Abstract
Two species of the fenestrate genus Fenestrapora Hall, 1885 are described from the Middle Devonian (middle Eifelian-lower Givetian) of the Rhenish Massif, Germany. The species Fenestrapora transcaucasica Morozova and Lavrentjeva, 1998 is known from the Middle Devonian (Eifelian) of Transcaucasia, Azerbaijan, and from the Middle Devonian (Eifelian) of Sauerland, Germany. One species is new: Fenestrapora tuberculata sp. nov. Numerical statistics were tested for species discrimination of the studied material of three Fenestrapora species from the Lower Devonian of Spain and Middle Devonian of Germany. Discrepancies in the taxonomical and numerical assignment of the studied samples are explained by restriction of the involved characters and their affection by environmental conditions.
Kurzfassung
Zwei Arten der fenestraten Bryozoen-Gattung Fenestrapora Hall, 1885 werden aus dem Mitteldevon des Rheinischen Schiefergebirges beschrieben. Die Art Fenestrapora transcaucasica Morozova and Lavrentjeva, 1998 ist aus dem Mitteldevon (Eifelium) von Transkaukasien (Aserbaidschan) und dem Sauerland (Deutschland) bekannt. Die neue Art Fenestrapora tuberculata sp. nov. wird vorgestellt und beschrieben. Eine numerische statistische Analyse zur Art-Abgrenzung innerhalb des untersuchten Materials (drei Fenestrapora-Arten) aus dem Unter- (Spanien) und Mitteldevon (Deutschland) wurde durchgeführt. Abweichungen in der taxonomischen und numerischen Zuordnung der untersuchten Proben können durch die geringe Anzahl der herangezogenen Merkmale und deren Beeinflussung durch Umweltverhältnisse erklärt werden.
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Introduction
Genus Fenestrapora Hall, 1885, existed for a short period from the Lower Devonian (Emsian) to the Middle Devonian (Givetian) of the USA and Europe. This genus includes only a few species: Fenestrapora biperforata Hall, 1885, from the Lower to Middle Devonian of New York, USA, F. infraporosa (Ulrich, 1886), F. occidentalis Ulrich, 1890, from the Middle Devonian (Givetian) of the USA and F. transcaucasica Morozova and Lavrentjeva, 1998, from the Middle Devonian (Eifelian) of Transcaucasia. The species Fenestrapora occidentalis Ulrich, 1890, has been recently identified from the Lower to Middle Devonian (Emsian-Eifelian) of NW Spain (Ernst 2012; Fig. 7f–h), whereas F. transcaucasica Morozova and Lavrentjeva, 1998, has been found in the Middle Devonian (lower Eifelian) of Sauerland, Germany (Ernst et al. 2012). The new species F. tuberculata sp. nov. is described from the Middle Devonian (Eifelian-Givetian) of the Rhenish Massif, Germany.
The genus Fenestrapora differs from other fenestrates by the presence of aviculomorphs, which are regarded being functionally analogous with avicularia of the cheilostome bryozoans (McKinney 1998; Morozova 2001). These structures are situated in the outer laminated skeleton, mainly on the reverse side of branches, widened crests of keels on the obverse side, or in the thickened skeleton around colony bases. Similar structures occur in Mirifenestella Morozova, 1974, which represent paired aviculomorphs situated on dissepiments and opened to the reverse side. In contrast to avicularia, aviculomorphs are not interpreted as heterozooecia (modified zooecia), but as colonial structures (McKinney 1998). The contrasting hypothesis regards aviculomorphs as remnants of avicularia-like heterozooecia (Morozova and Lavrentjeva 1998; Morozova 2001). The function of aviculomorphs must have been the same as of avicularia: protection and (or) cleaning (Winston 1984). The whole contents of the function of avicularia of cheilostomes is not well understood (McKinney and Jackson 1989).
The aim of this article is to provide a description of a new Fenestrapora species from the Middle Devonian (Eifelian-Givetian) of the Rhenish Massif, Germany, and a numerical comparison of three species from the Devonian of Europe: Fenestrapora occidentalis Ulrich, 1890, F. transcaucasica Morozova and Lavrentjeva, 1998, and F. tuberculata sp. nov.
