Rhynchonellide Brachiopods Research Articles

A new rhynchonellid fauna (Brachiopoda) from the Wordian (middle Permian) of Coahuila, Mexico: Stratigraphy and paleoenvironments

Seven brachiopod species of the order Rhynchonellida of a new locality (Las Margaritas I section) from the Las Delicias Formation in Coahuila, Mexico are described. The fauna includes four taxa identified as Bryorhynchus bisulcatum, Leiorhynchioidea schucherti, Leiorhynchoidea amygdaloidea, and Paranorella imperialis, as well as three species assigned with open nomenclature: Leiorhynchioidea cf. scelesta, Stenoscisma sp., and Rhynchopora sp. The brachiopod fauna identified, together with the record of different middle Permian ammonoids allowed us to establish a Wordian (middle Guadalupian) age for the Las Margaritas I section. The assignment of this relative age enabled restricting the stratigraphic range of Leiorhynchioidea schucherti and Paranorella imperialis to the middle Guadalupian since previously had only been related inaccurately to the middle Permian. The record of the species Bryorhynchus bisulcatum, Leiorhynchioidea cf. scelesta, and Leiorhynchoidea amygdaloidea, as well as the genus Stenoscisma is the first in Mexico. The preservation of specimens, lithological features, and associated fauna suggest that rhynchonellid brachiopods were deposited in different platform facies: shallow lagoonal or offshore, characterized by low to medium energy, stenohaline conditions, and continuous terrigenous input.

A new species and genus of Lower Jurassic rhynchonellide (Brachiopoda) from Livari (Rumija Mountain, Montenegro): taxonomic implications of the shell microstructure

ABSTRACT A new rhynchonellide brachiopod genus and species, Skadarirhynchia semicostata gen. et sp. nov., is described from the late Pliensbachian of Livari, Rumija Mountain, southeastern Montenegro. It occurs in shallow-water brachiopod-crinoid packstone beds (bioclastic limestones) of the periplatform facies of the Dinaric Carbonate Platform. Stratigraphy is constrained by means of 87Sr/86Sr dating indicating a late Pliensbachian age, and by the fact that the brachiopod beds lie immediately below the Toarcian marly limestones, which is consistent with the regional stratigraphical position. The new species has a circular to roundly pentagonal outline and semicostate shells with 10‒12 strong angular ribs. Internally, it shows reduced dental plates, narrow and thin hinge plates inclined dorsally with small crural bases, crescent-like and laterally convex, and hamiform crura. The shell microstructure of the new taxon is characterised by a homogeneous secondary layer (a single layer with no sublayers) built of rhombic fibres that are typically of coarse-fibrous type (eurinoid pattern) 35‒50 μm wide and 20‒30 μm thick. Other co-occurring rhynchonellide species such as Prionorhynchia fraasi and Cuneirhynchia dalmasi are also described. Shell microstructures for the genus Cuneirhynchia are presented.

Shell asymmetry in Cretaceous Cyclothyrididae (Brachiopoda): variability, ontogeny and terminology

The asymmetry observed in rhynchonellid brachiopod shells has been discussed for decades and continues to attract attention. This noteworthy modification of the anterior margin morphology during the ontogeny has evolved several times in rhynchonellids, and seems to reflect a genetic basis. First, we try to clarify the terminology regarding asymmetrical, dissymmetrical and symmetrical shells that has existed since the beginning of the 20th century. The Cretaceous populations observed clearly exhibit antisymmetry (also called random asymmetry). During the Cretaceous, some populations of Cyclothyris McKoy, 1844 include a mixture of truly asymmetrical specimens and others that exhibit an intermediate degree of asymmetry, herein called atypical morphologies. Shapes of specimens coming from two different locations in France were captured using geometric morphometrics. We used the range of different morphologies: 1) to test alternative hypotheses about the ontogeny of asymmetry; 2) to test for the possibility of several morphogroups; and 3) to discuss the determinism of the asymmetry.

