Leptaenine brachiopods are common and widespread on Gotland. Lepidoleptaena poulseni and Leptaena rhomboidalis retained a functional apical pedicle throughout ontogeny, and both had strong adductor muscles and robust ornamentation, allowing them to occupy shallow water and high energy environments. A pedicle-shortening muscle is present within the pedicle tube of Leptaena rhomboidalis. Leptaena sperion, L. depressa visbyensis, and L. depressa lata inhabited low energy environments, retaining very slender pedicles. L. depressa depressa and L. parvorugata atrophied the pedicle early and then lived ambitopically in deeper water. The presence or absence of the apical pedicle strongly influenced the cardinal process morphology. Leptaenine shells had a small gape. The lophophore was simple, similar to productids and Leptaenoidea. In closed valves, the inner epithelium of leptaenine trails remained exposed to the sea. This was probably important in gas exchange. The life position of pedically attached species was with the disc vertical. Some ambitopic specimens may have retained a similar attitude. Shells of L. depressa depressa and Lepidoleptaena poulseni commonly are encrusted by epibionts, apparently without problems for larger shells. Small shells are shown to have been killed by bryozoan epizoans. Repaired shell damage is rare on the disc but is common along the commisure. 1. Introduction The genus Leptaena is one of the most widespread and taxonomically diverse strophomenide brachiopods, with more than 50 named species worldwide and many more occurrences placed in open nomenclature. The temporal distribution is also notable in that the genus extends from the Middle Ordovician (Llanvirn) (e.g., [1]) into the Lower Devonian (Emsian) (e.g., [2, 3]), which amounts to a longevity of about 75 million years. In the Silurian succession of Gotland, Leptaena is a very common component of most brachiopod faunas from the late Llandovery to the Middle Ludlow, after which its role is taken over by the closely related Lepidoleptaena. The taxonomy of these two genera on Gotland has been revised elsewhere [4], following which the recognised species present in the Silurian of Gotland are Leptaena rhomboidalis, Wahlenberg [5]; L. depressa depressa Sowerby, [6]; L. depressa lata, Hoel [4]; L. depressa visbyensis, Hoel [4]; L. sperion, Bassett [7]; L. parvorugata, Hoel [4]; Lepidoleptaena poulseni, Kelly [8]; Lepidoleptaena sp. A and sp. B. In the course of that study several aspects of functional morphology and ecology came to light, which prompted the present paper.
References
[1]
N. Spjeldn？s, The Middle Ordovician of the Oslo Region, Norway. 8. Brachiopods of the Suborder Strophomenida, vol. 37 of Norsk Geologisk Tidsskrift, 1957.
[2]
C. W. Merriam, Paleontology and Stratigraphy of the Rabbit Hill Limestone and Lone Mountain Dolomite of Central Nevada, vol. 808 of US Geological Survey Professional Paper, 1973.
[3]
A. Williams, S. J. Carlson, C. H. C. Brunton, et al., Treatise on Invertebrate Paleontology. Part H: Brachiopoda, vol. 2-3, Geological Society of America, 2000.
[4]
O. A. Hoel, “Silurian Leptaeninae (Brachiopoda) from Gotland, Sweden,” Pal？ontologische Zeitschrift, vol. 79, no. 2, pp. 263–284, 2005.
[5]
G. Wahlenberg, Petrificata Telluris Svecanae, Nova Acta Regiae Societatis Scientiarium Upsaliensis 8, 1821.
[6]
J. D. C. Sowerby, The Mineral Conchology of Great Britain, Meredith, London, UK.
[7]
M. G. Bassett, The Articulate Brachiopods from the Wenlock Series of the Welsh Borderland and South Wales: Part 4, Monographs of the Palaeontographical Society, 1977.