Geological setting
The material for this study comes from five localities in the western Rhenish Massif, Germany (Fig. 1).
Map of Devonian bryozoan localities in the Rhenish Massif: 1 Brühlborn near Rommersheim; 2 abandoned Müllertchen quarry near Üxheim-Ahütte; 3 “Weinberg” quarry near Kerpen; 4 Gondelsheim; 5 Essingen-Hohenfels
The first locality is situated in the vicinity of Brühlborn near Rommersheim, Prüm Syncline (50°22′, 6°47′). The locality is a road cut in which limestones of the upper Nims Member of the Junkerberg Formation (Eifelian) crop out. These limestones are represented by rudstones and bindstones containing brachiopods, corals, stromatolites, echinoderms and abundant bryozoans.
The second locality is an abandoned Müllertchen quarry in the vicinity of Üxheim-Ahütte, Hillersheim Syncline (50°21′, 6°46′). This quarry contains muddy limestone containing corals, brachiopods, crinoids, sponges and bryozoans. These limestones belong to the Olifant Member of the Ahbach Formation (lowermost Givetian) and the Müllert Subformation of the Ahbach Formation (lowermost Givetian).
The third locality is the well-known abandoned “Weinberg” quarry near Kerpen (50°19′, 6°42′), which reveals the Middle Devonian carbonate succession. The studied material from the “Weinberg” Quarry comes from the Bohnert Member of the Freilingen Formation (upper Eifelian).
The fourth locality lies southwest of the village Gondelsheim, Prüm Syncline (50°14′, 6°28′). Muddy limestones of the Nims Member of the Upper Junkerberg Formation (Eifelian) at this locality contain corals, brachiopods, echinoderms and bryozoans.
The fifth locality is situated in the vicinity of the village Essingen-Hohenfels, eastern Gerolstein Syncline (50°15′, 6°44′), and contains muddy limestones of relatively uncertain stratigraphic position. These sediments represent a transition between the Ahrdorf and Junkerberg formations (Jan Bohatý, pers. comm. 2009).
The stratigraphic nomenclature of the Middle Devonian of the Eifel carbonate synclines follows Struve (1961, 1992, 1996). The terms “formation,” “subformation” and “member” are considered independent and hierarchic, respectively Fig. 2.
Materials and methods
Colonies of Fenestrapora species were studied in thin sections using a binocular microscope in transmitted light. Additionally, a scanning electron microscope was used to study an external morphology. The morphological terminology is modified from Hageman (1991a, b). The following morphological characters were measured: branch width, dissepiment width, fenestrule width, fenestrule length, distance between the branch centers, distance between the dissepiment centers, aperture spacing along the branch, diagonal aperture spacing, autozooecial aperture width, maximum chamber width, thickness of the reverse wall granular layer, thickness of the reverse wall laminated layer, branch thickness including the keel, branch thickness without the keel (measured from the reverse branch surface up to the level of the aperture), aviculomorph length, aviculomorph width, reproductive heterozooecium diameter and reverse surface node diameter (Fig. 3; Tables 1, 2, 3).
Overview of the morphology of Fenestrapora and important measurements. WB branch width, WD dissepiment width, WF fenestrule width, LW fenestrule length, DBC distance between the branch centers, DBD distance between the dissepiment centers, ADB aperture spacing along the branch, AAB diagonal aperture spacing, AW autozooecial aperture width, MAW maximum chamber width, TRW thickness of the reverse wall granular layer, RWT thickness of the reverse wall laminated layer, TB 1 branch thickness including the keel, TB 2 branch thickness without the keel (measured from the reverse branch surface up to the level of the aperture), AvW aviculomorph length, AvL aviculomorph width, GW reproductive heterozooecium diameter
The studied material is housed at the Senckenberg Museum in Frankfurt am Main, Germany, under numbers SMF 21.687–SMF 21.736.
Systematic palaeontology
Phylum Bryozoa Ehrenberg, 1831
Class Stenolaemata Borg, 1926
Superorder Palaeostomata Ma et al., 2014
Order Fenestrata Elias and Condra, 1957
Suborder Fenestellina Astrova and Morozova, 1956
Family Semicosciniidae Morozova, 1987
Genus Fenestrapora Hall, 1885
Type species
Fenestrapora biperforata Hall, 1885. Middle Devonian; NY, USA.
