ 23.8 –31◦ 24.0 N, 5◦ 00.8 –5◦ 01.2 W). It is tectonically complicated and does not present a larger part of a measurable stratigraphic section. It includes several outcrops of the top of the (most probably latest Early Cambrian) Tazlaft Formation and the basal strata (ca. >4 m) of the Jbel Wawrmast Formation. Detailed field investigations of T. Vincent (Aberdeen) based on earlier lithostratigraphic studies of Heldmaier (1997) enabled a precise correlation of the Tarhia Track localities with the Bou Tiouit section. Mr. Vincent’s investigations indicate that the quarried strata at the Tarhia Track localities belong to Heldmaier’s (1997) color cycle 4 of the Jbel Wawrmast Formation as identified at Bou Tiouit in the lower part of the Jbel Wawrmast Formation. Interestingly, the material of Shergoldiella vincenti n. gen., n. sp. was exclusively discovered in the strata of this color cycle 4, occurring together with such trilobites as Cephalopyge notabilis Geyer, 1988, Condylopyge eli Geyer, 1999, Hamatolenus (H.) vincenti Geyer et Landing, 2004, Hamatolenus (H.) cf. marocanus (Neltner, 1938), Hamatolenus (Myopsolenus) cf. magnus (Hup´e, 1953), Latoucheia (L.) epichara Geyer, 1990, Protolenus (P.) interscriptus Geyer, 1990, Protolenus (Hupeolenus)
Fig. 2. Field photography of the lower trilobite quarry at the northwestern corner of Bou Tiouit, near Tarhoucht, Anti-Atlas, the most productive site for Shergoldiella vincenti n. gen., n. sp. The excavations exploit strata ca. 2–3 m above the base of the Jbel Wawrmast Formation. The photographer (T. Vincent) was standing on the top of the Tazlaft Formation. The resitant large blocks are float from the cross-bedded quartzarenitic Jbel Afraou Formation which overlies the Jbel Wawrmast Formation (visible at the small escarpment in the upper part of the photography).
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dimarginatus Geyer, 1990, Kingaspidoides laetus Geyer, 1990, Kingaspidoides neglectus Geyer, 1990, Kingaspidoides sp. A, Ornamentaspis cf. usitata Geyer, 1990, Paradoxides (Acadoparadoxides) nobilis Geyer, 1999, Paradoxides (Acadoparadoxides) sp. B, Myopsolenites boutiouiti Geyer et Landing, 2004, Cambopallas telesto Geyer, 1993, Yuehsienzella? n. sp., and the obolellid brachiopod Trematobolus splendidus Geyer et Mergl, 1995. However, these strata with Shergoldiella vincenti are below the telesto level at Bou Tiouit (see Geyer, 1993), but are shared with numerous specimens of Cambopallas telesto at the Tarhia track location. All of the material is preserved in yellowish-green argillaceous coarse siltstones or fine-grained sandstones of the Jbel Wawrmast Formation. As a consequence, the specimens are usually slightly flattened and somewhat distorted due to a notable compression of the rocks. Remarkable, the cephala are usually more strongly affected by distortion than the pygidia so that none of the specimens shows a perfectly preserved cephalon. Due to the economic importance of the strata for the local population, the well-preserved specimens of Shergoldiella vincenti were obtained from the quarried material. Additional material from the Tarhia Track localities was found (three disarticulated pygidia, two pygidia with attached thorax, one partial cephalon) but is too poorly preserved to merit description and figuring. 3. West Gondwanan or yctocephalid trilobites Oryctocephalid trilobites are extremely rare in West Gondwana. The specimens of Shergoldiella vincenti n. gen., n. sp. represent the first findings of corynexochid trilobites from Morocco and entire Africa. The reason for the rarity of trilobites from this family is obviously a result of environmental constraints. Most oryctocephalids were discovered in paleo-equatorial regions. They preferred habitats with low wave agitation and thus avoided shallow marine environments. West Gondwana, however, was dominated by shallow to shallowest marine depositional environments from the late Early to the middle Middle Cambrian, which saw the peak occurrence of the oyctocephalids. An oryctocephalid trilobite was described from the Iberian Chains, northern Spain as Tonkinella sequei Li˜na´ n et Gozalo, 1999. It was found in the Hamatolenus ibericus Zone of the Valdemiedes Formation, representing the Cephalopyge notabilis Zone of the Agdzian Stage in the unified West Gondwanan chronostratigraphy (Geyer and Landing, 2004). Tonkinella sequei is thus coeval with Shergoldiella vincenti but would represent
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the oldest known species of Tonkinella. Unfortunately, only one slightly distorted cranidium and an incomplete, distorted pygidium are known so that it will be difficult to characterise the species unless additional and better preserved material is found in the type locality. As discussed below in detail, the pygidium of Tonkinella sequei shows characters that suggest a closer affinity to Shergoldiella than to Tonkinella. The cranidium is also comparable to that of Shergoldiella vincenti, but appears to show distinct differences against the coeval Moroccan species. Although Sundberg (2006) regards the Iberian material as representing a species of Tonkinella, it is considered herein to be more adequately placed under Shergoldiella although more and better preserved material needs to be discovered and examined until its generic assignment can be determined with enough certainty (see discussion in Section 5). It is remarkable that both species occur in associations which share a large percentage of common species and are fairly identical in generic composition. Shergoldiella? sequei is reported from a lower assemblage in the Valdemiedes Formation of the Rambla de Valdemiedes together with the trilobites Hamatolenus (H.) ibericus Sdzuy, 1958, Hamatolenus (H.) vincenti Geyer et Landing, 2004, Protolenus (Hupeolenus) jilocanus (Li˜na´ n and Gozalo, 1986), Protolenus (Hupeolenus) dimarginatus Geyer, 1990, Alueva undulata Sdzuy, 1961, Myopsolenites altus (Li˜na´ n and Gozalo, 1986), Kingaspis sp., Sdzuyia sanmamesi Li˜na´ n et Gozalo, 1999, and the obolellid Trematobolus simplex (Vogel, 1962) (nomenclature partly corrected herein; see also Li˜na´ n et al., 2004, and discussion in Geyer and Landing, 2004, pp. 193–194, 197). It should be noted, however, that this lower assemblage is below the first occurrence of Paradoxides (Acadoparadoxides) mureroensis Sdzuy, 1958 and thus below the traditional Iberian base of the Leonian stage and Middle Cambrian. It is also below the so-called Valdemiedes event (Li˜na´ n et al., 1993), which has been interpreted as a major faunal turnover at the traditional Lower–Middle Cambrian ´ boundary in Iberia (Alvaro et al., 1993; Gozalo et al., 1993; Li˜na´ n et al., 1993, etc.) and eventually the expression of a latest Early Cambrian mass extinction (Li˜na´ n et al., 2004). As detailed earlier, there is overwhelming faunal evidence that such a faunal turnover is absent in coeval strata in Morocco, where a faunal turnover can be illustrated in older strata at the base of the Agdzian Stage (Geyer, 2005; Geyer and Landing, 1995, 2004; Geyer et al., 1995; Landing et al., 2006). The Valdemiedes event, as shown from the sections in the Iberian Chains, is thus to be interpreted as a local faunal minimum for yet to be clarified reasons.
