© The Author(s) 2023. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits use, copy, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source. The rhynchonellide genus Cyclothyris M’Coy, 1844, is well represented in the Cretaceous of Europe (e.g., Owen, 1988). Nevertheless, the correct taxonomical classification, and therefore the stratigraphical range and the geographical distribution, of asymmetrical Upper Cretaceous species of Cyclothyris was very confusing until a few years ago, when the asymmetric forms of this genus were updated. This was the result of an intensive revision of numerous specimens of Cyclothyris stored in historical collections from Europe and Northern Africa (e.g., d’Orbigny and Coquand Col- lections, among others) and also the description of new species (Berrocal-Casero, 2020; Berrocal-Casero et al., 2020a, 2020b). For this previous research, it was essential to distinguish between the terms proposed by Fürsich and Palmer (1984) as ‘facultative’ type of asym- metry of the anterior commissure, in which the individ- uals of the same species can develop both symmetric and asymmetric shells [e.g., the Cenomanian Cyclo- thyris difformis (Valenciennes in Lamarck, 1819)], from Spanish Journal of Palaeontology 38, 2023 https://doi.org/10.7203/sjp.26294 Sociedad Española de Paleontología ISSN 2255-0550 / eISSN 2660-9568 OPEN ACCESS RESEARCH PAPER A new asymmetric rhynchonellide from the Cretaceous of the Eastern Prebetic (South- eastern Spain) Un nuevo rinconélido asimétrico del Cretácico del Prebético oriental (Sureste de España) Mélani BERROCAL-CASERO , José Francisco BAEZA-CARRATALÁ & Fernando GARCÍA JORAL Abstract: The external and internal features and the microstructure of the asymmetric rhynchonellides from the Albian–Cenomanian (Cretaceous) transition from the Alicante Province (Eastern Prebetic, Southeastern Spain) have been herein studied. Previous authors placed these rhynchonellides in Cyclothyris difformis, consequently attributing an unquestionable Cenomanian age (Upper Cretaceous) to the deposits in which they appear. The long dorsally concave crura and the leptinoid pattern microstructure of the shell confirm their attribution to the genus Cyclothyris. However, among other diagnostic criteria (e.g., ribbing pattern, relative width), C. difformis shows facultative type of asymmetry; while the forms studied here show obligate asymmetry. Therefore, the new species Cyclothyris ementitum sp. nov. is formally described, being characterized by the biconvexity of its shell, its obligate type of asymmetry and an ornamentation of around 25 ribs on each valve. Thus, the study and revision of these rhynchonellides has contributed to updating the record and distribution of the asymmetric Cretaceous rhynchonellides of the genus Cyclothyris. This work opens a new line of research to better understand the biostratigraphical calibration of the Cretaceous sediments from the Eastern Prebetic, and a new insight into the possible origin of the obligate asymmetry present in C. ementitum. Resumen: Se han estudiado las características externas, internas y la microestructura de los rinconélidos asimétricos de la transición Albiense–Cenomaniense (Cretácico) de la Provincia de Alicante (Prebético Oriental, Sureste de España). Autores anteriores clasifica- ron estos rinconélidos como Cyclothyris difformis, atribuyendo, por tanto, una edad Ceno- maniense (Cretácico Superior) a los materiales en los que aparecen. Las cruras largas y dorsalmente cóncavas, así como el patrón leptinoide de la microestructura de la concha confirman su atribución al género Cyclothyris. Sin embargo, entre otras características (densidad de costulación o anchura relativa), C. difformis muestra un tipo de asimetría facultativa, mientras que las formas aquí estudiadas presentan un tipo de asimetría obli- gada. Por tanto, se ha descrito la nueva especie Cyclotyris ementitum sp. nov., caracteri- zada por la biconvexidad de su concha, su tipo de asimetría obligada y por presentar alre- dedor de 25 costillas en cada valva. Este estudio ha contribuido a actualizar el registro y distribución de los rinconélidos asimétricos del género Cyclothyris. Esta investigación abre nuevas posibilidades para realizar estudios bioestratigráficos con el fin de afinar la edad de los materiales cretácicos del Prebético Oriental, así como una nueva línea de investigación para descubrir el posible origen de la asimetría obligada presente en C. ementitum. Received: 5 December 2022 Accepted: 28 February 2023 Published: 28 March 2023 Corresponding author: Mélani Berrocal-Casero melani.berrocal@ucm.es Keywords: Brachiopods Systematic palaeontology Cretaceous Cyclothyris Obligate asymmetry Spain Palabras-clave: Braquiópodos Paleontología Sistemática Cretácico Cyclothyris Asimetría obligada España INTRODUCTION http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0002-7215-213X https://orcid.org/0000-0002-3366-6090 https://orcid.org/0000-0001-6594-4561 mailto:melani.berrocal%40ucm.es?subject= https://sepaleontologia.es/spanish-journal-palaeontology/ Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 20232 an ‘obligate’ type of asymmetry, where all individuals of the same species display asymmetric shells [e.g., the Santonian–Campanian Cyclothyris globata (Arnaud, 1877)]. Although the systematics, distribution and questions related with the evolution of the asymmetry of the Upper Cretaceous asymmetric Cyclothyris were recently studied and updated, the knowledge about the asymmetric forms from the Lower Cretaceous is cur- rently less known. Cretaceous asymmetrical rhynchonellides from the External Betic Zones (Southeastern Spain) have been traditionally attributed to Cyclothyris difformis due to the presence of commissural asymmetry (Iñesta & Calzada, 1996; Iñesta, 1999; Mora-Morote, 2000). A recent revision