Diagnosis
Reticulate funnel-shaped colonies consisting of sinusoid, relatively wide and thick branches jointed by wide and short dissepiments, sometimes tending to anastomosing. Autozooecia arranged in two rows on the branches, opening onto outer surface of the cone. High median keel widening apically. Autozooecial chambers rectangular in mid-tangential section, short and relatively high, with moderately short vestibules. Autozooecial apertures circular, stellate structures occurring. Axial wall straight to slightly sinusoid, projecting in the median keel. Hemisepta absent. Apparent reproductive heterozooecia represented enlarged zooecia, situated preferably near dissepiments. Aviculomorphs representing circular to oval chambers with triangular projections, positioned on the reverse and obverse colony side, on dissepiments and keels. External laminated skeleton usually well developed, traversed by abundant microstyles. Vesicular skeleton (kenozooecia) often developed. Branch reverse side often with nodes of different sizes.
Comparison
Fenestrapora Hall, 1885 differs from Semicoscinium Prout, 1859, in possessing aviculomorphs, and from Tectulipora Hall, 1888, in possessing aviculomorphs and the absence of a reticulate protecting superstructure. Fenestrapora differs from Mirifenestella Morozova, 1974, in absence of paired aviculomorphs (parazooecia), which open to the reverse side of the colony.
Occurrence
Lower—Middle Devonian (Emsian-Givetian) of the USA, Germany, Spain; Middle Devonian (Eifelian) of Azerbaijan.
Fenestrapora transcaucasica Morozova and Lavrentjeva, 1998.
Fenestrapora transcaucasica Morozova and Lavrentjeva, 1998. a–c SMF 21.687, tangential section showing the reverse colony side with aviculomorphs and nodes. Brühlborn near Rommersheim, Germany; Upper Nims Member of the Junkerberg Formation, Middle Devonian, middle Eifelian. d SMF 21.696, tangential section showing reverse colony side with aviculomorphs and nodes. Üxheim-Ahütte, Germany; Müllert Subformation of the Ahbach Formation, Middle Devonian, lowermost Givetian. e–h SMF 21.701, tangential section showing fenestrules, autozooecial chambers and reproductive heterozooecia (arrow). Üxheim-Ahütte, Germany; Müllert Subformation of the Ahbach Formation, Middle Devonian, lowermost Givetian. i SMF 21.697, tangential section showing autozooecial apertures. Üxheim-Ahütte, Germany; Müllert Subformation of the Ahbach Formation, Middle Devonian, lowermost Givetian
a–h Fenestrapora transcaucasica Morozova and Lavrentjeva, 1998. Üxheim-Ahütte, Germany; Müllert Subformation of the Ahbach Formation, Middle Devonian, lowermost Givetian. a–c SMF 21.695, transverse section showing high keels, autozooecial chambers, internal granular and external laminated skeleton, and aviculomorph (arrow). d–e SMF 21.705, transverse section showing distribution of the internal granular and external laminated skeleton. f, h SMF 21.690, colony obverse surface showing autozooecial apertures and reproductive heterozooecia (arrows). g SMF 21.701, tangential section of reproductive heterozooecium. i Fenestrapora tuberculata sp. nov. Essingen-Hohenfels, Germany; Middle Devonian, middle Eifelian, paratype SMF 21.714, transverse section showing branches and keel with bioimmurated symbiont (Caupokeras calyptos McKinney 2009)
1998 Fenestrapora transcaucasica n. sp. Morozova and Lavrentjeva: p. 56–57, text-figs. 1–2, pl. 4, figs. 4–5, pl. 5, figs. 1–2.
2001 Fenestrapora transcaucasica Morozova and Lavrentjeva, 1998—Morozova: pl. 24, fig. 1, pl. 25, fig. 1.
2008 Fenestrapora transcaucasica Morozova and Lavrentjeva, 1998—Ernst: figs. 3.8–9.
2012 Fenestrapora caucasica Morozova and Lavrentjeva, 1998—Ernst et al.: p. 749, figs. 11a–h [wrong subsequent spelling].
