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Kalania pusilla, an exceptionally preserved non-calcified alga from the lower Silurian (Aeronian, Llandovery) of Estonia
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ScienceDirect Palaeoworld 24 (2015) 207–214
Kalania pusilla, an exceptionally preserved non-calcified alga from the lower Silurian (Aeronian, Llandovery) of Estonia Oive Tinn ∗ , Viirika Mastik, Leho Ainsaar, Tõnu Meidla Department of Geology, University of Tartu, Ravila 14a, Tartu 50411, Estonia Received 20 September 2014; received in revised form 20 November 2014; accepted 5 December 2014 Available online 15 December 2014
Abstract A Silurian (Llandovery, Aeronian) Lagerstätte in Kalana, Estonia, has revealed exceptionally preserved noncalcified flora of algal fossils. A new dasycladacean algal species Kalania pusilla has been described. The paper describes the fossil specimens, which demonstrate well preserved fine internal anatomy of these siphonous unicellular algae, specifically anatomy of fertile specimens. K. pusilla is characterized by cylindrical uniaxial thallus, two orders of lateral segments — perpendicularly arranged whorls of short bulbous primary laterals, which bear clusters of gametophores in their mature stage and fine hairy secondary laterals. © 2014 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved. Keywords: Fossil algae; Dasycladales; Aeronian; Silurian; Estonia; Kalana
1. Introduction Our knowledge of the early Palaeozoic marine fauna is fairly good — it has been estimated that we have a considerable amount of data of marine skeletal invertebrate fauna (Foote and Sepkoski, 1999; Kidwell and Holland, 2002; Hendy, 2011; Smith and McGowan, 2011) and as a result of intensive studies of “windows into the past” — Lagerstätten — palaeontologists have also got a glimpse of soft-bodied animals in the Earth’s past (Allison and Briggs, 1993; Bottjer et al., 2002). However, life on Earth is supported mainly by primary producers, mostly by phytoplankton in the oceans, but marine macroalgae also play an important role (Lee, 2008; Tait and Schiel, 2011). Although those of macroalgae which secret calcium carbonate (in the form of calcite or aragonite) to form a hard skeleton, have inscribed themselves in the fossil record, the others without such potential have left very scarce and patchy evidence only. Algae constitute a number of polyphyletic or paraphyletic groupings of primarily aquatic photoautotrophic organisms (Graham et al., 2009; Taylor et al., 2009). Molecular clock
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studies suggest that first algae evolved on Earth during the late Paleoproterozoic, some 1.5 Ma ago (Yoon et al., 2004; Taylor et al., 2009), but based on microfossils it has also been argued (Moczydlowska et al., 2011), that their origin predates 1.8 Ma. Although the Precambrian fossil record of algae is meagre, the oldest algal fossils being 1.2 billion years old (Butterfield, 2000), the Phanerozoic record has greatly benefited from the ability of several algal groups to precipitate or deposit CaCO3 (Brownlee and Taylor, 2002). However, as the vast majority of algae do not calcify (Taylor et al., 2009), all fossils of noncalcifying macroalgae are of special value. Although the fossil record of green algae is sparse, our knowledge has greatly progressed due to molecular phylogenetic studies (Heckman et al., 2001; Leliaert et al., 2012). The occurrence of non-calcified algal fossils is very rare, in the Silurian rocks they are known from a few Lagerstätten, where some of them show well preserved delicate morphology. Some green algal fossil localities have been discovered in North America, the best known of them are Waukesha, Wisconsin (LoDuca et al., 2003), Gasport, New York (Ruedemann, 1925; LoDuca and Brett, 1997), Hamilton, Ontario (LoDuca, 1995), Cornwallis Island, Canada (LoDuca et al., 2011), New Brunswick, Canada (LoDuca et al., 2013), and Anticosti Island, Canada (Wang et al., 2014). In Europe occasional exceptionally
http://dx.doi.org/10.1016/j.palwor.2014.12.001 1871-174X/© 2014 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved.