Quantitative Study of the Morphological Variations among Dzieduszyckia Populations from the Devonian Rongxian Formation, South China and their Influencing Factors

AbstractThe rhynchonellide brachiopod Dzieduszyckia Siemiradzki is widely distributed in the Lower Famennian strata, and exhibits a wide range of morphological variations among populations. 1272 autochthonous Devonian Rongxian Dzieduszyckia fossils were collected from three populations in South China, namely the Dazhai, Dalong, and Longmi sections. A series of quantitative morphological analyses were conducted to understand the morphological variation among populations and identify the triggers responsible for such variations. The results show that the Dazhai population differs significantly in morphospace from the Dalong and Longmi populations, while the latter two exhibit more similar morphological features, suggesting that geographic distribution may play a key role in affecting Dzieduszyckia morphology. The Longmi population shows a distinct morphospace from the Dazhai population and an overlapped morphospace with the Dalong population, indicating that habitat may not be the controlling factor. Lastly, the Dazhai and Dalong populations share some morphological similarities, but the Dazhai and Longmi populations occupy completely different morphospaces, indicating that evolution had a greater impact on phenotypic divergence than habitat. Our findings suggest that geographic distribution is the predominant factor influencing the morphological variation of Dzieduszyckia, while evolution and living habitat are less significant, the former of which might play a more important role.

Could the asymmetrical commissure in rhynchonellide brachiopods be an adaptive trait?

Could the asymmetrical commissure in rhynchonellide brachiopods be an adaptive trait?

First record of the brachiopod Erymnaria in the Chruteren Member (Euthal Formation) from a new Palaeogene site in the Br\xfclisau Schuppenzone of northeastern Switzerland (Canton St. Gallen) with remarks on shell asymmetry

A small, smooth-shelled rhynchonellid brachiopod, Erymnaria Cooper, 1959 was discovered in a previously unknown locality in the so-called Brülisau Schuppenzone (imbricate zone) of the South Helvetic region of northeastern Switzerland. It is the first record of this genus in this region and in Switzerland in general. It is comparable to the type species of Erymnaria, E. polymorpha (Massalongo, 1850). Its specific identity is currently undetermined, and the species is referred to Erymnaria sp. 1. The main characteristic of Erymnaria sp.1 is its asymmetric shell. This prompted a comparison of E. sp. 1 with other known asymmetric brachiopods. Questions of asymmetry and variability within the same genus and with brachiopods in general are discussed. Another, larger brachiopod species found at the new site is tentatively named Erymnaria? sp. 2. The site can be assigned to the Chruteren Member (Euthal Formation) of Early Ypresian age, dated by large Foraminifera. Thus, the previous distribution area of the Chruteren Member can be extended.

New Pliensbachian rhynchonellide (Brachiopoda) from Livari, (Rumija Mountain, Montenegro): the taxonomic implications of microstructure to disentangle cases of homeomorphism

ABSTRACT An interesting case of close external similarity (homoeomorphy) is revealed by the study of an Early Jurassic rhynchonellide brachiopod from Livari, Rumija Mountain, southern Montenegro. Shell microstructure was used as the primary diagnostic tool, applied before serial sectioning to study internal characters. Sepkoskirhynchia sphaerica gen. et sp. nov. is erected based on the presence of coarse fibrous shell microstructure and hamiform crura. Because of these primary diagnostic characters, the new genus is placed in the rhynchonellide family Basiliolidae. The shell microstructure of the new taxon is characterised by a differentiated secondary layer of coarse fibrous type. The fibres are rhombic or subquadrate in cross-section, in the external sublayer they are 55–60 μm wide and 40–50 μm thick, internally other sublayers are thinner with fibres 35–40 μm wide and 20–25 μm thick. The main character that distinguishes the new genus is that the secondary layer is differentiated into several sublayers, while in externally homoeomorphic Soaresirhynchia it is built of a single layer. The new taxon was found in the brachiopod and crinoidal limestones from the periplatform facies of the Dinaric Carbonate Platform.

Brachiopods in early Mesozoic cryptic habitats: Continuous colonization, rapid adaptation, and wide geographic distribution