of the Prebetic asymmetrical stock sug- gested that the attribution of these forms to C. difformis is not cogent (Berrocal-Casero et al., 2020b). Actually, the nominal species C. difformis has been commonly misinterpreted over the last several decades, as stated by previous authors (e.g., Owen, 1962, 1988; Gaspard, 1997; Motchurova-Dekova, 1995, 1997; Gaspard & Charbonnier, 2020; Berrocal-Casero et al., 2020a, 2020b). In this paper, asymmetric rhynchonellides from the genus Cyclothyris from the Albian–Cenomanian tran- sition of the Eastern Prebetic have been studied and compared with all known asymmetric species of Cyclo- thyris (specially with C. difformis), leading to the defini- tion of the new species Cyclothyris ementitum. GEOLOGICAL AND GEOGRAPHICAL SETTING Several localities in the Alicante Province, SE Spain (Fig. 1), containing asymmetrical brachiopods from the Albian–Cenomanian transition have been revised either by new sampling or from an assessment of selected literature. These localities are integrated in the Eastern Prebetic Domain (Vera et al., 2004) of the External Betic Zone. During the Cretaceous, the Eastern Prebetic was characterized by carbonate and mixed carbonate-siliciclastic shallow-water platform successions with environments ranging from tidal to outer platform, up to hemipelagic settings basinwards (Vilas et al., 2002; Vera et al., 2004). Based on structural and palaeogeographical sub- divisions (Arias et al., 2004) all the studied localities (except for the Moraig Cave; Fig. 1A) are located within the Aspe-Jijona-Alicante Domain of the Internal Preb- etic (Fig. 1B). In this domain, Jurassic–Cretaceous sediments correspond to pelagic/hemipelagic marls and marly limestone sequences, mainly cropping out in anticline structures, the synclines being better represented by Paleogene–Lower Miocene deposits (Martín-Chivelet et al., 2002). The prevailing orienta- tion of these structures is concurrent with the regional SW-NE Betic alignment (Vera et al., 2004). Depositional environment of the asymmetrical bra- chiopod-bearing sediments in the Eastern Prebetic The hemipelagic deposits from the Albian–Cenoma- nian transition in the Eastern Prebetic are mainly repre- sented by monotonous successions of marl and marly carbonate alternations (Leret et al., 1976). A concise description of the depositional framework and litho- stratigraphy of the Albian–Cenomanian transition is summarized for each locality where asymmetrical rhy- nchonellides are recorded in this timespan: Casa Costera outcrop (Monforte del Cid). The southernmost occurrences of asymmetrical Cyclothyris in the Alicante province are included in the diverse bra- chiopod assemblage previously reported near Novelda village (Fig. 1), attributed to the latest Albian by Azéma (1977) and to the Cenomanian by Iñesta and Calzada (1996). They are recorded in marly sediments (about 45 m thick) with yellowish burrowed calcarenite inter- calated with bioclastic limestone horizons. Towards the top of this outcrop, limestone beds become more massive and thick-bedded. Together with brachiopods, scarce echinoids are recorded, and occasional orbito- linids can be found in some sandy levels. This classical locality has almost totally disappeared today due to the uncontrolled collecting of fossils and farming activities. Sierra del Cid outcrops (Petrer). Several outcrops are located in the Sierra del Cid, nearby Petrer village (Fig. 1). A detailed bed by bed sampling and strati- graphical analysis has been carried out in this area due to the good exposure of the sediments and the pro- lific brachiopods, enabling analysis of their distribution and faunal successions. Brachiopod-bearing levels in the Sierra del Cid consist of a marly succession with alternating limestone-marly limestone beds. The basal part of these outcrops is dominated by marly limestone; marls dominate the middle-upper part; and a sporadic increase in carbonate content is observed towards the top of the outcrops. These facies were deposited in an external mixed platform environment (Vera et al., 2004). Palomaret-Rincón Bello outcrops (Petrer). The outcrops around Palomaret-Rincón Bello (Fig. 1) are attributed to the early? Cenomanian (Leret et al., 1976; Iñesta & Calzada, 1996; Mora-Morote, 2000). Asym- metrical brachiopods occur in a marl/sandy marlstone succession about 50 m thick. The record of brachio- pods in sandy levels is more frequent at this locality and the sediments consist of ochre to greenish bioc- alcarenite with fragments of brachiopods, echinoids, scarce bivalves, crinoid ossicles, and sponge spicules. These deposits typify a platform environment with fre- quent terrigenous input (Leret et al., 1976). SE Xixona outcrop. The occurrence of asymmetrical Cyclothyris in this area could only be substantiated in previous reports by Gallemí et al. (1997). These authors established the Albian–Cenomanian boundary Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 2023 3 included in an alternating yellowish marl/marly lime- stone unit with predominant calcareous marls. This unit starts with a basal bed with ammonites, bivalves, echi- noids, brachiopods, and abundant microfauna, and, just overlying this horizon, asymmetric Cyclothyris are recorded in the same mainly marly succession. The depositional environment corresponds to transitional areas between external platforms and more pelagic environments. Sierra del Sabinar outcrop (Sant Vicent del Ras- peig). The Upper Albian–Lower Cenomanian facies in this area are represented by a basal marly succession with carbonate and sandstone beds intercalated; a middle part where asymmetrical Cyclothyris especially occurs, with predominant marl-sandy limestone levels. The uppermost sediments are represented by rhythmic intercalations of carbonate and marly levels with abun- dant echinoids and calcarenite beds with orbitolinids. The depositional environment is interpreted as subsid- ing external platform areas where shallower intratidal facies linked to horsts were developed (Leret et al., 1976). Figure 1. A, Geographical distribution of the localities where asymmetrical rhynchonellides were collected and revised: 1, Sierra del Cid, 2, El Palomaret-Rincón Bello, 3, Casa Costera, 4, Sierra del Sabinar, 5, Xixona, 6, Moraig Cave; B, geological frame- work of these localities among the different regional Prebetic domains (Eastern Betic Range). Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 20234 Moraig Cave outcrop (Benitatxell). Difficult access to this outcrop has not allowed the construction of a detailed lithostratigraphical framework for the occur- rence of asymmetrical Cyclothyris from this area, as the specimens were sampled by professional divers in a submarine cave (picked up from the cave rocks) (Moraig Cave; Fig. 1). The surface lithostratigraphical units that crop out in the Sierra de Llorençà (where this site is located) correspond to the Sácaras, Jumilla, and Caliza de Jaén formations (Castro, 1998) spanning the lower Albian–Cenomanian interval. In this cave, these formations are displaced by a regional fault (Falla del Moraig) placing them in the submerged downfaulted block. Bearing in mind the regional vertical fault dis- placement (several hundred meters; Alfaro et al., 2004), the position where specimens were sampled (in a gallery 800 m from the cave entrance), and the presence of a greyish marly matrix filling the samples, it is possible that they are derived from the uppermost lithostratigraphical units (i.e., Late Albian–earliest Cen- omanian in age) deposited in this area in open external platforms to hemipelagic environments. MATERIAL AND METHODS For the present research, numerous well-preserved specimens of Cyclothyris ementitum sp. nov. from dif- ferent localities of Alicante (Eastern Prebetic, South- eastern Spain) housed at the Universidad de Alicante (UA) have been studied. Fieldwork to collect these specimens has been carried out mainly in the Represa Formation (Van Veen, 1969) in several outcrops such as Sierra del Cid, El Palomaret-Rincón Bello, Sierra del Sabinar, and the Moraig Cave (Fig. 1) from which the specimens herein have been collected. Besides studying their external and internal features, these brachiopods have been compared with other Upper Cretaceous rhynchonellides. Asymmetrical rep- resentatives of Cyclothyris M’Coy, 1844, were exam- ined from different European historical collections by MBC (see Berrocal-Casero et al., 2020a, 2020b). Specimens of Cyclothyris housed in the Owen Collec- tion (1962–1988) and undescribed representatives of Cyclothyris difformis (Valenciennes in Lamarck, 1819) and Cyclothyris globata (Arnaud, 1877) were examined at the Natural History Museum (NHM, London, UK). Material from the d’Orbigny Collection (1847–1851) contains the types of Cyclothyris? contorta (d’Or- bigny, 1847) and Rhynchonella difformis d’Orbigny, 1847, were reviewed at the Muséum National d’His- toire Naturelle (MNHN, Paris, France). Specimens of Cyclothyris globata (Arnaud, 1877) were examined in the Arnaud Collection at the Université Pierre et Marie Curie VI (UPMC, Paris, France) and in the Radulović/ Motchurova-Dekova collection (Radulović & Motchuro- va-Dekova, 2002; Radoičić et al., 2010) at the Univer- zitet u Beogradu, Rudarsko–Geološki Fakultet (RGF, Belgrade, Serbia). Additionally, Rhynchonella claudi- cans Coquand, 1879, R. globata, and R. vesicularis Coquand, 1860, were reviewed in the Coquand Col- lection (1860, 1862, 1879) at the Magyar Bányászati és Földtani Szolgálat (MBFS, Budapest, Hungary). In the Česká Geologická Služba (CGS, Prague, Czech Republic), the types of Cyclothyris zahalkai Nekvasilová, 1973 and specimens of C. aff. difformis in the Nekvasilová Collection (1973) were examined. The Natsionalen Prirodonauchen Muzey Sofia (NPMS, Sofia, Bulgaria) was visited to review specimens classi- fied as Rhynchonella compressa Lamarck var. difformis d’Orbigny, 1847, from the Tzankov Collection and as C. difformis from the Cenomanian of Beloslav (Northeast- ern Bulgaria) revised by Motchurova-Dekova (1995) and included in the Jolkičev Collection (undetermined years; see Berrocal-Casero et al., 2020b, annex 1). In this paper, some Cenomanian specimens of Cyclo- thyris difformis from England, housed at the Natural History Museum, belonging to the Owen Collection have been figured to make a better comparison with C. ementitum. Some of them comprise specimens pre- viously figured by Owen from Le Havre, Normandy, France (the type area) (specimen NHM.BB.41433), and from the Lower Chalk of the White Hart Sandpit, Wilmington, Devon, England (specimen BB41433). Other specimens in this collection from the latter area have been figured here for the first time (reference numbers NHMBF79–NHMBF97). The descriptive terminology applied in this paper for external and internal features follows Manceñido et al. (2002, 2007). Measures include: total length (L), total width (W), and total thickness (T) of the shell, and the height of the “step” of the frontal commissure (SH). The number of ribs (R) in each valve has also been counted. The coefficient (C) corresponds to the ratio R/W. To study the internal features, serial transverse sec- tions have been taken following the method proposed by Steward and Taylor (1965, p. 224–232), and ace- tate peels have been prepared. A Scanning Electron Microscope (SEM) examination of shell microstruc- ture of some acetate peels has also been performed. The peels were coated with gold using a Cressington sputter coater 108 AUTO, and then examined with a SEM JEOL JSM-IT500 scanning electron microscope at the Centro de Asistencia a la Investigación of the Universidad de Alcalá (UAH, Madrid, Spain). The microstructure of the secondary layer of the shell has been used as an additional taxonomic criterion follow- ing Motchurova-Dekova (2001) and Manceñido and Motchurova-Dekova (2010). The thickness of the sec- ondary layer and fibres have been measured close to the plane of symmetry. The long axis of the cross-sec- tion, parallel to the shell surface, is the width (wf) of the fibre. The short axis is the thickness (tf) of the fibre. The coefficient (cf) is the ratio wf/tf. Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 2023 5 SYSTEMATIC PALAEONTOLOGY Phylum BRACHIOPODA Duméril, 1806 Class RHYNCHONELLATA Williams, Carlson, Brun- ton, Holmer & Popov, 1996 Order RHYNCHONELLIDA Kuhn, 1949 Subfamily CYCLOTHYRINAE Makridin, 1955 Genus Cyclothyris M’Coy, 1844 Type-species. Cyclothyris latissima (Sowerby, 1829). Upper Aptian, United Kingdom. Cyclothyris ementitum sp. nov. Figures 2–3 1996 Cyclothyris difformis (Valenciennes in Lamarck, 1819); Iñesta & Calzada, p. 21, pl. 1, text-fig. 2. 1999 Cyclothyris difformis (Lamarck, 1819); Iñesta, p. 18, pl. 3, text-fig. 1. 2000 Cyclothyris difformis (Valenciennes in Lamarck, 1819); Mora-Morote, p. 47, pl. 1, text-fig. 2. Etymology. From the Latin [ementitum]: “who utters false auspices”, because of the prolific former attribu- tions of this species to Cyclothyris difformis by previ- ous authors, assigning a Cenomanian age to its occur- rence. Material and dimensions. (Figs. 2–3 and Tab. 1). 108 specimens from the Eastern Prebetic, Spain. Holo- type specimen SC1003 from Sierra del Cid (Fig. 2A). Paratypes, specimens SC2001 (Fig. 2B) and SC215 (Fig. 2C) from Sierra del Cid. Specimens CM.1 (Fig. 2D) from the Moraig Cave, MU.21 (Fig. 2E), and MU.221 (Fig. 2F) from the Palomaret-Rincón Bello area, PR.Cd.1998.1 (Fig. 2G) and SA.Cd.1 (Fig. 2H) from Sierra del Sabinar outcrop. The types and serial sections are deposited in the collections of the Depar- tamento de Ciencias de la Tierra y del Medio Ambiente, Universidad de Alicante (UA, Alicante, Spain). Diagnosis. Medium to large-sized equibiconvex rhyn- chonellides. The anterior commissure is asymmetric, showing a “step” in the middle that displaces the two halves of the shell dorso-ventrally. Shell with about 25 ribs on each valve. The crura are long and of canali- form type, dorsally concave. Description. External morphology (Fig. 2). Medium to large-sized (up to 30 mm in length) equibiconvex shells, with thickness about 3/4 of the length, oval to subtriangular in dorsal outline. Maximum width located in the anterior half of the shell. Maximum thickness located at midlength. The beak is erect, prominent, with a hypothyrid circular foramen (cyclothyrid foramen; i.e., deltidial plates protrude into a short tube around the pedicle foramen) (Fig. 2, A4). Well-defined interarea. The lateral commissure is straight to sinuous. Shell twisted anteriorly, with asymmetrical anterior com- missure showing a “step” between the two halves of the shell, that are displaced dorso-ventrally. The shell bears approximately 25 strong ribs on each valve, rounded to slightly sharp. Internal morphology (Fig. 3). Pedicle collar well-devel- oped (Fig. 3A, section 0.8; Fig. 3B) with thick conjunct deltidial plates. Dental plates are thin and subparallel, delimiting relatively narrow umbonal cavities (Fig. 3A, sections 1.6-2.3). Teeth massive, quadrate, crenulated and slightly recurved laterally, inserted in crenulated sockets (Fig. 3A, section 3.9, 3C). Lateral denticula and accessory sockets are well developed. The dor- sal median septum is revealed as a very low ridge. The hinge plates are short, wide and slightly ventrally inclined (section at 3.7 mm from the apex) becoming subhorizontal (section at 3.9 mm). The crura are long and canaliform in type, dorsally concave (Fig. 3A, sec- tion 5.7-6.2; Fig. 3E). Shell microstructure (Fig. 3F–3I). The secondary fibrous layer is 750 μm thick. Two main sublayers can be differentiated (Fig. 3F–3G). The thickness of the external sublayer is 302 μm thick, whereas the interior sublayer is 450 μm thick. The fibres show a rhomboi- dal to anvil form in cross section, being rhomboidal to anvil-like shape and more isometric towards the exte- rior part of the shell and mainly anvil like shaped and more anisometric towards the interior of the shell (Fig. 3G–3I). The fibres have been measured from the more isometric sublayer, being up to 40 µm wide (wf) and about 14 µm thick (tf) (cf = 2.85). Discussion. Cyclothyris M’Coy, 1844 is characterized by the presence of deltidial plates completely surround- ing the foramen (cyclothyrid foramen) and well-defined interarea. Regarding the internal structure, long canali- form crura with dorsal concavity are diagnostic criteria for the genus, as well as the typical low dorsal median septum and the subparallel dental plates (Owen, 1962, 1988; Manceñido et al., 2002). The shell microstructure of Cyclothyris ementitum sp. nov. shows a leptinoid pattern of the secondary layer, linked to crura from the raducal group (Radulović et al., 2007, fig. 7; Manceñido & Motchurova-Dekova, 2010, fig. 13). Usually, several packages of fibres can be differentiated in Cyclothyris (Motchurova-Dekova, 2001, p. 323, fig. 2), being char- acterized by the presence of anisometric anvil-shaped Specimen L (mm) W (mm) SH (mm) R C SC1003 30.58 30.48 10.3 28 0.91 SC2001 30.91 30.9 6.5 28 0.90 SC215 20.69 20.62 5.8 28 1.35 CM.1 30.39 30.62 9.8 24 0.78 MU.21 20.59 20.61 3 27 1.31 MU.221 40.1 30.83 5.8 27 0.87 PR.Cd.1998.1 30.98 30.71 7.8 20 0.65 SA.Cd.1 20.59 20.61 3 27 1.31 Table 1. Cyclothyris ementitum sp. nov., from the Albian–Cen- omanian transition of several localities from the Alicante prov- ince (Eastern Prebetic, Spain). Holotype specimen SC1003 from Sierra del Cid. Paratypes, specimens SC2001 and SC215 from Sierra del Cid. Specimens CM.1 from the Moraig Cave, MU.21, and MU.221 from the Palomaret-Rincón Bello area, PR.Cd.1998.1 and SA.Cd.1 from Sierra del Sabinar outcrop. Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 20236 Figure 2. Cyclothyris ementitum sp. nov., from the Albian–Cenomanian transition of several localities from the Alicante province (Eastern Prebetic, Spain). A, Holotype specimen SC1003 from Sierra del Cid; B, paratypes, specimens SC2001; C, SC215 from Sierra del Cid; D, specimen CM.1 from the Moraig Cave; E, specimen MU.21; F, specimen MU.221 from the Palomaret-Rincón Bello area; G, PR.Cd.1998.1; H, SA.Cd.1 from Sierra del Sabinar outcrop. Numbers indicate the views: dorsal (1), lateral (2), anterior (3), detail of the foramen (4); scale bars = 1 cm, except for A4, for which the scale corresponds to 0.5 cm. Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 2023 7 Figure 3. Cyclothyris ementitum sp. nov., from the Albian–Cenomanian transition of Sierra del Cid, Alicante (Eastern Prebetic, Spain). A, Serial sections of specimen SC1521; scale bar = 1 mm; B, acetate peel at 0.8 mm from the apex, in which the pedicle collar is observed; C, acetate peel at 3.5 mm from the apex, showing the teeth and crenulated sockets; D, acetate peel at 5 mm from the apex, showing the crural bases; E, acetate peel at 6.2 mm from the apex, showing the typical canaliform crura of Cyclothyris; scale bars for B–E = 1 mm; F–I, microstructure of the secondary layer of the shell; F–G, details of the secondary layer at two different magnifications, showing sublayers; H, detailed view of the more internal sublayer with anvil-like shaped fibres. I, detail of the more external sublayer with rhomboidal to anvil-like shaped fibres. Abbreviations: sl, secondary layer; scale bars = 500 µm for F, 100 µm for G, and 50 µm for H and I. Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 20238 (to rarely rhomboidal) fibres (Motchurova-Dekova, 2001, p. 327, tab. 1). Therefore, microstructural anal- ysis performed in C. ementitum appropriately corre- sponds to the typical Cyclothyris shell microstructure. Cyclothyris ementitum sp. nov. is similar to Cyclothy- ris regularis (Leymerie, 1869), from the Lower Cre- taceous of Southeastern France, since both species show asymmetry on their anterior commissure, but the Figure 4. Cyclothyris difformis (Valenciennes in Lamarck, 1819) from the Cenomanian of France and United Kingdom. A, Spec- imen NHM.BB.41433, from Le Havre, Normandy, France; B, specimens NHM.BB41433; C, NHMBF96; D, NHM.BB15294; E, NHMBF97; F, NHMBF79; G, NHMBF80; H, NHMBF81 from Wilmington, Devon, United Kingdom. Views: (1) dorsal view; (2) lateral view; (3) anterior view; (4) detail of the foramen; scale bars = 1 cm. Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 2023 9 type of asymmetry in C. regularis is facultative (only some specimens from the same species show asym- metry), while C. ementitum shows obligate asymmetry (all specimens from the same species are asymmet- rical). The holotype of C. regularis (Leymerie, 1869, p. 315, pl. 3, fig. 6a, 6b), labeled as specimen MHNT. PAL.2017.0.10 from Vimport, Pech de Foix, nord (Ph. Fauré, pers. commun., 2022) is wider, and shows a much greater number of ribs on each valve (45) if com- pared to C. ementitum. Cyclothyris parvula (Leymerie, 1869) can be included as a constituent of this asym- metrical stock and regarded as synonym of C. regularis (Ph. Fauré, pers. commun., 2022). Viera and Calzada (1991) figured asymmetric rhynchonellides classified as C. regularis from the Lower Albian of Aitzgorri Mas- sif (Guipuzcoa, Northern Spain). Although is not clear if these specimens show facultative or obligate asym- metry, they show 50 ribs, differing considerably form C. ementitum in showing double number of ribs. The new species C. ementitum has been customar- ily assigned to Cyclothyris difformis (Valenciennes in Lamarck, 1819) in the Prebetic Domain (Iñesta & Calzada, 1996; Iñesta, 1999; Mora-Morote, 2000). Nevertheless, a recent revision of the Upper Creta- ceous asymmetric rhynchonellides questioned this (Berrocal-Casero et al., 2020b). If compared to C. dif- formis (Fig. 4) from the Cenomanian of England and northwestern France, the Prebetic rhynchonellides are more biconvex, significantly less wide; the variability of their anterior commissure does not correspond to the asymmetry pattern of C. difformis (obligate asymme- try in C. ementitum vs facultative asymmetry in C. dif- formis) and their shell is ornamented with a considera- bly lower number of ribs (about 25 ribs in C. ementitum and 40 in C. difformis) (Figs. 2 and 4). According to Iñesta and Calzada (1996), these asym- metrical forms from Alicante are very similar in number of ribs to the specimen NHMB–M.61466 (Cyclothyris dimidiata=Cyclothyris difformis) figured by Owen (1962; pl. 4, fig. 2a–2c) and classified as an extreme variant of C. difformis or a pathological form. In this sense, the validity of the species C. dimidiata, included in the syn- onymy of C. difformis by Owen (1962), was discussed by Iñesta and Calzada (1996), considering a possible attribution to it of the asymmetric specimens from Ali- cante. However, C. dimidiata is represented by just one specimen from the Cenomanian of Halldown, South- east Devon, a locality where C. difformis has been intensively collected and studied (Owen, 1988). A revi- sion of the material of C. difformis housed at the NHM including hundreds of specimens of C. difformis from Devon (specimens labelled NHMBF79 to NHMBF97 and NHM.B.AQPAL2016110.1; see Berrocal-Casero et al., 2020b, annex 1) led to conclude that C. dimidiata is an extreme variant among the high intraspecific var- iability of C. difformis. Additionally, there are no reports of brachiopods with obligate asymmetry in the Creta- ceous of the United Kingdom, so in any