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preserved algal fossils of the Silurian age have been found in Kommersøy, Norway (Hoeg, 1937), Gotland and Skåne, Sweden (Nitecki and Spjeldnaes, 1993; Kenrick and Vinther, 2006), England (Elliott, 1971) and Podolia, Ukraine (Ischenko, 1985). An analogous locality with rare algal fossils has been mentioned (Korde, 1993) in the Eastern Sayan Mountains, Russia. The algal flora in the Kalana Lagerstätte, Estonia, comprises around ten morphologically distinguishable macroscopic species (Tinn et al., 2009). Many algal fossils in Kalana can be classified to the green algal order Dasycladales (Division Chlorophyta, Class Ulvophyceae), an extant group of tropical to subtropical shallow water marine green algae, with a long and highly diverse fossil record that is dominated by calcareous forms (Berger and Kaever, 1992; Kenrick and Vinther, 2006). Having been in existence since the Cambrian period (Deloffre and Genot, 1982; Berger and Kaever, 1992), the dasyclads constitute a large and significant component of the algal geological history that includes five families with nearly 200 genera, some of which with a fairly large number of species (Berger and Kaever, 1992). The dasyclad flora in Kalana includes Palaeocymopolia silurica (Mastik and Tinn, in press), Medusaegraptus mirabilis, Chaetocladus sp., Inopinatella sp., and several species which remain to be treated elsewhere. 2. Geological setting The specimens described here were collected from a quarry near Kalana village in Central Estonia (Fig. 1A, B). The working quarry opens limestone and dolomite succession of the early Aeronian (Llandovery, Silurian) age, in local stratigraphy known as the Raikküla regional stage (Fig. 1C). Biostratigraphically, the Raikküla Stage correlates with the Aspelundia Superzone (Männik, 2007), algal layers belong to Pranognathus tenuis conodont zone (Ainsaar et al., 2014). The outcrop area of the Raikküla Stage extends as an eastward widening zone from the west coast up to eastern Estonia. In boreholes the thickness of the Stage varies between 16.3 m in north-west up to 176.3 m in the south-west, in the outcrop area the thickness ranges mostly between 20 and 75 m (Nestor, 1997). The Raikküla Stage consists of a variety of carbonate rocks, the most characteristic of which are micro- and cryptocrystalline limestones cyclically interbedding with marl- or mudstones in the distal facies and wacke-, pack- and grainstones in the nearshore areas (Nestor, 1997). In several places the carbonates are secondarily dolomitized. However, lagoonal dolomites have also been described in some sections in Central Estonia, where they form the uppermost parts of the shallowing upwards sedimentary cycles (Nestor, 1997). The quarry opens the boundary section of the Jõgeva and Imavere beds, which involve wavy-bedded to nodular micritic secondary dolostone intercalating with thin interlayers or films of dolomitic marlstone. The marlstone intercalations are mostly light-brown, microlaminated, contain kerogenous material and distinctive organic algal detritus, which has been described as ‘dendroids’ Leveillites and Rhadinograptus (Kaljo, 1970; Nestor et al., 2003). The most abundant noncalcified macroscopic algal remains occur in the lowermost part of the quarry, in the light
to dark brown organic-rich, microlaminated, partly dolomitized limestones, which form thin laminae on the bedding planes of micritic limestone layers. The majority of the algal material occurs as fine interlayers in 2–10 cm thick dolomitic beds. Apart from the fossilized algae the beds yield also a number of faunal fossils. These are mostly calcitic, but occasional (partly) dolomitized or silicified specimens occur as well. The normal marine shelly carbonate fauna (rhynchonelliformean brachiopods and gastropods) occurs mostly as coquina lenses of variable thickness and extent, varying between one to several centimetres in thickness and a dozen centimetres to several metres in lateral extent. Occasional rugose and tabulate corals, sponges, nautiloids, crinoids, and bryozoans can also be found. Some surfaces show graptoloid graptolites; micropaleontological samples yield low diversity scolecodont and ostracode fauna. In addition to typical normal marine nearshore sediments and fauna, a few beds show thin lamination, layers with desiccation cracks, abundant leperditiid crustaceans, and occasional eurypterid remains, suggesting short-term periods of shallow lagoonal environments (Tinn et al., 2009). 3. Material The majority of the algal remains is preserved as coalified compressions; however, a few of them reveal three-dimensional preservation together with finely preserved details. As a rule, the algal fossils in Kalana are non-calcified and do not show any traces of possible carbonate skeleton (Tinn et al., 2009). Kalania pusilla occurs as black or dark brown carbonaceous compression fossils. The algal material includes complete intact thalli as well as fragments of different size and state of preservation. Part of the slabs are covered with fine, 1–2 mm thick darkcoloured organic-rich layer of algal thalli and their disintegrated fragments. The other type of material consists of sparse, randomly oriented specimens on light grey limestone, without organic-rich lamina on the top. These two types do not show much difference in the preservation of fine details of fossils. The vertical, as well as lateral distribution of algal fossils in the section is uneven — few surfaces are densely covered with fragmented or whole thalli, but several samples expose sparsely positioned occasional specimens only. The material for the present study includes 78 slabs with K. pusilla, with the total area about 10 m2 . The slabs have more than 200 thalli, plus a number of poorly preserved minuscule fragments. The density of algal fossils on a quadrat of 10 cm × 10 cm is uneven — whereas some slabs show a few (1–5) specimens only, the most densely covered slabs show 20–30 recognizable thalli in the quadrat. The characteristic problem related to the study of the algal fossils in Kalana is the differential exposure of the threedimensionally preserved, but compacted fossils with intricate and complex construction. Whereas the majority of fossils reveal the basic outline of the thalli only (Fig. 2A, left specimen), several specimens exhibit their anatomy at different parts of the longitudinal section (Fig. 2A, right specimen; 2F). Generally the slabs with K. pusilla reveal monospecific assemblage, exhibiting fossils of one algal species only.