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The only report of an unequivocal Tonkinella from West Gondwana comes from a single but well-preserved pygidium from the upper Agdzian (former Leonian) Oville Formation of the Cantabrian Mountains, northern Spain (Gozalo et al., 2003). The specimen, identified as Tonkinella aff. breviceps Kobayashi, 1934, was found relatively short distance below the base of the Badulesia tenera Zone and thus the base of the Caesaraugustian and in association with Eccaparadoxides asturianus and other trilobites of the Kymataspis arenosa or E. asturianus Zone (Gozalo et al., 2003). Shergoldiella vincenti and Shergoldiella? sequei both occur in the Cephalopyge notabilis Zone, Agdzian, two zones below the Kymataspis arenosa Zone. 4. Shergoldiella and its bearing on intercontinental correlation Shergoldiella vincenti and Shergoldiella? sequei are close relatives to Ovatoryctocara ovata (Chernysheva in Krys’kov et al., 1960), the type species of Ovatoryctocara, and Ovatoryctocara granulata (Chernysheva, 1962). Ovatoryctocara granulata has been identified as a valuable species for intercontinental correlation at the Early–Middle Cambrian boundary interval (summarized in Geyer, 2005, pp. 85–87; see also Fletcher, 2003). Both species were originally described from the lower Amgan of northern Siberia. In addition, Ovatoryctocara granulata has been identified in the Avalonian southeastern Newfoundland (Fletcher, 2003), most probably from North Greenland (Blaker and Peel, 1997; Geyer, 2005), and tentatively from the so-called Ovatoryctocara granulata–Bathynotus holopygus Zone (sensu Yuan et al., 2001, 2002), upper Duyunian (top of the former Lungwangmiaoan), Guizhou Province, South China, where it underlies the Oryctocephalus indicus Zone (Yuan et al., 2001, 2002). The specimens from eastern Guizhou have eye lobes in a slightly more anterior position than Ovatoryctocara granulata, and it would need a thorough investigation to clarify whether they represent a similar but yet undescribed species of Ovatoryctocara (Yuan et al., 2002: pl. 29, Figs. 4 and 5). Interestingly, the faunas in the stratigraphical position of Ovatoryctocara granulata in Siberia and Newfoundland share genera or even species which occur in the stratigraphic position of Shergoldiella vincenti in Morocco, such as Cephalopyge notabilis, Condylopyge eli, Hamatolenus spp., or Schistocephalus (Geyer, 1998; Fletcher, 2003) This occurrence does not contribute to a finer resolution of intercontinental correlations. However, it reinforces earlier suggestions for a correlation from West Gondwana into other Cambrian continents
(Geyer and Landing, 2004; Geyer, 2005). A further correlation from this level into other Cambrian areas is possible with auxiliary key taxa such as Kiskinella cristata Romanenko and Romanenko, 1962 and Peronopsis roddyi Resser and Howell, 1938 (see Fletcher, 2003, and Geyer, 2005, for further discussion). It should be emphasized, however, that Ovatoryctocara granulata has a larger stratigraphic range in Siberia than in other areas so that indirect correlations should be treated with a caveat. A by-product of the West Gondwanan oryctocephalids is a comparison of faunal changes during early Middle Cambrian. If one accepts a global correlation based on Tonkinella as done by Gozalo et al. (2003), the top Leonian of West Gondwana correlates with the top of the Ehmaniella and possibly the base of the Ptychagnostus (or Triplagnostus) gibbus Zone in Laurentia and the middle Taijiangian (former upper part of the Hsuchuangian) of South China (whereas the genus Tonkinella has a stratigraphic range from probably the Albertella Zone to the bottom of the Ptychagnostus (or Triplagnostus) gibbus Zone in North American standard; Sundberg, 2006). This indicates that the outer shelf deposits, such as in Laurentia and partly in South China, appear to have a fairly better resolvable biostratigraphy than the shallow marine strata in West Gondwana although there is not too much difference in the number of trilobite taxa which occur in the relevant stratigraphic interval. 5. Systematic Paleontology - Order Corynexochida Kobayashi, 1935. - Family Oryctocephalidae Beecher, 1897. - Subfamily Oryctocarinae Hup´e, 1953. Remarks: Tonkinella Mansuy, 1916 has been considered as sufficiently different from typical oryctocephalid trilobites due to the pygidial characters so that Reed (1934) introduced the new subfamily Tonkinellinae, which was maintained by other authors such as Hup´e (1955), Kobayashi (1961), and Suvorova (1964). Other than Kobayashi (1961), who regarded the Oryctocarinae Hup´e (1953) as a junior synonym, Suvorova (1964) treated the Tonkinellinae as a monogeneric taxon and emphasized particularly the lack of interpleural furrows and marginal spines. Subsequently, Chinese authors even raised the taxon to the family level. Whittington (1995) distinguished between Oryctocephalinae and Oryctocarinae based on the presence and absence of genal spines and thoracic and pygidial pleural spines. In this process, Whittington (1995) placed Tonkinella tentatively under the subfamily Oryc-
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tocephalinae because of the presence of genal spines, following McNamara’s hypothesis that Tonkinella is heterochronically derived from spiny oryctocephalids (McNamara, 1986; McNamara et al., 2006) such as Oryctocephalus (Oryctocephalites). Nevertheless, Tonkinella clearly is an intermediate between the subfamilies in Whittington’s (1995) concept. If one emphasizes the importance of genal and thoracic pleural spines, it seems to be equally important whether the pygidial margin carries spines. However, Sundberg (2006) introduces a new species of Tonkinella with pygidial spines. The new Moroccan material of Shergoldiella adds further to the problem of how to subdivide the Oryctocephalidae in a consequent phylogenetic approach because it has the Tonkinella-type pygidium without marginal spines, without a pygidial border furrow and border, and with a smooth pygidial margin but has a proparian facial suture and lacks cephalic genal spines. In addition, it shows interpleural furrows and a sagittal postaxial groove in the pygidium. The morphology of the glabella has a fairly large similarity with that in Ovatoryctocara and Oryctocephalus Walcott, 1886 or Oryctocephalites Resser, 1939 rather than typical species of Tonkinella, and also to a lesser extent with Arthricocephalus and Arthricocephalites). In addition, the stratigraphic occurrence is clearly earlier than that of Tonkinella. The morphology of the cephalon thus is that of Ovatoryctocara and related oryctocarine trilobites, but the pygidium is somewhat intermediate between oryctocarine and tonkinelline having moderately developed furrows and a slightly elongate outline. In summary, Shergoldiella is possibly ancestral to Tonkinella within a morphocline from oryctocarines such as Arthricocephalus and Ovatoryctocara leading to further effacement of pygidial furrows and the development of a slightly expanding glabella although this hypothesis involves speculation and has to be proved by more oryctocephaloid species yet to be discovered. However, accepting this as a lineage, Tonkinella and Shergoldiella are both genera of a subfamily Oryctocarinae, with a slight modification of the ancestry suggested by Yuan et al. (2001). 5.1. Genus Shergoldiella n. gen Etymology: Named after the trilobitologist and former Chairman of the International Subcommission on Cambrian Stratigraphy, John H. Shergold, who deceased briefly before this article was completed. Type species: Shergoldiella vincenti n. gen., n. sp.; from the Jbel Wawrmast Formation of the eastern AntiAtlas, Morocco.
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Other species tentatively assigned to Shergoldiella: Shergoldiella? sequei (Li˜na´ n and Gozalo, 1999), from the Valdemiedes Formation of the Iberian Chains, northern Spain. Diagnosis: Axial region moderately wide; glabella subcylindrical, slightly expanded medially, widest across S2 or L3; lateral glabellar furrows with S1 moreor-less transverse, S2–S3 developed merely as shallow circular pits; S4 shallow; preglabellar field absent; eye lobe situated midway across cheek; facial suture proparian. Librigenae small. Thorax of six to eight segments, with pleural tips subtruncate. Pygidium with axis of six rings plus terminal axial piece; pleural regions with distinct pleural furrows and shallow interpleural furrows; pygidial border furrow and border not defined; lateral margin with sawtooth-like aspect in dorsal view because of the steep, deflected margin. Remarks: Shergoldiella is mainly characterized by a proparian suture, thoracic segments without pleural spines, and a pygidium without a defined border and border furrow and with somewhat bulbous distal portions of the pygidial pleura creating a wavy lateral pygidial margin. The most similar genus is Ovatoryctocara Chernysheva, 1962, sharing the absence of pygidial marginal spines and the absence of distinct pygidial border as well as a post-axial sagittal groove. Ovatoryctocara has a gonatoparian suture, which, however, does not differ considerably from the proparian suture of Shergoldiella. Although one might consider to regard the newly described species from Morocco as well as the species from the Iberian Chains as additional species of Ovatoryctocara if the generic concept is emended, a number of differences between Ovatoryctocara ovata and Ovatoryctocara granulata and the West Gondwanan species and the present mode of taxonomic treatment among the Oryctocephalidae suggests that the West Gondwanan species are better dealt with as a new genus. By comparison with Shergoldiella, Ovatoryctocara is a genus with a glabella of similar outline but a less constricted or even expanded frontal lobe; with eye lobes in a more adaxial position; with a thorax consisting of four or five rather than 6–8 segments; with the thoracic pleurae extending in stout spines; with a pygidial axis of seven or more (up to 12?) axial rings plus terminal axial piece and, resultingly, more segments involved in the pleural fields and the pygidium in general. It should be noted that very few figures of Ovatoryctocara ovata are published which clearly illustrate details of the morphology. Some of these illustrations appear to represent species different from Ovatoryctocara ovata (e.g., Yegorova et al., 1976, pl. 48, Fig. 17) but
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this figured material is usually insufficient for a revision. Ovatoryctocara granulata not only differs essentially in a coarse granulation of the carapax but offers additional characters which clearly differentiate it from the type species of the genus, particularly the tendency of having more extended glabellar impressions rather than a set of paired circular pits and a more anterior position of the eye lobes. The oryctocephaloid-type of glabella with paired pits suggests that Shergoldiella is more closely to the early phase of diversification within the oryctocephalids. The absence of pygidial spines causes resemblance to other oryctocarine trilobites such as Sandoveria Shergold, 1969. However, except for the absence of marginal spines these genera have a typical oryctocephaline-type pygidium with a clear demarcation of the pygidial pleurae. Barklyella Shergold, 1969 differs in having a distinctly expanded glabella. Pygidia which can be assigned unequivocally to Barklyella are unknown. The pygidia described as Barklyella by Yuan et al. (2002) have a broad pygidial axis, but come from strata with Ovatoryctocara granulata and may belong to this species (Sundberg, 2006). Among other characters, Arthricocephalus Bergeron, 1899 differs in having a clearly more slender glabella, a more slender pygidial axis, a well-developed pygidial border furrow, and a postaxial ridge. Arthricocephalites Chien et Lin, 1974 (in Lu et al., 1974) has gonatoparian rather than proparian sutures, a distinctly expanded frontal lobe, and a narrow but distinct pygidial border. Haliplanktos Blaker et Peel, 1997 differs from Shergoldia in having an anteriorly expanding glabella with furrows that tend to be transglabellar, a rastellate pygidial border furrow, and a well developed pygidial border. It should be noted that this genus is regarded as a junior synonym of Arthricocephalus by some authors (Yuan et al., 2001; Yuan and Zhao, 2002). Shergoldiella is generally similar to Tonkinella in size, overall morphology of the cranidium, thorax, and particularly the pygidium, notably in the absence of distinct marginal spines in the thoracic and pygidial pleurae (although Tonkinella has short pointed terminations to the thoracic segments). This similarity, however, is partly
superficial because it derives from differences to the other genera of the Oryctocephalidae. In his comprehensive analysis of the species of Tonkinella, Sundberg (1994) concentrated on the characters of the pygidium, primarily on the number of axial rings and the relative width (tr.) of the simple postaxial (“posterior”) pleural lobe. The pygidium of Shergoldiella is clearly differentiated from that of Tonkinella in the presence of interpleural furrows and a postaxial median groove so that a postaxial pleural lobe is not developed. In the cephalon, the overall relief is clearly advanced in Tonkinella, which is particularly visible in fairly undeformed material (compare Tonkinella sisimica Repina, 1960 in Khalfina, 1960, pl. Cm-XXIII, Fig. 8a; or Tonkinella breviceps Kobayashi, 1934 as figured by Sundberg, 1994, Fig. 24,1). Shergoldiella has a typical oryctocephalid glabella with moderate convexity and a pattern of glabellar furrows which is mainly derived from the paired circular pits rather than clear furrows as in mature individuals of Tonkinella. The frontal glabellar lobe in Shergoldiella is distinctly narrower (tr.) than the lobe behind, with the maximum width across S2 or L3, whereas the glabella in Tonkinella tends to progressively broaden towards the front. The librigena of Shergoldiella is fairly small, defined by strongly diverging posterior branches of the facial suture in a way that creates a proparian suture so that the librigena is devoid of a genal spine. These characters also differentiate Shergoldiella from Tonkinella. 5.2. Shergoldiella vincenti n. gen., n. sp Etymology: Named after Tony Vincent (Aberdeen), who made available part of the type material and collected important field data. Types: Holotype, PIW 2006-I-01, entire carapace (Fig. 3 A, D and E), from Bou Tiouit section, Tarhoucht, ca. 2–3 m above the base of the Jbel Wawrmast formation. Paratypes, seven more or less entire carapaces, PIW 2006-I-02, PIW 2006-I-03, PIW 2006-I-04, PIW 2006-I05, PIW 2006-I-06, PIW 2006-I-07, and PIW 2006-I-08. Additional, poorly preserved material not kept in repository.