case, C. emen- titum cannot be related to any known British asymmet- ric species. The specimens from the lower Cenomanian of Iran classified as C. difformis by Arab (2010) and Binaz- adeh (2017) show the shell surface ornamented with 20–25 costae on each valve. Since the number of ribs is an important feature of the species, its attribution to C. difformis is questionable (see Berrocal-Casero et al., 2020b). This discrepancy has also been noted by Binazadeh (op. cit.). These asymmetric Cyclothyris from Iran are similar to C. ementitum in the number of ribs; however, the forms from Iran show facultative asymmetry (see Binazadeh, 2017, p. 341) and their shell is less globose. Cyclothyris ementitum also differs from Cyclothyris nekvasilovae (Berrocal-Casero et al., 2020b, fig. 2d–2f), from the Cenomanian of Prédboj, Czech Republic, from Cyclothyris zahalkai Nekvasilova, 1973, from the Turo- nian of the Czech Republic (Nekvasilová, 1973, figs. 17, 18, 20a–20b, 20d, 21e; pl. 5, figs. 1–2; pl. 7, figs. 3–4; pl. 11, figs. 1–4; pl. 5, fig. 1; Berrocal-Casero et al., 2020b, fig. 2j–2o); and from Cyclothyris claudicans (Coquand, 1879), from the Santonian of La Cadiére, France (Coquand, 1879, p. 214; Berrocal-Casero et al., 2020b, fig. 2v–2x), mainly because these three species show facultative asymmetry. Concerning other Upper Cretaceous Cyclothyris with obligate type of asymmetry [Cyclothyris cardiatelia Berrocal-Casero, 2020, from the Coniacian of North- ern Spain; Cyclothyris globata (Arnaud, 1877) from the basal Campanian of Southwestern France; and Cyclothyris vesicularis (Coquand, 1879), from the upper Campanian of France], all of them are different in age and show clear differences when compared to C. ementitum. In Cyclothyris cardiatelia, the ante- rior commissure shows a “step” dividing the shell into two unequally developed lobes, one larger than the other, and the beak is usually hooked towards the lobe of shorter length (Berrocal-Casero et al., 2020a, figs. 9–10; 2020b, figs. 2s–2u). Cyclothyris globata is con- siderably smaller than C. ementitum, with a character- istic globose shell showing a more convex dorsal valve than the ventral one, and the lateral commissure has a well-developed squama–glotta (Arnaud, 1877, p. 83, pl. 8, figs. 33–38; Berrocal-Casero et al., 2020b, fig. 2y–2d’). Finally, Cyclothyris vesicularis is much wider than C. ementitum and it shows two well-differentiated lobes, considerably staggered, with a characteristic ‘S’-shaped anterior commissure and ornamentation consisting of 50–70 very fine ribs (Coquand, 1860, p. 122; Berrocal-Casero et al., 2020b, fig. 2e’–2j’). Occurrence. Uppermost Albian–lowermost Cenoma- nian of the Eastern Prebetic (Southeastern Spain). Most of the specimens have been recorded in the Represa Formation (Van Veen, 1969) from the Sierra del Cid (Alicante), considered the type-locality for the new erected species. Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 202310 LINKING THE CYCLOTHYRIS DIFFORMIS ATTRIBUTIONS TO THE BIOSTRATIGRAPH- ICAL APPROACH OF THE C. EMENTI- TUM-BEARING DEPOSITS The genus Cyclothyris was erected by M’Coy (1844); subsequently Buckmann (1906) designated Terebrat- ula latissima (Sowerby, 1829) as the type species of the genus. Several Cretaceous asymmetrical species have been placed into this genus, which is frequently reported from European basins, but with controversial taxonomic attributions. The correct taxonomic classifi- cation, and therefore the stratigraphical range and the geographical distribution of the asymmetrical species of Cyclothyris were widely discussed (e.g., Muñoz, 1985, 1994; Gaspard, 1991; Motchurova-Dekova, 1995, 1997; Radulović & Motchurova-Dekova, 2002; Radoičić et al., 2010; Berrocal-Casero et al., 2017, 2020a, 2020b). Among them, C. difformis is probably the most prolific taxon. It was first defined by Valenci- ennes (in Lamarck, 1819) as Terebratula difformis from a picture selected from the “Tableau Encyclopédique et Méthodique” (Bonnaterre, 1789, p. 131, pl. 242, fig. 5), ascribed to the Cenomanian but with unspecified origin. Since then, recurrent ambiguity in attributions to R. dif- formis proliferated. D’Orbigny (1851, pl. 498, figs. 6–9) arranged into this species the Santonian material from La Cadiére (SE-France) whereas Coquand (1879) considered these specimens synonymous with the Santonian R. claudicans from Argelia. Subsequently, Rh. difformis was reported in the Coniacian–Santonian from France (Péron, 1877; Toucas, 1886). Fage (1935) went even farther in considering most of the Late Cre- taceous asymmetrical rhynchonellides as varieties of R. difformis (R. difformis var. globata; var. rudis; var. vesicularis; var. lamarckiana). In this confusing taxonomic context, Owen (1962, 1988), studying the British Cyclothyris, re-established the original concept of the species, both from the sys- tematic and biostratigraphic perspectives and excluded from C. difformis all the previously reported non-Cen- omanian records, constraining its distribution range to the lower-middle Cenomanian and selected as lec- totype of C. difformis the specimen deposited in the Lamarck Collection figured by Clerc and Favre (1918, pl. 15, fig. 84a–84d) from the lower Cenomanian of Le Havre (Normandy). Since the erection of the lectotype, the Cenomanian condition of C. difformis was conventionally accepted. Thus, Nekvasilová (1973) reported Cyclothyris aff. difformis in the Cenomanian from Bohemia; Gaspard (1985) assigned some Cenomanian forms from Aquit- aine to C. difformis, also suggesting the distinction of the Coniacian asymmetrical forms previously consid- ered as Rhynchonella difformis from the true-difformis Cenomanian species (Gaspard, 1991); Motchuro- va-Dekova (1995) analyzed the genus Cyclothyris in the Late Cretaceous from Bulgaria, constricting C. dif- formis to the