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Fig. 1. (C) The stratigraphical column demonstrates the Kalana quarry, combined from the eastern and western parts of the quarry. (A and B) The geographical position and simplified geological map of Estonia. Grey colour indicates the outcrop area and the thick line the boundary of the distribution area of the Raikküla regional stage.
Occasional slabs show also rare fragments of Palaeocymopolia silurica (Mastik and Tinn, in press), Leveilleites hartnageli Foerste, 1923 or Medusaegraptus sp. 4. Systematic palaeobotany Empire Eukaryota Kingdom Plantae Division Chlorophyta Pascher, 1914, emend. Lewis and McCourt, 2004 Class Ulvophyceae Mattox and Stewart, 1984 Order Dasycladales Pascher, 1931 Family Dasycladaceae Kützing, 1843 Genus Kalania n. gen. Diagnosis. Thallus simple, cylindrical, uniaxial and unbranched. Pyriform primary laterals regularly arranged around the main axis in whorls of six, each branched to form two long and slender secondary laterals. In the mature stage of the cell ovate gametophores connected to the sides of the primary laterals are produced. Kalania pusilla n. gen. n. sp. (Figs. 2–4) Types. Holotype TUG 1269-33 (Fig. 2F), paratype TUG 1269-2 (Fig. 2G).
Etymology. The genus name refers to the locality, the species name indicates the small size of the specimens from the Kalana Lagerstätte. Gender feminine. Type locality. Kalana quarry, Estonia. Diagnosis. As for genus. Repository. The described and photographed material is housed at the Natural History Museum of the University of Tartu, Estonia, under the collection number TUG 1269. Description. The unbranched cylindrical thallus is straight or gently curved (Fig. 2A, B). The longest of the fragmentary specimens measures 67 mm, mean length of the complete thalli is 40 mm. The diameter of the thalli ranges between 2.5 and 4.2 mm, mean diameter is 3.1 mm. A few specimens show well preserved carbonaceous central axis (Fig. 2A, B, E). The collection does not contain any thalli with the full length of the central axis visible beneath the laterals, but portions of the main axis can be observed with at least six whorls of primary laterals. The distance between two successive whorls is about 500 m (Fig. 3A). The diameter of the central axis is around 190 m, tapering slightly from the base to the top of the thallus. Occasionally, in some specimens, the central axis shows slight but regular widening at the whorls of the primary laterals (Fig. 3A, B). The whorls consist of six short perpendicularly positioned primary laterals, each with pyriform shape, widening towards the distal end (Fig. 3A1, A2). The length of the primary lateral is about 85 m, the diameter, measured at the tip, is
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Fig. 2. Kalania pusilla n. gen. n. sp. from the Aeronian of Estonia. (A) TUG 1269-27 (left) and TUG 1269-28 (right); two almost complete specimens, the right one demonstrating partly preserved central axis. (B) TUG 1269-29, specimen showing well-preserved second order laterals. (C) TUG 1269-30, specimen showing a tuft of short filaments at the top of the thallus. (D) TUG 1269-31, specimen showing a tuft of short filaments at the top of the thallus. (E) TUG 1269-32, specimen showing well-preserved central axis, whorls of primary laterals (pl) and fragments of second order laterals (sl). (F) TUG 1269-33, specimen showing non-calcified thallus in the lower part and gametophores near the tip of the thallus. (G) TUG 1269-2, specimen showing second order laterals.
66.6–70 m. Each of the primary laterals branch to form two sterile, about 2 mm long slender secondary laterals (Fig. 2B, E, G). The thallus terminates with a bundle of short fine filaments (Fig. 2C, D). No higher order branchings of the laterals have been observed. In the mature stage of the cell each of the primary branches produces gametophores located along their sides (Figs. 2F, 3A2, C–F). Gametophores are ovate (Figs. 2F1, 3C–F), with variable length which ranges between 44 and 82 m. The distal ends of the gametophores show small depression (Fig. 3E). Remarks. The number and exact position of gametophores on the sides of the primary laterals are difficult to determine, it seems that each lateral bears clusters of two or three gametophores at their sides (Figs. 2F, 4A, B).
