a new givetian athyridid species from northwest africa discovered by three-dimensional...

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A New Givetian Athyridid Species from Northwest Africa Discovered By Three-Dimensional Reconstruction of Shell Morphology of Internal MoldsAuthor(s): Mena Schemm-GregorySource: Journal of Paleontology, 88(4):708-718. 2014.Published By: The Paleontological SocietyDOI: http://dx.doi.org/10.1666/13-086URL: http://www.bioone.org/doi/full/10.1666/13-086

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A NEW GIVETIAN ATHYRIDID SPECIES FROM NORTHWEST AFRICADISCOVERED BY THREE-DIMENSIONAL RECONSTRUCTION OF SHELL

MORPHOLOGY OF INTERNAL MOLDS

MENA SCHEMM-GREGORY†

Centro de Geociencias, Universidade de Coimbra, Largo Marques de Pombal, P-3000-272 Coimbra, Portugal, ,[email protected].,,[email protected]. †Deceased

ABSTRACT—A new method of analyzing the internal shell morphology (including the complete brachidium of internalmolds) of articulated brachiopod shells through the use of serial sections and digital three-dimensional reconstruction ispresented. The method introduced is essential for the study of internal shell structures such as brachidia, or cardinalia, ifcomputed tomography (CT) is not suitable or if a CT scanner is not available. A new species of Athyris from Givetian bedsof Northwest Africa was selected to exemplify this method. To compare this species with figured serial sections in theliterature, two-dimensional drawings of grinding surfaces are provided. Athyris africana n. sp. is only preserved as internalmolds of articulated specimens. The new species is included in the evolutionary lineage of the group around Athyrisconcentrica. The faunal assemblage of A. africana n. sp. shows affinities to Western European and North Americanbrachiopod faunas.

INTRODUCTION

BRACHIOPODS ARE known in the fossil record since theCambrian. Throughout Earth history, they have been

preserved in a range of different ways, such as articulated andisolated shells, or internal and external molds. Each kind ofpreservation requires a different methodology in order to fullystudy external and internal shell morphologies (Schemm-Gregory and Feldman, 2012). The study of brachiopod materialpreserved as molds usually is done through the preparation oflatex casts. The latex cast is a copy of the actual shell whichallows easy measurements of length, thickness, and angles ofdifferent shell features. In the case of articulated shells, serialsections were traditionally the most common method forstudying the internal shell morphology, and in publicationsdrawings of selected grinding surfaces are typically illustrated.In addition, select peels may also have been prepared in order tostudy shell structures and to keep a record of the sectionedspecimen. In recent years, the non-destructive scanning methodcomputed tomography (CT) has become popular, and the 3-Dreconstructions produced using this approach illustrate in greatdetail the internal shell morphology, facilitating the measure-ment of distances and angles, and demonstrating unexpectedecologic and anatomic life habits (Sutton et al., 2005; Schemm-Gregory, 2010a, 2010b; Schemm-Gregory and Sutton, 2010).Once the CT scanner is set up, a dataset of CT images can beobtained very quickly and easily, whereas the preparation ofserial sections, sometimes including the preparation of acetatepeels to preserve some parts of the fossil (which is destroyed bythe procedure), is very time consuming. However, CT scans areusually only suitable if the mineralogical contrast between shellmaterial and sediment matrix is sufficient to differentiate thefossil from the rock.

The mineralogical preservation and the preservation asinternal molds of articulated shells complicate the taxonomicidentification of specimens. Up to now, the preservation ofinternal molds of articulated shells has prevented the study ofthe brachidium of brachiopods, which is only preserved inarticulated shells. However, due to its fragile connection to the

dorsal valve, the brachidium is often broken inside of anarticulated shell and never preserved in isolated shells. Thepreparation of latex casts of internal molds of articulated shellsonly shows the posterior part of the crura and the cardinalia ofthe hinge structure (Schemm-Gregory, 2008). Serial sections ofthis material have been problematic and rarely successful,especially because of the lack of calcareous shell material andthe usually calcareous-free matrix, typical for this mode ofpreservation, does not allow the preparation of acetate peels.This article describes a way to visualize the brachidium of abrachiopod preserved as an internal mold of an articulated shellwith the help of serial sections and digital 3-D reconstructions.