Fig. 3. Shergoldiella vincenti n. gen., n. sp. Scale bar equals 1 mm in D–F and H; scale bar equals 2 mm in A–C, and G. All specimens from Jbel Wawrmast Formation, basal part of Br`eche a` Micmacca Member, Tarhoucht. (A, D and E) PIW 2006-I-01, holotype, entire dorsal carapace; (A) view of entire specimen; (D) enlarged anterior part of carapace showing slightly telescoped librigenae and differentiation of anterior thoracic segments; note pleural facets and different shapes of pleural tips and course of eye ridges along frontal part of glabella; (E) entire posterior part of carapace. (B) PIW 2006-I-03, entire, slightly deformed carapace; pygidium shows clear interpleural furrows. (C), PIW 2006-I-04, entire specimens with anterior part of cephalon split off and permitting view on external mold of hypostome. (F) PIW 2006-I-02, small, immature specimen with strongly tapering pygidial axis, relatively posterior position of posterior facial suture, and imprint of hypostome. (G) PIW 2006-I-05, imperfectly preserved small specimen with five thoracic segments and almost parallel-sided glabella. (H) PIW 2006-I-06, dorsal carapace.
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Diagnosis: Shergoldiella with subparallel glabella slightly expanded across L2 to S3; eye lobes (exsag.) of ca. 25% length, with posterior ends opposite L1 or shortly behind S1 and with anterior ends opposite posterior part of L3, width 15–18% width of maximum glabellar width (tr.), slightly to gently curved. Description: Cranidium small, length 3.0–6.1 mm in the studied specimens; subpentagonal, length 70% width; sagittal and transverse convexity moderate; anterior margin moderately curved; anterior branch of facial suture slightly outward directed from anterior ends of eyes, slightly converging across anterior border furrow and anterior border; posterior branch of facial suture distinctly diverging from posterior ends of eyes, curving backward short distance before lateral margin, thus creating a proparian suture. Glabellar length (inclusive occipital ring) ca. 92–96% of cranidial length, maximum width 27–32% of maximum cephalic width; expanded across S2 or L3, greatest expansion ca. 110% of width across L1; width across frontal lobe ca. 80–85% maximum glabellar width and ca. 84–88% occipital ring width; sagittally and transversely with moderate convexity; frontal lobe subtrapezoidal, with shallow curvature anteriorly and without median sulcus; S1 a shallow transverse glabellar furrow, slightly bent backward medially, connected with circular pits, S2 and S3 developed merely as shallow circular pits with faintly indicated indentations between; S4 a very shallow glabellar furrow. Occipital ring width (sag.) of 10–16% cephalic length, not elevated above glabella, posterior margin gently curved, without spine or node; occipital furrow straight or with a faint median posterior curvature, transverse, shallow, between distinctly incised elongated pits, faintly connected with axial furrows. Axial furrows moderately deep, shallower adjacent to L1, slightly sinuous around glabellar pits. Frontal area sagittally of about 5–7% cephalic length. Preglabellar field absent. Anterior border slightly convex to almost flat; widest and most elevated area medially, faintly tapering towards facial sutures, more-or-less evenly curved; anterior border furrow shallow, poorly defined, shallower than axial furrows. Fixigena subtrapezoidal, with slightly extending and rearward projecting postocular areas; maximum width 120–125% maximum glabellar width, width across eye lobes 55–60% maximum glabellar width, with moderately low convexity. Postocular areas sharply terminated, posterolateral extension distally almost fused with posterior border. Eye lobe narrow, weakly curved; width 15–18% width of maximum glabellar width; length (exsag.) ca. 25% cephalic length; anterior end opposite L3, poste-
rior end opposite L1 in smaller specimens but almost opposite S1 in mature specimens. Palpebral furrow shallow, narrow, poorly defined against fixigena. Eye ridge moderately well developed, with gentle forward curvature from eyes, confluent with glabella at S4 or trending forward along sides of frontal lobe (Fig. 3D), directed distinctly backward from glabella at approximately 60◦ to longitudinal axis. Posterior border moderately convex, width (exsag.) slightly expanding distally; border furrow sinuous, with clear rearward swing posterior to eye lobes, moderately deep, deepening slightly distally. Librigena small, exsagitally less than two-thirds cephalic length, moderately wide, width across eye lobes approximately 40% maximum length; lateral margin slightly curved. Genal field slightly convex. Librigenal border of approximately 15% librigenal width; convex; librigenal lateral border furrow narrow, moderately incised, of uniform width. Hypostoma known only from specimens PIW 2006I-02 and PIW 2006-I-04, where it is preserved relatively poorly as an external mold of the ventral side; probably fused to rostral plate and librigenal doublure; moderately small, length ca. 2.2 mm; oval, width ca. 70% length, sagittally and transversely moderately convex; lateral margins slightly curved. Median body moderately convex (sag. and tr.), suboval, probably slightly less than two-thirds hypostomal length; macula shallow. Posterior lobe narrow, ca. 20% hypostomal length, moderately convex, extending to the medial position of the median lobe; furrow moderately deep, probably extending to anterior margin. Posterior border narrow, ca. 5% hypostomal length, convex; posterior border furrow narrow, moderately deep. These characters suggest that the hypostoma of Shergoldiella vincenti is typical of oryctocephalids, and the two hypostomata are among the few known from non-spinose oryctocephalids. Thorax consists of six to eight segments, widest portion across fourth segment; segments slightly decreasing in width from there, decreasing posteriorly to about 80% width across fourth segment. Axial furrows well defined, shallower next to anterior pleural band. Axial ring with straight, convex (sag. and tr.) median portion and nodular lateral portions in a slightly more anterior position; width of axial rings decreases progressively backward to 80% width of axial ring at first segment. Thoracic pleura moderately wide, length 98–115% of axial width; anterior pleural band of roughly constant width (exsag.); posterior pleural band narrows distally, usually faintly more elevated than anterior pleural band, merged with distal portion of anterior pleural band to form stout, triangularly truncated, posterolaterally