5. Discussion Dasyclads, or dasycladacean algae, are an order of unicellular organisms within the Division Chlorophyta or green algae. The main characteristics of the order are the radially symmetrical thallus architecture and the siphonous body plan of the cell (Lee, 2008). The basic criteria, on which the classification of the dasycladales is based, are the arrangement of primary laterals, the position of cysts at the maturity of the thallus, and the presence or absence of the branching of the laterals (Deloffre and Genot, 1982; Berger and Kaever, 1992). Whereas in the aspondyl type the primary branches do not show any particular positioning, in the euspondyl type they are arranged in verticils around the main axis, and in the third, metaspondyl type,
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Fig. 3. Kalania pusilla n. gen. n. sp., scanning electron microscope images. (A) TUG 1269-34, central axis with whorls of primary laterals (pl). (B) TUG 1269-35, central axis with whorls of primary laterals and imprints of gametophores. (C) TUG 1269-36, fragment of K. pusilla showing clusters of gametophores on the rock. (D–F) TUG 1269-36, close images of gametophores (g).
the primary branches in verticils are grouped into clusters. The specimens of K. pusilla with exposed well-preserved principal axis reveal the euspondyl type of arrangement of the branches (Fig. 3A, B). The second parameter is the position of the reproductive structures when the cell reaches maturity. In the most primitive type, and evolutionarily the earliest (Pia, 1920; LoDuca et al., 2011), the cysts remain in the main axis; in the more advanced, the cladospore type, the cysts are produced in the laterals. In the third, choristospore type, the cysts are produced in specialized structures called gametophores. Some rare specimens of K. pusilla reveal the position of the reproductive organs (Fig. 2F). These are arranged at the sides of the first order laterals and although the specimens do not expose all details of the arrangement, we assume that they are organized in clusters at the sides of the first order branch (Figs. 3A, B, 4A, B).
The third criterion is presence or absence of branching of the laterals. Some specimens have preserved faint traces of fine and long second order laterals (Fig. 2A, B), a few specimens show more robust carbonized second order laterals (Fig. 2E); any higher order laterals have not been detected. The tufts at the tips of the thalli consist of unbranched short fine filaments (Figs. 2C, D, 4C). To some extent Kalania pusilla is similar to an extant dasyclad genus Bornetella Munier-Chalmas, 1877, which inhabits tropical and subtropical seas in the southern hemisphere. Bornetella is a 2 to 3 cm long, club-shaped to cylindrical seaweed with blunt and rounded end, sometimes with tufts of filaments at the tips. The thallus of Bornetella is composed of minute first and second order branches, which are packed tightly around the central axis to form the cylindrical shape. The gametophores of Bornetella are positioned along the sides of the primary
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Fig. 4. Kalania pusilla n. gen. n. sp. (A) Reconstruction of the vertical section of the thallus. (B) Reconstruction of the cross-section of the thallus. (C) Reconstruction of living thalli of Kalania pusilla on the sea-bottom.
laterals. The recent species are moderately calcified (Berger and Kaever, 1992). Several characteristics distinguish Kalania from the recent genus Bornetella. First, the number of primary branches around the axis in Bornetella is 24–28; in Kalania the number is considerably smaller. Second, the fertile primary branches in Bornetella are long, extending almost to the cortex, which is composed of the inflated ball-shaped ends of the short secondary laterals. The extent of calcification also differentiates Bornetella from Kalania. Another conceivably close taxon is the fossil dasyclad genus Jodotella L. Morellet and J. Morellet, 1913, which has been described from the Maastrichtian (Parente, 1997; Schlueter et al., 2008) and Palaeocene of Italy (Vecsei and Moussavian, 1997), France (Segonzac, 1976; Genot, 1980), and Slovenia (Deloffre and Radoicic, 1978). Although this genus is known only from poor record of heavily calcified fragments, the general shape, construction, and anatomy is comparable with Kalania. The thallus of Jodotella is cylindrical and uniaxial, the central axis bears whorls of short primary laterals, each of which bears two secondary laterals and lateral clusters of two to three gametophores (Deloffre and Genot, 1982). The main differences between these two genera lie in the number of primary laterals in the whorls of primary laterals and in the extent of calcification.
Possibly one of the closest taxon to Kalania is Callisphenus gracilis Hoeg, 1937 from the Silurian (Wenlock) of Norway. The largest of the two described specimens is 22 mm long and 5 mm wide, the other slightly smaller. The specimens are uncalcified, without any detectable verticillation, but showing tubular laterals radiating from the central axis towards the surface and forming a coherent tissue. The general morphology — the shape and size of the uniaxial uncalcified thallus are comparable to that of Kalania, the major difference lies in the laterals. Whereas Kalania shows regularly arranged whorls of short pyriform primary laterals which give rise to fine long secondary laterals, the Callisphenus specimens show only fine first order laterals, no higher order laterals have been detected. However, as the material of C. gracilis is rather poor, it is difficult to draw further conclusions about its taxonomic relationships with K. pusilla. Finally, we conclude that although there do exist several dasycladacean algae with comparable shape and construction, the above described Kalania pusilla with its uncalcified thallus and details of its internal anatomy is unique among them. Acknowledgements The research was supported by Estonian Science Agency projects GLOOM 9231 and IUT 20-34; this paper is also a
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contribution to the IGCP Project 591. We thank the anonymous reviewers, who provided helpful suggestions that improved the quality of the manuscript.