GEOLOGICAL SETTINGS

Close to the military town Smara along the southern flank ofthe Tindouf Basin in Northwest Africa, formerly known as theWestern or Spanish Sahara, several reef complexes of differentsizes occur (Figs. 1, 2). Extensive invertebrate fossils werecollected during field sampling conducted as part of theGerman-Moroccan cooperation ‘‘Genesis of Devonian Reefs.’’The Middle and Upper Devonian beds in the study area aredominated by sandstones, siltstones, and shales; thin beds oflimestones and associated bioherms and biostromes occur atseveral levels. The homoclinal structure of this area, the lack ofvegetation, and the removal of the surrounding shale createdunique exposures revealing the structure of reefs and associatedoff-reef sedimentary successions. For political reasons it hasbeen difficult to gain access to this region. As a result, thespectacular outcrops are still poorly known from a paleonto-logical point of view. The present work is one of a seriesdescribing the invertebrate fauna and its paleoecology andpaleoenvironment. The first geological studies of this area wereconducted during petroleum explorations between 1930 and1950 by Spanish and French geologists (e.g., Jacquet, 1936;Hernandez-Pacheco et al., 1949). Dumestre and Illing (1967)described the development of Middle Devonian reefs of thisregion and compared them with reefs of equivalent age in theRainbow area of northwestern Alberta (Canada). The study areaitself lacks a modern geological and paleontological study, thus

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Journal of Paleontology, 88(4), 2014, p. 708–718

Copyright � 2014, The Paleontological Society

0022-3360/14/0088-708$03.00

DOI: 10.1666/13-086

the lithology is still undescribed and the strata lack formalformation names. However, correlation with Western Europeanand North African strata based on faunal content is possible andbiostratigraphical assignment can be done with different fossilgroups. In recent years, a few studies of the bryozoan and

stromatoporid faunas have been published (Scholz et al., 2005;Konigshof and Kershaw, 2006; Ernst and Konigshof, 2010). Thebrachiopod faunas recovered from the study area indicatecorrelation of the reefs to the middle–upper Givetian (upperMiddle Devonian) and lower Frasnian (lower Upper Devonian)(Schemm-Gregory and Jansen, 2005). Conodont samples did notprovide sufficient data for stratigraphic assignment (P. Konig-shof, personal commun., 2010). Paleobiogeographic studies onthe terebratulid genus Paracrothyris (Wu in Wang et al., 1974)discuss the global faunal exchange between Nevada (western

FIGURE 1—Map of the Western Sahara region of Northwest Africa showingthe location of the study area.

FIGURE 2—Geographical grid with the locations of the fossil localities in thestudy area plotted. Athyris africana n. sp. was found in the Sabkhat Layfarinareef complex.

FIGURE 3—Laboratorial and computer work. 1, Woko 50P grinding machine at the Senckenberg Research Institute; 2, grinding of a brachiopod specimenembedded in resin; 3, photography of the grinding surfaces; note the adjustment of the specimen/object on the reproduction table; 4, screenshot of SPIERSalignwhile aligning a dataset of digitized images of grinding surfaces of Athyris africana n. sp.; note marker lines to support and ease the alignment; white arrowspoint to the spirals of the brachidium; 5, screenshot of SPIERSedit while editing an aligned dataset of Athyris africana. n. sp.; note different colors of masks:ventral shell (red), dorsal shell (blue), and brachidium (green); 6, studying a 3-D reconstruction of Athyris africana n. sp. in SPIERSview, viewing the internalventral shell with the brachidium.

SCHEMM-GREGORY—3-D RECONSTRUCTION OF NEW GIVETIAN ATHYRIDID INTERNAL MOLD 709

U.S.A.), South China, and the Western Sahara during this time

interval (Schemm-Gregory and Jansen, 2008). The presence of

Cyrtospirifer tindoufensis Schemm-Gregory, 2011 supports the

onset of a global faunal (brachiopod) migration based on the

worldwide abundance of Cyrtospirifer in the Frasnian. The

studied outcrops form a belt in a northwest-southeast direction

consisting of bioherms of different sizes. In previous works, the

largest of the studied reefs, a stromatoporoid-bryozoan-coral

reef complex situated in the southeast, was named ‘‘Sabkhat

Lafayrina’’; a smaller one ‘‘Gor-al Hessen’’ is located in the

northeast of the study area (Konigshof et al., 2003). The other

reefs are numbered 1 to 10 (Fig. 2). Athyris africana was found

in proximal off-reef strata near the Sabkhat Layfarina reef

complex. Judging from the brachiopod fauna, such as Nalivki-naria issoumourensis (Drot, 1971), ‘‘Kransia parallelepipeda’’(Bronn, 1837), and Cyrtospirifer tindoufensis Schemm-Gregory,2011, the age of this reef complex is assigned to the lateGivetian (late Middle Devonian) (Schemm-Gregory and Jansen,2005, 2008; Schemm-Gregory, 2011).