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directed tip. Pleural facets developed at pleurae of segments 1–4 in distal position, all of slightly different size and ventral deflection in dependence of the necessity to overlap with adjacent pleura during enrollment; particularly well developed in segments 1 and 2. Pleurae of segment 1 terminated distally by rearward directed posterior margin of cephalon and therefore slightly posterolaterally directed; pleurae of segment 2 affected by posterolaterally directed pleurae of segment 1 and slightly posterolaterally directed in the anterior part; pleurae of segments 3 almost transverse, pleurae posterior to it projecting progressively posterolaterally. Pygidium relatively large, length 2.7–5.4 mm in the studied specimens; variably subelliptical, length ca. 69–80% width; anterior margin curved moderately posterolaterally. Eight pairs of marginal tips present, creating in dorsal view a sawtooth-like aspect of the lateral margins, all deflected ventrally in a moderate way, decreasing in size rearward and successively more posteriorly projecting; without macropleural segment. Axis composed of six axial rings plus a terminal axial piece, with moderate convexity; moderately tapering, length two-thirds pygidial length, width across anteriormost axial ring one-third total pygidial width across first segment, width at midlength 85–94% width across anteriormost axial ring, width across posteriormost ring 58–53% width across anteriormost axial ring; terminal axial piece very narrow (sag.), developed only as a small transverse lobe. Without postaxial ridge. Axial ring furrows moderately wide and moderately deep medially, deepen to well-incised transverse, slightly curved furrows close to axial furrows. Pleural regions well defined, with low to moderate convexity; divided by five distinct, relatively deep and moderately wide pleural furrows and four shallower and much narrower interpleural furrows, all posterolaterally to slightly posteriorly directed at posterior ends, extending to margin. Anterior and posterior pleural bands merge distally. Sagittal median groove developed posterior to axis, variably developed fairly well impressed and relatively broad in larger specimens. Without defined pygidial border and border furrow. Measurements: Specimens 7.3–16 mm in length in the studied specimens. Cranidial length ranges from 2.6–5.8 mm, maximum cranidial width 5.0–9.8 mm, glabellar length (including occipital ring) 2.4–5.1 mm, maximum glabellar width 1.6–2.5 mm. Pygidial length ranges from 3.0–5.7 mm, maximum pygidial width 4.5–6.9 mm, pygidial axial length 2.1–4.8 mm, maximum pygidial axial width 1.2–2.3 mm. Remarks: Shergoldiella? sequei (Li˜na´ n and Gozalo, 1999), originally described as Tonkinella sequei, and pre-
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viously figured as a specimen of “Hamatolenus (Myopsolenus)? jilocanus” in Li˜na´ n and Gozalo (1986, pl. 5, Fig. 8), has similar characters as Shergoldiella vincenti n. gen., n. sp. The single known, imperfectly preserved pygidium of Shergoldiella? sequei (Li˜na´ n and Gozalo, 1999, Fig. 2) shows weak interpleural furrows and a faint postaxial furrow but in general resembles very much pygidia of Tonkinella. However, it is impossible to identify the precise number of axial rings in this specimen. The single known cranidium is also somewhat distorted and lacks the preglabellar area. The glabella shows a similar pattern of glabellar furrows with S2 und S3 mainly formed by pits rather than displaying more typical short transverse furrows as in Tonkinella (although T. sibirica and T. valida both have glabellar pits). Connecting furrows are not visible but their absence could be a result of preservation. However, the glabella is more club-shaped than in Shergoldiella vincenti with its maximum width across S3 and thus resembling the glabella in Oryctocephalites Resser, 1939, and with an apparently stronger transverse and sagittal convexity. The eye lobes are relatively long (as already emphasized by Li˜na´ n and Gozalo, 1999), with the posterior ends opposite L1 and the anterior anterior ends opposite the middle part of L3. This length is comparable to that in smaller specimens of Shergoldiella vincenti. However, mature individuals have slightly shorter eye lobes with their posterior ends opposite shortly behind S1 so that the postocular area is larger in Shergoldiella vincenti. In addition, it seems that Shergoldiella sequei has broader (tr.) and less curved eye lobes. These characters are regarded herein as more closely resembling Shergoldia than Tonkinella and a sufficiently different from Tonkinella to place to species under the latter genus. Therefore, the species is tentatively placed under Shergoldiella although more and better preserved material may exhibit distinct differences to Shergoldiella vincenti. Occurrence: Cephalopyge notabilis Zone, lower Jbel Wawrmast Formation, Br`eche a` Micmacca Member, Tarhoucht area, eastern Anti-Atlas, Morocco. Acknowledgments Grateful acknowledgment is given for support of field work by the Deutsche Forschungsgemeinschaft (DFG). Tony Vincent (Aberdeen) provided invaluable help, making available part of the described material and collecting detailed information on the Tarhia Track localities. Heiko Sonntag (Hirschburg) provided additional material as permanent loan for this study. Fred Sundberg (Show Low, AZ) and Yuan Jinliang (Nanjing) provided valuable reviews of the manuscript, and I am particularly
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indebted to Fred Sundberg for his critical and helpful annotations. References ´ Alvaro, J.J., Li˜na´ n, E., Gozalo, R., Sdzuy, K., 1993. The palaeogeography of the northern Iberia at the Lower–Middle Cambrian transition. Bull. Soc. G´eol. France 164, 843–850. Beecher, C.E., 1897. Outline of a natural classification of the trilobites. Am. J. Sci. 4 (3), 89–106, 181–207. ´ Bergeron, J.N., 1899. Etude de quelques trilobites du Chine. Bull. Soc. G´eol. France 3 (27), 181–207. Blaker, M.R., Peel, J.S., 1997. Lower Cambrian trilobites from North Greenland. Meddelelser om Grønland Geosci. 35, 145. Chernysheva, N.Y., 1962. Kembriyskie trilobity semeystva Oryctocephalidae. In: Shvedov, N.A. (Ed.), Problemy Neftegazonosnosti Sovetskoy Arktiki, Paleontologiya I Biostratigrapfiya, vol. 3. Trudy nauchno-issledovatel’skiy institute geologi Arktiki (NIIGA) 127, pp. 3–52 (in Russian). Fletcher, T.P., 2003. Ovatoryctocara granulata: the key to a global Cambrian stage boundary and the correlation of the olenellid, redlichiid and paradoxidid realms. Paleontology 70, 73–102. Geyer, G., 1988. Agnostida aus dem h¨oheren Unterkambrium und dem Mittelkambrium von Marokko, Teil 2: Eodiscina. Neues Jahrbuch f¨ur Geologie und Pal¨aontologie. Abhandlungen 177 (1), 93–133. Geyer, G., 1990. Die marokkanischen Ellipsocephalidae (Trilobita: Redlichiida). Beringeria 3, 363. Geyer, G., 1993. The giant Cambrian trilobites of Morocco. Beringeria 8, 71–107. Geyer, G., 1999. Intercontinental, trilobite-based correlation of the Moroccan early Middle Cambrian. Can. J. Earth Sci. 35, 374–401. Geyer, G., 2005. The base of a revised Middle Cambrian: are suitable concepts for a series boundary in reach? Geosci. J. 9 (2), 81–99. Geyer, G., Landing, E., 1995. The Cambrian of the Moroccan Atlas region. MOROCCO ’95—the Lower–Middle Cambrian Standard of Western Gondwana. In: Geyer, G., Landing, E. (Eds.), Beringeria (2), 7–46 (special issue). Geyer, G., Landing, E., 2004. A unified Lower–Middle Cambrian chronostratigraphy for West Gondwana. Acta Geol. Pol. 54 (2), 179–218. Geyer, G., Landing, E., Heldmaier, W., 1995. Faunas and depositional environments of the Cambrian of the Moroccan Atlas region. In: Geyer, G., Landing, E. (Eds.), Beringeria (2), 47–119 (special issue). ´ Gozalo, R., Alvaro, J.J., Li˜na´ n, E., Sdzuy, K., Truyols, J., 1993. La distribuci´on de Paradoxides (Acadoparadoxides) mureroensis Sdzuy, 1958 (C´ambrico Medio basal) y sus implicaciones paleobiogeogr´aficas. Cuadernos do Laboratorio Xeol´oxico de Laxe 18, 217–230. Gozalo, R., Mayoral, E., G´amez Vintaned, J.A., Dies, M.E., Mu˜niz, F., 2003. A new occurrence of the genus Tonkinella in northern Spain and the Middle Cambrian intercontinental correlation. Geol. Acta 1 (1), 121–126. Heldmaier, W., 1997. The Lower–Middle Cambrian transition along the northwestern margin of Gondwana (Anti-Atlas and High Atlas ranges, Morocco). Unpublished Ph.D. Dissertation. Bayerische Julius-Maximilians-Universit¨at W¨urzburg, 273 pp. Hup´e, P., 1953. Classe de trilobites. In: Piveteau, J. (Ed.), Trait´e de Pal´eontolgie Tome III. Masson & Cie, Paris, pp. 44–246. Hup´e, P., 1955. Classification des trilobites. Ann. Pal´eontol. 41, 91–325.