Material
SMF 21.687, SMF 21.690, SMF 21.693–SMF 21.705.
Exterior description
Reticulate colonies in the form of flaring cones, composed of moderately wide branches jointed by wide and short dissepiments. Autozooecia arranged in two rows on branches, situated on the outer colony side, 3–6 spaced on the length of a fenestrule. Fenestrules oval to lens-shaped sharpened toward colony growth direction. Narrow, high median keel present, often club-shaped because of apical widening. Locally lateral projections on keels developed. Vesicular skeleton locally well developed, concentrated near the base of colonies. Nodes on the reverse branch surface present, 0.025–0.070 mm in diameter.
Interior description
Autozooecial chambers rectangular in mid-tangential section, short and relatively high, with moderate vestibules. Axial wall straight, thick, projecting in the median keel. Hemisepta absent. Internal granular skeleton continuous with obverse keel, nodes, microstyles, peristome and across dissepiments, 0.010–0.025 mm thick on the reverse wall. Basal granular wall in autozooecia straight, protruding laterally into fenestrule space and continuous across dissepiments. External laminated skeleton well developed, 0.08–0.165 mm thick on the reverse wall, coarsely laminated and traversed by microstyles. Microstyles 0.005–0.010 mm in diameter. Aviculomorphs occurring only on reverse side of branches, usually arranged in single longitudinal row, 0.11–0.16 mm wide and 0.22–0.40 mm long (Fig. 4a–d). Apparent reproductive heterozooecia representing rounded chambers (enlarged zooecia) occurring preferably on dissepiments (Figs. 4f, 5f–h), 0.26–0.37 mm in diameter. Nodes on the reverse branch surface present, 0.025–0.070 mm in diameter.
Comparison
Fenestrapora transcaucasica Morozova and Lavrentjeva, 1998 is similar to F. occidentalis Ulrich, 1890, from the Middle Devonian of the USA and Lower Devonian of Spain. However, it differs in having 3–5 apertures per fenestrule length vs. 4–7 in F. occidentalis and in shorter distances between dissepiment centers (average 1.09 vs. 1.23 mm in F. occidentalis). Fenestrapora transcaucasica differs from F. tuberculata sp. nov. in having 3–5 apertures per fenestrule length vs. 4–6 in F. tuberculata sp. nov and in shorter distances between dissepiment centers (average 1.09 vs. 1.45 mm in F. tuberculata). Fenestrapora transcaucasica is similar to F. biperforata Hall, 1885, from the Middle Devonian of the USA, but differs from it in having longer fenestrules (0.60–1.05 vs. 0.60–0.70 mm in F. biperforata). Moreover, aviculomorphs in F. transcaucasica are arranged in regular rows on the branch reverse side, whereas aviculomorphs in F. biperforata are more abundant and spaced irregularly on the reverse branch and dissepiment surface.
Remark
One colony of Fenestrapora transcaucasica contains the symbiont Caupokeras calyptos McKinney, 2009, which was apparently a bioimmurated worm-like organism (Fig. 5i).
Occurrence
Meinerzhagener Korallenkalk (=upper Cultrijugatus Beds), lower Eifelian and Upper Nims Member of the Junkerberg Formation, middle Eifelian; Müllert Subformation of the Ahbach Formation, lowermost Givetian, Middle Devonian; Germany; Mucrospirifer diluvianoides–Radiomena irregularis brachiopod zone, upper Eifelian, Middle Devonian, Azerbaijan.
Fenestrapora tuberculata sp. nov.
