- Email: [email protected]
The first European Cretaceous stonefly (Insecta, Perlida=Plecoptera)
Cretaceous Research (1998) 19, 317±321
Article No. cr980108
The ®rst European Cretaceous stone¯y (Insecta, Perlida Plecoptera) Nina D. Sinitshenkova Palaeontological Institute of the Russian Academy of Sciences, Profsoyuznaya 123, Moscow, Russia Revised manuscript accepted 7 February 1997
Ecdyoperla fairlightensis gen. et sp. nov. is described from the Wealden Hastings Group (Lower Cretaceous) of southern England. # 1998 Academic Press KEY WORDS: England; Lower Wealden; Insecta; Plecoptera.
1. Introduction Aquatic insect larvae in the Wealden succession of southern England are rare. A unique stone¯y nymph from the Fairlight Clays facies of the Ashdown Formation tentatively identi®ed as such by Dr E. A. Jarzembowski represents a new stone¯y genus and species which seems to be remarkable in several respects. The Wealden fossil is important because of its geographical location. The Mesozoic stone¯y fauna of Asia is rich and diverse but the order is rare in coeval deposits of Europe from which only one species was known previously, Dobbertinopteryx capniomimus Ansorge, from the Lower Jurassic of Germany (Ansorge, 1993). The nymph described below is the ®rst European Cretaceous representative of this insect order. Its rarity is not surprising because a number of islands existed there in the Mesozoic instead of continental land, and the present-day island faunas of stone¯ies, as well as other stream-dwelling insects, are often extremely impoverished (Zwick, 1980); in addition, the climate of Europe was warm and thus unfavourable for a group of aquatic insects intolerant of oxygen de®ciencies like stone¯ies. Nowadays in areas of warm climate stone¯ies, with a few exceptions, are restricted to highlands (Zwick, 1980). With regards to the systematic position of the Wealden stone¯y, it certainly represents a new genus belonging to the infraorder Perlomorpha but, like many other fossil perlomorph nymphs, it cannot be classi®ed to family level in the present state of knowledge. The Mesozoic genera currently recognised seem to represent a small part of the Mesozoic perlomorph fauna, and most of them are probably unrelated to each other; thus it is dif®cult to reconstruct the phylogenetic relationships within this small and inadequate sample of taxa. The deposit in which the stone¯y was found is within the lowest argillaceous development of the Wealden Supergroup in southern England and has yielded relatively few insect remains (Jarzembowski, 1976, 1984). However, an extensive caddis tube (indusia) fauna has recently been described from the upper Ashdown Formation (Jarzembowski, 1995). 0195 ± 6671/98/030317 + 5 $30.00/0
# 1998 Academic Press
318
N. D. Sinitshenkova
2. Systematic palaeontology Order Plecoptera Latreille, 1802 Suborder Perlina Latreille, 1802 Infraorder Perlomorpha Latreille, 1802 Family incertae sedis Genus Ecdyoperla gen. nov. Etymology. From the extant genera Ecdyonurus and Perla. Type species. E. fairlightensis Sinitshenkova sp. nov.; see below. Diagnosis. Nymph. Stone¯ies of medium size with streamlined body. Pronotum with projections on its hind angles. Wing pads on meso- and metathorax short. Femora and tibiae ¯attened and very broad. Abdomen twice as long as thorax, abdominal segments short and broad, the last one with a median projection. Composition. Type species. Comparison. Ecdyoperla differs from other known stone¯ies (recent and fossil) by the presence of projections on the pronotal hind angles. Ecdyoperla fairlightensis Sinitshenkova sp. nov. Figures 1, 2 1976 Exopterygote larva Jarzembowski: p. 444 Etymology. After the Fairlight fossil site. Diagnosis. As for genus. Description. Nymph. Pronotum with hind angles rounded, projecting distinctly backwards. Wingpads on meso- and metathorax short and broadly rounded. Femora very broad and ¯attened, about 1.7 times as long as broad. Tibiae slightly longer than femora and half the width. Two basal joints of middle tarsus combined are approximately as long as the third one; claws short. Abdomen slightly fusiform, abdominal segments 4±5 times as wide as long, the sixth one being the widest. Median projection of the last abdominal segment pointed and as long as the segment. Dimensions (mm): length of fossil 8.7; total estimated body length c. 9; femur length: fore 1.1, middle 1.6, hind 2.1; femur width: fore 0.65, middle 0.95, hind 