MATERIAL AND METHODS

Almost all the material is preserved as internal molds ofarticulated shells. In rare cases, parts of the shell are preserved,mostly in the apical region, but externally they are extremelyweathered. The internal molds consist of a calcareous-freematrix which was removed by the use of hydrochloric acid (10%concentration). Specimens were coated with ammonium

FIGURE 4—Selected photos of grinding surfaces of Athyris Africana, SMF 94007.4, at varying distances from the apex: 1, 0.500 mm; 2, 2.575 mm; 3, 4.550mm; 4, 7.675 mm; 5, 8.875 mm; 6, 11.550 mm.

710 JOURNAL OF PALEONTOLOGY, V. 88, NO. 4, 2014

chloride prior to photographing. Drawings of internal moldswere made with a camera lucida. Drawings of selected grindingsurfaces were prepared in CorelDraw X5. All specimens weremeasured with a digital caliper and measurements were roundedto the nearest 0.1 mm; grinding surfaces were measured with thefree software ImageJ 1.45s. All specimens are stored in theSenckenberg Research Institute, Frankfurt am Main, Germany(SMF 94000–94007.1–4, 94008.1–106).

Preparation of serial sections.—Four well-preserved internalmolds of articulated shells were selected for serial sectioning(SMF 94007.1–4), with special attention paid to undistorted andunfractured material to increase the chances of obtaining acomplete brachidium. As the first step, 3-D plaster casts of all ofthe fossils were prepared to keep a physical record of the internalmolds that were destroyed by sectioning. Serial sections wereprepared using a Woko 50P grinding machine (Fig. 3.1). Thegrinding distances were 25 microns resulting in up to almost 700grinding surfaces for each specimen. Prior to sectioning,specimens were embedded in resin and attached to a metal slideperpendicular to the commissural plane to guarantee parallelgrinding surfaces were produced at the same distances apart (Fig.3.2). Each grinding surface was photographed with a Canon 300Dcamera that was manually focused. The distance between thecamera and the object was controlled after each mm to guaranteethe same size of the photographed object. A 908 angle wasadjusted to a table-top shooting studio to align the obtainedpictures. A scale was photographed with each grinding surface(Figs. 3.3, 4, online Supplemental Data file 1).

Preparation of 3-D reconstructions.—Digital 3-D reconstruc-tions were produced using the SPIERS software suite forregistration, virtual preparation, and interactive visualization(http://spiers-software.org). The reconstruction methods aresimilar to those of Sutton et al. (2001, 2005). SPIERS consistsof three packages. In the program SPIERSalign, images arealigned manually to obtain a non-deformed reconstruction of thefossil (Fig. 3.4). As a first step, the dataset of photographs isrenamed as increasing continuous numbers (e.g., 000–150) andthe files are converted into ‘png’ format to allow fast editing.Even though the object was adjusted to a certain position, drillholes prepared through the resin, and the distance betweencamera and object kept equal, a perfect alignment is impossible toachieve due to manual preparation throughout the completeprocedure (Fig. 3.5). After alignment has been completed, thedataset is imported into SPIERSedit where images are editedslice-by-slice. For each morphological feature of interest, a‘‘mask’’ is manually defined which can later be shown or hiddenin the 3-D reconstruction. In the case of the athyrididbrachiopods, three masks were used: ventral, dorsal, andbrachidium. Each mask is assigned a different color in order toaid the editing process. Colors can be changed according topersonal preferences throughout the entire procedure and for finalpresentation. The final reconstruction is viewed in SPIERSview,where it can be magnified, rotated, and selected masks dissected(Fig. 3.6, online Supplemental Data file 2). This technique allowsdetailed study of the shell morphology and comparison withisolated shells or latex casts of mold material. To improve the