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Research paper
First African oryctocephalid trilobites from the Lower–Middle Cambrian boundary interval Gerd Geyer Institut f¨ur Pal¨aontologie, Bayerische Julius-Maximilians-Universit¨at W¨urzburg, Pleicherwall 1, 97070 W¨urzburg, Germany Received 14 February 2006; received in revised form 9 May 2006; accepted 16 October 2006
Abstract Oryctocephalid trilobites from Lower Middle Cambrian strata of the eastern Anti-Atlas, Morocco, are the first described Oryctocephalidae known from Africa. They represent the new genus and species Shergoldiella vincenti. However, a similar species was earlier described as Tonkinella sequei Li˜na´ n et Gozalo, 1999, from coeval lower Middle Cambrian strata of the Iberian Chains, northern Spain. This Iberian species is imperfectly preserved and assigned herein to Shergoldiella with reservations. If this assignment is correct, it would reinforce earlier suggested correlations between Morocco and Spain. Nevertheless, Shergoldiella suggests a morphocline from a typical oryctocephalid-type morphology towards the Tonkinella-type morphology. Close similarity with Ovatoryctocara ovata suggests a similar stratigraphic position in accordance with earlier suggested intercontinental correlations. © 2006 Nanjing Institute of Geology and Palaeontology, CAS. Published by Elsevier Ltd. All rights reserved. Keywords: Trilobita; Middle Cambrian; Biostratigraphy; West Gondwana
1. Introduction Oryctocephalid trilobites are among the most distinctive and short-lived trilobites in the Lower–Middle Cambrian boundary interval and thus play a major role in the discussion, at which stratigraphic level the base of the Cambrian Series 3 (replacing the traditional Lower–Middle Cambrian boundary) and Stage 5 should be placed (Sundberg et al., 1999; Fletcher, 2003; Zhao et al., 2004, 2005; Geyer, 2005). At the moment, most scientists favor the placement of a GSSP for the base of this series and stage at the FAD of Oryctocephalus indicus (Reed, 1910) although additional concepts may be suitable. Other oryctocephalid trilobites, such as Arthricocephaus chauveaui Bergeron, 1899, Ovatoryctocara granulata (Chernysheva, 1962), and, less clearly, Lancastria spp., Oryctocephalites spp. and Microryctocara
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spp. also play key roles in this discussion (see Geyer, 2005, for comprehensive discussion). A major disadvantage of a GSSP based on the FAD of Oryctocephalus indicus is that this level cannot be identified with sufficient precision in Baltica and West Gondwana at this moment (Geyer, 2005) so that additional biostratigraphic data are needed for an improved intercontinental correlation. Shergoldiella vincenti n. gen., n. sp. is the first discovered oryctocephalid trilobite from Africa, found in the traditional Lower–Middle Cambrian boundary interval. Its affinities and potential for correlation is discussed in this article with reference to the few other known West Gondwanan Oryctocephalidae. 2. Material, stratigraphic occurrence and preservation The material described herein as Shergoldiella vincenti n. gen., n. sp. comes from the Jbel Wawrmast
1871-174X/$ – see front matter © 2006 Nanjing Institute of Geology and Palaeontology, CAS. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.palwor.2006.10.004
G. Geyer / Palaeoworld 15 (2006) 348–359
Formation of the well-known Tarhoucht area in the eastern Anti-Atlas of Morocco. The Jbel Wawrmast Formation largely consists of yellowish-weathering, fine-grained sandstones and green and blue-green siltstones. The lower part of the formation, from which the material was recovered, is characterized by thin, lithologically variable limestones which are rhythmically intercalated into the sandstones.
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This part of the formation is termed the Br`eche a` Micmacca Member. The formation has a thickness of ca. 150 m in the Tarhoucht area, but all the specimens found so far are apparently coming from the basal meters (Fig. 1). The small village of Tarhoucht has gained international reputation because of an extensive quarrying for fossils, particularly trilobites, with most of the inhab-
Fig. 1. Profile of the Jbel Wawrmast Formation at the Tarhoucht-Bou Tiouit section, illustrating graing-size profile, color changes, sedimentologic features, paleoenvironmental interpretation, and biostratigraphic sequence. Thickness (left margin) in meters from the base of the formation. Asterisk indicates strata with Shergoldiella vincenti n. gen., n. sp. Color legend: p/r, purple or red; bl, blue; bl gr, bluish green; y, yellow; y gr, yellowish green; l gr, light green, m gr, medium green; d gr, dark green; gy, grey; b, black, w, white. Modified from Geyer et al. (1995, fig. 25).
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itants being involved in the fossil trade. Cambropallas telesto Geyer, 1993, the youngest known olenelloid trilobite, Paradoxides (Acadoparadoxides) briareus Geyer, 1993, Protolenus (P.) interscriptus Geyer, 1990, and Hamatolenus (H.) vincenti Geyer et Landing, 2004 are examples for nicely preserved trilobites from the area which occur frequently on the international fossil market. The locality and its stratigraphy have been described in detail by Geyer (1993), Geyer et al. (1995), and Heldmaier (1997). Two sections in this area yielded the material of Shergoldiella vincenti described herein. 2.1. Bou Tiouit section The classical outcrops are in the lower part of the Jbel Wawrmast Formation on the northern slope of Bou Tiouit, a mountain just south of the village, where Cambopallas telesto and Paradoxides (Acadoparadoxides) briareus were obtained from low quarries in two stratigraphic levels, which are exploited by the local people by comparatively primitive techniques. Both levels fall into the lower (but not lowest) Middle Cambrian Cephalopyge notabilis Zone, Agdzian Stage, which represents all but the lowermost stratum of the Jbel Wawrmast Formation (Fig. 2). As described earlier (Geyer et al., 1995, pp. 112–117), there exist fairly diverse assemblages, mostly composed of different species of trilobites, plus a few brachiopods, hyoliths, helcionellids, pelagiellids, echinoderms, and trace fossils, dependent on the particular lithofacies.
2.2. Tarhia Track localities A second area for exploration of fossil material was opened by the local fossil dealers in 2001. This area, termed Tarhia Track localities, is situated west of the road from Tarhoucht to Tarhia about one kilometer to the north of the village of Tarhoucht (31◦ 23.8 –31◦ 24.0 N, 5◦ 00.8 –5◦ 01.2 W). It is tectonically complicated and does not present a larger part of a measurable stratigraphic section. It includes several outcrops of the top of the (most probably latest Early Cambrian) Tazlaft Formation and the basal strata (ca. >4 m) of the Jbel Wawrmast Formation. Detailed field investigations of T. Vincent (Aberdeen) based on earlier lithostratigraphic studies of Heldmaier (1997) enabled a precise correlation of the Tarhia Track localities with the Bou Tiouit section. Mr. Vincent’s investigations indicate that the quarried strata at the Tarhia Track localities belong to Heldmaier’s (1997) color cycle 4 of the Jbel Wawrmast Formation as identified at Bou Tiouit in the lower part of the Jbel Wawrmast Formation. Interestingly, the material of Shergoldiella vincenti n. gen., n. sp. was exclusively discovered in the strata of this color cycle 4, occurring together with such trilobites as Cephalopyge notabilis Geyer, 1988, Condylopyge eli Geyer, 1999, Hamatolenus (H.) vincenti Geyer et Landing, 2004, Hamatolenus (H.) cf. marocanus (Neltner, 1938), Hamatolenus (Myopsolenus) cf. magnus (Hup´e, 1953), Latoucheia (L.) epichara Geyer, 1990, Protolenus (P.) interscriptus Geyer, 1990, Protolenus (Hupeolenus)
Fig. 2. Field photography of the lower trilobite quarry at the northwestern corner of Bou Tiouit, near Tarhoucht, Anti-Atlas, the most productive site for Shergoldiella vincenti n. gen., n. sp. The excavations exploit strata ca. 2–3 m above the base of the Jbel Wawrmast Formation. The photographer (T. Vincent) was standing on the top of the Tazlaft Formation. The resitant large blocks are float from the cross-bedded quartzarenitic Jbel Afraou Formation which overlies the Jbel Wawrmast Formation (visible at the small escarpment in the upper part of the photography).
