Fossils from the Azorejo Formation (Lower Cambrian; Central Iberian

Bol. R. Soc. Esp. Hist. Nat., 113, 2019: 43-65

Fossils from the Azorejo Formation (Lower Cambrian, Central Iberian Zone) in the Guadiana river section at Picón, Ciudad Real Fósiles de la Formación Azorejo (Cámbrico Inferior, Zona Centroibérica) en la sección del río Guadiana en Picón, Ciudad Real

Julián Simón López-Villalta Dpto. Biología y Geología IES Peñalba, Calle Molinos de Viento, s/n 13350 Moral de Calatrava, Ciudad Real, Spain [email protected]

Recibido: 31 de julio de 2018. Aceptado: 24 de mayo de 2019. Publicado electrónicamente: 18 de junio de 2019.

Keywords: Astropolichnus, Cambrian radiation, Gondwana, Ichnofossils, Neritic zone, Cambrian Stage 3. Palabras clave: Astropolichnus, Cámbrico Edad 3, Gondwana, Icnofósiles, Radiación cámbrica, Zona nerítica

Abstract During the Stage 3 of the Cambrian, several siliciclastic formations were deposited in a shallow platform that would become part of the Iberian Massif, containing abundant trace fossils and the conspicuous ichnospecies Astropolichnus hispanicus, endemic to southwestern Europe during the regional Ovetian stage. The fossil record of these formations has been explored mainly in northern Spain; in southern Spain, the Azorejo Formation (Azorejo Sandstone) is the only unit of this kind, but its paleobiological content has never been described in detail. In this work, the fossil record of the Azorejo Formation is documented from one of its least known outcrops: the Guadiana river section at Picón, Ciudad Real. In this section, the Azorejo Forma- tion contains a diverse trace fossil record for a neritic environment, comprising Agrichnium?, Astropolichnus hispanicus, Belorhaphe, Bergaueria cf. hemispherica, Cochlichnus, Conichnus conicus, Cruziana, Dimorphichnus, Diplichnites, Diplocraterion, Monocraterion, Monomorphichnus bilinearis, Monomorphichnus lineatus, Monomorphichnus lineatus var. giganticus, Palaeophycus, Palaeophycus cf. imbricatus, Planolites, Psammichnites, Rusophycus avalonensis?, Skolithos, Treptichnus pedum, and trace fossils similar to Nereites and Zoophycos. A structure interpreted as the body fossil of a radial organism is also described. Some of these fossils are firstly cited to the Azorejo Formation and the Lower Cambrian of the Iberian Massif.

Resumen Durante la Edad 3 del Cámbrico, varias formaciones siliciclásticas fueron depositadas en una plataforma somera que habría de convertirse en parte del Macizo Ibérico, conteniendo abundantes pistas fósiles y la icnoespecie Astropolichnus hispanicus, endémica del sudoeste euro- peo durante el piso regional Ovetiense. El registro fósil de estas formaciones ha sido explorado principalmente en el norte de España; en el sur, la Formación Azorejo (Areniscas del Azorejo) es la única unidad de este tipo, pero su contenido paleobiológico nunca ha sido descrito en detalle. En este trabajo, el registro fósil de la Formación Azorejo es documentado para uno de sus afloramientos menos conocidos: la sección del río Guadiana en Picón, Ciudad Real. En él la Formación Azorejo contiene variadas pistas fósiles, incluyendo Agrichnium?, Astropolichnus hispanicus, Belorhaphe, Bergaueria cf. hemispherica, Cochlichnus, Conichnus conicus, Cruziana, Dimorphichnus, Diplichnites, Diplocraterion, Monocraterion, Monomorphichnus bilinearis, Monomorphichnus lineatus, Monomorphichnus lineatus var. giganticus, Palaeophycus, Palaeophycus cf. imbricatus, Planolites, Psam- michnites, Rusophycus avalonensis?, Skolithos, Treptichnus pedum, una pista similar a Nereites y otra a Zoophycos. Se describe una estructura interpretada como el fósil corporal de un organismo radial. Algunos de estos fósiles se citan por primera vez para las Areniscas del Azorejo y el Cámbrico Inferior del Macizo Ibérico.

doi: 10.29077/bol/113/ce06_simon ISSN: 2659-2703 -43- J. Simón López-Villalta

I. Introduction

The rapid evolutionary radiation of animals at the beginning of the Phanerozoic, during the first 20-25 million years of the Cambrian period (the “Cambrian explosion”), represents the unfolding of the main branches of bilateral animals, the rise of abundance of shelly fossils, the transition from the fossil-poor Precambrian to the fossil-rich Pha- nerozoic, and the onset of bioturbation as an important biogeochemical process (Budd & Jensen 2000; Fedonkin et al., 2007; Kouchinsky et al., 2012; Mángano & Buatois, 2016; Seilacher, 2007). Because of all these reasons, the Cambrian radiation could be seen as the most decisive episode in the history of life on Earth second only to the oxygena- tion of the atmosphere by cyanobacteria. Trace fossils are especially important in our understanding of this radiation (Seilacher, 1956; Mángano & Buatois, 2016), because skeletal fossils from the earliest Cambrian tend to be scarce and usually problematic (Kouchinsky et al., 2012) and soft-bodied fossils document only the end of the process (the Chengjiang biota, Guang et al., 2007). Thus the ichnology of the Lower Cambrian has been intensely studied worldwide (Young, 1972; Alpert, 1977; Brasier et al., 1979; Crimes et al., 1977; Liñán et al., 1984; Crimes & Anderson, 1985; Narbonne et al., 1987; Crimes, 1987; Crimes, 1992; Jensen, 1997; see a brief summary in Geyer & Landing, 2016). The Iberian Massif contains wide outcrops of Lower Cambrian sediments that document the Cambrian radiation with skeletal fossils, carbonaceous remains, and especially trace fossils (as a summary, see Liñán et al., 2004). Since the pioneering ichnological monograph of the Lower Cambrian in Spain by Crimes et al. (1977), trace fossils have been reported from many sections but usually focusing on the dominant forms and especially on the very few traces with biostratigraphic value. After decades of this preliminary perspective, a more comprehensive and paleobiological approach to the trace fossil record of the Cambrian radiation in the Iberian Massif would be desirable. The present work, aimed from this point of view, focuses on one of the least known formations of the Lower Cambrian in the Iberian Massif, namely the Azorejo Formation, in one of its least explored outcrops, the Guadiana river section at Picón (Ciudad Real).

