The Pa/aeobotanisr 59/20}0) .' }07-JJ9 003/-0/74/20/0 $100 Contemporary taxonomic perspectives offossil Coralline Red Algae: their possible origin and evolution AMIT K. GHOSH AND SUMANSARKAR Birbal Sahni Insti(ute ofPalaeobotany, 53 University Road, Lucknow 226007, India. (Received 0I July, 20 I0; revised version accepted 26 August, 20 I0) ABSTRACf Ghosh AK & Sarkar S 20 IO. Contemporary taxonomic perspectives offossil Coralline Red Algae: their possible origin and evolution. The Palaeobotanist 59(1-3) : 107-119. Studies done by various phycologists have brought about remarkable changes in the present-day coralline algal taxonomy. The taxonomy offossil coralline red algae also has been under the process of continuous revision and modification since 1993. Prior to 1993 it was believed that several diagnostic characters used in recent coralline red algae were unpreservable in fossil forms. Palaeoalgologists have now understood the value ofunification oftaxonomy, for extant and fossil corallines to accurately interpret the phylogeny, palaeoecology and palaeobiogeography. Phylogenetically, the corallines are very important as they represent a major evolutionary line within the red algae as evidenced by anatomical studies on recent forms as well as various studies on gene sequence analysis. The present contribution deals with the remarkable changes that have taken place since 1993 in the taxonomic aspects offossil coralline algae and the modern trends ofresearch in this context. Presently, an attempt has been made to establish the possible origin and evolution ofcoralline red algae. Key-words-Coralline Red Algae, Classification, Taxonomy, Possible Origin, Evolution. ~ ~ ~ ~ ~ if ti'iCflI{ift'1 cllffCfl{OI: \RCflT B'-qq ~ ~ fctcf;m ~ cf;. mrsr ~ ~ meIR mu~ ~ ~ ~ J1~ ~ ~ ~ ~ ~ &m Fcm "l1Q; B q#fit it -mnqf{UT Wrr ~ ~ ~ ;;ftm~11 ~ ~ ~ Trtt~ ~ tl~i't'-R ~ 'T<IT ~ I <5T q#fit 1993 B <5T mr <f; Wrr ~ fcl~qm ~~ ~ ~ ~ ~ ~ ~ ;;frcrr~11 'T<IT ~ I 1993 <f; "lTIi Wrr 'T<IT m F<li it m f.RR ~ ~ ~ TT~<'1fil$1I~41 ~, ~ ~~ <r~~ ~ ~ it I ;r om <5T B ams<lT 'liB ~ ;;ftm~11 ~ ~ ~ V1IRi<i~lq ~ ~ fcml1R r:;cT <f; q#fit cfi cfi 11R 'h1 J1q wrn fW1r 'T<IT I B wum ~ ~ ~ ~ ~ ~ ~TTf\ft<P J1~ m~-m~;;fA ~ fcl~WroT ~ ~ ~ F<li 1R cfi cfi IRMt <f; it ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ;;ftm~11 it tl5lT m I -mnqf{UT it q;rf 'Iirill <5T ~ ~ ~ ~ ~ ~QR "1f~ ~ ~ ~ ~I ~ ~i't~ ~ it <5T it 1993 B fW1r it ~ ~ ~ ~ 'limT~T ~ ~ cfi r:;cT fcrcm:r 'h1 'liB it c% <5T 7J{ I . ~-~~ ~ ~, ~, q#fit, tl'l1cl' ~, fcrcm:r I © Birbal Sahni Institute of Palaeobotany, India 108 THE PALAEOBOTANIST INTRODUCTION relationships between fossil taxa and groups of extant taxa. He emphasized on the significance of reassessment RAY (1977), Poignant (1984) and several other and revision of well known fossil taxa along with detailed Wpalaeoalgologists opined that fossil and recent measurements and statistical analysis because many of coralline algae have to be classified in different manners the fossil coralline taxa were suffering from excessive and consequently different diagnostic characters were splitting only on the basis of very few characters. used for the identification of fossil and extant coralline According to Bosence (1991) in case of fossil algae. Various diagnostic suprageneric criteria were corallines, palaeoalgologists should increase the use of proposed for extant as well as fossil material which potential taxonomic characters which can be revealed included type and location of conceptacles, character by excessive analysis of thin sections and SEM of hypothallium and perithallium (core/primigenous and observations. Later on, Rasser and Piller (1999) applied peripheral/postigenous filaments respectively as per the the neontological taxonomic concepts to coralline algae. recent literature) and also the presence or absence and Presently, all these potential taxonomic characters are arrangement of heterocysts (trichocytes). Discovery of commonly used by the palaeoalgologists (Fig. 1). interfilamental cell-connections (Johansen, 1969) and Various taxonomic measures proposed for living application of some other diagnostic features like shape and fossil algae facilitate their use as effective of epithallial cells (Adey, 1970), number of epithallial palaeoenvironmental indicators and at the same time cells (Johansen, 1976) and pattern of cell elongation in favour the understanding of the evolutionary biology of recognizing suprageneric taxa (Woelkerling & Irvine, the group. In most cases, diagnostic features used for 1986) were employed for the taxonomy of extant separating genera in present-day corallines can be coralline algae by the phycologists. However, the post- identified in fossil plants except the uncalcified 1993 phase saw prominent work by various workers reproductive