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Atopidae (Trilobita) in the Upper Marianian (Cambrian Series 2, Stage 4) of Iberia

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Atopidae (Trilobita) in the Upper Marianian (Cambrian Series 2, Stage 4) of Iberia Journal of Paleontology, 95(1), 2021, p. 123–132 Copyright © The Author(s), 2020. Published by Cambridge University Press on behalf of The Paleontological Society 0022-3360/21/1937-2337 doi: 10.1017/jpa.2020.71 Atopidae (Trilobita) in the upper Marianian (Cambrian Series 2, Stage 4) of Iberia Luis Collantes,1 Eduardo Mayoral,1,2 Eladio Liñán,3 and Rodolfo Gozalo4 1Departamento de Ciencias de la Tierra, Facultad de Ciencias Experimentales, Campus de El Carmen, Universidad de Huelva, Avda. 3 de Marzo, s/n, 21071 Huelva, Spain <[email protected]><[email protected]> 2CCTH—Centro de Investigación Científico Tecnológico, Universidad de Huelva, Avda. 3 de Marzo, s/n, 21071 Huelva, Spain 3Departamento de Ciencias de la Tierra, Facultad de Ciencias-Instituto de Ciencias Ambientales (IUCA), Universidad de Zaragoza, 50009 Zaragoza, Spain <[email protected]> 4Departamento de Botánica y Geología, Universitat de València, Dr. Moliner 50, 46100 Burjassot, Spain <[email protected]> Abstract.—New atopid trilobites are described from the early Cambrian Cumbres beds and Herrerías shale of northern Huelva Province (Andalusia, Spain) and are dated as middle–late Marianian (Cambrian Series 2, Stage 4). New speci- mens of Atops calanus Richter and Richter, 1941 are described and the Laurentian species Pseudatops reticulatus (Wal- cott, 1890b) is recognized for the first time in the Mediterranean subprovince. The associated trilobite assemblage studied herein suggests an age close to the base of Cambrian Stage 4. Introduction In the Cumbres block (Cumbres Cubeta), the siliciclastic Atopidae Hupé, 1954 is a little investigated trilobite family sandstones and shales of the Cumbres beds (350–1100 m) are based on Atops Emmons, 1844. Family membership has had a dated as middle–late Marianian, based on the trilobites Delga- long and contentious history (Howell and Stubblefield, 1950) della Walcott, 1912, Hicksia Delgado, 1904, Rinconia Hupé, and constituent genera were regularly included in the Conocor- 1953, and Triangulaspis Lermontova, 1940 in the lower part yphidae based on their secondary blindness; this assignment and Serrodiscus Richter and Richter, 1941 and Triangulaspis continued beyond Hupe’s(1954) erection of the family (Harrin- in the upper part (Liñán and Mergl, 1982; Liñán et al., 2002). gton et al., 1959; Korobov, 1973; Jell et al., 1992). In Spain, this The Cumbres fossil site (CU1) is located in the upper Cumbres genus was doubtfully recognized by Richter and Richter (1941) beds (Collantes et al., 2020). The 24-m section at CU1 is as Atops? calanus Richter and Richter, 1941 in the ‘Fauna von between 38°02′45.74′′N, 006°43′07.40′′W and 38° Cala’ from Huelva, and that occurrence has been cited by 02′43.90′′N, 006°43′07.80′′W. Atopid trilobites occur 17, 19, Lotze (1958, 1961) and Sdzuy (1961, 1962). Herein, we and 20 m from the base in association with Serrodiscus silesius describe several cranidia and fragments that enable positive Richter and Richter, 1941, Calodiscus ibericus Sdzuy, 1962, assignment to Atops. Triangulaspis fusca Sdzuy, 1962, Hicksia? sp. indet., Marocella Pseudatops Lake, 1940 is described for the first time in the morenensis (Yochelson and Gil Cid, 1984), brachiopods, and Iberian Peninsula, with recognition of the Taconic North Ameri- hyoliths. can species Pseudatops reticulatus (Walcott, 1890b). Its pres- In the Herrerías block (Herrerías Cubeta), the Herrerías ence allows biostratigraphic and paleobiogeographic shale (200–500 m) (Schneider in Richter and Richter, 1941) correlations with other Avalonian and Taconic localities. consists of purple shales with spilitic intercalations and has an age ranging from middle to late Marianian, based on Delga- Geological setting della, Rinconia, Atops, Gigantopygus Hupé, 1953, Hicksia, Protaldonaia Sdzuy, 1961, Sdzuyomia Lieberman, 2001, and The trilobites were collected in northern Huelva Province, Strenuaeva Richter and Richter, 1940 in the lower part and southwestern Spain (Fig. 1), in the Sierra de Aracena y Picos Serrodiscus, Calodiscus Howell, 1935, and Triangulaspis in de Aroche Natural Park. Cambrian rocks of the Ossa-Morena the upper part (Richter and Richter, 1941; Sdzuy, 1962; Zone are placed in distintict belts or ‘blocks’—named ‘Cubetas’ Ruiz López et al., 1979; Liñán and Mergl, 1982). The El in Spanish—with a notable change of facies and thickness, most Pozuelo fossil site (POZ1) is in the upper level Herrerías shale likely related to downthrow and tilting along an active growth with Serrodiscus silesius, C. ibericus, Protaldonaia morenica fault at the time of sediment deposition (Liñán and Quesada, Sdzuy, 1961, Delgadella sp. indet., Strenuaeva sp. indet., 1990)(Fig. 1). Marocella morenensis, and brachiopods. Base and top of The stratigraphy of the different Cambrian blocks in nor- the 48-m section at the collecting site are at 37°58′59.17′′N, thern Huelva has been little studied. Only early Cambrian for- 006°24′18.92′′W and 37°58′56.90′′N, 006°24′19.93′′W, respect- mations have been established (Collantes et al., 2020) ively, with atopid trilobites 7 and 9 m from the base (Collantes although not formally defined. et al., 2020). 