FIGURE 5—Three-dimensional reconstructions of the internal shell surface, brachidium, teeth, and cardinalia of Athyris africana n. sp., SMF 94007.4, SabkhatLayfarina reef complex, Northwest Africa, upper Givetian (upper Middle Devonian). 1, dorsal view of articulated shell with brachidium, dorsal shell 50%transparent; 2, dorsal view of internal ventral shell with brachidium; 3, ventral view of internal dorsal shell with brachidium; 4, oblique anterior view of internalventral shell; 5, oblique anterior view of internal dorsal shell; 6, oblique anterolateral view of internal ventral shell; 7, dorsal view of internal ventral shell; 8,ventral view of internal dorsal shell; 9, dorsal view of brachidium; 10, posterior view of brachidium; 11, anterior view of brachidium. All images at original size.


quality of the final reconstruction, masks can be smoothed. Thisfunction is especially helpful for 3-D reconstructions based onmanually aligned images, which usually show obvious ‘steps’between different sections (especially compared to reconstruc-tions based on CT). The view of the reconstructions illustrated(Fig. 5) were copied from SPIERSview by screen shots andarranged in Photoshop.

SYSTEMATIC PALEONTOLOGY

Order ATHYRIDIDA Boucot, Johnson and Staton, 1964

Suborder ATHYRIDIDINA Boucot, Johnson and Staton, 1964

Superfamily ATHYRIDIDAE Davidson, 1881Family ATHYRIDINA Davidson, 1881

Subfamily ATHYRIDINAE Davidson, 1881Genus ATHYRIS M’Coy, 1844

Type species.—Terebratula concentrica von Buch, 1834, bysubsequent designation of King, 1850, p. 136.

Diagnosis.—Small- to medium-sized, dorsi- to stronglydorsibiconvex, equidimensional to slightly transverse, androunded subpentagonal shells covered by numerous, regular,thin, and slightly lamellose growth lamellae; uniplicate anterior

FIGURE 6—Athyris africana n. sp., Sabkhat Layfarina reef complex, Northwest Africa, upper Givetian (upper Middle Devonian). Different view of internalmold with articulated shell and remains of shell material; a–d, ventral, dorsal, posterior, anterior, respectively, e, f, lateral views. 1, SMF 94000; 2, SMF 94001;3, SMF 94002, holotype; 4, SMF 94007.4; 5, SMF 94007.2; 6, SMF 94007.3; 7, SMF 94003, SMF 94004. All images of original size.


commissure with well-defined fold in anterior half of adult shelland relatively narrow sulcus originating at ventral beak, groove-like posteriorly but widening strongly anteriorly to about halfwidth of very flat ventral valve; ventral muscle field gently tomoderately impressed; cardinal plate flat or slightly concaveventrally; low myophragm may be present (after Alvarez andRong, 2002, p. 1497.)

Occurrence.—Devonian, ?Lower Carboniferous; cosmopoli-tan.

ATHYRIS AFRICANA new speciesFigures 5–10

Diagnosis.—Small and equi- to dorsibiconvex Athyris withthick and parallel dental plates, clearly subdivided and embeddedmuscle fields in both valves, a long and V-shape jugal arch, and along jugal stem.

Description.—Form and size: shells small to medium,subcircular, and equiconvex to strongly dorsibiconvex inlongitudinal section. Dorsal valve slightly wider than long.Anterior margin uniplicate. Exterior: external shell surfacesmooth with moderate coarse concentric growth lamellae (Fig.6). Sulcus inconspicuous, deep to shallow and with a short andanteriorly rounded sulcus tongue that is curved in dorsal direction.Fold low, rounded, and inconspicuous. Ventral interarea apsa-cline, not very high, and apsacline to gently curved. Foramensubmesothyrid. Delthyrium open and restricted by a pair of

clearly developed deltidial lamellae that are not fused to build adeltidium. Dorsal interarea low and anacline. Preserved parts ofthe shell show calcitic fiber with characteristic athyrididediamond-shaped cross-section (Fig. 7).