1.2; midtibia length 2.3, width 0.45; midtarsus length 0.9. Material. Holotype, Natural History Museum (NHM), London, Palaeontology Dept. no. I.15135 [Dechardin & Pelletier coll.]; a moulted skin of a middle instar stone¯y nymph. Stratum typicum. Fairlight Clays facies, Ashdown Formation, Hastings Group; Berriasian, Lower Cretaceous. Locus typicus. Fairlight, near Hastings, East Sussex, UK. Discussion. The general appearance of the fossil is rather unusual for a stone¯y. The streamlined body shape combined with an extremely wide, ¯at femora resembles a nymph of the may¯y family Heptageniidae; in particular, the peculiar lateral projections of the pronotum somewhat resemble the living may¯y genus Ecdyonurus Eaton. However, the long antennae, the short wingpads on the mesothorax, the strongly developed metathorax with clearly visible wingpads, the three-segmented tarsi with two claws, the presence of paraprocts at the end of the abdomen, and the absence of lateral gills indicate that this similarity with may¯ies is only super®cial. Among living stone¯ies, only the nymphs of the family Pelto-
The first European Cretaceous stonefly
319
Figure 1. Ecdyoperla fairlightensis Sinitshenkova gen. et sp. nov., holotype, NHM, London, I.15135. A-nymphal exuvia, B-midtibia and midtarsus. Scale 1.0 mm.
perlidae may be compared with Ecdyoperla. They are unique in having a characteristic `roach-like' body shape with the thoracic segments unusually large. The femora and tibiae in peltoperlids are remarkably wide and ¯at, resembling those of Ecdyoperla. The body shape was considered by Zwick (1973) to be one of the most important autapomorphies of the Peltoperlidae. Unfortunately, other important features, namely the number of ocelli and the fusion of basal segments of the male cerci, cannot be established with certainty in Ecdyoperla. Therefore the placement of the fossil genus in the Peltoperlidae seems to be premature, the more so that the shape of abdomen is different: in living peltoperlids it is distinctly narrower from base to apex and the ®rst abdominal segment is strongly reduced, which is not the case in Ecdyoperla. The shape of the pronotum of Ecdyoperla differs considerably from that of known peltoperlid nymphs (many peltoperlid species are described only from adult stages), and the body is probably less convex. Moreover, in some Mesozoic stone¯ies unrelated to Peltoperlidae, especially in the siberioperlid genus Sharaperla Sinitshenkova (Sinitshenkova, 1995), the structure of the legs is similar, demonstrating that the likeness in this respect may be a matter of convergence.
320
N. D. Sinitshenkova
Figure 2. Ecdyoperla fairlightensis Sinitshenkova, gen. et sp. nov., holotype, NHM, London, I.15135. Nymphal exuvium.
At ®rst glance it would seem that the super®cial similarity of Ecdyoperla to nymphs of Ecdyonurus and other torrent-adapted may¯ies suggests an adaptation to life in rapidly ¯owing (lotic) water. Although extant stone¯y nymphs are lotic with few exceptions, none of them show similar adaptations (Brodsky, 1976). In fact they usually avoid torrential ¯ows, preferring the undersides of stones, logs and other submerged objects which shelter them from the water current. The only previously described stone¯y nymph resembling a rheophilous may¯y is Barathronympha victima Sinitshenkova from the Lower Permian of Chekarda, Urals, Russia (Sinitshenkova, 1987); however, it differs strongly from the Wealden fossil in many important characters such as the tarsal structures, the shape of the pronotum, wing pads and legs. The Wealden nymph is not related to Barathronympha but may represent the same extinct morpho-ecological type of free-living rheophiles (Sinitshenkova, 1987). On the other hand, modern peltoperlids inhabit a quite different environment, namely small spring brooks with slow, if any, current where plant debris accumulates in large quantities (Claassen, 1931). Unfortunately, the behaviour of peltoperlid nymphs has not been described in detail, and the adaptive signi®cance of their unique body and leg shape is unclear. Almost
The first European Cretaceous stonefly
321