123 Downloaded from https://www.cambridge.org/core. Universidad de Zaragoza, on 16 Feb 2021 at 08:59:14, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/jpa.2020.71 124 Journal of Paleontology 95(1):123–132 Figure 1. Geological setting of fossil sites in the Cambrian Cubetas (fault-bounded blocks) of the Ossa-Morena Zone, with white stars indicating the positionsof the studied fossil sites in each Cubeta. 1 = Cumbres de San Bartolomé site (CU1); 2 = Arroyomolinos de León site (AM1-2); 3 = El Pozuelo site (POZ1). Modified from Liñán and Quesada (1990). In the Arroyomolinos block (Arroyomolinos Cubeta), the Systematic paleontology Herrerías shale (300–400 m) includes purple, gray, and green shales, with metric intercalations of acid volcanic tuffs and spi- Class Trilobita Walch, 1771 lites. Base and top of the 65-m section at the AM1 collecting site Order uncertain are at 38°00′49.58′′N, 006°44′47.27′′W and 38°00′57.50′′N, Family Atopidae Hupé, 1954 006°24′50.14′′W, respectively. Pseudatops reticulatus occurs with Serrodiscus silesius 46 m from the base. The AM2 section Included genera.—Atops Emmons, 1844 (=Ivshiniellus ′ ′′ ′ ′′ (37°59 15.90 N, 006°21 17.95 W) is no longer accessible. Korobov, 1966), Pseudatops Lake, 1940, and Atopina Korobov, 1966. Materials and methods Diagnosis.—See Cotton (2001, p. 185, 186). The available material consists of isolated cranidia preserved as internal and external molds in purple shales with limonitic min- Remarks.—Cotton (2001) carried out a systematic review and a eralization. Most of the studied specimens are deformed and/or phylogenetic proposal of several blind ptychoparid trilobites, fragmented. which had been previously included in Conocoryphidae, concluding that it was a polyphyletic group. Within that Repositories and institutional abbreviations.—Figured review, he amended the diagnosis of Atopidae, which he specimens are housed in the Department of Earth Sciences included within the superfamily Ellipsocephaloidea. Given the (Laboratory of Tectonics and Paleontology) of the Faculty of classification problems, Adrain (2011) proposed not to assign Experimental Sciences, University of Huelva (UHU). Other it to any order until a complete revision of the trilobite basal cited repositories are: SMF = Senckenberg Museum, Frankfurt, groups was carried out. Germany; USNM = Smithsonian Institution, National Museum Jell et al. (1992) included Ivshiniellus nikolai Korobov, of Natural History, Washington, DC. 1966, I. patulus Korobov, 1966, and I. briandailyi Jenkins Downloaded from https://www.cambridge.org/core. Universidad de Zaragoza, on 16 Feb 2021 at 08:59:14, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/jpa.2020.71 Collantes et al.—Atopidae in the upper Marianian of Iberia 125 and Hasenohr, 1989 in Atops. Cotton (2001) pointed out that in 1961 Atops? calanus; Lotze, p. 164. I. briandailyi, the tapering of the glabella represented in their 1961 Atops? calanus; Sdzuy, p. 230. reconstruction (Jenkins and Hasenohr, 1989, fig. 4) is not matched 1962 Atops? calanus; Sdzuy, p. 212, pl. 23, figs. 14, ?15, 16. by that of the specimens, and the species closely resembles the 2018 Atops sp. cf. calanus; Collantes et al., p. 567, fig. 4.7. other Australian species, Atops rupertensis Jell, Jago, and Gehling, 1992. We accept that Ivshiniellus is a junior subjective synonym of Holotype.—SMF X 1227. Atops as proposed by Jell et al. (1992) and Cotton (2001). Jell et al. (1992) suggested that Atopina could be a junior Emended diagnosis.—Atops with long, conical, tapered synonym of Pseudatops, arguing that Atopina was erected glabella, subtle ridge between anterior border furrow and based on distorted material, in which diagnostic differences preglabellar furrow. Glabella extends to marginal border compared to Pseudatops are due to tectonic distortion. The holo- furrow, giving rise to a preglabellar area laterally. Anterior type of the type species Atopina antiqua Korobov, 1966 (figured border upturned, slightly convex anteriorly. Prominent occular by Korobov, 1973, pl. 12, fig. 5) shows several characters that ridge running laterally from frontal lobe. Suture cutting the resemble Pseudatops. However, the phylogenetic analysis car- gena close to the lateral furrow. ried out by Cotton (2001, figs. 2, 3) shows that Atopina is closer to Atops than to Pseudatops. Therefore, we prefer to keep Ato- Occurrence.—The new specimens come from the upper part of pina as a separate genus, pending better-preserved specimens. Cumbres beds and Herrerías shale, late Marianian (Cambrian Several conocoryphids from the Sekwi Formation, Mac- Stage 4). Richter and Richter (1941) cited Atops? calanus in kenzie Mountains, Canada (Fritz, 1973) have been moved to their horizon cbM2/cbM3, which corresponds with the Atops (Jell et al., 1992; Cotton, 2001) based on their blindness, uppermost middle Marianian.
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