[8]
F. B. Kelly, “Silurian Leptaenids (Brachiopoda),” Palaeontology, vol. 10, pp. 590–602, 1967.
[9]
V. Jaanusson, “Ecology and faunal dynamics,” in Lower Wenlock Faunal and Floral Dynamics—Vattenfallet Section, Gotland, V. Jaanusson, S. Laufeld, and R. Skoglund, Eds., vol. 762 of Sveriges Geologiska Unders？kning C, pp. 253–294, 1979.
[10]
M. G. Bassett, “Life strategies of Silurian brachiopods,” Special Papers in Palaeontology, vol. 32, pp. 237–263, 1984.
[11]
F. G. Blight and D. F. Blight, “Flying spiriferids: some thoughts on the life style of a Devonian spiriferid brachiopod,” Palaeogeography, Palaeoclimatology, Palaeoecology, vol. 81, no. 1-2, pp. 127–139, 1990.
[12]
M. J. S. Rudwick, Living and Fossil Brachiopods, Hutchinson University Library, London, UK, 1970.
[13]
R. P. Richards, “Autecology of Richmondian brachiopods (late Ordovician of Indiana and Ohio),” Journal of Paleontology, vol. 46, pp. 386–405, 1972.
[14]
C. C. Emig, “Functional disposition of the lophophore in living Brachiopoda,” Lethaia, vol. 25, no. 3, pp. 291–302, 1992.
[15]
J. S. Peel, “Systematics, ontogeny and functional morphology of Silurian trilobed bellerophontacean gastropods,” Bulletin of the Geological Society of Denmark, vol. 23, pp. 231–264, 1974.
[16]
H. L. Lescinsky, “The life orientation of concavo-convex brachiopods: overturning the paradigm,” Paleobiology, vol. 21, no. 4, pp. 520–551, 1995.
[17]
K. Dewing, “Hinge modifications and musculature of strophomenoid brachiopods: examples across the Ordovician-Silurian boundary, Anticosti Island, Quebec,” Canadian Journal of Earth Sciences, vol. 38, no. 2, pp. 125–141, 2001.
[18]
A. E. Timms and C. H. C. Brunton, “Growth rates and periodicity in Antiquatonia and Plicatifera, lower carboniferous productacean brachiopods,” in Proceedings of the 2nd International Brachiopod Congress, Brachiopods through Time, D. I. Mackinnon, D. E. Lee, and J. D. Campbell, Eds., pp. 41–47, Balkema, Dunedin, New Zealand, 1991.
[19]
A. Williams, S. J. Carlson, C. H. C. Brunton, et al., Treatise on Invertebrate Paleontology. Part H: Brachiopoda, vol. 1, Geological Society of America, 1997.
[20]
N. Spjeldn？s, “Epifauna as a tool in autecological analysis of Silurian brachiopods,” Special Papers in Palaeontology, vol. 32, pp. 225–235, 1984.
[21]
M. Calner and L. Jeppsson, “Carbonate platform evolution and conodont stratigraphy during the middle Silurian Mulde Event, Gotland, Sweden,” Geological Magazine, vol. 140, no. 2, pp. 173–203, 2003.
[22]
R. R. Alexander, “Phenotypic lability of the Brachiopod Rafinesquina alternata (Ordovician) and its correlation with the sedimentologic regime,” Journal of Paleontology, vol. 49, pp. 607–618, 1975.
[23]
R. R. Alexander, “Function of external skeletal characteristics of articulate brachiopods,” in Functional Morphology of the Invertebrate Skeleton, E. Savazzi, Ed., pp. 371–398, Wiley & Sons, New York, NY, USA, 1999.
[24]
R. R. Alexander, “Functional morphology and biomechanics of articulate brachiopod shells,” Paleontological Society Papers, vol. 7, pp. 145–169, 2001.
[25]
L. Leighton and M. Savarese, “Functional and taphonomic implications of Ordovician strophomenide brachiopod valve morphology,” in Brachiopods, P. Copper and J. Jin, Eds., pp. 161–168, A. A. Balkema, Rotterdam, The Netherlands, 1996.