certainly, the fossil of a moulted skin is allochthonous and has been transported to the site of burial by water currents. In general, the sediments of the Hastings Group exposed near Hastings were deposited mainly in a braided ¯uvial environment and the Fairlight Clays represent overbank and ¯oodplain deposits with a mottling suggesting an in¯uence of pedogenic processes (Allen, 1990, and references therein; Ruffell et al., 1996). Acknowledgements I am grateful to A. J. Ross, the curator of the fossil arthropod collection in the Natural History Museum (London), who kindly gave me the opportunity to study the fossil stone¯y nymph described. I thank Edmund A. Jarzembowski for his critical reading of the manuscript. References Allen, P. 1990. Wealden research-ways ahead. Proceedings of the Geologists' Association 100 (for 1989), 529±564. Ansorge, J. 1993. Dobbertinopteryx capniomimus gen. et sp. nov.-die erste stein¯iege (Insecta: Plecoptera) aus dem europaischen jura. PalaÈontologische Zeitschrift 67, 287±292. Brodsky, K. A. 1976. Gorny potok Tyan-Shanya. Ekologo-faunistichesky ocherk, 243 pp. (Nauka, Leningrad). Claassen, P. W. 1931. Plecoptera nymphs of America (north of Mexico), 199 pp. (C. C. Thomas, Spring®eld, Illinois). Jarzembowski, E. A. 1976. Insect fossils from the Wealden of the Weald. Proceedings of the Geologists' Association 87, 443±446. Jarzembowski, E. A. 1984. Early Cretaceous insects from southern England. Modern Geology 9, 71±93. Jarzembowski, E. A. 1995. Fossil caddis¯ies (Insecta: Trichoptera) from the Early Cretaceous of southern England. Cretaceous Research 16, 695±703. Ruffell, A., Ross, A. & Taylor, K. 1996. Early Cretaceous environments of the Weald. Geologists' Association Guide 55, 1-81. Sinitshenkova, N. D. 1987. Istoricheskoe razvitie vesnyanok. Trudy Paleontologicheskogo Instituta AN SSSR 221, 1±143, pls 1±8. Sinichenkova [Sinitshenkova], N. D. 1995. New Late Mesozoic stone¯ies from Shara-Teeg, Mongolia (Insecta: Perlida = Plecoptera). Paleontological Journal 29, 93±104, pl 9. Zwick, P. 1973. Insecta: Plecoptera. Phylogenetisches System und Katalog. Das Tierreich, B 94, 1±465. È berordnung Plecopteroidea (Perloidea) mit der einzigen Ordnung. 7. Ordnung Zwich, P. 1980. 6. U Plecoptera (Stein¯iegen). Handbuch der Zoologie 4, 1±115.
Article No. cr980108
The ®rst European Cretaceous stone¯y (Insecta, Perlida Plecoptera) Nina D. Sinitshenkova Palaeontological Institute of the Russian Academy of Sciences, Profsoyuznaya 123, Moscow, Russia Revised manuscript accepted 7 February 1997
Ecdyoperla fairlightensis gen. et sp. nov. is described from the Wealden Hastings Group (Lower Cretaceous) of southern England. # 1998 Academic Press KEY WORDS: England; Lower Wealden; Insecta; Plecoptera.
1. Introduction Aquatic insect larvae in the Wealden succession of southern England are rare. A unique stone¯y nymph from the Fairlight Clays facies of the Ashdown Formation tentatively identi®ed as such by Dr E. A. Jarzembowski represents a new stone¯y genus and species which seems to be remarkable in several respects. The Wealden fossil is important because of its geographical location. The Mesozoic stone¯y fauna of Asia is rich and diverse but the order is rare in coeval deposits of Europe from which only one species was known previously, Dobbertinopteryx capniomimus Ansorge, from the Lower Jurassic of Germany (Ansorge, 1993). The nymph described below is the ®rst European Cretaceous representative of this insect order. Its rarity is not surprising because a number of islands existed there in the Mesozoic instead of continental land, and the present-day island faunas of stone¯ies, as well as other stream-dwelling insects, are often extremely impoverished (Zwick, 1980); in addition, the climate of Europe was warm and thus unfavourable for a group of aquatic insects intolerant of oxygen de®ciencies like stone¯ies. Nowadays in areas of warm climate stone¯ies, with a few exceptions, are restricted to highlands (Zwick, 1980). With regards to the systematic position of the Wealden stone¯y, it certainly represents a new genus belonging to the infraorder Perlomorpha but, like many other fossil perlomorph nymphs, it cannot be classi®ed to family level in the present state of knowledge. The Mesozoic genera currently recognised seem to represent a small part of the Mesozoic perlomorph fauna, and most of them are probably unrelated to each other; thus it is dif®cult to reconstruct the phylogenetic relationships within this small and inadequate sample of taxa. The deposit in which the stone¯y was found is within the lowest argillaceous development of the Wealden Supergroup in southern England and has yielded relatively few insect remains (Jarzembowski, 1976, 1984). However, an extensive caddis tube (indusia) fauna has recently been described from the upper Ashdown Formation (Jarzembowski, 1995). 0195 ± 6671/98/030317 + 5 $30.00/0