1.1. The Azorejo Formation

This formation was defined by San José et al. (1974) in the anticline of the Pusa river (Toledo Mountains), at the southern part of the Central Iberian Zone. There, the Azorejo Formation is a siliciclastic unit, about 550-600 m thick, composed mainly by sandstones, quartz-arenites, graywackes and mudstones; some levels show abundant ripples, bioturbation, or oblique lamination (San José et al., 1974). According to these features, it was deposited in littoral to shallow sublittoral environments (Liñán et al., 2004). San José et al. (1974) considered within the formation six informal subunits that appear in continuity along the Azorejo stream. The Azorejo Formation has an abundant trace fossil record that has never been described in detail. San José et al. (1974) simply noticed the abundance of traces in the unit. A summary of the subsequent progress appears in Table 1. Briefly stated,M oreno et al. (1976) identified, described and illustrated the first traces (Astropolichnus hispanicus, and some “Scolicia” now better interpreted as the lower surface of Psammichnites), in a paper focused mainly on Cruziana stratigraphy of Lower Ordovician beds nearby. Starting from this first work onwards, the Azorejo Formation has never been the main subject of paleontological research in the papers where it has appeared. There are comments about traces of the lower part of the formation in some works dealing with the possible Precambrian—Cambrian transition in the Uso river section (Pusa anticline), but always without illustrations or descriptions (Brasier et al., 1979; Liñán et al. 1984; Palacios, 1989; Gámez Vintaned, 1996; Gámez Vintaned et al., 1995; Gámez Vintaned & Liñán, 2007). The only published images of ichnofossils from the Azorejo Formation after those in Moreno et al. (1976) are Astropolichnus from the Pusa anticline in Jensen et al. (2010) and Astropolichnus, Psammichnites and Oldhamia in a very brief account of new fossil sites attributed to the formation in the Cabañeros National Park (Toledo Mountains) by Gutiérrez-Marco et al. (2010). All these papers depicts an ichnodiversity of about 14 genera (Table 1), which represents a relatively high diversity for a Lower Cambrian formation of the neritic zone –see typical values in Seilacher, 1977, although they cannot be compared directly with the present case. Anyway, this seems to support

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Figure 1. Geological map of the studied area, after the sheet 759 of the MAGNA 50 map (1:50, 000) with some additional measurements of strikes and dips. No stratigraphic column of the Azorejo Forma- tion is provided due to the uncertainty introduced by the presence of large covered stretches in the southern half of the section. The points N1to N9 and S1 to S7 identify sampling localities following a geographic ordination that does not imply any stratigraphic order. CIZ = Central Iberian Zone; the other zones of the Iberian Massif appear in light grey.

the idea by Seilacher (1977) that a modern level of ichnodiversity was achieved in the neritic zone as early as in the Lower Cambrian. The Azorejo Formation is one of the Lower Cambrian formations of the Iberian Massif containing the index trace fossil Astropolichnus hispanicus (Brasier et al., 1979; Liñán et al., 2004), which is very conspicuous in the field and belongs to an ichnogenus restricted to the Stage 3 of the Cambrian (Jensen et al., 2010, 2013; Mángano & Buatois, 2016), that is, approximately 521—514 million years ago according to the Internatio- nal Chronostratigraphic Chart (2018). This stage corresponds to the final part of the Cambrian radiation and contains the first apparition in the fossil record of many ecdi- sozoan lineages (trilobites, bradoriids, lobopodians, palaeoscolecids) and echinoderms (Kouchinsky et al., 2012). In the regional chronology, A. hispanicus is an index fossil of the Ovetian stage, with an upper range in the middle Upper Ovetian (Pillola et al., 1994; Jensen et al., 2010). The age of the Azorejo Formation is probably lower Upper Ovetian, as argued by Jensen et al. (2010) on the basis of their finding of very early trilobites (cf. Abadiella bourgini) and other body fossils in the upper part of the underlying Pusa For- mation in the Toledo Mountains. The Ovetian stage has been tentatively correlated to the Atdabanian stage of the Siberian Platform (Liñán et al., 2004; Perejón, 1984; Perejón & Moreno-Eiris, 2006). 1.2. The Guadiana section in Picón

The Azorejo Formation is not restricted to the central part of the Toledo Moun- tains: southwards there are other outcrops attributed to this formation that have been widely neglected. A section crossed by the Guadiana river near Ciudad Real, at Picón, was assigned to the Azorejo Formation by Portero et al. (1989) on the basis of lithology and trace fossils (Figure 1). This section is in the Picón anticlinorium (Portero et al., 1989) at the southern border of the Toledo Mountains. There are two Cambrian rock units in the anticline according to Portero et al. (1989), who authored the report of the corresponding sheet of the geological map MAGNA 50 (Magna nº 759, Piedrabuena).

Bol. R. Soc. Esp. Hist. Nat., 113, 2019 -45- J. Simón López-Villalta

The oldest unit is dominated by laminar mudstones, its outcrops are very scarce and no fossils have been documented from them. This unit was identified as the uppermost part of the Pusa Formation due to lithology and stratigraphic position (Portero et al., 1989). Above it in the anticline, the Azorejo Formation has an estimated thickness of 700-800 m and consists on banks of dm-thick quartz-arenites and quartzitic sandstones alternating with irregular levels of mudstones, silty sandstones and quartzitic sandstones, with a thickness of cm to dm (Portero et al., 1989). The sedimentary features of the sequence, including abundant ripple marks and hummocky cross bedding, were interpreted as the record of a shallow marine platform subject to storm wave action (Portero et al., 1989). Stratigraphically above the Azorejo Formation, near the Vicario dam there are outcrops of beds with a distinctive lithology and very abundant Skolithos, representing the lowermost record of the Ordovician in the section (Figure 1). Two localities with trace fossils were reported by Gutiérrez-Marco (1986) in the upper part of the Azorejo Formation in the section here studied. In the paleontological report of the geological map nº 759 (Piedrabuena), Gutiérrez-Marco identified the ich- notaxa Diplichnites ichnosp. and Phycodes? ichnosp. from the first locality (sampling point 9104, Figure 1), whereas the second point (9105, Figure 1) yielded Plagiogmus ichnosp., Monomorphichnus lineatus, Palaeophycus ichnosp., Agrichnium? ichnosp., Skolithos ichnosp. and Bifungites? ichnosp. Gutiérrez-Marco (1986) remarked that the presence of Plagiog- mus in the second locality would indicate a Lower Cambrian age. The report contains neither descriptions nor illustrations, and it does not clarify whether the fossils were collected. However, according to the report, the general aspect of the trace fossils, especially the abundant Monomorphichnus, reminds typical sections of the Azorejo For- mation. Apart from these observations from 1986, nothing has been published about the Cambrian materials of the Picón anticlinorium. The objective of the present work is to examine and study in more detail the fossil record of this section.

2. Material and Methods Fossil prospection was carried on along the cliffs and hills surrounding the Gua- diana river valley (Figure 1). Specimens were photographed using a Canon 7D MkII DSLR camera with a standard lens Canon 50mm f1.8 or the macro lenses Canon 100mm f2.8 or Canon 60mm f2.8. Collected specimens are deposited in the Museo de Paleontología de Castilla-La Mancha (Cuenca) under accession codes MPCM-PI-0001 to MPCM-PI-0029.

3. Systematic ichnology An abundant and varied trace fossil record was found in the section, together with a structure interpreted as the body fossil of an organism similar to a sea anemone that will be described in the caption of systematic palaeontology. The following report is focused mainly on ichnogenera, since they are the usual unit in ichnology and their identification tends to be much clearer and objective compared to ichnospecies. Thus, ichnospecies have been identified only when they are very distinctive and the specimens are unambiguous. As a whole, 17 ichnogenera are here documented, containing 5 trace fossils identified at ichnospecies level. Three additional ichnofossils are described in open nomenclature at ichnogenus level.

Ichnogenus Agrichnium? Pfeiffer, 1968 Agrichnium? ichnosp. (Figure 2B) Material: tens of specimens studied in the field. Points N2 and S5. Description: Series of three or more tiny furrows, about 1 mm wide and 4-7 mm long, which are almost side by side, subparallel, sometimes diverging, smooth, and une- qual in length, preserved as positive reliefs in the sole of thin muddy beds. Remarks: These marks cannot be attributed to Monomorphichnus because they are burrows, thus lacking the sharp extremes typical of scratch marks. The subparallel arrangement is consistent and improbable if these burrows were simply Planolites- Palaeophycus specimens. So they seem to be a different trace, resembling Agrichnium (Häntzschel, 1975). Quite common in some levels, this trace probably represents grazing trails, like Agrichnium itself (Häntzschel, 1975). Agrichnium was tentatively identified by Gutiérrez-Marco (1986) in this section, whereas other authors have cited this ichnogenus, with doubts, in the Uso river section (Brasier et al., 1979).