Cenomanian as well. Recently, Gaspard and Charbonnier (2020) adhered to the same stand- point in several records from Normandy and some other Western European localities. In her PhD Thesis, one of the authors of this work (MBC) revised the stock of Cyclothyris difformis housed in the Natural History Museum (London, UK) as well as all taxa of Upper Cretaceous asymmetric Cyclothyris from Europe and Northern Africa housed at different Euro- pean institutions (see “Materials and Methods” section in the present paper and Berrocal-Casero, 2020; Ber- rocal-Casero et al., 2020a; 2020b). This examination concluded that the Prebetic material differs from the British Cenomanian C. difformis in being more bicon- vex and a considerably narrower form, in the obligate type of asymmetry and in the lower number of ribs, therefore substantiating that a rhynchonellide asym- metrical stock separate from C. difformis occurs in the Prebetic area. The deposits in which C. ementitum was found were formerly assigned to the Cenomanian because of the attribution of this asymmetric form to C. difformis (e.g., Iñesta & Calzada, 1996), while regional data from sev- eral localities led some authors to place these deposits in the Albian–Cenomanian transition (see above). Thus, to date, it can be concluded that the Albian–Cenoma- nian transition is the chronostratigraphical range for C. ementitum. A review of more accurate biostratigraphi- cal markers from these outcrops is necessary in order to update more precisely the stratigraphical range from which this form is recorded. With this intent ongoing research to study the faunal assemblages occurring with C. ementitum is in progress. CYCLOTHYRIS EMENTITUM AND THE OBLI- GATE TYPE OF ASYMMETRY Reviewing the data about the asymmetry in the genus Cyclothyris, a hypothesis about the functional meaning of the asymmetry in the Coniacian (Upper Cretaceous) Cyclothyris cardiatelia Berrocal-Casero, 2020, from the Northern Castilian Platform has been proposed by Berrocal-Casero et al. (2017). This hypothesis was based on palaeoenvironmental and taphonomical observations suggesting that this species lay inclined in life position, partially buried, as a consequence of an important increase in fine detritic sediment inputs on the platform which made the substrate much softer. Taphonomical and palaeoenvironmental evidences support this hypothesis (see Berrocal-Casero et al. 2017, fig. 13; Berrocal-Casero et al., 2022). Berrocal-Casero et al. (2020b) proposed another hypothesis concerning the origin of obligate asym- metry in Upper Cretaceous Cyclothyris from Europe. These authors suggested that the facultative asymme- try of some species with phenotypic plasticity (such as Cyclothyris segurai) could have been fixed by adap- tation in succeeding species (such as C. cardiatelia) and then genetically assimilated to become obligate Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 2023 11 asymmetry. Thus, other subsequent species possibly related to C. cardiatelia, such as C. globata and C. vesicularis, which may occur in various different facies, would maintain the obligate asymmetry even in pala- eoenvironmental conditions differing from those that induced the adaptive change (Berrocal-Casero et al., 2020b, fig. 6). This constitutes, for the moment, the single scenario in which a group with facultative com- missural asymmetry could have evolved into taxa with obligate asymmetry. At this point, the question is: can these hypotheses be applied to the asymmetric C. ementitum from the Eastern Prebetic? C. ementitum shows obligate type of asymmetry, being possibly the oldest known Cyclo- thyris showing this feature, but there is no information about possible precursors of this species adapted to a specific palaeoenvironment or circumstance that could induce the change leading to the asymmetry. Although the paleoenvironment in the previously mentioned scenario and those that induced the asymmetry in C. ementitum precursors were different, the physiologi- cal response may have been common in both cases, related to the origin of the asymmetry. According to Berrocal-Casero and García Joral (2023), starting from the morphogenetic plasticity of the anterior com- missure present in some lineages of rhynchonellides, different palaeoenviromental factors could lead the lophophore to works in an asymmetric way because the water currents enter in the shell preferentially by only one of the two sides. This could have occurred in response to limitations in vital space for living in closely packed clusters; to prevailing or unidirectional currents as usual in reefal or para-reefal environments; and/or to living on soft substrates. The common physiological response in these different scenarios seems to be the differential growth of the lophophore arms, which can lead to external asymmetry. The selection by adap- tation of this asymmetry and its genetic assimilation would suppose the fixation of this trait giving rise to the obligate type of asymmetry, which could appear even when the palaeoenvironmental conditions are different to those that induced the adaptation (Berrocal-Casero et al., 2020b, Berrocal-Casero & García Joral, 2023, fig. 7). It will be necessary to study further cases with a continuous record of facultative and obligate asymmet- ric rhynchonellides in the same phyletic line to confirm this process. Currently, only one of these scenarios is documented (Berrocal-Casero et al., 2020b). Following on from this new research is focusing on the recon- struction of the phylogeny of Lower Cretaceous asym- metric Cyclothyris (Fig. 5). CONCLUSIONS The study of Albian–Cenomanian (Cretaceous) asym- metric rhynchonellides from several localities from the Alicante province (Southeastern Spain, Eastern Preb- etic), formerly classified by previous authors as Cyclo- thyris