Fenestrapora tuberculata sp. nov. a Paratype SMF 21.688, external view of a colony with wide base and wide keels as protective structure. b holotype SMF 21.710, tangential section showing branches, fenestrules and autozooecial chambers. Essingen-Hohenfels, Germany; Middle Devonian, middle Eifelian. c Paratype SMF 21.712, tangential section showing branches, fenestrules, and autozooecial chambers. Essingen-Hohenfels, Germany; Middle Devonian, middle Eifelian. d–e Paratype SMF 21.711, tangential section showing branches, fenestrules, autozooecial chambers and giant aviculomorph (arrow). Essingen-Hohenfels, Germany; Middle Devonian, middle Eifelian. f–g Paratype SMF 21.723, tangential section showing reverse branch side with large nodes and giant aviculomorph (arrow). Quarry Weinberg near Kerpen, Germany; Bohnert Member, Freilingen Formation, Middle Devonian, upper Eifelian. h Paratype SMF 21.721, tangential section showing autozooecial apertures. Quarry Weinberg near Kerpen, Germany; Bohnert Member, Freilingen Formation, Middle Devonian, upper Eifelian. i Paratype SMF 21.717, tangential section showing autozooecial apertures and a reproductive heterozooecium. Quarry Weinberg near Kerpen, Germany; Bohnert Member, Freilingen Formation, Middle Devonian, upper Eifelian
a–e Fenestrapora tuberculata sp. nov. a Paratype SMF 21.717, tangential section showing autozooecial aperture with nodes (arrow). Quarry Weinberg near Kerpen, Germany; Bohnert Member, Freilingen Formation, Middle Devonian, upper Eifelian. b Paratype SMF 21.719, transverse section showing distribution of internal granular and external laminated skeleton (arrow: overlapping of the basal walls of two neighboring autozooecia). Quarry Weinberg near Kerpen, Germany; Bohnert Member, Freilingen Formation, Middle Devonian, upper Eifelian. c Paratype SMF 21.734, branch longitudinal section showing autozooecial chambers. Gondelsheim, Germany; Nims Member of the upper Junkerberg Formation, Middle Devonian, middle Eifelian. d Paratype SMF 21.722, branch transverse section showing high keel. Quarry Weinberg near Kerpen, Germany; Bohnert Member, Freilingen Formation, Middle Devonian, upper Eifelian. e Paratype SMF 21.731, branch transverse section showing high keel widened apically. Gondelsheim, Germany; Nims Member of the upper Junkerberg Formation, Middle Devonian, middle Eifelian. f–h Fenestrapora occidentalis Ulrich, 1890, mid-tangential section showing autozooecial chambers, apertures and aviculomorphs (h), GZG.IN.0.010.523a; Llama de Colle near Villayandre, Rio Esla Region, Cantabrian Mountains, NW Spain; lower part of the upper Emsian, Lower Devonian
Etymology
The species name refers to the presence of large nodes on the reverse branch surface.
Holotype
SMF 21.710.
Paratypes
SMF 21.688, SMF 21.691–SMF 21.692, SMF 21.706–709, SMF 21.711–SMF 21.736.
Locality and horizon
Essingen-Hohenfels, eastern Gerolstein syncline, Rhenish Slate Massif, Germany; transition from the Ahrdorf Formation to the Junkerberg Formation, middle Eifelian, Middle Devonian.
Diagnosis
Reticulate colony composed of moderately wide sinusoid branches jointed by wide and short dissepiments; autozooecia in two rows on the branches, situated on the outer colony side, 3–6 spaced on the length of a fenestrule; fenestrules oval to lens-shaped or sub-rectangular; median keel high, often widened apically; autozooecial chambers rectangular in mid-tangential section, short and relatively high, with moderate vestibules; axial wall straight; hemisepta absent; external laminated skeleton well developed, traversed by microstyles and nodes on the reverse branch side; aviculomorphs and apparent reproductive heterozooecia present; giant aviculomorphs occurring.
Exterior description
Reticulate colonies in form of flaring cones, composed of moderately wide branches jointed by wide and short dissepiments. Autozooecia arranged in two rows on the branches, situated on outer colony side, 3–6 spaced on the length of a fenestrule. Fenestrules oval to sub-rectangular or lens-shaped sharpened toward colony growth direction. Narrow, locally very high median keel present, often widening apically. Vesicular skeleton locally well developed, concentrated near the base of colonies. Nodes on the reverse branch surface present, 0.08–0.17 mm in diameter.