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Figure 2. (A) Palaeophycus cf. imbricatus, point N7. (B) Agrichnium?, point N2. (C) aff. Nereites, MPCM-PI-0007, point S3. (D) Belorhaphe and other traces, point N8. All scale bars = 1 cm.

Ichnogenus Astropolichnus Crimes and Anderson, 1985 Astropolichnus hispanicus Crimes et al., 1977 (Figure 3A) Material: one specimen (MPCM-PI-0002) found loose in the outcrop of point N9. A possible epichnial trace in point N5. Description: Hypichnial cast of a discoidal and flattened structure, with an estimated diameter of approximately 6 cm, having a sharply defined central plug surrounded by a series of radiating lobes separated by thin grooves. A total of approximately 40 segments are inferred, since there are 10 of them in about a quarter of the disc. The specimen is tectonically deformed into an ellipsoidal shape, and broken. Remarks: The specimen is a rather large Astropolichnus and an unusual one, because its central protrusion consists on two plugs which are partially overlapping but slightly displaced. One of them corresponds to the typical plug of the ichnogenus, whereas the other probably records the movement of escape of the organism in response to burial by sediment. This adds a further observation, together with those in Crimes et al. (1977) and Pillola et al. (1994), supporting that Astropolichnus is a trace and not a body fossil. A. hispanicus was interpreted by its describers and reviewers (Crimes et al., 1977; Pemberton et al., 1988; Pillola et al., 1994) as the resting or dwelling trace of a radial polypoid organism with a lifestyle similar to a sand anemone. It is not very frequent but conspicuous in many Lower Cambrian successions in Spain (Pillola et al., 1994; Liñán et al., 2004) and especially in the Azorejo Formation of the Toledo Mountains (Table 1). The ichnospecies is endemic to southwestern Europe and an index fossil of the Ovetian regional stage (Pillola et al., 1994; Jensen et al., 2010, 2013).

Ichnogenus Belorhaphe Fuchs, 1895 Belorhaph eichnosp. (Figure 2D, Figure 4B arrow “Bel”) Material: one specimen studied in the field (point N8) and another in a collected slab (MPCM-PI-0009, point N2). Description: Burrow preserved as positive hyporelief, with a narrow zigzag shape and about 1 mm wide. The specimen in Figure 4B shows a distorted zigzag path. In the

Bol. R. Soc. Esp. Hist. Nat., 113, 2019 -47- J. Simón López-Villalta

Figure 3. Traces of polypoid organisms. (A) Astropolichnus hispanicus MPCM-PI-0002, point N9. (B) Conichnus conicus (arrow Con) and a fragment of a vertical spreiten-burrow (arrow spr), MPCM-PI-0025, point N9. (C) Mass occurrence of Bergaueria cf. hemispherica, point N6. All scale bars = 1 cm. specimen of Figure 2D there are some angles with very short horizontal branches more or less perpendicular to the trace length. Remarks: This ichnogenus is interpreted as a farming trace (graphoglyptid), having at each corner a ventilation shaft that was occasionally preserved as the lateral short branches here noticed (Seilacher, 2007). Since these branches are short and not regular, the ichnogenus Belorhaphe seems better suited instead of Protopaleodictyon (see Seila- cher, 2007). In the compendium by Häntzschel (1975), Belorhaphe is said to be found in flysch deposits from the Cretaceous and early Tertiary, butA lpert (1977) reported the ichnogenus from the Lower Cambrian of the White Inyo Mountains (California) and Gámez Vintaned (1996) cited it, without any description or illustration, from the lowermost Cambrian of the Pusa Formation in the Uso river section (Toledo Moun- tains, Spain). These precedents, and its occurrence in the Guadiana section, mean that

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Figure 4. (A) Cochlichnus, MPCM-PI-0010, point N7. (B) Treptichnus pedum (arrow Tre), Belorhaphe (arrow Bel) and Monomorphichnus bilinearis (arrow Mbi), MPCM-PI-0009, point N2. (C) Monocraterion, MPCM-PI-0029, point N8a. (D) Specimen of Planolites describing a meander, MPCM-PI-0024, point N9. (E) Palaeophycus showing a thick border, point S7. All scale bars = 1 cm.

Bol. R. Soc. Esp. Hist. Nat., 113, 2019 -49- J. Simón López-Villalta

Belorhaphe is an example of trace typical of deep sea environments during most of the Phanerozoic but present in shallow marine settings during the Lower Cambrian (Crimes & Fedonkin, 1994). The maker of Belorhaphe is unknown, but, like other graphoglyptids, it is supposed to have been an animal that cultivated bacteria in the walls of its mucus-lined burrows (Seilacher, 2007). Other graphoglyptids are probably traps for meiobenthos (Uchman, 2003), but in Belorhaphe the presence of lateral ventilation shafts suggests bacterial farming (Seilacher, 1977). A new ichnogenus for the Azorejo Formation (Table 1).

Ichnogenus Bergaueria Prantl, 1945 Bergaueria cf. hemispherica Crimes et al., 1977 (Figure 3C) Material: about twenty specimens concentrated in two slabs studied in the field (point N6), others scattered nearby (point N5) and probably in point N2. Description: Low hemispherical hyporeliefs, semicircular to cylindrical in vertical section, sometimes flattened or deformed, usually crowded. Diameter: 6-20 mm; protruding about 3-5 mm. No ornaments are apparent. Some flattened specimens enter the bed base producing crescent shapes. Remarks: A number of flattened specimens may be better ascribed to B. sucta (Seilacher, 1990), but they appear together with many typical hemispheric forms in the same slab and so they are probably preservational variants of B. hemispherica. Ber- gauerians are usually interpreted as dwelling burrows, or resting traces, of burrowing polypoid animals similar to anemones, but the assertion that the trace maker belonged to Actiniaria (Pemberton et al. 1988) seems unjustified.Bergaueria sucta may be a preservational form related to Nemiana or Beltanelloides (Jensen, 1997). Structures similar to B. sucta can originate from abiotic processes (e.g. pot casts, Seilacher, 2007), but the present bergauerians are interpreted as biogenic because (a) there are neither flute marks nor typical load casts in their beds, and (b) they are accompanied by trace fossils in the same slab, namely the possible hypichnial form of Psammichnites (“Scolicia”). The oldest records of Bergaueria are from the late Ediacaran (Mángano & Buatois, 2016), being the ichnogenus much more frequent in Lower Paleozoic beds than later (Pemberton et al., 1988). It was found in many Lower Cambrian sections of northern Spain by Crimes et al. (1977), in the Iberian chains (Gámez Vintaned, 2007; Schimitz, 1971), and in the Lower Ovetian Pedroche Formation by Gámez Vintaned et al. (2006). Bergaueria is here firstly cited to the Azorejo Formation.