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ScienceDirect Palaeoworld 24 (2015) 207–214
Kalania pusilla, an exceptionally preserved non-calcified alga from the lower Silurian (Aeronian, Llandovery) of Estonia Oive Tinn ∗ , Viirika Mastik, Leho Ainsaar, Tõnu Meidla Department of Geology, University of Tartu, Ravila 14a, Tartu 50411, Estonia Received 20 September 2014; received in revised form 20 November 2014; accepted 5 December 2014 Available online 15 December 2014
Abstract A Silurian (Llandovery, Aeronian) Lagerstätte in Kalana, Estonia, has revealed exceptionally preserved noncalcified flora of algal fossils. A new dasycladacean algal species Kalania pusilla has been described. The paper describes the fossil specimens, which demonstrate well preserved fine internal anatomy of these siphonous unicellular algae, specifically anatomy of fertile specimens. K. pusilla is characterized by cylindrical uniaxial thallus, two orders of lateral segments — perpendicularly arranged whorls of short bulbous primary laterals, which bear clusters of gametophores in their mature stage and fine hairy secondary laterals. © 2014 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved. Keywords: Fossil algae; Dasycladales; Aeronian; Silurian; Estonia; Kalana
1. Introduction Our knowledge of the early Palaeozoic marine fauna is fairly good — it has been estimated that we have a considerable amount of data of marine skeletal invertebrate fauna (Foote and Sepkoski, 1999; Kidwell and Holland, 2002; Hendy, 2011; Smith and McGowan, 2011) and as a result of intensive studies of “windows into the past” — Lagerstätten — palaeontologists have also got a glimpse of soft-bodied animals in the Earth’s past (Allison and Briggs, 1993; Bottjer et al., 2002). However, life on Earth is supported mainly by primary producers, mostly by phytoplankton in the oceans, but marine macroalgae also play an important role (Lee, 2008; Tait and Schiel, 2011). Although those of macroalgae which secret calcium carbonate (in the form of calcite or aragonite) to form a hard skeleton, have inscribed themselves in the fossil record, the others without such potential have left very scarce and patchy evidence only. Algae constitute a number of polyphyletic or paraphyletic groupings of primarily aquatic photoautotrophic organisms (Graham et al., 2009; Taylor et al., 2009). Molecular clock
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studies suggest that first algae evolved on Earth during the late Paleoproterozoic, some 1.5 Ma ago (Yoon et al., 2004; Taylor et al., 2009), but based on microfossils it has also been argued (Moczydlowska et al., 2011), that their origin predates 1.8 Ma. Although the Precambrian fossil record of algae is meagre, the oldest algal fossils being 1.2 billion years old (Butterfield, 2000), the Phanerozoic record has greatly benefited from the ability of several algal groups to precipitate or deposit CaCO3 (Brownlee and Taylor, 2002). However, as the vast majority of algae do not calcify (Taylor et al., 2009), all fossils of noncalcifying macroalgae are of special value. Although the fossil record of green algae is sparse, our knowledge has greatly progressed due to molecular phylogenetic studies (Heckman et al., 2001; Leliaert et al., 2012). The occurrence of non-calcified algal fossils is very rare, in the Silurian rocks they are known from a few Lagerstätten, where some of them show well preserved delicate morphology. Some green algal fossil localities have been discovered in North America, the best known of them are Waukesha, Wisconsin (LoDuca et al., 2003), Gasport, New York (Ruedemann, 1925; LoDuca and Brett, 1997), Hamilton, Ontario (LoDuca, 1995), Cornwallis Island, Canada (LoDuca et al., 2011), New Brunswick, Canada (LoDuca et al., 2013), and Anticosti Island, Canada (Wang et al., 2014). In Europe occasional exceptionally
http://dx.doi.org/10.1016/j.palwor.2014.12.001 1871-174X/© 2014 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved.