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dimarginatus Geyer, 1990, Kingaspidoides laetus Geyer, 1990, Kingaspidoides neglectus Geyer, 1990, Kingaspidoides sp. A, Ornamentaspis cf. usitata Geyer, 1990, Paradoxides (Acadoparadoxides) nobilis Geyer, 1999, Paradoxides (Acadoparadoxides) sp. B, Myopsolenites boutiouiti Geyer et Landing, 2004, Cambopallas telesto Geyer, 1993, Yuehsienzella? n. sp., and the obolellid brachiopod Trematobolus splendidus Geyer et Mergl, 1995. However, these strata with Shergoldiella vincenti are below the telesto level at Bou Tiouit (see Geyer, 1993), but are shared with numerous specimens of Cambopallas telesto at the Tarhia track location. All of the material is preserved in yellowish-green argillaceous coarse siltstones or fine-grained sandstones of the Jbel Wawrmast Formation. As a consequence, the specimens are usually slightly flattened and somewhat distorted due to a notable compression of the rocks. Remarkable, the cephala are usually more strongly affected by distortion than the pygidia so that none of the specimens shows a perfectly preserved cephalon. Due to the economic importance of the strata for the local population, the well-preserved specimens of Shergoldiella vincenti were obtained from the quarried material. Additional material from the Tarhia Track localities was found (three disarticulated pygidia, two pygidia with attached thorax, one partial cephalon) but is too poorly preserved to merit description and figuring. 3. West Gondwanan or yctocephalid trilobites Oryctocephalid trilobites are extremely rare in West Gondwana. The specimens of Shergoldiella vincenti n. gen., n. sp. represent the first findings of corynexochid trilobites from Morocco and entire Africa. The reason for the rarity of trilobites from this family is obviously a result of environmental constraints. Most oryctocephalids were discovered in paleo-equatorial regions. They preferred habitats with low wave agitation and thus avoided shallow marine environments. West Gondwana, however, was dominated by shallow to shallowest marine depositional environments from the late Early to the middle Middle Cambrian, which saw the peak occurrence of the oyctocephalids. An oryctocephalid trilobite was described from the Iberian Chains, northern Spain as Tonkinella sequei Li˜na´ n et Gozalo, 1999. It was found in the Hamatolenus ibericus Zone of the Valdemiedes Formation, representing the Cephalopyge notabilis Zone of the Agdzian Stage in the unified West Gondwanan chronostratigraphy (Geyer and Landing, 2004). Tonkinella sequei is thus coeval with Shergoldiella vincenti but would represent
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the oldest known species of Tonkinella. Unfortunately, only one slightly distorted cranidium and an incomplete, distorted pygidium are known so that it will be difficult to characterise the species unless additional and better preserved material is found in the type locality. As discussed below in detail, the pygidium of Tonkinella sequei shows characters that suggest a closer affinity to Shergoldiella than to Tonkinella. The cranidium is also comparable to that of Shergoldiella vincenti, but appears to show distinct differences against the coeval Moroccan species. Although Sundberg (2006) regards the Iberian material as representing a species of Tonkinella, it is considered herein to be more adequately placed under Shergoldiella although more and better preserved material needs to be discovered and examined until its generic assignment can be determined with enough certainty (see discussion in Section 5). It is remarkable that both species occur in associations which share a large percentage of common species and are fairly identical in generic composition. Shergoldiella? sequei is reported from a lower assemblage in the Valdemiedes Formation of the Rambla de Valdemiedes together with the trilobites Hamatolenus (H.) ibericus Sdzuy, 1958, Hamatolenus (H.) vincenti Geyer et Landing, 2004, Protolenus (Hupeolenus) jilocanus (Li˜na´ n and Gozalo, 1986), Protolenus (Hupeolenus) dimarginatus Geyer, 1990, Alueva undulata Sdzuy, 1961, Myopsolenites altus (Li˜na´ n and Gozalo, 1986), Kingaspis sp., Sdzuyia sanmamesi Li˜na´ n et Gozalo, 1999, and the obolellid Trematobolus simplex (Vogel, 1962) (nomenclature partly corrected herein; see also Li˜na´ n et al., 2004, and discussion in Geyer and Landing, 2004, pp. 193–194, 197). It should be noted, however, that this lower assemblage is below the first occurrence of Paradoxides (Acadoparadoxides) mureroensis Sdzuy, 1958 and thus below the traditional Iberian base of the Leonian stage and Middle Cambrian. It is also below the so-called Valdemiedes event (Li˜na´ n et al., 1993), which has been interpreted as a major faunal turnover at the traditional Lower–Middle Cambrian ´ boundary in Iberia (Alvaro et al., 1993; Gozalo et al., 1993; Li˜na´ n et al., 1993, etc.) and eventually the expression of a latest Early Cambrian mass extinction (Li˜na´ n et al., 2004). As detailed earlier, there is overwhelming faunal evidence that such a faunal turnover is absent in coeval strata in Morocco, where a faunal turnover can be illustrated in older strata at the base of the Agdzian Stage (Geyer, 2005; Geyer and Landing, 1995, 2004; Geyer et al., 1995; Landing et al., 2006). The Valdemiedes event, as shown from the sections in the Iberian Chains, is thus to be interpreted as a local faunal minimum for yet to be clarified reasons.
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The only report of an unequivocal Tonkinella from West Gondwana comes from a single but well-preserved pygidium from the upper Agdzian (former Leonian) Oville Formation of the Cantabrian Mountains, northern Spain (Gozalo et al., 2003). The specimen, identified as Tonkinella aff. breviceps Kobayashi, 1934, was found relatively short distance below the base of the Badulesia tenera Zone and thus the base of the Caesaraugustian and in association with Eccaparadoxides asturianus and other trilobites of the Kymataspis arenosa or E. asturianus Zone (Gozalo et al., 2003). Shergoldiella vincenti and Shergoldiella? sequei both occur in the Cephalopyge notabilis Zone, Agdzian, two zones below the Kymataspis arenosa Zone. 4. Shergoldiella and its bearing on intercontinental correlation Shergoldiella vincenti and Shergoldiella? sequei are close relatives to Ovatoryctocara ovata (Chernysheva in Krys’kov et al., 1960), the type species of Ovatoryctocara, and Ovatoryctocara granulata (Chernysheva, 1962). Ovatoryctocara granulata has been identified as a valuable species for intercontinental correlation at the Early–Middle Cambrian boundary interval (summarized in Geyer, 2005, pp. 85–87; see also Fletcher, 2003). Both species were originally described from the lower Amgan of northern Siberia. In addition, Ovatoryctocara granulata has been identified in the Avalonian southeastern Newfoundland (Fletcher, 2003), most probably from North Greenland (Blaker and Peel, 1997; Geyer, 2005), and tentatively from the so-called Ovatoryctocara granulata–Bathynotus holopygus Zone (sensu Yuan et al., 2001, 2002), upper Duyunian (top of the former Lungwangmiaoan), Guizhou Province, South China, where it underlies the Oryctocephalus indicus Zone (Yuan et al., 2001, 2002). The specimens from eastern Guizhou have eye lobes in a slightly more anterior position than Ovatoryctocara granulata, and it would need a thorough investigation to clarify whether they represent a similar but yet undescribed species of Ovatoryctocara (Yuan et al., 2002: pl. 29, Figs. 4 and 5). Interestingly, the faunas in the stratigraphical position of Ovatoryctocara granulata in Siberia and Newfoundland share genera or even species which occur in the stratigraphic position of Shergoldiella vincenti in Morocco, such as Cephalopyge notabilis, Condylopyge eli, Hamatolenus spp., or Schistocephalus (Geyer, 1998; Fletcher, 2003) This occurrence does not contribute to a finer resolution of intercontinental correlations. However, it reinforces earlier suggestions for a correlation from West Gondwana into other Cambrian continents
(Geyer and Landing, 2004; Geyer, 2005). A further correlation from this level into other Cambrian areas is possible with auxiliary key taxa such as Kiskinella cristata Romanenko and Romanenko, 1962 and Peronopsis roddyi Resser and Howell, 1938 (see Fletcher, 2003, and Geyer, 2005, for further discussion). It should be emphasized, however, that Ovatoryctocara granulata has a larger stratigraphic range in Siberia than in other areas so that indirect correlations should be treated with a caveat. A by-product of the West Gondwanan oryctocephalids is a comparison of faunal changes during early Middle Cambrian. If one accepts a global correlation based on Tonkinella as done by Gozalo et al. (2003), the top Leonian of West Gondwana correlates with the top of the Ehmaniella and possibly the base of the Ptychagnostus (or Triplagnostus) gibbus Zone in Laurentia and the middle Taijiangian (former upper part of the Hsuchuangian) of South China (whereas the genus Tonkinella has a stratigraphic range from probably the Albertella Zone to the bottom of the Ptychagnostus (or Triplagnostus) gibbus Zone in North American standard; Sundberg, 2006). This indicates that the outer shelf deposits, such as in Laurentia and partly in South China, appear to have a fairly better resolvable biostratigraphy than the shallow marine strata in West Gondwana although there is not too much difference in the number of trilobite taxa which occur in the relevant stratigraphic interval. 5. Systematic Paleontology - Order Corynexochida Kobayashi, 1935. - Family Oryctocephalidae Beecher, 1897. - Subfamily Oryctocarinae Hup´e, 1953. Remarks: Tonkinella Mansuy, 1916 has been considered as sufficiently different from typical oryctocephalid trilobites due to the pygidial characters so that Reed (1934) introduced the new subfamily Tonkinellinae, which was maintained by other authors such as Hup´e (1955), Kobayashi (1961), and Suvorova (1964). Other than Kobayashi (1961), who regarded the Oryctocarinae Hup´e (1953) as a junior synonym, Suvorova (1964) treated the Tonkinellinae as a monogeneric taxon and emphasized particularly the lack of interpleural furrows and marginal spines. Subsequently, Chinese authors even raised the taxon to the family level. Whittington (1995) distinguished between Oryctocephalinae and Oryctocarinae based on the presence and absence of genal spines and thoracic and pygidial pleural spines. In this process, Whittington (1995) placed Tonkinella tentatively under the subfamily Oryc-
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tocephalinae because of the presence of genal spines, following McNamara’s hypothesis that Tonkinella is heterochronically derived from spiny oryctocephalids (McNamara, 1986; McNamara et al., 2006) such as Oryctocephalus (Oryctocephalites). Nevertheless, Tonkinella clearly is an intermediate between the subfamilies in Whittington’s (1995) concept. If one emphasizes the importance of genal and thoracic pleural spines, it seems to be equally important whether the pygidial margin carries spines. However, Sundberg (2006) introduces a new species of Tonkinella with pygidial spines. The new Moroccan material of Shergoldiella adds further to the problem of how to subdivide the Oryctocephalidae in a consequent phylogenetic approach because it has the Tonkinella-type pygidium without marginal spines, without a pygidial border furrow and border, and with a smooth pygidial margin but has a proparian facial suture and lacks cephalic genal spines. In addition, it shows interpleural furrows and a sagittal postaxial groove in the pygidium. The morphology of the glabella has a fairly large similarity with that in Ovatoryctocara and Oryctocephalus Walcott, 1886 or Oryctocephalites Resser, 1939 rather than typical species of Tonkinella, and also to a lesser extent with Arthricocephalus and Arthricocephalites). In addition, the stratigraphic occurrence is clearly earlier than that of Tonkinella. The morphology of the cephalon thus is that of Ovatoryctocara and related oryctocarine trilobites, but the pygidium is somewhat intermediate between oryctocarine and tonkinelline having moderately developed furrows and a slightly elongate outline. In summary, Shergoldiella is possibly ancestral to Tonkinella within a morphocline from oryctocarines such as Arthricocephalus and Ovatoryctocara leading to further effacement of pygidial furrows and the development of a slightly expanding glabella although this hypothesis involves speculation and has to be proved by more oryctocephaloid species yet to be discovered. However, accepting this as a lineage, Tonkinella and Shergoldiella are both genera of a subfamily Oryctocarinae, with a slight modification of the ancestry suggested by Yuan et al. (2001). 5.1. Genus Shergoldiella n. gen Etymology: Named after the trilobitologist and former Chairman of the International Subcommission on Cambrian Stratigraphy, John H. Shergold, who deceased briefly before this article was completed. Type species: Shergoldiella vincenti n. gen., n. sp.; from the Jbel Wawrmast Formation of the eastern AntiAtlas, Morocco.