Ichnogenus Cochlichnus Hitchcock, 1858 Cochlichnus ichnosp. (Figure 4A) Material: one slab with two specimens and possible stretches of additional ones (MPCM-PI-0010, point N7). Description: Regularly meandering hypichnial trace, in positive relief, smooth and about 1 mm wide. Remarks: Typical of flysch deposits, but also found in non-marine environments, this ichnogenus is known from the first stage of the Cambrian onwards (Mángano & Buatois, 2016). The tracere minds sinuous locomotion by a nematode-like organism (Seilacher, 2007). In the Lower Cambrian of the Iberian Massif, Cochlichnus has been cited from the Pusa Shale of the Uso river section (Palacios, 1989) and it has been documented in the Pedroche Formation too (Lower Ovetian, Gámez Vintaned et al., 2006). First appearance to the Azorejo Formation (Table 1).

Ichnogenus Conichnus Männil, 1966 Conichnus conicus Männil, 1966 (Figure 3B, arrow Con) Material: a complete specimen collected from very thin silty beds, in point N9 (MPCM- PI-0025). Description: The breakage of the slab allowed the study of this trace in longitudinal and transversal section. It is a plug-shaped, conical lined burrow, with rounded apex and neither ornaments nor internal structures. The specimen is complete, measuring 6 x 11 mm (max. diameter x length), which yields a diameter-to-length ratio of 0.55, relatively close to the mean value of 0.47 obtained by Pemberton et al. (1988) for the ichnogenus. Remarks: The characteristics of this trace point unambiguously to Conichnus. The concentric structures diagnostic of Cylindrichnus are lacking, and the burrow seems too short for that ichnogenus (Häntzschel, 1975). Conichnus is known from the Fortunian onwards (Mángano & Buatois, 2016) - it appears 8.1 m above the GSSP of the Cam-

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Table 1. Data summary of the trace fossil record of the Azorejo Formation. AfterMoreno et al. (1976), Brasier et al. (1979), Liñán et al. (1984), Palacios (1989), Gutiérrez-Marco (1986), Gámez Vintaned (1996), Gámez Vintaned & Liñán(2007), Gutiérrez-Marco et al. (2010), Jensen et al. (2010), Savazzi (2015), and the present work. Sites: (1) Boquerón del Estena (Navas de Estena, point 1 in Moreno et al., 1976) (2) Gévalo river (point 4 in Moreno et al., 1976) (3) Río Uso section, unspecified localities B( rasier et al., 1979; Liñán et al., 1984; Gámez-Vintanted, 1996) (3a) Río Uso section, Baños de la Retortilla locality (point 11 in Gámez Vintaned et al., 1995) (4) Cabañeros, points 3, 4 or 9 (unspecified) inG utiérrez-Marco et al. (2010) (5) Robledillo section, Toledo Mountains (Jensen et al., 2010) (6) Estenilla river section II, Toledo Mountains (Palacios, 1989), detrital beds above the Pusa Formation that would correspond to the Azorejo Formation (7) Guadiana river section in Picón, points 9104 and 9105 in Gutiérrez-Marco (1986) (8) Guadiana river section in Picón, present work.

Trace fossil Type Possible maker Site Agrichnium? or ?Agrichnium grazing trail vermiform animal 3, 7, 8 Allocotichnus? scratch mark trilobites or similar 6 Astropolichnus hispanicus resting trace sand polyp 1, 2, 3, 4, 5, 8 Belorhaphe farming trace vermiform animal 8 Bergaueria cf. hemispherica resting trace sand polyp 8 Bifungites? (probably Diplocraterion) spreiten burrow filter feeder 7 Cochlichnus simple burrow nematode? 8 Conichnus conicus resting trace sand polyp 8 Cruziana (ichnosp. A and ichnosp. B) furrowing trail trilobites or similar 8 Didymaulichnus furrowing trail arthropod or annelid 3 Dimorphichnus grazing trail trilobites or similar 8 Dimorphichnus obliquus grazing trail trilobites or similar 3 Diplichnites walking trail trilobites or similar 3, 4, 6, 8 Diplocraterion spreiten burrow filter feeder 3, 8 Eophyton (tool mark) drag mark sessile organism 3 Gordia looping burrow vermiform animal 3, 6 Monocraterion vertical burrow filter feeder 8 Monomorphichnus bilinearis scratch mark trilobites or similar 8 Monomorphichnus lineatus scratch mark trilobites or similar 3, 4, 7, 8 Monomorphichnus lineatus var. giganticus scratch mark trilobites or similar 8 aff. Nereites two series of lobes uncertain 8 Oldhamia? (may be Agrichnium?) grazing trail vermiform animal 4 Palaeophycus simple burrow vermiform animal 7, 8 Palaeophycus cf. imbricatus simple burrow vermiform animal 8 Phycodes burrow system vermiform animal 3, 3a Phycodes? burrow system vermiform animal 7 Planolites simple burrow vermiform animal 3, 4, 6, 8 Psammichnites (= “Scolicia”, “Plagiogmus”) complex burrow vermiform with 2, 3, 7, 8 snorkel Psammichnites gigas complex burrow vermiform with 4 snorkel Rusophycus resting trace trilobites or similar 3, 3a Rusophycus avalonensis? resting trace trilobites or similar 8 Rusophycus gr. radwanskii resting trace trilobites or similar 3 Skolithos vertical burrow filter feeder 6, 7, 8 Treptichnus pedum burrow system priapulid or similar 8 aff. Zoophycos feeding burrow vermiform animal 8

brian System at Fortune Head (Newfoundland, Canada) (Narbonne et al., 1987). This plug-shaped trace is interpreted as the dwelling burrow or resting trace of a burrowing polypoid animal (a sand anemone implies an unjustified taxonomic affiliation, but see Frey & Howard, 1981; Seilacher, 2007). The specimen here described is a tiny Conichnus according to the size ranges provided by Pemberton et al. (1988) from the study of se-

Bol. R. Soc. Esp. Hist. Nat., 113, 2019 -51- ven specimens only. However, there are modern sand anemones within this size, and they enter the sediment deep enough to originate traces with the observed ratio (e.g. Nematostella vectensis). In the literature consulted there are no reports of Conichnus in the Lower Cambrian of Spain until the present work.

Ichnogenus Cruziana d’Orbigny, 1842 Remarks: Seilacher (1970) grouped Cruziana with the ichnogenus Rusophycus, but most authors maintain them as separate ichnogenera, distinguishing Rusophycus as the stationary version of Cruziana (Crimes et al., 1977; Bromley, 1996), a distinction I apply here. This ichnogenus of bilobed furrows, usually with scratch marks, is generally interpreted as trails of trilobites or similar arthropods, but caution is recommended because other animals can produce Rusophycus-like structures (for example, some annelids; Seilacher, 2007). Cruziana appeared in the Fortunian. In the present work, the ichnogenus is firstly cited to the Azorejo Formation.

Cruziana ichnosp. A (Figure 5B) Material: a single specimen found loose in point 2a (MPCM-PI-0028). Description: Fragment of the cast of a bilobed furrow, approximately 7 cm long and 4.5 cm wide, with gross scratch marks, 3-4 mm wide, forming acute V-angles. Remarks: This weathered specimen lacks diagnostic details. It resembles Cruziana pormensis from the Herrería Formation (northern Spain, see Crimes et al., 1977), a formation with Astropolichnus-bearing levels and so a probable correlate of the Azorejo Formation (Liñán et al., 2004).