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preserved algal fossils of the Silurian age have been found in Kommersøy, Norway (Hoeg, 1937), Gotland and Skåne, Sweden (Nitecki and Spjeldnaes, 1993; Kenrick and Vinther, 2006), England (Elliott, 1971) and Podolia, Ukraine (Ischenko, 1985). An analogous locality with rare algal fossils has been mentioned (Korde, 1993) in the Eastern Sayan Mountains, Russia. The algal flora in the Kalana Lagerstätte, Estonia, comprises around ten morphologically distinguishable macroscopic species (Tinn et al., 2009). Many algal fossils in Kalana can be classified to the green algal order Dasycladales (Division Chlorophyta, Class Ulvophyceae), an extant group of tropical to subtropical shallow water marine green algae, with a long and highly diverse fossil record that is dominated by calcareous forms (Berger and Kaever, 1992; Kenrick and Vinther, 2006). Having been in existence since the Cambrian period (Deloffre and Genot, 1982; Berger and Kaever, 1992), the dasyclads constitute a large and significant component of the algal geological history that includes five families with nearly 200 genera, some of which with a fairly large number of species (Berger and Kaever, 1992). The dasyclad flora in Kalana includes Palaeocymopolia silurica (Mastik and Tinn, in press), Medusaegraptus mirabilis, Chaetocladus sp., Inopinatella sp., and several species which remain to be treated elsewhere. 2. Geological setting The specimens described here were collected from a quarry near Kalana village in Central Estonia (Fig. 1A, B). The working quarry opens limestone and dolomite succession of the early Aeronian (Llandovery, Silurian) age, in local stratigraphy known as the Raikküla regional stage (Fig. 1C). Biostratigraphically, the Raikküla Stage correlates with the Aspelundia Superzone (Männik, 2007), algal layers belong to Pranognathus tenuis conodont zone (Ainsaar et al., 2014). The outcrop area of the Raikküla Stage extends as an eastward widening zone from the west coast up to eastern Estonia. In boreholes the thickness of the Stage varies between 16.3 m in north-west up to 176.3 m in the south-west, in the outcrop area the thickness ranges mostly between 20 and 75 m (Nestor, 1997). The Raikküla Stage consists of a variety of carbonate rocks, the most characteristic of which are micro- and cryptocrystalline limestones cyclically interbedding with marl- or mudstones in the distal facies and wacke-, pack- and grainstones in the nearshore areas (Nestor, 1997). In several places the carbonates are secondarily dolomitized. However, lagoonal dolomites have also been described in some sections in Central Estonia, where they form the uppermost parts of the shallowing upwards sedimentary cycles (Nestor, 1997). The quarry opens the boundary section of the Jõgeva and Imavere beds, which involve wavy-bedded to nodular micritic secondary dolostone intercalating with thin interlayers or films of dolomitic marlstone. The marlstone intercalations are mostly light-brown, microlaminated, contain kerogenous material and distinctive organic algal detritus, which has been described as ‘dendroids’ Leveillites and Rhadinograptus (Kaljo, 1970; Nestor et al., 2003). The most abundant noncalcified macroscopic algal remains occur in the lowermost part of the quarry, in the light
to dark brown organic-rich, microlaminated, partly dolomitized limestones, which form thin laminae on the bedding planes of micritic limestone layers. The majority of the algal material occurs as fine interlayers in 2–10 cm thick dolomitic beds. Apart from the fossilized algae the beds yield also a number of faunal fossils. These are mostly calcitic, but occasional (partly) dolomitized or silicified specimens occur as well. The normal marine shelly carbonate fauna (rhynchonelliformean brachiopods and gastropods) occurs mostly as coquina lenses of variable thickness and extent, varying between one to several centimetres in thickness and a dozen centimetres to several metres in lateral extent. Occasional rugose and tabulate corals, sponges, nautiloids, crinoids, and bryozoans can also be found. Some surfaces show graptoloid graptolites; micropaleontological samples yield low diversity scolecodont and ostracode fauna. In addition to typical normal marine nearshore sediments and fauna, a few beds show thin lamination, layers with desiccation cracks, abundant leperditiid crustaceans, and occasional eurypterid remains, suggesting short-term periods of shallow lagoonal environments (Tinn et al., 2009). 3. Material The majority of the algal remains is preserved as coalified compressions; however, a few of them reveal three-dimensional preservation together with finely preserved details. As a rule, the algal fossils in Kalana are non-calcified and do not show any traces of possible carbonate skeleton (Tinn et al., 2009). Kalania pusilla occurs as black or dark brown carbonaceous compression fossils. The algal material includes complete intact thalli as well as fragments of different size and state of preservation. Part of the slabs are covered with fine, 1–2 mm thick darkcoloured organic-rich layer of algal thalli and their disintegrated fragments. The other type of material consists of sparse, randomly oriented specimens on light grey limestone, without organic-rich lamina on the top. These two types do not show much difference in the preservation of fine details of fossils. The vertical, as well as lateral distribution of algal fossils in the section is uneven — few surfaces are densely covered with fragmented or whole thalli, but several samples expose sparsely positioned occasional specimens only. The material for the present study includes 78 slabs with K. pusilla, with the total area about 10 m2 . The slabs have more than 200 thalli, plus a number of poorly preserved minuscule fragments. The density of algal fossils on a quadrat of 10 cm × 10 cm is uneven — whereas some slabs show a few (1–5) specimens only, the most densely covered slabs show 20–30 recognizable thalli in the quadrat. The characteristic problem related to the study of the algal fossils in Kalana is the differential exposure of the threedimensionally preserved, but compacted fossils with intricate and complex construction. Whereas the majority of fossils reveal the basic outline of the thalli only (Fig. 2A, left specimen), several specimens exhibit their anatomy at different parts of the longitudinal section (Fig. 2A, right specimen; 2F). Generally the slabs with K. pusilla reveal monospecific assemblage, exhibiting fossils of one algal species only.