Internal ventral valve: juvenile forms with little development ofsecondary shell material in ventral apical region. Due torecrystallization, adult forms were not suitable for serial sections(Fig. 3.2); whether there is more accretion of secondary shellmaterial in adults remains speculative. Lateral apical cavities thin,short, and posteriorly filled with secondary shell material (Figs. 8,9). Ventral muscle field gently embedded into shell material,elongate in longitudinal direction, and has rounded anteriormargins. A myophragm runs through the entire muscle field in ananterior direction. Diductor scars are preserved as longitudinalstriae on the internal mold. A fine muscle bounding ridge isdeveloped around the muscle field, and is preserved as a furrowon the internal mold. Visceral impressions are preserved as radial,short striae and gonoglyphes as small, round knob-like dots on theinternal mold (Fig. 10).

Internal dorsal valve: there is little development of secondaryshell material in the apical region. Dental sockets cone-shapedwith a thin pointing posterior end, rounded in cross-section, andradially straight. Inner socket ridges fine, either straight or gentlycurved over the dental sockets. Inner hinge plates orientedparallel to commissural plane. Outer hinge plates gentlyconvergent in a ventral direction. Outer and inner hinge plates

FIGURE 7—SEM images of the microstructure of shell material of Athyris africana n. sp., Sabkhat Layfarina reef complex, Northwest Africa, upper Givetian(upper Middle Devonian). 1, 3, SMF 94004; 2, 4, SMF 94005. Scale bar¼50 lm.


fused to build the hinge plate which is perforated by a smallforamen. Well-developed cardinal flanges mark the suturebetween inner and outer hinge plates and lead into flat and broadcrura that begin in a ventral direction perpendicular to thecommissural plane. Dorsal adductor field subelliptically elongatein longitudinal section, but shorter than the ventral muscle field,and weakly embedded into the shell material. It is separated by afine myophragm which is preserved as a fine furrow on theinternal mold. The posterior part is separated by a fine medianprocess, the anterior margin is round. Adductor scars arepreserved as radial striae on the internal mold. Posterior andanterior adductors separated by a fine ridge leaving a furrow onthe internal mold. Brachidium consisting of a maximum of 10whorls in specimens with a width of 12 mm. Cones orienteddirectly lateral with tendency to curve gently in an anteriordirection at the distal end. Whorl diameter diminishes equallytowards the lateral end. Whorls elliptical in anterior direction butless curved in ventral valve until almost flat. Stem of jugum notdivided and sharply directed to ventral side. Jugum with a V-shape jugal arch situated shortly anterior of the midpoint of dorsalvalve. Gonoglyphs preserved as knob-like dots arranged in radialstriae on the internal mold. Impressions of growth lamellae at theanterior margin.

Etymology.—Adjective, africana, latinization of African.

Types.—Holotype (SMF 94002), paratypes (all other speci-mens); 117 internal molds of articulated shells. All specimens arestored in the Senckenberg Research Institute, Frankfurt am Main,Germany under the inventory numbers SMF 94000–94007.1–4,94008.1–106. They were collected from the Sabkhat Layfarinareef complex and are of late Givetian (late Middle Devonian).Measurements of the material are given in the online Supple-mental Data file 3.

Occurrence.—Sabkhat Layfarina reef complex, NorthwestAfrica, upper Givetian (Fig. 2).

Remarks.—Athyris africana is compared to coeval specimensfrom northern Gondwanan terranes and North America due to thefact that the assemblage fauna shows affinities to the NorthAmerican Givetian Hamilton Group as has already been stated bySchemm-Gregory and Jansen (2005). Athyris concentrica is oftenregarded as a garbage taxon, with almost all small athyrididespecimens named after the type species; a modern revision is stilllacking. For comparison, specimens of A. concentrica, the typespecies of Athyris, were obtained from the Eifel region inGermany and from the Cantabrian Mountains. The material usedin this work is of Eifelian to Givetian age and has recently beenstudied and figured (e.g., Alvarez et al., 2011). In the followingtext, the number of whorls represents one cone of the brachidiumbut the width refers to a complete specimen. A morphologicalcomparison of the species discussed herein is provided in Table 1.

FIGURE 8—Serial sections of Athyris africana n. sp., SMF 94007.4. Sectioning perpendicular to commissural plane, sectioning distance in mm from posterior.Dotted line represents abraded shell, shell material is highlighted in gray. Abbreviations: dp¼dental plate; dv¼dorsal valve; ja¼jugal arch; jst¼jugal stem;pl¼primary lamella; s¼spiral; ssm¼secondary shell material; vv¼ventral valve. All figures magnified 32.0.