Cruziana ichnosp. B (Figure 5C, lower arrow) Material: one specimen in a loose slab (MPCM-PI-0028), from point N7. Description: Bilobed furrowing trail, approximately 1.5 cm wide and 5 cm long, preserved in positive hyporelief. It has a tapering shape, suggesting a rusophyciform origin. There are scratch marks in bundles of uncertain number, forming acute V-angles with the central groove. There is also a narrow external furrow, parallel to the trace and with lobes formed by scratches (arrowed in Figure 5C). Nearby in the slab there are many scratch marks in bundles (upper arrow) and a single furrow with almost parallel scratches. Remarks: This trace shows diagnostic features different from other Cruziana from the Lower Cambrian of the Iberian Massif (Crimes et al., 1977), and so it could represent a new ichnospecies, but more material would be required in order to describe it as such.

Ichnogenus Dimorphichnus Seilacher, 1955 Dimorphichnus ichnosp. (Figure 6A) Material: one specimen in a slab found loose in point N2. Description: A series of subparallel and rather straight scratch marks where the same extreme of at least two of them is associated with tiny, blunt knobs. Remarks: The lack of sigmoidal scratches prevents assignation to D. obliquus Seila- cher, 1955. The ichnogenus probably records the feeding activity of an arthropod that scratched the sea bottom in search of food with legs from one side while it was an- chored to the substrate with legs from the other side, which formed the row of knobs (Seilacher, 1955). The ichnospecies Dimorphichnus obliquus was cited by Gámez Vintaned (1996) in the Azorejo Formation of the Uso river section (Toledo Mountains, Table 1), but the fossil was neither described nor illustrated.

Ichnogenus Diplichnites Dawson, 1873 Diplichnites ichnosp. (Figure 5D) Material: one specimen in the sole of a loose siltstone slab in point N2. Description: Two parallel series of nine short ridges, preserved as positive hyporelief. The entire trace is about 2 cm long and 8 mm wide. The series as well as the ridges are separated by a quite uniform distance, but one of the series has shorter ridges than the other. Remarks: This ichnogenus is probably the walking trace of an arthropod or arthropod-like animal (Seilacher, 2007). Consistent with this, the left series of this specimen shows larger scratches from the center to the upper and lower ends, a feature that suggest the record of two metachronal waves of leg movement. This ichnogenus was previously reported in the Guadiana river section and in the Azorejo Formation of Fossils from the Azorejo Formation

Figure 5. Arthropod-like traces. (A) Monomorphichnus lineatus (lower arrow) and other trace fossils including Palaeo- phycus cf. imbricatus (upper arrow), MPCM-PI-0005, point S2. (B) Cruziana ichnosp. A, point S2a. (C) Cruziana ichnosp. B(lower arrow) and scratch marks (upper arrow), MPCM-PI-0028, point N7. (D) Diplichnites, point N2. All scale bars = 1 cm.

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Figure 6. More arthropod-like traces. (A) Dimorphichnus with other traces, point N2. (B) Monomorphichnus bilinearis showing large scratch marks arranged in pairs, point N2. (C) Monomorphichnus lineatus var. giganticus, point S7. (D) Rusophycus avalonensis?, MPCM-PI-0001, point S7. All scale bars = 1 cm.

the Toledo Mountains (Brasier et al. 1979; Palacios, 1989). Apart from the specimen here illustrated, a row of comma-shaped scratch marks was found loose in point N2 and it seems to be part of a Diplichnites of the same kind described by Crimes et al. (1977, Figure 5-g) for the Herrería Formation.

Ichnogenus Diplocraterion Torell, 1870 Diplocraterion ichnosp. (Figure 7B, 7C) Material: tens of specimens examined in the field, one of them collected (MPCM- PI-0026, point N5), from points S3, N5, N7, and especially N9. Possible specimens are MPCM-PI-0021 and MPCM-PI-0025, both from point N9; the latter may be the lowermost part of a Diplocraterion or a specimen of Teichichnus (Figure 3B arrow spr). Description: Spreiten burrow resembling a U-tube with vertical limbs, usually observed in horizontal section as a dumbbell shape, typically about 2-4 cm long. The spreite can be seen in Figure 7C. A surface in point N9 contains crowded specimens preserved as negative epireliefs and much smaller, about 3-10 mm. Even the biggest specimens of the Guadiana section seem to be shallow, reaching as much as 3-4 cm

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Figure 7. (A) Bed top plenty of Skolithos (isolated burrows) and Diplocraterion (pairs of burrows of similar size and connected with blackish sediment), with some scratch marks (Monomorphichnus lineatus var. giganticus), point N9. (B) Diplocraterion, slab in the wall of the ruins above point N6. (C) Oblique section of a Diplocraterion showing the spreite, point N7. C, Psammichnites preserved in full relief, with a median furrow (arrowed) and very fine transversal striation, MPCM-PI-0003, point N10. D, Psammichnites, “Plagiogmus” form, with sausage-shaped segments (arrow), MPCM-PI-0013, point N4. All scale bars = 1 cm.

deep, according to the thickness of the slabs whose tops show the trace but whose soles do not. Remarks: Very common in some levels (point N9), this is probably the trace that Gutiérrez-Marco (1986) identified tentatively as Bifungites?, but the arrow or fun- gi shape characteristic of the vertical sections of that ichnogenus (Häntzschel, 1975; Seilacher, 2007) has not been observed in the material. Other possible ichnogenera of

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spreiten burrows (Corophioides, Teichichnus, Rhizocorallium) were considered but ruled out due to the characteristics of these traces (Seilacher, 2007). Thus they are better ascribed to Diplocraterion, a trace previously reported from the Azorejo Formation in the Toledo Mountains by Brasier et al. (1979). Diplocraterion can be interpreted as the dwelling burrow of a suspension feeder (Seilacher, 2007), a feeding mode that seems to fit the mass occurrence of the trace in point N9. There are protrusive (Figure 7C) and retrusive examples, being probably protrusive the forms with a clear dumbbell shape (Goldring, 1962). This ichnogenus first appeared in Cambrian Stage 2, according to Mángano & Buatois (2016), being an example of the radiation of traces attributable to suspension feeders that these authors proposed to have occurred during that stage.

Ichnogenus Monocraterion Torell, 1870 Monocraterion ichnosp. (Figure 4C) Material: a single specimen in a loose slab from point N8a (MPCM-PI-0029). A structure observed in point N5, similar to a small Tiernavia tiernae (Fedonkin et al., 1985), was probably the cast of a Monocraterion crater. Description: Elliptical, crater-like concave epirelief, flattened, about 1.5-2 cm wide and approximately 3 mm deep. At the bottom there is the filled opening of a cylindrical tube, about 4 mm wide. Remarks: The trace fits the diagnosis of Monocraterion in Häntzschel (1975) and resembles Lower Cambrian specimens illustrated by Crimes et al. (1977) from the upper part of the Herrería Formation. The main differences between Monocraterion and Sko- lithos are the funnel of the former and the usual occurrence in large numbers and close proximity of the latter, being Monocraterion specimens much more isolated and separated in their bedding planes (Häntzschel, 1975; Crimes et al., 1977). Distinguishing with confidence one ichnogenera from the other could be impossible when only a section of the tube is preserved, which is not the present case. Monocraterion has been interpreted as the dwelling burrow of a gregarious suspension feeder, probably vermiform (Häntzs- chel, 1975). This ichnogenus is here cited for the first time in the Azorejo Formation.