difformis, has allowed to reassign them to the new species Cyclothyris ementitum, formally described in the present work. The diagnostic criteria of this new species are the biconvexity of the shell, its obligate type of asymmetry (commissural asymmetry), shell orna- mented with about 25 strong ribs, and the presence of long and dorsally concave crura. C. ementitum is, so far, endemic to South-eastern Spain. This study allows Figure 5. On the left, proposed scheme for the evolution of commissural asymmetry in rhynchonellides (modified from Berro- cal-Casero & García Joral, 2023). On the right, in the red rectangle is shown the proposed evolution of commissural asymmetry in Upper Cretaceous (Coniacian–Campanian) Cyclothyris (modified from Berrocal-Casero et al., 2020b). C. ementitum (black discontinuous rectangle) possibly corresponds to the last stage of this evolution in the Lower Cretaceous, but earlier forms that would have played an equivalent role to C. segurai or C. cardiatelia are still unknown. Berrocal-Casero, M. et al. - New asymmetric rhynchonellide from the Cretaceous of Spain - Spanish Journal of Palaeontology 38, 202312 to update and refine the taxonomy and distribution of Cretaceous asymmetric Cyclothyris and remove some of the confusion surrounding these forms. Previous misidentifications of Cyclothyris ementitum as C. difformis resulted in dating the outcrops in which the newly recognized species occurred as Cenomanian. In this regard, it is necessary to review the stratigra- phy and faunal assemblages of the classical localities in which C. difformis has been recorded, to accurately elucidate the biostratigraphical range of this taxon and associated brachiopod assemblages. C. emmentitum is preliminarily attributed in this work to the Albian– Cenomanian transition. This study has revealed that obligate asymmetry has occurred several times along the Cretaceous in the genus Cyclothyris. The new species here described could constitute one of the oldest Cyclothyris with this type of asymmetry recorded to date, also opening a new research line looking for its possible precursors and the possible scenarios who leaded to this asym- metry. Supplementary material. New taxonomic name proposed in this paper has been registered in Zoobank, the online regis- tration system for the ICZN: https://zoobank.org/References/ B119EB42-C240-4C2D-B2C5-9EEB12624E14 Author contributions. MB-C carried out fieldwork, prepared and studied the material, both external and internal features (by preparing serial sections and acetate peels), as well as the microstructure (SEM), compared with material reviewed in her Thesis from other institutions from Europe, wrote the original draft and made Figs. 2–5. JFB–C realized previous fieldwork in the outcrops mentioned and directed the present and preliminary studies in the area, collecting some of the brachiopods. He carried out fieldwork in Sierra del Cid with MB–C and FGJ and contributed to the design and implemen- tation of the research. He provided material from the Univer- sity of Alicante from different localities and prepared material, preparing also some specimens in Fig. 2, wrote the geological and geographical context, and prepared Fig. 1, the biostrati- graphical approach, provided bibliography and reviewed and improved the rest of the original draft. FGJ contributed to the design and implementation of the research, carried out fieldwork in Sierra del Cid, contributed to the preparation of specimens, contributed with his knowledge on asymmetric Cyclothyris and reviewed and supervised the manuscript. Competing Interest. The authors declare no competing inter- ests. Funding. Grant for young researchers to MB-C from the Span- ish Society of Palaeontology 2021 (AJISEP-2021-XXXX1). Author details. Mélani Berrocal-Casero1,2, José Francisco Baeza-Carratalá3 & Fernando García Joral1. 1Departa- mento de Geodinámica, Estratigrafía y Paleontología (Grupo Procesos Bióticos Mesozoicos), Universidad Complutense de Madrid, 28040 Madrid, España; melani.berrocal@ucm. es; fgjoral@ucm.es; 2Departamento de Geología y Geografía (Grupo PaleoIbérica), Universidad de Alcalá, 28871 Alcalá de Henares, España; melani.berrocal@uah.es; 3Departamento de Ciencias de la Tierra y del Medio Ambiente, Universidad Alicante, Apdo. 99, San Vicente del Raspeig, 03080 Alicante, España. jf.baeza@ua.es Acknowledgements. The authors would like to thank to Dr. Philipe Fauré from the Muséum of Toulouse, France, for his help with specimens from the Leymerie Collection providing us with photographs and measurements of the holotype of Cyclothyris regularis. To Prof. Fernando Barroso-Barcenilla from the University of Alcalá, Spain, for facilitating access to the SEM of the Research Assistance Center of the same University. To the reviewer Michael R. Sandy, Emeritus Pro- fessor at University of Dayton, United Kingdom, the anony- mous reviewer and the editors of the Spanish Journal of Pal- aeontology (Dr. Carlos Martínez Pérez from the University of Valencia and Dr. Sonia Ros-Franch from the University of Valencia, Spain) whose comments have allowed to improve the manuscript. This research has been partially financed by a Grant for young researchers to MB-C from the Span- ish Society of Palaeontology 2021 (AJISEP-2021-XXXX1), and is a contribution to the Research groups Procesos Bióti- cos Mesozoicos from the Complutense University of Madrid (UCM), PaleoIbérica from the University of Alcalá (UAH), and VIGROB-167 (University of Alicante). 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Introduction GEOLOGICAL AND GEOGRAPHICAL SETTING MATERIAL AND METHODS SYSTEMATIC PALAEONTOLOGY LINKING THE CYCLOTHYRIS DIFFORMIS ATTRIBUTIONS TO THE BIOSTRATIGRAPHICAL APPROACH OF THE C. EMENTITUM-BEARING DEPOSITS CYCLOTHYRIS EMENTITUM AND THE OBLIGATE TYPE OF ASYMMETRY CONCLUSIONS REFERENCES