Late Triassic and early Jurassic dikes and fissures in the Dachstein Limestone in the Northern Calcareous Alps harbor mass occurrences of the rhynchonellide brachiopods Sulcirostra juvavica and Halorella amphitoma . To test recent hypotheses about their paleoecology, we characterized these habitats using petrography, carbon stable isotopes, and trace element patterns, and found no evidence for hydrocarbon seepage or hydrothermal venting. Thus the brachiopods lived under normal-marine conditions, in darkness and absence of local photosynthetic primary production, hence relying on the supply of limited and presumably small-sized food washed into the dikes and fissures. Because Halorella and Sulcirostra occur in dikes and fissures since the beginning of their stratigraphic ranges, these rhynchonellides are not relics of formerly widely distributed taxa, but instead are two genera that rapidly adapted to these habitats. Both Halorella and Sulcirostra occur also in late Triassic and early Jurassic deep-water settings such as deep-marine sills and hydrocarbon seeps, indicating that close phylogenetic relationships between submarine cave faunas and deep-sea faunas, as seen today, existed also in the early Mesozoic, albeit among very different taxa. Another analogy to the modern cave fauna is the wide but disjunct geographic distribution of Sulcirostra and Halorella , both found throughout the Tethys and Panthalassa oceans. Our findings support the view that submarine cave habitats were continuously colonized by new taxa throughout Earth's history.

Artificial intelligence approach to palaeogeography and evolutionary trend analysis of Laurentian brachiopod fauna in the Rhynchotrema-Hiscobeccus lineage

Previous studies, based on the qualitative morphological description on the Late Ordovician brachiopod fauna hypothesized that the earliest species of Hiscobeccus, which is one of the diagnostic taxa in North American epicontinental brachiopod fauna, evolved from Rhynchotrema, a well-known rhynchonellide brachiopod, which lived in pericratonic regions of Laurentia. A quantitative approach conducting multivariate analysis, which was based on biometric characters of rhynchonellide brachiopod specimens from the Late Ordovician (upper Sandbian–upper Katian) in North America, supported this hypothesis that the younger and larger species of Hiscobeccus evolved from older and smaller species of Rhynchotrema during the Late Ordovician.The current study proposes the first report of employing an artificial intelligence model based on neural networks to map a set of quantitative morphological measurements of the Rhynchotrema-Hiscobeccus lineage of North America to their locality and evolutionary trend. For this purpose, a total of 171 morphometric measurements of the Late Ordovician brachiopods from 11 localities of North America were divided into 114 training and validation samples and 57 testing sets. The input morphometric parameters of the studied brachiopods include shell length (L), shell width (W), shell thickness (T), sulcus depth (T1), sulcus maximum width (W1), sulcus floor width (W2), apical angle (AA), lamella-covered shell length (L1), lamella number (Ln). Artificial neural network tries to find a mathematical formulation between the mentioned morphometric parameters and their corresponding localities from North America. The results showed that the accuracy of the neural network approach in estimating the locality of the testing brachiopod samples is 81%. In the light of satisfactory results of neural networks, having a set of the morphometric data from the unseen Late Ordovician brachiopods, their localities can be estimated.

Lower Tithonian and lower Berriasian brachiopods from the M\xe1r\xe9v\xe1r Limestone Formation, Zeng\u0151v\xe1rkony (Mecsek Mountains Hungary), and remarks on their palaeoenvironment

A new collection provided some brachiopods assigned to Lacunosella hoheneggeri, Pygope diphya and P. janitor from the lower Tithonian (Micracanthoceras ponti Zone) and lower Berriasian (Calpionella Zone), and from the limestone succession at Zengővárkony, Mecsek Mountains, Hungary. This is the first taxonomic description and photographic documentation of these fossils. We provide reliable documentation of pygopid brachiopods from the Mecsek Mountains, known since 1880, but previously not described. For the moment, three pygopid brachiopod species are reliably reported from the Mecsek Mountains: Pygope diphya, P. janitor and Pygites diphyioides. The Lacunosella hoheneggeri described herein is the first record of Berriasian rhynchonellide brachiopods from the Mecsek Mountains. The lower Berriasian brachiopods may belong to a normal palaeoenvironment, with the usual size distribution.

The debated question of asymmetrical rhynchonellids (Brachiopoda, Rhynchonellida): examples from the Late Cretaceous of Western Europe