Ichnogenus Monomorphichnus Crimes, 1970 Remarks: This ichnogenus was originally assigned to “series of straight or slightly sigmoidal ridges sometimes repeated laterally and produced by a number of clawed limbs” (Crimes, 1970). It differs from Dimorphichnus in the absence of a series of blunt marks associated to the scratches and suggesting lateral progression of the animal, but Seilacher (2007) interpreted Monomorphichnus as a preservational variant of Diplichni- tes, or Dimorphichnus, implying undertrace deficiency. Leaving these uncertainties apart, Monomorphichnus is one of the commonest traces found in the Guadiana river section, as previously noticed by Gutiérrez-Marco (1986). These scratch marks were initially interpreted by Crimes (1970) as the trace of trilobites caught in a current and raking the sediment surface, but if they are preservational variants of Dimorphichnus, as Seilacher thought, then they should be considered as walking or grazing traces of trilobites, or trilobite-like animals. Considering the high phylogenetic diversity of arthropods during the Lower Cambrian, other makers apart from trilobites deserve consideration, at least in some instances.

Monomorphichnus bilinearis Crimes, 1970 (Figure 6B, Figure 4B arrow Mbi) Material: tens of specimens studied in the field, one of them collected (MPCM- PI-0009, point N2). Description: A series of scratches arranged in pairs, preserved as positive hyporeliefs. They are slightly curved and each pair tends to converge towards one extreme, sometimes originating a fork or hairpin with very acute V-angle. Usually there are about 4-7 pairs of scratches, with individual ones being approximately 1 to 5 cm long or more. Remarks: These traces are clearly the ichnospecies described by Crimes (1970). In the field it was observed that some of them continue into series of single scratches, thus linking M. bilinearis to M. lineatus. The ichnospecies M. bilinearis seems to be new for the Azorejo Formation as well as for the Lower Cambrian of the Iberian Massif.

Monomorphichnus lineatus Crimes et al., 1977 (Figure 5A arrow Mli) Material: collected specimens in a fine sandstone slab (MPCM-PI-0005, point S2), and many tens observed in the field.Points N2, N5, N6, N7a, N8, N9, S1, S2, S2a and S7.

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Description: Isolated series of scratch marks, straight to sigmoidal, appearing as ridges in hyporelief. There are as much as 7 scratches per series. The largest marks in each set are about 1-3 cm long. Remarks: This is probably the most frequent trace fossil in the Guadiana section. Crimes et al. (1977) defined the ichnospecies from beds slightly above a level withAstropolichnus in the Herrería Formation, being thus correlatable to the Azorejo Formation (Liñán et al., 2004). The material observed in the Guadiana section is virtually identical to the original description and illustrations of this ichnospecies. An abiotic origin is untenable for the material observed since the specimens follow different directions and no flow marks (flutes, etc.) are present in the slabs. M. lineatus was previously reported for the Azorejo Formation in the Toledo Mountains and the Guadiana river section (Brasier et al., 1979; Gutiérrez-Marco, 1986).

Monomorphichnus lineatus var. giganticus Crimes et al., 1977 (Figure 6C) Material: about ten specimens observed in the field, one of them collected (MPCM- PI-0018, point N2). Points N2, N7, N8 and S7. Description: A gigantic version of the typical M. lineatus, with individual scratches reaching about 6-8 cm long - some specimens probably more than 10 cm. A spacing of approximately 1 cm or more is common. The number of scratches usually ranges from 4 to 6 per series. Remarks: This trace was originally described by Crimes et al. (1977) from material of Astropolichnus-bearing levels of the Cándana Formation (northern Spain), being thus correlatable to the Azorejo Formation (Liñán et al., 2004). A body length estimate of about 25 cm is reasonable according to usual trilobite proportions and leg numbers, the same value provided by Crimes et al. (1977) in the original description of this ichno- variety. Not reported before to the Azorejo Formation.

Ichnogenus aff. Nereites Quatrefages, 1849 (Figure 2C) Material: Two collected specimens in a loose siltstone slab (MPCM-PI-0007) from point S2, and another specimen, much smaller, observed in the field in point N7. Description: Two series of almond-shaped hypichnial lobes, about 3 mm wide and up to 6 mm long, forming a trail, preserved as positive relief. In Figure 5C, the specimen in the left has a straight border out of the lobes, forming a ribbon-shaped structure that contains the two series of lobes. The specimen in the right lacks any border and has only one row of lobes adequately preserved, so its structure is less clear. Remarks: The presence of two series of lobes reminds the ichnogenus Nereites (Häntzschel, 1975; Seilacher, 2007), but no similar traces have been found in the literature of the Lower Cambrian in the Iberian Massif or elsewhere. In the absence of more revealing specimens, this fossil is published in open nomenclature and no ethological interpretation is attempted.

Ichnogenus Palaeophycus Hall, 1847 Remarks: Lined burrows, usually horizontal and relatively straight, with an infill not different from the surrounding rock, according to Pemberton & Frey (1982), who interpreted Palaeophycus as the burrows of suspension feeders or predators. The first compelling specimens of the ichnogenus are from the Late Ediacaran (Mángano & Bua- tois, 2016). It was cited by Gutiérrez-Marco (1986) in the Guadiana river section, but, in most cases, the burrows observed in the section could not be identified asPalaeophycus or Planolites, due to the lack of clear diagnostic features.

Palaeophycus ichnosp. (Figure 4E) Material: Two specimens studied in the field, the first one in a slab with Monomor- phichnus lineatus var. giganticus from point S7, and the second in a bed top at point S5. Description: Thick lined burrow preserved in full relief, approximately 1 cm wide. The lining is approximately 1-2 mm in thickness. The infill does not seem to be different from the surrounding sediment. Remarks: The presence of a thick lining suggests the ichnospecies P. heberti (Sapor- ta, 1872) or P. tubularis (Hall, 1847), according to the keys by Pemberton & Frey (1982). Since the distinction of both species seems subtle and few well preserved specimens have been found in the section, no ichnospecies is here assigned.

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Palaeophycus cf. imbricatus Torell, 1870 (Figure 2A, Figure 5A upper arrow) = Halopoa imbricata Torell, 1870 Material: on especimen found in a loose boulder at point N5, and other from a loose slab with Monomorphichnus lineatus and other traces (MPCM-PI-0005), from point N2. Description: The specimen of Figure 5A is a bilobed burrow, about 5 mm wide, with rather irregular surface. It follows a quite straight path and is preserved as a full relief in a bed sole. The specimen in Figure 2A (upper arrow) is a small lined burrow with a seemingly bilobed core, straight, about 3.5 mm wide, and preserved as positive hyporelief. Remarks: This kind of trace resembles Didymaulichnus but they are burrows in full-relief instead of furrows in semirelief. According to Jensen (1997), Palaeophycus imbricatus is here used as the right synonym for Halopoa imbricata (Torell, 1870), which he interprets as a Palaeophycus-type burrow. In the Guadiana section, the scarcity of specimens of this kind recommends publishing them in open nomenclature until more revealing material is found. It would be a new ichnospecies for the Azorejo Formation.