# 1998 Academic Press
318
N. D. Sinitshenkova
2. Systematic palaeontology Order Plecoptera Latreille, 1802 Suborder Perlina Latreille, 1802 Infraorder Perlomorpha Latreille, 1802 Family incertae sedis Genus Ecdyoperla gen. nov. Etymology. From the extant genera Ecdyonurus and Perla. Type species. E. fairlightensis Sinitshenkova sp. nov.; see below. Diagnosis. Nymph. Stone¯ies of medium size with streamlined body. Pronotum with projections on its hind angles. Wing pads on meso- and metathorax short. Femora and tibiae ¯attened and very broad. Abdomen twice as long as thorax, abdominal segments short and broad, the last one with a median projection. Composition. Type species. Comparison. Ecdyoperla differs from other known stone¯ies (recent and fossil) by the presence of projections on the pronotal hind angles. Ecdyoperla fairlightensis Sinitshenkova sp. nov. Figures 1, 2 1976 Exopterygote larva Jarzembowski: p. 444 Etymology. After the Fairlight fossil site. Diagnosis. As for genus. Description. Nymph. Pronotum with hind angles rounded, projecting distinctly backwards. Wingpads on meso- and metathorax short and broadly rounded. Femora very broad and ¯attened, about 1.7 times as long as broad. Tibiae slightly longer than femora and half the width. Two basal joints of middle tarsus combined are approximately as long as the third one; claws short. Abdomen slightly fusiform, abdominal segments 4±5 times as wide as long, the sixth one being the widest. Median projection of the last abdominal segment pointed and as long as the segment. Dimensions (mm): length of fossil 8.7; total estimated body length c. 9; femur length: fore 1.1, middle 1.6, hind 2.1; femur width: fore 0.65, middle 0.95, hind 1.2; midtibia length 2.3, width 0.45; midtarsus length 0.9. Material. Holotype, Natural History Museum (NHM), London, Palaeontology Dept. no. I.15135 [Dechardin & Pelletier coll.]; a moulted skin of a middle instar stone¯y nymph. Stratum typicum. Fairlight Clays facies, Ashdown Formation, Hastings Group; Berriasian, Lower Cretaceous. Locus typicus. Fairlight, near Hastings, East Sussex, UK. Discussion. The general appearance of the fossil is rather unusual for a stone¯y. The streamlined body shape combined with an extremely wide, ¯at femora resembles a nymph of the may¯y family Heptageniidae; in particular, the peculiar lateral projections of the pronotum somewhat resemble the living may¯y genus Ecdyonurus Eaton. However, the long antennae, the short wingpads on the mesothorax, the strongly developed metathorax with clearly visible wingpads, the three-segmented tarsi with two claws, the presence of paraprocts at the end of the abdomen, and the absence of lateral gills indicate that this similarity with may¯ies is only super®cial. Among living stone¯ies, only the nymphs of the family Pelto-
The first European Cretaceous stonefly
319
Figure 1. Ecdyoperla fairlightensis Sinitshenkova gen. et sp. nov., holotype, NHM, London, I.15135. A-nymphal exuvia, B-midtibia and midtarsus. Scale 1.0 mm.
perlidae may be compared with Ecdyoperla. They are unique in having a characteristic `roach-like' body shape with the thoracic segments unusually large. The femora and tibiae in peltoperlids are remarkably wide and ¯at, resembling those of Ecdyoperla. The body shape was considered by Zwick (1973) to be one of the most important autapomorphies of the Peltoperlidae. Unfortunately, other important features, namely the number of ocelli and the fusion of basal segments of the male cerci, cannot be established with certainty in Ecdyoperla. Therefore the placement of the fossil genus in the Peltoperlidae seems to be premature, the more so that the shape of abdomen is different: in living peltoperlids it is distinctly narrower from base to apex and the ®rst abdominal segment is strongly reduced, which is not the case in Ecdyoperla. The shape of the pronotum of Ecdyoperla differs considerably from that of known peltoperlid nymphs (many peltoperlid species are described only from adult stages), and the body is probably less convex. Moreover, in some Mesozoic stone¯ies unrelated to Peltoperlidae, especially in the siberioperlid genus Sharaperla Sinitshenkova (Sinitshenkova, 1995), the structure of the legs is similar, demonstrating that the likeness in this respect may be a matter of convergence.