Many Cretaceous asymmetrical rhynchonellid brachiopods (Brachiopoda, Rhynchonellida) have long been considered asRhynchonella difformis(ValenciennesinLamarck, 1819). After a revision, Owen (1962) included the Cenomanian specimens from Europe inCyclothyrisM’Coy, 1844. Later, Manceñidoet al.(2002) confirmed this decision and critically mentioned the name of another asymmetrical rhynchonellid genus from Spain,OwenirhynchiaCalzadainCalzada and Pocovi, 1980. Specimens with an asymmetrical anterior margin (non particularly ecophenotypical), from the Late Coniacian and the Santonian of Les Corbières (Aude, France) and Basse-Provence (SE France) are here compared to specimens of the original Cenomanian speciesC. difformis. They are also compared to new material from the Northern Castilian Platform (Coniacian-Santonian, N Spain) and toRhynchonella globataArnaud, 1877 (Campanian, Les Charentes, Dordogne, SW France) andRh. vesicularisCoquand, 1860 (Campanian, Charente, SW France). These observations document the great morphological diversity among all these species and lead us to erect a new species:Cyclothyris grimarginanov. sp. from the type material of Arnaud, and two new genera:Contortithyrisnov. gen. includingContortithyris thermaenov. sp.,Beaussetithyrisnov. gen. includingBeaussetithyrisasymmetricanov. sp. All of these brachiopods fundamentally present an asymmetrical state which origin is discussed.

PHYLOGENETIC RELATIONSHIPS OF THE SILURIAN AFRO-SOUTH AMERICAN BRACHIOPODS ANABAIA , HARRINGTONINA AND CLARKEIA : NEW INSIGHTS FROM THEIR ONTOGENY

Hundreds of specimens of the rhynchonellide brachiopod Clarkeia antisiensis (d’Orbigny) recovered from the stratotype of the Tarabuco Formation of Bolivia form a complete series of growth stages providing a good opportunity for reconstructing its ontogenetic development. The fact that juvenile specimens of C. antisiensis are nearly indistinguishable from adult individuals of Harringtonina australis Boucot strongly suggests that Clarkeia evolved from Harringtonina by the heterochronic process of peramorphosis. On the other hand, adult specimens of both the Brazilian Anabaia paraia Clarke and the Precordilleran specimrens of Anabaia never exceed the youngest ontogenetic stage of Harringtonina australis, to which share small hinge plates supported by a septalium-like structure and absence of cardinal process. The overlap of adult morphology of Anabaia with the juvenile morphology of Harringtonina australis allows interpreting this succession as an evolutionary lineage showing increasingly more peramorphic characters. This hypothesis is supported by the correlation between the stratigraphic record of taxa and the inferred developmental sequence being Anabaia the oldest member (Early Silurian), Harringtonina australis the intermediate form (Wenlock-Ludlow), and Clarkeia antisiensis the youngest (Pridoli). This interpretation raises a systematic problem because the leptocoeliids Anabaia and Harringtonina are currently classified within the superfamily Uncinuloidea whereas Clarkeia is placed among the Rhynchotrematoidea. If the hypothesis is proven, these superfamilies, as presently constituted, would be polyphyletic groups.

A taxonomic review of the brachiopod genus Australocoelia (Boucot amp; Gill, 1956) in the Devonian of Brazil.

The rhynchonellide brachiopod genus Australocoelia was widely distributed across the Southern Hemisphere in the Devonian with three species recognized; A. palmata, A. peruviana and A. polyspera. In Brazil, A. palmata was initially reported from the Ponta Grossa and São Domingos formations (Paraná Basin), later recorded from the western border of the Parnaíba Basin (Pimenteira Formation, State of Tocantins), and is now shown to occur on the eastern border of the same basin (Pimenteira Formation, State of Piauí). In this paper, we describe a fourth species from the Paraná Basin as Australocoelia boucoti n. sp. It differs from A. palmata and the other species of Australocoelia in features of ornamentation and interspace, in addition to paleoecological characteristics.

The Middle to Upper Jurassic stable isotope record of Madagascar: Linking temperature changes with plate tectonics during the break-up of Gondwana

Stable isotope (δ18O, δ13C) analyses were performed on well preserved belemnites, oysters, and rhynchonellid brachiopods from the Middle to Upper Jurassic of the Morondava Basin in southern Madagascar. Both brachiopods and oysters indicate similar average temperatures of 18.7 to 19.3 °C in the Early Callovian, followed by a temperature decrease towards the Middle Oxfordian (13.9 °C) and a minimum in the Early Kimmeridgian (12.3 °C). In contrast, belemnites from the Oxfordian show lower average temperatures of 10.0 °C, which is likely caused by specific conditions for these organisms (e.g., different fractionation or life habits). Additionally, three oysters from the Upper Oxfordian and Lower Kimmeridgian were used for high-resolution stable isotope analyses. The data show seasonal fluctuations of >6 °C around averages between 14.4 and 14.7 °C. Latitudinal temperature gradients for the Callovian and Kimmeridgian are similar to today at the examined low latitudes of the southern hemisphere. The observed cooling of around 5 °C from the Callovian to the Oxfordian/Kimmeridgian can be attributed to a concurrent southward drift of Madagascar during the break-up of Gondwana. Thus, the study underlines the importance of considering palaeogeography in interpreting stable isotope data as well as the potential of detecting and timing palaeogeographic events by using stable isotope analyses.