Ichnogenus Planolites Nicholson, 1873 Planolites ichnosp. (Figure 4D, 8D) Material: many tens of specimens studied in the field, one of them collected (MPCM-PI-0024, point N9). Points N5, N7, N9, S2 and S6. Description: Burrows of varied width, about 1-10 mm wide, unlined, smooth, usually straight and quite horizontal but sometimes sinuous. They have a clearly different infill compared to the surrounding rock. Found as positive hyporeliefs or full reliefs. Sometimes the burrows are quite tortuous and with a small vertical component in their path (MPCM-PI-0024, Figure 4D), which is anyway compatible with the ichnogenus according to Pemberton & Frey(1982). Remarks: This ichnogenus of unlined and quite indistinct burrows, characterized by an infill different from the surrounding rock, was interpreted by Pemberton & Frey (1982) as the traces of sediment feeders. Although it is usually cited as one of the oldest ichnogenera, ranging from the late Ediacaran, the first apparition date of compelling Planolites is Cambrian (Fortunian) according to the recent review by Mángano & Bua- tois (2016). It was previously cited in the Azorejo Formation of the Toledo Mountains (Brasier et al., 1979; Palacios, 1989), but in the Guadiana section it is a new ichnogenus. Although some specimens may be ascribed to P. montanus (Nicholson, 1873) and others resemble P. beverleyensis (Billings, 1862), no ichnospecies is assigned to the material due to the lack of consistent and clearly defined typologies in the fossils. The specimen of Figure 8C describes meanders that remind the ichnogenus Helminthopsis, but the presence of some abrupt changes in the direction of the trace and the lack of more revealing material showing meanders suggests it could be an unusual array of curved Planolites.

Ichnogenus Psammichnites Torell, 1870 Psammichnites ichnosp. (Figs. 7D, 7E and 8A) Material: two collected specimens: MPCM-PI-0003 from point N10, and MPCM- PI-0013 from point N4; three specimens observed in the field in points N6, N7 and N8a. Description: The specimen MPCM-PI-0003 (Figure 7D) is a Psammichnites preserved in full relief. It is gently curved and about 6.5 mm wide, showing an infill different from the surrounding rock, very fine transversal striation (visible with lateral light), and a tiny bilobed ridge extending along the middle part of the burrow (arrowed), representing the trace of the siphon; it is very similar to the Psammichnites illustrated in Häntzschel (1975: pp. W100, Figure 2C). The lower surface of Psammichnites is very probably present in the section, in the form of burrows 5-10 mm wide, preserved in positive hyporelief and showing a surface with gross transversal, crescent-shaped striation (Figure 8A). Another preservational variant of Psammichnites, the “Plagiogmus” form, is exemplified by the specimen MPCM-PI-0013 (Figure 7E). This trace, with lateral light, reveals a poorly preserved structure resembling a ribbon-like trail that contains a longitudinal row of sausage-shaped segments (arrow in Figure 7E). Remarks: The Psammichnites organism is hypothesized to be a vermiform animal similar to a mollusk (may be a halkieriid), which bulldozed the sediment, creating a mucus-lined burrow with meniscate backfill, while it cropped food from the seafloor using a siphon that originated the dorsal furrow of the trace (Seilacher & Gámez Vin- taned, 1996; Seilacher, 2007). Psammichnites is a typical trace of the Lower Cambrian

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Figure 8. (A) Psammichnites, “Scolicia” form, hypichnial burrow with transversal, crescent grooves, point N8a. (B) aff. Zoophycos, point N9. (C) Meandering burrow, may be Planolites, point N7. (C) Planolites, point S7. All scale bars = 1 cm.

(Mángano & Buatois, 2014). This complex burrow has many different ichnological ex- pressions, which could difficult its identification, but the specimen MPCM-PI-0003 is unambiguously a Psammichnites according to the emended diagnosis by Mángano et al. (2002). The probable examples of the lower surface of this ichnogenus are very similar to the traces called Scolicia by Moreno et al. (1976: fig. 3f) in the Azorejo Formation of the Toledo Mountains, whereas Brasier et al. (1979) cited Scolicia and Psammichnites from the same formation and zone. The “Plagiogmus” form was reported from the Guadiana river section by Gutiérrez-Marco (1986).

Ichnogenus Rusophycus Hall, 1852 Rusophycus avalonensis? Crimes & Anderson, 1985 (Figure 6D) Material: one specimen (MPCM-PI-0001) in a loose boulder fallen from the cliffs of the western side of the road CM-412, point S7. Description: Short, bilobed, convex hyporelief with a slight tapering shape, showing at least 3 scratch marks in one lobe. The scratches are oblique to the median line, forming a contact that points to wider extreme of the trace. Maximum width and length are 5.5 and 4.8 cm, respectively. Remarks: The characteristics and size of the specimen reminds Rusophycus avalonensis according to the diagnosis and illustrations by Crimes & Anderson (1985), but

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the scratch marks are not clear enough to sustain identification as this ichnospecies. In the original description of the ichnospecies, the authors indicate that it corresponds to the resting trace of Cruziana fasciculata and that the holotype comes from the Herrería Formation, whose upper part can be correlated to the Azorejo Formation (Liñán et al., 2004). In this last formation, Rusophycus has been cited for the Uso section only (Liñán et al., 1984; Gámez Vintaned, 1996).

Ichnogenus Skolithos Haldemann, 1840 Skolithos ichnosp. (Figure 7A) Material: some specimens observed in the field in points N3 and N9; the slab MPCM-PI-0022 (point N3) is a surface with many of these traces. Description: Vertical burrows of cylindrical shape, unlined and with a diameter of about 2-5 mm. Their length is difficult to estimate because they are usually preserved as transversal sections in bed surfaces. A shallow depth of about 1-2 cm is consistent with the disappearance of the burrows from one side to the other in slabs only a few cm thick. Sometimes the burrows are crowded, with many tubes separated by about 1-3 cm. Remarks: The lack of well preserved specimens recommends no ichnospecies assignation, but according to the monography by Alpert (1974) these burrows may be Skolithos verticalis. Some specimens in vertical section seem to widen towards their upper end, but the difference in diameter is very slight, so it cannot be taken as the funnel typical of Monocraterion (Crimes et al., 1977). Shallow Skolithos were previously reported from the Azorejo Formation in the Toledo Mountains (Palacios, 1989) and in the Guadiana river section (Gutiérrez-Marco, 1986). Skolithos first appeared during the Lower Cambrian, in Stage 2 according to Mángano & Buatois (2016). In his review of the ichnogenus, Alpert (1974) interpreted Skolithos as dwelling burrows of animals such as phoronids or annelids.

Ichnogenus Treptichnus Miller, 1889 Treptichnus pedum Seilacher, 1955 (Figure 4B arrow Tre) Material: one collected slab with Belorhaphe and Monomorphichnus bilinearis (MPCM-PI-0009, point N2). Description: A series of short burrows, or segments of burrows, preserved as positive hyporeliefs along a sinuous line, with little angular divergence between consecutive burrows. They are about 1 mm wide and 4 mm long. Remarks: A main burrow is inferred to have connected the series of burrows here preserved. The low divergence angle between consecutive burrows is compatible with the ichnospecies T. pedum, according to the drawings by Seilacher (2007) – see Jensen (1997) for other ichnospecies of Treptichnus from late Lower Cambrian silici- clastics. This complex burrow system, whose first appearance almost coincides with the beginning of the Phanerozoic eon (Geyer & Landing, 2016), is a series of feeding probes excavated by infaunal animals that were very probably stem-group priapulids or priapulid-like worms (Vannier et al., 2001). According to the considerations detailed in Jensen (1997), the ichnospecies T. pedum has preference over Phycodes pedum. The ichnogenus Phycodes was previously cited for the Azorejo Formation (Gámez Vintaned et al., 1995; Gámez Vintaned, 1996), but not “Phycodes” pedum. In the Guadiana section, Gutiérrez-Marco (1986) reports the presence of Phycodes?.