320
N. D. Sinitshenkova
Figure 2. Ecdyoperla fairlightensis Sinitshenkova, gen. et sp. nov., holotype, NHM, London, I.15135. Nymphal exuvium.
At ®rst glance it would seem that the super®cial similarity of Ecdyoperla to nymphs of Ecdyonurus and other torrent-adapted may¯ies suggests an adaptation to life in rapidly ¯owing (lotic) water. Although extant stone¯y nymphs are lotic with few exceptions, none of them show similar adaptations (Brodsky, 1976). In fact they usually avoid torrential ¯ows, preferring the undersides of stones, logs and other submerged objects which shelter them from the water current. The only previously described stone¯y nymph resembling a rheophilous may¯y is Barathronympha victima Sinitshenkova from the Lower Permian of Chekarda, Urals, Russia (Sinitshenkova, 1987); however, it differs strongly from the Wealden fossil in many important characters such as the tarsal structures, the shape of the pronotum, wing pads and legs. The Wealden nymph is not related to Barathronympha but may represent the same extinct morpho-ecological type of free-living rheophiles (Sinitshenkova, 1987). On the other hand, modern peltoperlids inhabit a quite different environment, namely small spring brooks with slow, if any, current where plant debris accumulates in large quantities (Claassen, 1931). Unfortunately, the behaviour of peltoperlid nymphs has not been described in detail, and the adaptive signi®cance of their unique body and leg shape is unclear. Almost
The first European Cretaceous stonefly
321
certainly, the fossil of a moulted skin is allochthonous and has been transported to the site of burial by water currents. In general, the sediments of the Hastings Group exposed near Hastings were deposited mainly in a braided ¯uvial environment and the Fairlight Clays represent overbank and ¯oodplain deposits with a mottling suggesting an in¯uence of pedogenic processes (Allen, 1990, and references therein; Ruffell et al., 1996). Acknowledgements I am grateful to A. J. Ross, the curator of the fossil arthropod collection in the Natural History Museum (London), who kindly gave me the opportunity to study the fossil stone¯y nymph described. I thank Edmund A. Jarzembowski for his critical reading of the manuscript. References Allen, P. 1990. Wealden research-ways ahead. Proceedings of the Geologists' Association 100 (for 1989), 529±564. Ansorge, J. 1993. Dobbertinopteryx capniomimus gen. et sp. nov.-die erste stein¯iege (Insecta: Plecoptera) aus dem europaischen jura. PalaÈontologische Zeitschrift 67, 287±292. Brodsky, K. A. 1976. Gorny potok Tyan-Shanya. Ekologo-faunistichesky ocherk, 243 pp. (Nauka, Leningrad). Claassen, P. W. 1931. Plecoptera nymphs of America (north of Mexico), 199 pp. (C. C. Thomas, Spring®eld, Illinois). Jarzembowski, E. A. 1976. Insect fossils from the Wealden of the Weald. Proceedings of the Geologists' Association 87, 443±446. Jarzembowski, E. A. 1984. Early Cretaceous insects from southern England. Modern Geology 9, 71±93. Jarzembowski, E. A. 1995. Fossil caddis¯ies (Insecta: Trichoptera) from the Early Cretaceous of southern England. Cretaceous Research 16, 695±703. Ruffell, A., Ross, A. & Taylor, K. 1996. Early Cretaceous environments of the Weald. Geologists' Association Guide 55, 1-81. Sinitshenkova, N. D. 1987. Istoricheskoe razvitie vesnyanok. Trudy Paleontologicheskogo Instituta AN SSSR 221, 1±143, pls 1±8. Sinichenkova [Sinitshenkova], N. D. 1995. New Late Mesozoic stone¯ies from Shara-Teeg, Mongolia (Insecta: Perlida = Plecoptera). Paleontological Journal 29, 93±104, pl 9. Zwick, P. 1973. Insecta: Plecoptera. Phylogenetisches System und Katalog. Das Tierreich, B 94, 1±465. È berordnung Plecopteroidea (Perloidea) mit der einzigen Ordnung. 7. Ordnung Zwich, P. 1980. 6. U Plecoptera (Stein¯iegen). Handbuch der Zoologie 4, 1±115.