structures or developmental features that leading to the view that some key features, e.g. cell- are not preserved in relic material and hence cannot be connections, cell-fusions, epithallial cell and meristem used for generic identification. Recently, there has been characteristics can also be recognized in fossil corallines a trend to propose reproductive and developmental using light microscopy as well as appropriate SEM features as prevalent diagnostic criteria for modern techniques (as specified by Braga et al., 1993). In this coralline taxonomy. However, their consistency and context the present review summarizes the contributions systematic significance is still a point of discussion. In on morphological/anatomical studies of fossil corallines, cases when diagnostic criteria are not preserved then present day corallines, their ultrastructural studies as the ancillary characters recognizable in fossil material well as gene sequence analysis. Based on these or the application of informal generic names with a attributes, characteristics of families and subfamilies of broader circumscription as compared to the living the order Corallinales have been discussed in detail. In representatives can be used as the best options for addition, possible evolutionary lineages of this algal group palaeontological taxonomy. have been drawn hovering on recent discoveries. Various diagnostic characters used for the separation of taxa at different taxonomic levels have POTENTIAL TAXONOMIC CHARACTERS changed throughout the history of biological and IN PRESENT DAY AND FOSSIL palaeobiological research, with coralline red algae not CORALLINE ALGAE being an exception. Secondly, till date no general agreement on classification scheme for modern and Bosence (1991) raised some important questions fossil coralline algae has been formulated and regarding the preservation of taxonomic characters and Fig. 1—Potential taxonomic characters in Recent and Fossil coralline algae (modified after Bosence, 1991; Rasser & Piller, 1999). GHOSH & SARKAR—CONTEMPORARY TAXONOMIC PERSPECTIVES OF FOSSIL CORALLINE RED ALGAE 109 GENERAL CHARACTERS OCCURRENCE OF CHARACTERS* RECENT FOSSIL Commonly used Potentially usable Growth Form Encrusting ◙ ◙ ◙ Warty ◙ ◙ ◙ Lumpy ◙ ◙ ◙ Fruticose ◙ ◙ ◙ Layered ◙ ◙ ◙ Foliose ◙ ◙ ◙ Arborescent ◙ ◙ ◙ Articulated ◙ ◙ ◙ Articulated branching ◙ □ □ Epithallium Thickness ◙ □ ◙ Cell shape ◙ □ ◙ Meristematic cells ◙ □ ◙ Trichocytes ◙ □ ◙ Thallus organization Monomerous ◙ ◙ ◙ Coaxial ◙ ◙ ◙ Non-coaxial ◙ ◙ ◙ Peripheral filaments ◙ ◙ ◙ Core filaments ◙ ◙ ◙ Palisade cells ◙ ◙ ◙ Dimerous ◙ ◙ ◙ Postigenous filaments ◙ ◙ ◙ Primigenous filaments ◙ ◙ ◙ Primary pit connections ◙ ◙ ◙ Secondary pit connections ◙ ◙ ◙ Cell fusions ◙ ◙ ◙ Genicula ◙ ◙ ◙ Asexual conceptacles Location ◙ ◙ ◙ Perforations ◙ ◙ ◙ Shape ◙ ◙ ◙ Primordia ◙ □ ◙ Tetraspores ◙ □ ◙ Sexual conceptacles Location ◙ ◙ ◙ Shape ◙ ◙ ◙ Spermatangium ◙ □ ◙ Carpogonium ◙ □ ◙ Carpospore ◙ □ ◙ Biochemical Staining of sporangial caps ◙ □ □ Developmental Spore cell division ◙ □ □ Conceptacle developments ◙ □ ◙ * ◙ = Yes, □ = No. 110 THE PALAEOBOTANIST Character Corallinaceae Sporolithaceae Hapalidiaceae Arrangement of spores within Zonate Cruciate Zonate tetrasporangia Tetra/bisporangia producing No Yes Yes apical plugs Tetra/bisporangia produced No No Yes beneath multiporate plates Tetra/bisporangia borne Conceptacles Calcified Conceptacles within conceptacles or compartments calcified compartments Fig. 2—Diagnostic characteristics of the three families of Corallinales based on the reproductive organs (after Harvey et al., 2003). Subfamily Genicula No. of pores in Predominant Sporangial sporangial interfilamental plugs conceptacles cell connections Amphiroideae present uniporate Secondary pits absent Corallinoideae present uniporate Cell fusions absent Metagoniolithoideae present uniporate Cell fusions absent Choreonematoideae absent uniporate Absent present Lithophylloideae absent uniporate Secondary pits absent Mastophoroideae absent uniporate Cell fusions absent Melobesioideae absent multiporate Cell fusions present Fig. 3—Key characters of subfamilies of the Corallinaceae according to Woelkerling (1988). modifications are being continuously made by the spermatangia, have been categorized as diagnostic workers pertaining to unification of taxonomic analysis. (Penrose, 1992; Chamberlain & Keats, 1994; The monographic work of Woelkerling (1988) was Woelkerling, 1996a, b, c), making the identification for a long time considered as the most complete and process very difficult or rather nearly impossible for comprehensive study of generic and suprageneric the fossil specimens. taxonomy of the Corallinales. Key features for delimiting subfamilies, and most of the characteristic features used DIFFERENT