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Fig. 1. (C) The stratigraphical column demonstrates the Kalana quarry, combined from the eastern and western parts of the quarry. (A and B) The geographical position and simplified geological map of Estonia. Grey colour indicates the outcrop area and the thick line the boundary of the distribution area of the Raikküla regional stage.
Occasional slabs show also rare fragments of Palaeocymopolia silurica (Mastik and Tinn, in press), Leveilleites hartnageli Foerste, 1923 or Medusaegraptus sp. 4. Systematic palaeobotany Empire Eukaryota Kingdom Plantae Division Chlorophyta Pascher, 1914, emend. Lewis and McCourt, 2004 Class Ulvophyceae Mattox and Stewart, 1984 Order Dasycladales Pascher, 1931 Family Dasycladaceae Kützing, 1843 Genus Kalania n. gen. Diagnosis. Thallus simple, cylindrical, uniaxial and unbranched. Pyriform primary laterals regularly arranged around the main axis in whorls of six, each branched to form two long and slender secondary laterals. In the mature stage of the cell ovate gametophores connected to the sides of the primary laterals are produced. Kalania pusilla n. gen. n. sp. (Figs. 2–4) Types. Holotype TUG 1269-33 (Fig. 2F), paratype TUG 1269-2 (Fig. 2G).
Etymology. The genus name refers to the locality, the species name indicates the small size of the specimens from the Kalana Lagerstätte. Gender feminine. Type locality. Kalana quarry, Estonia. Diagnosis. As for genus. Repository. The described and photographed material is housed at the Natural History Museum of the University of Tartu, Estonia, under the collection number TUG 1269. Description. The unbranched cylindrical thallus is straight or gently curved (Fig. 2A, B). The longest of the fragmentary specimens measures 67 mm, mean length of the complete thalli is 40 mm. The diameter of the thalli ranges between 2.5 and 4.2 mm, mean diameter is 3.1 mm. A few specimens show well preserved carbonaceous central axis (Fig. 2A, B, E). The collection does not contain any thalli with the full length of the central axis visible beneath the laterals, but portions of the main axis can be observed with at least six whorls of primary laterals. The distance between two successive whorls is about 500 m (Fig. 3A). The diameter of the central axis is around 190 m, tapering slightly from the base to the top of the thallus. Occasionally, in some specimens, the central axis shows slight but regular widening at the whorls of the primary laterals (Fig. 3A, B). The whorls consist of six short perpendicularly positioned primary laterals, each with pyriform shape, widening towards the distal end (Fig. 3A1, A2). The length of the primary lateral is about 85 m, the diameter, measured at the tip, is
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Fig. 2. Kalania pusilla n. gen. n. sp. from the Aeronian of Estonia. (A) TUG 1269-27 (left) and TUG 1269-28 (right); two almost complete specimens, the right one demonstrating partly preserved central axis. (B) TUG 1269-29, specimen showing well-preserved second order laterals. (C) TUG 1269-30, specimen showing a tuft of short filaments at the top of the thallus. (D) TUG 1269-31, specimen showing a tuft of short filaments at the top of the thallus. (E) TUG 1269-32, specimen showing well-preserved central axis, whorls of primary laterals (pl) and fragments of second order laterals (sl). (F) TUG 1269-33, specimen showing non-calcified thallus in the lower part and gametophores near the tip of the thallus. (G) TUG 1269-2, specimen showing second order laterals.
66.6–70 m. Each of the primary laterals branch to form two sterile, about 2 mm long slender secondary laterals (Fig. 2B, E, G). The thallus terminates with a bundle of short fine filaments (Fig. 2C, D). No higher order branchings of the laterals have been observed. In the mature stage of the cell each of the primary branches produces gametophores located along their sides (Figs. 2F, 3A2, C–F). Gametophores are ovate (Figs. 2F1, 3C–F), with variable length which ranges between 44 and 82 m. The distal ends of the gametophores show small depression (Fig. 3E). Remarks. The number and exact position of gametophores on the sides of the primary laterals are difficult to determine, it seems that each lateral bears clusters of two or three gametophores at their sides (Figs. 2F, 4A, B).