Interior description
Autozooecial chambers rectangular in mid-tangential section, short and relatively high, with moderate vestibules. Axial wall straight, projecting in the median keel. Hemisepta absent. Internal granular skeleton continuous with obverse keel, nodes, microstyles, peristome and across dissepiments, 0.010–0.035 mm thick on the reverse wall. Basal granular wall in autozooecia straight, protruding laterally into fenestrule space and continuous across dissepiments, often overlapping with basal wall of neighboring branch (Fig. 7b). External laminated skeleton well developed, 0.05–0.35 mm thick on the reverse wall, coarsely laminated, and traversed by microstyles. Microstyles 0.005–0.010 mm in diameter. Aviculomorphs of two sizes present. Normal aviculomorphs occurring on reverse side of branches, occasionally arranged in single longitudinal row, on the obverse side of the colony on dissepiments and on keels, 0.12–0.17 mm wide and 0.25–0.30 mm long. Giant aviculomorphs regularly occurring on the reverence branch surface near fenestrules, triangular shaped, 0.25–0.35 mm wide and 0.54–0.69 mm long (Fig. 6d–f). Apparent reproductive heterozooecia representing rounded chambers (enlarged zooecia) occurring preferably on dissepiments or opening into fenestrules, 0.22–0.38 mm in diameter (Fig. 6i).
Comparison
Fenestrapora tuberculata sp. nov. is similar to F. occidentalis Ulrich, 1890, from the Middle Devonian of the USA and Lower Devonian of Spain. However, the new species differs in the presence of large nodes on the reverse branch surface, in having giant aviculomorphs and in larger distances between dissepiment centers (average 1.45 vs. 1.23 mm in F. occidentalis). Fenestrapora tuberculata differs from F. transcaucasica Morozova and Lavrentjeva, 1998 in having more apertures per fenestrule length (average 4.8 apertures vs. 3.8 apertures in F. transcaucasica) and in larger nodes on the reverse surface (average node diameter 0.13 vs. 0.048 mm in F. transcaucasica). Fenestrapora tuberculata differs from F. biperforata Hall, 1885, from the Middle Devonian of the USA in having giant aviculomorphs and longer fenestrules (0.66–1.50 vs. 0.60–0.70 mm in F. biperforata).
Occurrence
Nims Member of the upper Junkerberg Formation, middle Eifelian; Bohnert Member of the Freilingen Formation, upper Eifelian, Middle Devonian; Germany.
Numerical statistics
Fenestrate bryozoans reveal complex external and internal morphology, which allows various approaches to numerical statistics (e.g., Hageman 1991a, b; Snyder 1991a, b; Holdener 1994; Hageman and McKinney 2010). The aim of the statistical analysis was to estimate relations between species of Fenestrapora from the Devonian of Europe. Measurements on 12 colonies of three species were included in the analysis. Two colonies of Fenestrapora transcaucasica Morozova and Lavrentjeva, 1998, come from the Middle Devonian of the western Rhenish Massif: FTR 1 (locality 2) and FTR 2 (locality 1). The third sample comes from the Middle Devonian (lower Eifelian) of Kierspe, Sauerland (Ernst et al. 2012): FTR 3. Four colonies of Fenestrapora tuberculata sp. nov. come from the Middle Devonian (Eifelian) of the western Rhenish Massif: FTU 1 (locality 5), FTU 2 (locality 4), FTU 3 (locality 3) and FTU 4 (locality 3). Five colonies of Fenestrapora occidentalis Ulrich, 1890, come from the Lower Devonian (Emsian) of the Cantabrian Mountains, NW Spain (Ernst 2012; Fig. 7f–h): FO 1, FO 2, FO 3, FO 4, and FO 5.
The following ten characters were involved in the analysis: branch width (WB), dissepiment width (WD), fenestrule width (WF), fenestrule length (LF), distance between branch centers (DBC), distance between dissepiment centers (DBD), aperture width (AW), aperture spacing along branch (ADB), aperture spacing diagonally (AAB) and number of apertures per fenestrule length (AF) (Fig. 3). Each character was measured ten times (raw measurements). This set of measurements was chosen because of its availability and the biological importance of individual characters for a bryozoan.