Ichnofossil A – aff. Zoophycos Massalongo, 1855 (Figure 8B) Material: one specimen in a slab from a bed top in point N9, studied in the field. Description: A predominantly horizontal burrow, approximately 4 cm long, with a wide, lobe-shaped bottom that passes more or less gradually into a narrower neck, preserved as negative epirelief. A blackish, muddy structure exists in one border of the bottom suggesting the remains of a spreite. Remarks: The overall shape of the trace and the possible remains of a spreite suggest a trace similar to Zoophycos, but much simpler. This ichnogenus is usually interpreted as a feeding burrow and tends to occur in fine sediments containing abundant nutritional particles (Seilacher, 2007). Zoophycos first appeared in Cambrian Stage 3, according to Mángano & Buatois (2016). It is typical of the fine sediments deposited at about the bathyal zone, but it can also be found elsewhere (Seilacher, 2007). Thus something similar to this trace could be present in the Azorejo Formation, as this speci-

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men testifies. Anyway, the ichnofossil here described is new to this formation and to the Lower Cambrian of the Iberian Massif.

4. Systematic paleontology Phylum Cnidaria? Hatschek, 1888 (Figure 9A, 9B) Material: One collected specimen in a slab from point S1(MPCM-PI-0027). Description: Bag-shaped, approximately hemispherical object protruding from the bed sole. Its height is about half its width, with a maximum of 1.3 cm (from the slab base) x 3 cm, respectively. The bag is slightly squashed laterally, its surface is rough, and it is surrounded by some vermiform traces. The fossil has in the other side a set of more or less radial grooves around a central mound slightly displaced from the bag axis. Out of the radial marks there are two curved thin grooves like stretches of a cir- cumference, defining a diameter of about 4.5 cm. Remarks: The possibility that this object is the preserved crater of a Monocrate- rion is ruled out due to the lack of any hint of a vertical tube, a feature that cannot be attributed to a preservational defect. The characteristics of this fossil make sense only as the result of differential sinking of sediment during the decay of a buried radial organism, being other hypotheses not compelling. Thus the entire structure is here interpreted as the body fossil of a polyp-like animal whose upper part was displaced by the sediment avalanche that buried it, moving the future impressions of the oral part away from the bag-shaped cast of the body base. According to the number of grooves observed, approximately 16 mesenteria are inferred. The bag resembles the trace fossil Bergaueria hemispherica rather than Cambrian body fossils interpreted as radial organisms (e.g. Astropolichnus, Cordubia, Protolyellia, or Tiernavia), so it may be the fossil of a Bergaueria-maker.

Figure 9. Structure interpreted as the body fossil of an organism similar to a sand anemone, MPCM-PI-0027, point S1. (A) Top view showing radial marks. (B) Bottom view with the body bag. Scale bars = 1 cm.

5. Discussion The trace fossil record here described is quite typical for an Astropolichnus-bearin- gformation from the Iberian Massif. For example, it shares with the Herrería Formation the presence of Astropolichnus hispanicus, Bergaueria, Cruziana, Diplichnites, Diplocrate- rion, Monocraterion, “Plagiogmus”, Planolites, Rusophycus, Skolithos, and the peculiarity of comma-shaped Diplichnites (Crimes et al., 1977; Liñán et al., 2004). Monomorphichnus lineatus var. giganticus establishes a similarity with the Cándana Formation (Crimes et al., 1977), which seems to be the only other unit in the Iberian Massif where this giant scratch mark has been documented. With that formation, the Guadiana section shares the occurrence of Astropolichnus hispanicus, Bergaueria, Cochlichnus, Diplocraterion, Mono-

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morphichnus lineatus, Planolites, Rusophycus, Treptichnus pedum (as “Phycodes” pedum), and Skolithos (Crimes et al., 1977; Liñán et al., 2004). The present work adds to the paleobiological record of the Lower Cambrian in the Iberian Massif the ichnofossils Conichnus conicus, Cruziana ichnosp. B, Monomor- phichnus bilinearis, the traces here described as aff. Nereites and aff. Zoophycos, and the bag-shaped body fossil of Figure 9. Apart from them, Belorhaphe, Bergaueria, Cruziana, Monocraterion and Monomorphichnus lineatus var. giganticus are firstly cited to the Azo- rejo Formation. All these novelties mean that more sampling effort is required in order to obtain a reasonably accurate picture of the paleontological heritage of this and other pre-Ordovician units from the area of the Toledo Mountains. The complex burrow Trep- tichnus pedum could be new to the formation but it may have been described in earlier reports as the ichnogenus Phycodes. According to its ichnofossil content (Table 1), the Azorejo Formation seems to be considerably diverse for a unit deposited in a shallow marine environment. This fits the idea that typical Phanerozoic levels of ichnodiversity were achieved in neritic settings at the end of the Cambrian radiation (Seilacher, 1977; Mángano & Buatois, 2016). However, there were distinguishing features in Lower Cambrian trace fossils compared to the rest of the Phanerozoic. One of the most outstanding of them is the presence of farming traces (graphoglyptids) in shallow depths, whereas these “bacterial farms” or “microbenthos traps” are typical of deep-water environments during the rest of the Phanerozoic (Crimes & Fedonkin, 1994). The finding of Belorhaphe in the Guadiana section is an example of this difference. The frequency of traces of polypoid organisms is another peculiarity of the earliest trace fossil record, mainly during the Cambrian and Ordovician (Pemberton et al. 1988; Mángano & Buatois, 2016). In the Guadiana section, this feature is exemplified by the occurrence ofAstropolichnus, Bergaueria and Conichnus. Other traces of the section are examples of an important ecological change that happened during the Cambrian radiation, namely the assembly of communities with suspension feeders for the first time in Cambrian Stage 2, which is the first apparition date (FAD) of Diplocraterion and Skolithos (Mángano & Buatois, 2016). Exclusive to Stage 3 is Astropolichnus, and Monocraterion first appeared in this last interval of the Cambrian radiation (Mángano & Buatois, 2016). The remaining ichnogenera here identified have Fortunian FADs with the exception of Bergaueria, Palaeophycus and Treptichnus, whose first compelling occurrences are of Ediacaran age M( ángano & Buatois, 2016). An interesting approach to the evolution of trace fossils during the Cambrian radiation is to examine the composition of the assemblages at different times in terms of the FADs of their ichnogenera (Mángano & Buatois, 2016). From this scope, the trace fossil record of the Azorejo Formation in the Guadiana section is composed mainly by ichnogenera of Fortunian origin combined with minor contributions of traces that first appeared earlier or later in the geological record. Therefore, it can be seen as an ecological and evolutionary relict of the very beginning of the Cambrian radiation, with the expansion of suspension feeding being the only relevant novelty added to a basically Fortunian structure of arthropod-like marks and sediment feeders. This quite relict nature may not be surprising when we consider that most ichnogenera from shallow environments in the Phanerozoic first appeared in the Cambrian (Crimes, 1974), which means that strong conservatism is a general feature in the realm of trace fossils. In the Guadiana section, as well as in the Azorejo Formation as a whole, and similar formations, we would be watching this trend extended into the Lower Cambrian. In this way, the main ecological structure of the trace fossils from the neritic zone during the Phanerozoic may be the memory of a pattern that was largely set by the Cambrian radiation (Crimes, 1974). This kind of perspective to the trace fossil record of the Cam- brian radiation would deserve further examination.

Acknowledgements To Mª José Merino Espinosa for her assistance, encouragement, and help in the field; to Rodolfo Gozalo for his comments, and to the reviewers of this work. The specimens have been collected with permission from the heritage section of the Junta de Comunidades de Castilla-La Mancha (Exp. 170814-P1), under the project “Prospección de fósiles en rocas del Precámbrico y Cámbrico de Ciudad Real”.

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