5. Discussion Dasyclads, or dasycladacean algae, are an order of unicellular organisms within the Division Chlorophyta or green algae. The main characteristics of the order are the radially symmetrical thallus architecture and the siphonous body plan of the cell (Lee, 2008). The basic criteria, on which the classification of the dasycladales is based, are the arrangement of primary laterals, the position of cysts at the maturity of the thallus, and the presence or absence of the branching of the laterals (Deloffre and Genot, 1982; Berger and Kaever, 1992). Whereas in the aspondyl type the primary branches do not show any particular positioning, in the euspondyl type they are arranged in verticils around the main axis, and in the third, metaspondyl type,
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Fig. 3. Kalania pusilla n. gen. n. sp., scanning electron microscope images. (A) TUG 1269-34, central axis with whorls of primary laterals (pl). (B) TUG 1269-35, central axis with whorls of primary laterals and imprints of gametophores. (C) TUG 1269-36, fragment of K. pusilla showing clusters of gametophores on the rock. (D–F) TUG 1269-36, close images of gametophores (g).
the primary branches in verticils are grouped into clusters. The specimens of K. pusilla with exposed well-preserved principal axis reveal the euspondyl type of arrangement of the branches (Fig. 3A, B). The second parameter is the position of the reproductive structures when the cell reaches maturity. In the most primitive type, and evolutionarily the earliest (Pia, 1920; LoDuca et al., 2011), the cysts remain in the main axis; in the more advanced, the cladospore type, the cysts are produced in the laterals. In the third, choristospore type, the cysts are produced in specialized structures called gametophores. Some rare specimens of K. pusilla reveal the position of the reproductive organs (Fig. 2F). These are arranged at the sides of the first order laterals and although the specimens do not expose all details of the arrangement, we assume that they are organized in clusters at the sides of the first order branch (Figs. 3A, B, 4A, B).
The third criterion is presence or absence of branching of the laterals. Some specimens have preserved faint traces of fine and long second order laterals (Fig. 2A, B), a few specimens show more robust carbonized second order laterals (Fig. 2E); any higher order laterals have not been detected. The tufts at the tips of the thalli consist of unbranched short fine filaments (Figs. 2C, D, 4C). To some extent Kalania pusilla is similar to an extant dasyclad genus Bornetella Munier-Chalmas, 1877, which inhabits tropical and subtropical seas in the southern hemisphere. Bornetella is a 2 to 3 cm long, club-shaped to cylindrical seaweed with blunt and rounded end, sometimes with tufts of filaments at the tips. The thallus of Bornetella is composed of minute first and second order branches, which are packed tightly around the central axis to form the cylindrical shape. The gametophores of Bornetella are positioned along the sides of the primary
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Fig. 4. Kalania pusilla n. gen. n. sp. (A) Reconstruction of the vertical section of the thallus. (B) Reconstruction of the cross-section of the thallus. (C) Reconstruction of living thalli of Kalania pusilla on the sea-bottom.
laterals. The recent species are moderately calcified (Berger and Kaever, 1992). Several characteristics distinguish Kalania from the recent genus Bornetella. First, the number of primary branches around the axis in Bornetella is 24–28; in Kalania the number is considerably smaller. Second, the fertile primary branches in Bornetella are long, extending almost to the cortex, which is composed of the inflated ball-shaped ends of the short secondary laterals. The extent of calcification also differentiates Bornetella from Kalania. Another conceivably close taxon is the fossil dasyclad genus Jodotella L. Morellet and J. Morellet, 1913, which has been described from the Maastrichtian (Parente, 1997; Schlueter et al., 2008) and Palaeocene of Italy (Vecsei and Moussavian, 1997), France (Segonzac, 1976; Genot, 1980), and Slovenia (Deloffre and Radoicic, 1978). Although this genus is known only from poor record of heavily calcified fragments, the general shape, construction, and anatomy is comparable with Kalania. The thallus of Jodotella is cylindrical and uniaxial, the central axis bears whorls of short primary laterals, each of which bears two secondary laterals and lateral clusters of two to three gametophores (Deloffre and Genot, 1982). The main differences between these two genera lie in the number of primary laterals in the whorls of primary laterals and in the extent of calcification.
Possibly one of the closest taxon to Kalania is Callisphenus gracilis Hoeg, 1937 from the Silurian (Wenlock) of Norway. The largest of the two described specimens is 22 mm long and 5 mm wide, the other slightly smaller. The specimens are uncalcified, without any detectable verticillation, but showing tubular laterals radiating from the central axis towards the surface and forming a coherent tissue. The general morphology — the shape and size of the uniaxial uncalcified thallus are comparable to that of Kalania, the major difference lies in the laterals. Whereas Kalania shows regularly arranged whorls of short pyriform primary laterals which give rise to fine long secondary laterals, the Callisphenus specimens show only fine first order laterals, no higher order laterals have been detected. However, as the material of C. gracilis is rather poor, it is difficult to draw further conclusions about its taxonomic relationships with K. pusilla. Finally, we conclude that although there do exist several dasycladacean algae with comparable shape and construction, the above described Kalania pusilla with its uncalcified thallus and details of its internal anatomy is unique among them. Acknowledgements The research was supported by Estonian Science Agency projects GLOOM 9231 and IUT 20-34; this paper is also a
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contribution to the IGCP Project 591. We thank the anonymous reviewers, who provided helpful suggestions that improved the quality of the manuscript.
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