Cluster analysis was performed using PAST software (Hammer et al. 2001). The numerical statistics was carried out using an unweighted pair-group average method (UPGMA), in which clusters are joined based on the average distance between all members in the two groups (Fig. 8). Distances were measured using the Euclidean distance metric. Euclidean distance is the most common use of distance and examines the root of square differences between coordinates of a pair of objects. This method is useful for raw data rather than for standardized ones.
Cluster diagram showing similarities between Fenestrapora species from the Devonian of Europe (UPGMA, unweighted pair group method with arithmetic mean, Euclidean distances metric, PAST ver. 2.01, Hammer et al. 2001)
Discussion
The computed dendrogram (Fig. 8) is based on characters of different taxonomic value. Branch width reflects the size of autozooecia chambers and surrounding extrazooecial material. The latter character can vary strongly with the age of the colony or its part. Younger colonies are usually thinner than the older ones. Dissepiment width corresponds mainly with the thickness of the outer laminated skeleton. Both these characters can affect the fenestrule width and length (wider branches and dissepiments would automatically narrow the fenestrule space). Fenestrule width and length as well as the distances between branch centers and between dissepiment centers reflect the filtering capacity of the colony meshwork (Cowen and Rider 1972; Hageman 1991a, b).
Aperture width, aperture spacing along the branch and diagonally as well as the number of apertures per fenestrule length are characters related to the size and spacing of feeding structures of bryozoans, lophophores (Winston 1977, 1978; McKinney and Jackson 1989; Hageman 1991a, b). These characters usually show the highest stability (low variation) within the colony.
The computed dendrogram shows that the measured specimens produce more or less distinct clusters. Specimen FTU 1 (holotype of Fenestrapora tuberculata sp. nov.) is separated from the rest of the specimen set (clusters 1–4). Cluster 1 is built by two specimens of F. transcaucasica (FTR 1 and FTR 2) and neighbors cluster 2, formed by three specimens of F. occcidenatlis (FO 1, FO 3 and FO4). Three remnant specimens of F. tuberculata are clustered together in cluster 3 (FTU 2, FTU 3 and FTU 4), which neighbors cluster 4, consisting of one specimen of F. transcaucasica (FTR 2) and two specimens of F. occidentalis (FO 2 and FO 5).
The reason for such a discrepancy may be that the feature set does not reflect the whole morphological characteristic of a fenestrate bryozoan. It also shows that at least some of the features are affected by the ecological situation. Spanish material on Fenestrapora occidentalis produces two distinct clusters (material comes from various sources, but seems to be quite homogeneous, see Ernst 2012). Two specimens from locality 3 (FTU 3 and FTU 4) are clustered together within cluster 3. Sample FTU 1 comes from the oldest locality with muddy limestones reflecting low water energy conditions with quite high precipitation rates of fine sediment. Such environments are extreme for bryozoans, which suffer under high levels of sedimentation. Analysis of the character set shows that this sample differs in having the largest fenestrules: average fenestrule width 0.69 mm and fenestrule length 1.28 mm. The second largest fenestrule width is in FTU 4 (0.56 mm) and the second largest fenestrule length in FTU 3 (1.09 mm). This difference could be explained by the effect of the muddy environment in which larger fenestrules gained an advantage in order to avoid occluding the fenestrules by sediment.
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Acknowledgments
Wolfgang Reimers (Kiel) is thanked for his assistance in preparing the thin sections. The late Robert Leunissen, Wollersheim, and Jan Bohatý, Wiesbaden, are thanked for providing interesting samples and help in the field. Steven Hageman, Boone, is thanked for his useful comments during the work on the manuscript. Patrick Wyse Jackson, Dublin, and Zoya Tolokonnikova, Krasnodar, are appreciated for their helpful and constructive reviews. The Deutsche Forschungsgemeinschaft is thanked for financial support (DFG project ER 278/4.1 and 2). This paper is a contribution to IGCP 596 “Climate change and biodiversity patterns in the Mid-Paleozoic.”
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Ernst, A. Fenestrapora (Fenestrata, Bryozoa) from the Middle Devonian of Germany. Paläontol Z 90, 19–32 (2016). https://doi.org/10.1007/s12542-016-0284-x
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DOI: https://doi.org/10.1007/s12542-016-0284-x