Athyris africana n. sp. differs from Athyris concentrica (vonBuch, 1834) in having smaller and gently dorsibiconvex shellswhich are slightly larger and more strongly dorsibiconvex in thetype species. The fold and sulcus in A. africana are less welldeveloped resulting in a lower sulcus tongue. The lateral apicalcavities are usually not preserved or, if still preserved, filled bysecondary shell material. In A. concentrica they are small,triangular, and posteriorly filled by secondary shell material.Muscle scars in A. africana are embedded into shell material andclearly subdivided in both valves; A. africana shows a clearlydeveloped median septum in both valves, whereas A. concentricaonly shows a short dorsal median septum. Athyris africana shows10 whorls in specimens with a width of 12 mm, whereas A.concentrica shows 10 whorls in a specimen 13.5 mm width. Thejugal arch in A. africana is longer and broader than in A.concentrica; both are V-shape and acute, but distal ends of thearch are almost parallel in A. concentrica, whereas they areradially divergent in A. africana.

Athyris africana differs from A. howardi Alvarez, Modzalev-skaya and Brime, 2011 in having smaller, rounded shells, whereasA. howardi has small to medium shells that are ventribiconvexand rounded to gently transverse. The fold and sulcus in A.

howardi are rounded and only faintly developed so that the sulcustongue in A. howardi is only gently uniplicate. The lateral apicalcavities are small and ovate and almost not filled by secondaryshell material; the dental plates in A. howardi are parallel, thin,and short, whereas they are thick, slightly longer, and parallel inA. africana. In A. howardi only the ventral muscle field is gentlyimpressed and the dorsal median septum is short. In Athyrisafricana both muscle fields are impressed and clearly subdividedby long median septa. Athyris howardi shows nine whorls in 11mm, whereas A. africana shows 10 whorls in 12 mm. The jugalarch in A. howardi is U-shaped and long, whereas it is V-shapedand long in A. africana. Both species show a long jugal stem.

Athyris africana differs from A. murchisoni Brice, 1988 inhaving small and rounded shells, whereas the shells in A.murchisoni are medium to large and transverse; both forms areequi- to dorsibiconvex. The fold and sulcus in A. murchisoni areweakly developed or lacking, in A. africana they are gentlydeveloped but always present. The anterior commissure in A.murchisoni is rectimarginate to gently uniplicate, but alwaysuniplicate in A. africana. The lateral apical cavities in A.murchisoni are small and mostly filled with secondary shellmaterial, in A. africana they are filled or not preserved. In both

FIGURE 9—Serial sections of Athyris africana n. sp., SMF 94007. Sectioning perpendicular to commissural plane, sectioning distance (in mm) from posterior.Dotted line represents abraded shell, shell material is highlighted in gray. Abbreviations: ac¼apical cavity; ajl¼accessory jugal lamella; dc¼denticular cavity;dp¼dental plate; dms¼dorsal median septum; ds¼dental socket; dv¼dorsal valve; ihp¼inner hinge plate; isr¼inner socket ridge; ja¼jugal arch; jst¼jugal stem;lac¼lateral apical cavity; ohp¼outer hinge plate; osr¼outer socket ridge; pc¼pedicle chamber; pl¼primary lamella; s¼spiral; ssm¼secondary shell material;t¼tooth; vv¼ventral valve. All figures magnified 32.0.


species dental plates are thick, but they are divergent to parallel andshort in A. murchisoni and parallel and large in A. africana. Theoutline of the muscle scars in A. murchisoni is unknown but thisspecies shows a long and well-developed dorsal median septum.

Athyris africana differs from A. vittata Hall, 1860 in havingsmaller, rounded and equi- to dorsibiconvex shells, whereas shellsin A. vittata are medium to large, subquadrate, and equi- toventribiconvex. The fold and sulcus in A. vittata are broad,

FIGURE 10—Morphological terms of Athyris africana n. sp., different views of internal molds of articulated shell. 1, ventral, SMF 94004; 2, dorsal, 1010 SMF94003. Scale bar¼10 mm.


subangular to rounded, and deep, which results in a highlyelevated and rounded sulcus tongue at the anterior margin. In A.africana the fold and sulcus are narrower and less pronounced,consequently, the sulcus tongue is lower. Dental plates in A.vittata are thin, short, and divergent to parallel, whereas they arelarge, thick, and parallel in A. africana. The brachidium of A.vittata has 13 whorls in 15 mm wide specimens and a short,parallel, and U-shaped jugal arch. In contrast, A. africana has 10whorls in a 12 mm wide specimen and a long, V-shaped, andacute jugal arch. Muscle scars, lateral apical cavities, and thejugal stem in A. vittata are unknown.