[26]
B. F. Dattilo, “A new angle on strophomenid paleoecology: trace-fossil evidence of an escape response for the plectambonitoid brachiopod Sowerbyella rugosa from a tempestite in the Upper Ordovician Kope Formation (Edenian) of Northern Kentucky,” Palaios, vol. 19, no. 4, pp. 332–348, 2004.
[27]
M. LaBarbera, “Brachiopod orientation to Water movement: functional morphology,” Lethaia, vol. 11, pp. 67–79, 1978.
[28]
O. A. Hoel, “Cementing strophomenide brachiopods from the Silurian of Gotland (Sweden): morphology and life habits,” Geobios, vol. 40, no. 5, pp. 589–608, 2007.
[29]
S. M. Stanley, Relation of Shell form to Life Habits of the Bivalves (Mollusca), Geological Society of America Memoir 125, 1970.
[30]
R. R. Alexander, “Resistance to and repair of shell breakage induced by durophages in Late Ordovician brachiopods,” Journal of Paleontology, vol. 60, no. 2, pp. 273–285, 1986.
[31]
J. O. R. Ebbestad and A. E. S. H？gstr？m, “Shell repair following failed predation in two Upper Ordovician brachiopods from central Sweden,” Geologiska F？reningens I Stockholm F？rhandlingar, vol. 122, no. 3, pp. 307–312, 2000.
[32]
K. Dewing, Late Ordovician and Early Silurian Strophomenid Brachiopods of Anticosti Island, Québec, Canada, vol. 17, Palaeontographica Canadiana, 1999.
[33]
H. Hedstr？m, über die Gattung Phragmoceras in der Obersilurformation Gotlands, vol. 15 of Sveriges Geologiska Underso？kning, 1917.
[34]
B. B. Bancroft, Welsh Valentian Brachiopods and the Strophomena Antiquata Group of Fossil Brachiopods, Privately printed, Mexborough, UK, 1949.
[35]
V. Jaanusson and H. Neuhaus, “Mechanism of the diductor muscles in articulate brachiopods,” Stockholm Contributions in Geology, vol. 13, pp. 1–8, 1965.
[36]
J. Armstrong, “Analysis of the function of the diductor muscles in articulate brachiopods,” Neues Jahrbuch für Geologie und Pal？ontologie, vol. 11, pp. 641–654, 1968.
[37]
T. Davidson, British Fossil Brachiopoda, vol. 3, part 7, no. 4, Monograph of the Palaeontological Society, London, UK, 1871, index and appendix for volume III, and general index to volume I-III.
[38]
C. H. C. Brunton, “The functional morphology and palaeoecology of the Dinantian brachiopod Levitusia,” Lethaia, vol. 15, pp. 149–167, 1982.
[39]
H. Hedstr？m, Ueber Einige mit der Schale Befestigte Strophomenidae aus dem Obersilur Gotlands, vol. 276 of Sveriges Geologiska Unders？kning C, 1917.
[40]
F. Surlyk, “Life habit, feeding mechanism and population structure of the Cretaceous brachiopod genus Aemula,” Palaeogeography, Palaeoclimatology, Palaeoecology, vol. 15, no. 3, pp. 185–203, 1974.
[41]
H. Zorn, “Form und funktion von Geh？use und Lophophor der Strophomenida (Brachiopoda),” Neues Jahrbuch für Geologie und Pal？ontologie, pp. 49–64, 1979.
[42]
M. J. S. Rudwick, “The feeding mechanism of the Permian brachiopod Prorichthofenia,” Palaeontology, vol. 3, pp. 450–471, 1961.
[43]
P. Westbroeck, J. Yanagida, and Y. Isa, “Functional morphology of brachiopod and coral skeletal structures supporting ciliated epithelia,” Paleobiology, vol. 6, pp. 313–330, 1980.