A reappraisal of the genus Tethyrhynchia Logan, 1994 (Rhynchonellida, Brachiopoda): a conflict between phylogenies obtained from morphological characters and molecular data.

The genus Tethyrhynchia Logan in Logan Zibrowius, 1994 is revised on the basis of different methods of analysis including SEM observations, detailed ontogenetic study of the crural development, transverse serial sections, and shell microstructure. Some morphological characters cited in the original diagnosis are analysed and contested by the ontogenetic results. The type of crura of Tethyrhynchia, often placed in the arcual group, appears to be of the raducal group, instead. Paedomorphosis and heterochronic development offer the possibility of opening a dialogue between morphological and phylogenetic approaches to classification of rhynchonellide brachiopods.

Altaethyrella(Brachiopoda) from the Late Ordovician of the Tarim Basin, Northwest China, and its significance

AbstractAltaethyrella tarimensis, a new species of rhynchonellide brachiopod, is described from the late Katian (Late Ordovician) Hadabulaktag Formation in the Kuruktag region of Xinjiang, Northwest China on the northeastern edge of the Tarim Basin. Serial sections of the shell clearly show no dorsal median septum or septalium in the dorsal valve, and no spiralia or atrypide-style crura. Like other species of the genus,A.tarimensisn. sp. exhibits a high degree of intraspecific variation, including variations in shell shape and size, number of ribs in the sulcus at the anterior, and degree of asymmetry. The discovery ofAltaethyrellain Tarim has important paleogeographic implications, indicating a close relationship between the Late Ordovician brachiopod faunas of Tarim and those of the Kazakh terranes and North and South China paleoplates, supporting a recently published paleogeographic projection that places Tarim near the Chu-Ili terrane during the Late Ordovician. The abundant large biconvex shells ofA.tarimensisn. sp. would have provided a firm substrate for encrusting filter feeders like bryozoans to establish on the Kuruktag Platform.UUID:http://zoobank.org/df8843cd-4db0-48e7-ba03-bf0ce81c4f01

Match and mismatch of morphological and molecular phylogenies: causes, implications, and new light on cladistics

Established methods of exploratory data analysis reveal conflicts in morphological data from rhynchonellide brachiopods, conflicts that result in mismatches between morphological, combined, and molecular phylogenies. Consideration of the mismatches uncovers several findings of general applicability: causes of conflict include the inherent genealogical deficit of comparative morphology, and genetic signal erosion caused by genome remodelling. Because of genetic signal erosion, cladistic analysis cannot be used safely on taxa whose remote ancestors diverged in deep time. In theory, if not practice, morphological-molecular conflict may be avoided by use of genetically validated characters. The preliminary (prior) classification of the organisms concerned is a hitherto-overlooked first step of cladistic analysis; its integral roles are to enable homology hypotheses, and at least partly to determine cladistic results through classification bias. Thus hitherto, cladistics has been misunderstood and misrepresented; many reported taxon relationships may have been determined more by the prior classification than by the supporting characters. If the prior classification is artificial and does not accurately mirror evolutionary history, morphological and molecular phylogeny mismatches will register as spurious homoplasy. To avoid logical circularity in cladistic analysis there must be clear separation of input (taxon descriptions) from output (clades). This requirement rules out PhyloCode-like approaches to systematics if they allow (named) output of cladistic analysis to serve as the input to further such analyses.