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Other species tentatively assigned to Shergoldiella: Shergoldiella? sequei (Li˜na´ n and Gozalo, 1999), from the Valdemiedes Formation of the Iberian Chains, northern Spain. Diagnosis: Axial region moderately wide; glabella subcylindrical, slightly expanded medially, widest across S2 or L3; lateral glabellar furrows with S1 moreor-less transverse, S2–S3 developed merely as shallow circular pits; S4 shallow; preglabellar field absent; eye lobe situated midway across cheek; facial suture proparian. Librigenae small. Thorax of six to eight segments, with pleural tips subtruncate. Pygidium with axis of six rings plus terminal axial piece; pleural regions with distinct pleural furrows and shallow interpleural furrows; pygidial border furrow and border not defined; lateral margin with sawtooth-like aspect in dorsal view because of the steep, deflected margin. Remarks: Shergoldiella is mainly characterized by a proparian suture, thoracic segments without pleural spines, and a pygidium without a defined border and border furrow and with somewhat bulbous distal portions of the pygidial pleura creating a wavy lateral pygidial margin. The most similar genus is Ovatoryctocara Chernysheva, 1962, sharing the absence of pygidial marginal spines and the absence of distinct pygidial border as well as a post-axial sagittal groove. Ovatoryctocara has a gonatoparian suture, which, however, does not differ considerably from the proparian suture of Shergoldiella. Although one might consider to regard the newly described species from Morocco as well as the species from the Iberian Chains as additional species of Ovatoryctocara if the generic concept is emended, a number of differences between Ovatoryctocara ovata and Ovatoryctocara granulata and the West Gondwanan species and the present mode of taxonomic treatment among the Oryctocephalidae suggests that the West Gondwanan species are better dealt with as a new genus. By comparison with Shergoldiella, Ovatoryctocara is a genus with a glabella of similar outline but a less constricted or even expanded frontal lobe; with eye lobes in a more adaxial position; with a thorax consisting of four or five rather than 6–8 segments; with the thoracic pleurae extending in stout spines; with a pygidial axis of seven or more (up to 12?) axial rings plus terminal axial piece and, resultingly, more segments involved in the pleural fields and the pygidium in general. It should be noted that very few figures of Ovatoryctocara ovata are published which clearly illustrate details of the morphology. Some of these illustrations appear to represent species different from Ovatoryctocara ovata (e.g., Yegorova et al., 1976, pl. 48, Fig. 17) but
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this figured material is usually insufficient for a revision. Ovatoryctocara granulata not only differs essentially in a coarse granulation of the carapax but offers additional characters which clearly differentiate it from the type species of the genus, particularly the tendency of having more extended glabellar impressions rather than a set of paired circular pits and a more anterior position of the eye lobes. The oryctocephaloid-type of glabella with paired pits suggests that Shergoldiella is more closely to the early phase of diversification within the oryctocephalids. The absence of pygidial spines causes resemblance to other oryctocarine trilobites such as Sandoveria Shergold, 1969. However, except for the absence of marginal spines these genera have a typical oryctocephaline-type pygidium with a clear demarcation of the pygidial pleurae. Barklyella Shergold, 1969 differs in having a distinctly expanded glabella. Pygidia which can be assigned unequivocally to Barklyella are unknown. The pygidia described as Barklyella by Yuan et al. (2002) have a broad pygidial axis, but come from strata with Ovatoryctocara granulata and may belong to this species (Sundberg, 2006). Among other characters, Arthricocephalus Bergeron, 1899 differs in having a clearly more slender glabella, a more slender pygidial axis, a well-developed pygidial border furrow, and a postaxial ridge. Arthricocephalites Chien et Lin, 1974 (in Lu et al., 1974) has gonatoparian rather than proparian sutures, a distinctly expanded frontal lobe, and a narrow but distinct pygidial border. Haliplanktos Blaker et Peel, 1997 differs from Shergoldia in having an anteriorly expanding glabella with furrows that tend to be transglabellar, a rastellate pygidial border furrow, and a well developed pygidial border. It should be noted that this genus is regarded as a junior synonym of Arthricocephalus by some authors (Yuan et al., 2001; Yuan and Zhao, 2002). Shergoldiella is generally similar to Tonkinella in size, overall morphology of the cranidium, thorax, and particularly the pygidium, notably in the absence of distinct marginal spines in the thoracic and pygidial pleurae (although Tonkinella has short pointed terminations to the thoracic segments). This similarity, however, is partly
superficial because it derives from differences to the other genera of the Oryctocephalidae. In his comprehensive analysis of the species of Tonkinella, Sundberg (1994) concentrated on the characters of the pygidium, primarily on the number of axial rings and the relative width (tr.) of the simple postaxial (“posterior”) pleural lobe. The pygidium of Shergoldiella is clearly differentiated from that of Tonkinella in the presence of interpleural furrows and a postaxial median groove so that a postaxial pleural lobe is not developed. In the cephalon, the overall relief is clearly advanced in Tonkinella, which is particularly visible in fairly undeformed material (compare Tonkinella sisimica Repina, 1960 in Khalfina, 1960, pl. Cm-XXIII, Fig. 8a; or Tonkinella breviceps Kobayashi, 1934 as figured by Sundberg, 1994, Fig. 24,1). Shergoldiella has a typical oryctocephalid glabella with moderate convexity and a pattern of glabellar furrows which is mainly derived from the paired circular pits rather than clear furrows as in mature individuals of Tonkinella. The frontal glabellar lobe in Shergoldiella is distinctly narrower (tr.) than the lobe behind, with the maximum width across S2 or L3, whereas the glabella in Tonkinella tends to progressively broaden towards the front. The librigena of Shergoldiella is fairly small, defined by strongly diverging posterior branches of the facial suture in a way that creates a proparian suture so that the librigena is devoid of a genal spine. These characters also differentiate Shergoldiella from Tonkinella. 5.2. Shergoldiella vincenti n. gen., n. sp Etymology: Named after Tony Vincent (Aberdeen), who made available part of the type material and collected important field data. Types: Holotype, PIW 2006-I-01, entire carapace (Fig. 3 A, D and E), from Bou Tiouit section, Tarhoucht, ca. 2–3 m above the base of the Jbel Wawrmast formation. Paratypes, seven more or less entire carapaces, PIW 2006-I-02, PIW 2006-I-03, PIW 2006-I-04, PIW 2006-I05, PIW 2006-I-06, PIW 2006-I-07, and PIW 2006-I-08. Additional, poorly preserved material not kept in repository.
Fig. 3. Shergoldiella vincenti n. gen., n. sp. Scale bar equals 1 mm in D–F and H; scale bar equals 2 mm in A–C, and G. All specimens from Jbel Wawrmast Formation, basal part of Br`eche a` Micmacca Member, Tarhoucht. (A, D and E) PIW 2006-I-01, holotype, entire dorsal carapace; (A) view of entire specimen; (D) enlarged anterior part of carapace showing slightly telescoped librigenae and differentiation of anterior thoracic segments; note pleural facets and different shapes of pleural tips and course of eye ridges along frontal part of glabella; (E) entire posterior part of carapace. (B) PIW 2006-I-03, entire, slightly deformed carapace; pygidium shows clear interpleural furrows. (C), PIW 2006-I-04, entire specimens with anterior part of cephalon split off and permitting view on external mold of hypostome. (F) PIW 2006-I-02, small, immature specimen with strongly tapering pygidial axis, relatively posterior position of posterior facial suture, and imprint of hypostome. (G) PIW 2006-I-05, imperfectly preserved small specimen with five thoracic segments and almost parallel-sided glabella. (H) PIW 2006-I-06, dorsal carapace.