Athyris africana differs from A. spiriferoides (Eaton, 1831) inhaving small to medium and equi- to dorsibiconvex shells,whereas in A. spiriferoides the shells are very large, equi-biconvex, and subcircular. Fold and sulcus are absent or weaklydeveloped in A. spiriferoides and always present in A. africana.The anterior commissure in A. africana is always uniplicate,whereas it is rectimarginate to uniplicate in A. spiriferoides. Thelateral apical cavities in A. spiriferoides are triangular to ovaland almost free of secondary shell material, whereas they arefilled or not preserved in A. africana. The dental plates in A.africana are large, thick, and parallel to each other, whereasthey are short, thin, and divergent in A. spiriferoides. Musclescars in A. africana are well impressed into the shell material,but only weakly impressed in A. spiriferoides. Geitzenauer andJanowski (1964) illustrated a pyritized brachidium of A.spiriferoides from the Givetian Silica Shale which shows 17whorls in a specimen of 17 mm width. Jugal arch and jugal stemin A. spiriferoides are unknown.

CONCLUSIONS

The new species Athyris africana is herein erected; thistaxon is most similar to A. howardi. Both species are restrictedto northern Gondwana, but A. africana shows again that evenduring times of faunal exchange (e.g., Ma and Day, 2003;Schemm-Gregory and Jansen, 2008), the Northwest Africanbrachiopod fauna yields endemic taxa (Schemm-Gregory,2011). In agreement with Alvarez (1990) and Alvarez et al.(2011), it is suggested that A. africana evolved together withA. howardi and A. murchisoni out of A. concentrica, which isslightly older but also exists until the Givetian. Even thoughthe faunal affinities to the North American Hamilton Groupfrom the Middle Devonian were already stated (e.g., Schemm-Gregory and Jansen, 2005), A. vittata and A. spiriferoides areless closely related forms.

This work shows that a method of creating 3-D reconstruc-tion of brachiopod shell material, including the highly fragilebrachidium, from internal molds can be regarded as analternative method if a CT scanner is not available or if thestudied material is not suitable for this technique. Even thoughthe preparation of serial sections and their digital treatment istime consuming, this method allows a very detailed compar-ison of specimens of differing preservation which was notpossible in the past (Schemm-Gregory, 2012; Schemm-Gregory and Feldman, 2012). It is assumed that furtherknowledge of brachiopod taxonomy, systematics, and based onthese data, a more detailed knowledge of phylogeny andbrachiopod evolution lineages will be gained from thisapproach. As an additional benefit, new paleobiogeographicimplications will be obtained in future studies.

ACKNOWLEDGMENTS

Special thanks are due to U. Jansen, P. Konigshof, G.Plodowski, and E. Schindler for collecting the material, to T.Emmel and M. Ricker for laboratorial help, and to C. Frantz (allT

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Senckenberg Research Institute, Frankfurt am Main, Germany)for preparation of SEM pictures. The field work in NorthwestAfrica received financial support from the Paul UngererFoundation (Frankfurt am Main, Germany). E. Schindler kindlyprovided laboratory facilities. M. Sutton (Imperial CollegeLondon, UK) and R. Garwood (University of Manchester, UK)are kindly acknowledged for installation and introduction of theSPIERS software suite. M. H. Henriques (University of Coimbra,Portugal) provided working space for the final preparation of themanuscript. The manuscript profited greatly by the criticalsuggestions and comments of R. B. Blodgett (Anchorage) andH. R. Feldman (American Museum of Natural History, NewYork). This is a contribution to the IGCP Project 596 ‘‘ClimateChange and Biodiversity Patterns in the Mid-Paleozoic.’’

ACCESSIBILITY OF SUPPLEMENTAL DATA

Supplemental data deposited in Dryad repository: http://dx.doi.org/10.5061/dryad.687q0.

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a new givetian athyridid species from northwest africa discovered by three-dimensional...

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