Eressella, a new uncinuloid brachiopod genus from the Middle Devonian of Europe and Africa

Eressella , a new genus of rhynchonellide brachiopods belonging to the superfamily Uncinuloidea Rzhonsnitskaya, 1956, is described with Rhynchonella coronata Kayser, 1871, as the type and only species. It is characterised by a dorsibiconvex profile with a resupinate ventral valve, costae rounded posteriorly, but acute and developing ventrally directed spur-like protuberances anteriorly, small dental cavities, cardinal process multilobed posteriorly and massive anteriorly, and the presence of a septalium and thick dorsal median septum. Given the present state of flux in the systematics of the superfamily, it is conventionally placed within the family Uncinulidae Rzhonsnitskaya, 1956, although similarities with the subfamily Betterbergiinae Savage, 1996 and the family Eucharitinidae Sartenaer, 2015 are also noted. Eressella coronata , hitherto the only representative of the genus, is known from the Eifel Hills (Eifelian, mainly middle Eifelian), from central Poland (especially from the Eifelian of the Holy Cross Mts.), and from the Moroccan Anti-Atlas (late Eifelian to early Givetian, details uncertain).

A new occurrence of the Early Jurassic brachiopod Anarhynchia from the Canadian Cordillera confirms its membership in chemosynthesis-based ecosystems

Cold seeps, where seepage of hydrocarbon-rich fluids occurs in the sea floor, are sites that harbor highly specialized ecosystems associated with distinctive carbonate sediments. Although their Mesozoic record is scarce and patchy, it commonly includes dimerelloid rhynchonellide brachiopods. Here we report a monospecific assemblage of Anarhynchia from a limestone boulder of early Pliensbachian (Early Jurassic) age in the Inklin Formation of the Whitehorse Trough in the Stikine terrane, from a locality at Atlin Lake in northern British Columbia. Specimens are among the largest known Mesozoic brachiopods, up to 9 cm in length, and described here as Anarhynchia smithi n. sp. Early precipitated carbonate cement phases of the limestone have carbon isotopic composition highly depleted in 13C, indicative of the influence of microbial oxidation of methane derived from a cold seep. Carbonate petrography of the banded-fibrous cement and other characteristic components supports this paleoenvironmental inference. Volcanogenic detrital grains in the matrix are indistinguishable from those in the sandstone layers in the siliciclastic sequence, suggesting that the seep carbonate is broadly coeval with the enclosing conglomerate. The new record extends the geographic range and species-level diversity of the genus, but supports its endemism to the East Pacific and membership in chemosynthesis-based ecosystems. The distribution of three distinct but congeneric species suggests that allopatric speciation occurred at separate sites along the active margin of western North America and Anarhynchia was restricted to seep and vent habitats in the Early Jurassic.

Functional meaning of asymmetrical commissures in Coniacian (Upper Cretaceous) rhynchonellide brachiopods from Northern Spain

The functional meaning of asymmetry in brachiopods has been a matter of discussion for over a century. Several hypotheses have been proposed to explain why these morphologies appear, the predominant idea in the literature being that it might be a non-adaptive characteristic. Here we present an in-depth study of the asymmetry present in the commissure of the rhynchonellide brachiopod Cyclothyris aff. globata from three Upper Cretaceous sections of northern Spain, with the aim to establish whether it is correlated to some kind of palaeoenvironmental factor. A new hypothesis interpreting this asymmetry as a functional feature is proposed after the results obtained from the palaeoecological and taphonomical study of the specimens. A noteworthy aspect of the asymmetry displayed by this species is that juvenile forms are fully symmetric while adult specimens are asymmetrical, but internal structures remain symmetric throughout ontogeny. In adult forms, asymmetry is expressed as the division of the shell into two vertically displaced lobes, one of which is invariably shorter than the other. Characteristically, the beak is twisted towards the shorter lobe, and in some individuals the larger lobe is seen to be completely flattened due to burial and compaction. When the occurrence of these asymmetrical forms was analyzed, it became evident that they appeared wherever the lithology was mainly marly, thus seeming to be related to the predominance of fine detrital components in the sediments (soft bottom). These features enable us to suggest that C. aff. globata lived partially buried, with one side of the shell placed inside the soft sediment. Asymmetry developed gradually as the shell grew, being evident once it attained a certain size. This hypothesis fits well with the morphological and structural features displayed by this species and, particularly with its relationship with the consistency of the substrate in which these asymmetric brachiopods lived, corresponding to an adaptation of the growing to soft and unstable bottom conditions.Although this paper does not aim to conduct a systematic review of the species, the geometric morphometric analysis performed in order to describe the asymmetry provided results that give a basis for the discussion of the taxonomic relationships between certain Upper Cretaceous asymmetric Cyclothyris species.