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Diagnosis: Shergoldiella with subparallel glabella slightly expanded across L2 to S3; eye lobes (exsag.) of ca. 25% length, with posterior ends opposite L1 or shortly behind S1 and with anterior ends opposite posterior part of L3, width 15–18% width of maximum glabellar width (tr.), slightly to gently curved. Description: Cranidium small, length 3.0–6.1 mm in the studied specimens; subpentagonal, length 70% width; sagittal and transverse convexity moderate; anterior margin moderately curved; anterior branch of facial suture slightly outward directed from anterior ends of eyes, slightly converging across anterior border furrow and anterior border; posterior branch of facial suture distinctly diverging from posterior ends of eyes, curving backward short distance before lateral margin, thus creating a proparian suture. Glabellar length (inclusive occipital ring) ca. 92–96% of cranidial length, maximum width 27–32% of maximum cephalic width; expanded across S2 or L3, greatest expansion ca. 110% of width across L1; width across frontal lobe ca. 80–85% maximum glabellar width and ca. 84–88% occipital ring width; sagittally and transversely with moderate convexity; frontal lobe subtrapezoidal, with shallow curvature anteriorly and without median sulcus; S1 a shallow transverse glabellar furrow, slightly bent backward medially, connected with circular pits, S2 and S3 developed merely as shallow circular pits with faintly indicated indentations between; S4 a very shallow glabellar furrow. Occipital ring width (sag.) of 10–16% cephalic length, not elevated above glabella, posterior margin gently curved, without spine or node; occipital furrow straight or with a faint median posterior curvature, transverse, shallow, between distinctly incised elongated pits, faintly connected with axial furrows. Axial furrows moderately deep, shallower adjacent to L1, slightly sinuous around glabellar pits. Frontal area sagittally of about 5–7% cephalic length. Preglabellar field absent. Anterior border slightly convex to almost flat; widest and most elevated area medially, faintly tapering towards facial sutures, more-or-less evenly curved; anterior border furrow shallow, poorly defined, shallower than axial furrows. Fixigena subtrapezoidal, with slightly extending and rearward projecting postocular areas; maximum width 120–125% maximum glabellar width, width across eye lobes 55–60% maximum glabellar width, with moderately low convexity. Postocular areas sharply terminated, posterolateral extension distally almost fused with posterior border. Eye lobe narrow, weakly curved; width 15–18% width of maximum glabellar width; length (exsag.) ca. 25% cephalic length; anterior end opposite L3, poste-
rior end opposite L1 in smaller specimens but almost opposite S1 in mature specimens. Palpebral furrow shallow, narrow, poorly defined against fixigena. Eye ridge moderately well developed, with gentle forward curvature from eyes, confluent with glabella at S4 or trending forward along sides of frontal lobe (Fig. 3D), directed distinctly backward from glabella at approximately 60◦ to longitudinal axis. Posterior border moderately convex, width (exsag.) slightly expanding distally; border furrow sinuous, with clear rearward swing posterior to eye lobes, moderately deep, deepening slightly distally. Librigena small, exsagitally less than two-thirds cephalic length, moderately wide, width across eye lobes approximately 40% maximum length; lateral margin slightly curved. Genal field slightly convex. Librigenal border of approximately 15% librigenal width; convex; librigenal lateral border furrow narrow, moderately incised, of uniform width. Hypostoma known only from specimens PIW 2006I-02 and PIW 2006-I-04, where it is preserved relatively poorly as an external mold of the ventral side; probably fused to rostral plate and librigenal doublure; moderately small, length ca. 2.2 mm; oval, width ca. 70% length, sagittally and transversely moderately convex; lateral margins slightly curved. Median body moderately convex (sag. and tr.), suboval, probably slightly less than two-thirds hypostomal length; macula shallow. Posterior lobe narrow, ca. 20% hypostomal length, moderately convex, extending to the medial position of the median lobe; furrow moderately deep, probably extending to anterior margin. Posterior border narrow, ca. 5% hypostomal length, convex; posterior border furrow narrow, moderately deep. These characters suggest that the hypostoma of Shergoldiella vincenti is typical of oryctocephalids, and the two hypostomata are among the few known from non-spinose oryctocephalids. Thorax consists of six to eight segments, widest portion across fourth segment; segments slightly decreasing in width from there, decreasing posteriorly to about 80% width across fourth segment. Axial furrows well defined, shallower next to anterior pleural band. Axial ring with straight, convex (sag. and tr.) median portion and nodular lateral portions in a slightly more anterior position; width of axial rings decreases progressively backward to 80% width of axial ring at first segment. Thoracic pleura moderately wide, length 98–115% of axial width; anterior pleural band of roughly constant width (exsag.); posterior pleural band narrows distally, usually faintly more elevated than anterior pleural band, merged with distal portion of anterior pleural band to form stout, triangularly truncated, posterolaterally
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directed tip. Pleural facets developed at pleurae of segments 1–4 in distal position, all of slightly different size and ventral deflection in dependence of the necessity to overlap with adjacent pleura during enrollment; particularly well developed in segments 1 and 2. Pleurae of segment 1 terminated distally by rearward directed posterior margin of cephalon and therefore slightly posterolaterally directed; pleurae of segment 2 affected by posterolaterally directed pleurae of segment 1 and slightly posterolaterally directed in the anterior part; pleurae of segments 3 almost transverse, pleurae posterior to it projecting progressively posterolaterally. Pygidium relatively large, length 2.7–5.4 mm in the studied specimens; variably subelliptical, length ca. 69–80% width; anterior margin curved moderately posterolaterally. Eight pairs of marginal tips present, creating in dorsal view a sawtooth-like aspect of the lateral margins, all deflected ventrally in a moderate way, decreasing in size rearward and successively more posteriorly projecting; without macropleural segment. Axis composed of six axial rings plus a terminal axial piece, with moderate convexity; moderately tapering, length two-thirds pygidial length, width across anteriormost axial ring one-third total pygidial width across first segment, width at midlength 85–94% width across anteriormost axial ring, width across posteriormost ring 58–53% width across anteriormost axial ring; terminal axial piece very narrow (sag.), developed only as a small transverse lobe. Without postaxial ridge. Axial ring furrows moderately wide and moderately deep medially, deepen to well-incised transverse, slightly curved furrows close to axial furrows. Pleural regions well defined, with low to moderate convexity; divided by five distinct, relatively deep and moderately wide pleural furrows and four shallower and much narrower interpleural furrows, all posterolaterally to slightly posteriorly directed at posterior ends, extending to margin. Anterior and posterior pleural bands merge distally. Sagittal median groove developed posterior to axis, variably developed fairly well impressed and relatively broad in larger specimens. Without defined pygidial border and border furrow. Measurements: Specimens 7.3–16 mm in length in the studied specimens. Cranidial length ranges from 2.6–5.8 mm, maximum cranidial width 5.0–9.8 mm, glabellar length (including occipital ring) 2.4–5.1 mm, maximum glabellar width 1.6–2.5 mm. Pygidial length ranges from 3.0–5.7 mm, maximum pygidial width 4.5–6.9 mm, pygidial axial length 2.1–4.8 mm, maximum pygidial axial width 1.2–2.3 mm. Remarks: Shergoldiella? sequei (Li˜na´ n and Gozalo, 1999), originally described as Tonkinella sequei, and pre-
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viously figured as a specimen of “Hamatolenus (Myopsolenus)? jilocanus” in Li˜na´ n and Gozalo (1986, pl. 5, Fig. 8), has similar characters as Shergoldiella vincenti n. gen., n. sp. The single known, imperfectly preserved pygidium of Shergoldiella? sequei (Li˜na´ n and Gozalo, 1999, Fig. 2) shows weak interpleural furrows and a faint postaxial furrow but in general resembles very much pygidia of Tonkinella. However, it is impossible to identify the precise number of axial rings in this specimen. The single known cranidium is also somewhat distorted and lacks the preglabellar area. The glabella shows a similar pattern of glabellar furrows with S2 und S3 mainly formed by pits rather than displaying more typical short transverse furrows as in Tonkinella (although T. sibirica and T. valida both have glabellar pits). Connecting furrows are not visible but their absence could be a result of preservation. However, the glabella is more club-shaped than in Shergoldiella vincenti with its maximum width across S3 and thus resembling the glabella in Oryctocephalites Resser, 1939, and with an apparently stronger transverse and sagittal convexity. The eye lobes are relatively long (as already emphasized by Li˜na´ n and Gozalo, 1999), with the posterior ends opposite L1 and the anterior anterior ends opposite the middle part of L3. This length is comparable to that in smaller specimens of Shergoldiella vincenti. However, mature individuals have slightly shorter eye lobes with their posterior ends opposite shortly behind S1 so that the postocular area is larger in Shergoldiella vincenti. In addition, it seems that Shergoldiella sequei has broader (tr.) and less curved eye lobes. These characters are regarded herein as more closely resembling Shergoldia than Tonkinella and a sufficiently different from Tonkinella to place to species under the latter genus. Therefore, the species is tentatively placed under Shergoldiella although more and better preserved material may exhibit distinct differences to Shergoldiella vincenti. Occurrence: Cephalopyge notabilis Zone, lower Jbel Wawrmast Formation, Br`eche a` Micmacca Member, Tarhoucht area, eastern Anti-Atlas, Morocco. Acknowledgments Grateful acknowledgment is given for support of field work by the Deutsche Forschungsgemeinschaft (DFG). Tony Vincent (Aberdeen) provided invaluable help, making available part of the described material and collecting detailed information on the Tarhia Track localities. Heiko Sonntag (Hirschburg) provided additional material as permanent loan for this study. Fred Sundberg (Show Low, AZ) and Yuan Jinliang (Nanjing) provided valuable reviews of the manuscript, and I am particularly
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