(Brachiopoda; Lower Silurian) Occurrence from the ...

PALEONTOLOGICAL NOTES J. Paleont., 65(3), 1991, pp. 512-514 Copyright O 1991, The Paleontological Society

0022-3360/91/0065-0512SO3.00

FIRST CLARKEIA AND HETERORTHELLA (BRACHIOPODA; LOWER SILURIAN) OCCURRENCE FROM THE PARANA BASIN IN EASTERN PARAGUAY A. J. BOUCOT,' JOSE HENRIQUE G. DE MEL0,2 EUGENIO V. SANTOS NETO,2 AND SVEN WOLFF3 I Department of Zoology, Oregon State University, Corvallis 9733 1, Petrobrás/Cenpes/Divex, Cidade Universitária, Ilha do Fundâo, 21910 Rio de Janeiro, RJ, Brazil, and ' Petrobrás Nexpar, R. Padre Camargo, 261-285, 80060 Curitiba, Brazil THEEXISTENCE of the Malvinokaffnc Realm dunng the Silunan (Boucot, 1990) is based on the presence of three endemic brachiopod genera (Anabaia, Clarkeia, Heterorthella), and their absence in the coeval North Silurian Realm, where roughly 100 other brachiopod genera Aegiria to Zygospiraella are present. Within the Malvinokaffnc Realm the vast reaches of the Paraná Basin, covenng an area almost equivalent to the United States east of the Mississippi River, has previously yielded only Anabaia, and that from a single area. In light of this, the recognition of both Clarkeia and Heterorthella within the confines of the Paraná Basin is notewoqhy. Brazilian (PETROBRAS) and Paraguayan geologists, while making a joint field t n p in eastem Paraguay, discovered the typical Silunan, Malvinokaffnc Realm Silunan brachiopods Clarkeia and Heterorthella in the Ayala Sandstone of the Itacurubí Group. This locality is in a clay pit (Cantera San Fernando) situated severa1kilometers northeast of Itaugua and south of Lago Ypacaraí, north of the Itauguá-Ypacaraí road (Ruta 2) and not too far from the main excavation of the type locality of the Vargas Pena Shale at the Vargas Pena Quarry to the eastsoutheast. The charactenstic, endemic Malvinokaffnc Silunan brachiopods Clarkeia and Heterorthella are accompanied in one sample by a homalonotid tnlobite segment, and in another by a leptostrophiid brachiopod and a Holopea-like gastropod; a11 of this from the uppermost Ayala Sandstone. Ecologically the material belongs in the shallow subtidal Benthic Assemblage 2 Clarkeia Community. The fossils occur in slabs of micaceous, red-weathenng, very shelly, argillaceous sandstone, with bedding thicknesses measured in the decimetnc range, that crop out in situ at ground leve1 in a n abandoned clay pit (the "clay" of the Vargas Pena Shale is used for bnckmaking) from which a11 shale cover has long since been removed. Horizontal, parallel bedding is the only sedimentary structure observed in the poorly exposed sandstone. Some 500 m to the northeast of this site, towards Lago Ypacaraí, another clay pit exposes soft, light-gray to whitish or mottled, deeply weathered shales and siltstones typical of the Vargas Pena Shale. A few specimens of the tnlobite Calymene boettneri Hamngton and indeterminate brachiopods were collected in the shales here, which locally dip up to 30 degrees to the northeast due to the proximity of faults bordenng the Ypacaraí Graben (see Hamngton in Berry and Boucot, 1972, fig. 3). Hamngton (in Berry and Boucot, 1972, fig. 2) assigned an early Llandovenan age to the Vargas Pena Shale, as well as the underlying Ayala Sandstone, on the basis of megafossil evidence (graptolites, tnlobites, brachiopods, etc.). However, organic-

walled microfossils from the Vargas Pena Shale, obtained from boreholes about 45 km east of the Vargas Pena Quarry, indicate that a late (C 2-3 or slightly older) Llandovenan age is reasonable (Gray in Babcock et al., 1990), whereas restudy of graptolites from the Vargas Pena Shale collected at the Vargas Peiia Quarry (Rickards in Me10 and Boucot, 1990) indicates a latest middle Llandovenan, Monograptus convolutus Zone age. Chitinozoans and microplankton (acntarchs) recovered from shale samples collected at the unit's type locality, the Vargas Pena Quarry, are consistent with a Llandovenan-Wenlockian age (Wood et al., 1989). The age of the Ayala Sandstone, immediately underlying the Vargas Pena Shale, is probably close to that of the Vargas Pena because the presence of Anabaia paraguayensis (Hamngton, 1972) in both the Ayala Sandstone from beneath the Vargas Pena, and the Cany Sandstone, above the Vargas Pena, is consistent with a short age range. Additionally, the earlier Llandovenan Anabaia paraia would be expected in this region in beds of this age if they were present, as in southem Peru and north of the Amazon (Me10 and Boucot, 1990). One slab (CENPES 640-I), measunng about 20 x 20 cm, contains the impressions of about 20 brachiopods, chiefly Clarkeia antisiensis and a few Heterorthella freitana, plus a single homolanotid thoracic segment. The brachiopods are disarticulated. Similar faunas are widespread in the Andean Silunan from northem Argentina to southem Peru (Titicaca region) (see accounts in Berry and Boucot, 1972, and Laubacher et al., 1982). The brachiopods are illustrated here for the record (Figure 1). Two additional slabs (CENPES 648-1) are laden with abundant specimens of Clarkeia, together with moderately abundant Heterorthella, and a single specimen of an abraded intemal impression of a leptostrophiid brachiopod pedicle valve. This latter specimen may represent Hamngton's (1950) "Australostrophia" conradii. Hamngton's species was unintentionally overlooked by Harper and Boucot (1978) when monographing the stropheodontids, and does not belong to Australostrophia (Boucot, 1975, pointed out that the genus is a chonetid, and that Hamngton's species is a leptostrophiid). Re-examination of Hamngton's (1950) figures suggests that "A." conradii is a parvicostellate leptostrophiid with an unusual, very strongly developed pedicle valve muscle field that easily differentiates it from other, contemporary, Silunan, pa~icostellateleptostrophiids. It could provisionally be included in Mesoleptostrophia Harper and Boucot, 1978. One of the two slabs also bears the impression of a Holopea-like gastropod.

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From 1-1-3, Clarkeia antisiensis; 4-7, Heterorthellafreitana, from the uppermost Ayala Sandstone, Cantem San Fernando. The 6gwed material is CENPES 640-1. I , impression of exterior of brachial valve, x 1.5, note the coarse,radial costae; 2, impression, m d i y damaged antenorly, of interior of pedicle valve, x 1.5, note the form of the muscle field; 3, impression of interior of brachial valve, x 1.5, note the discrete hinge plates and the myophragm; 4, impression of extexior of pedicle valve, x 1.5, note the gentle convexity of the valve, as contrasted with the flat to slightly concave brachial valve, x 1.5; 5, impression of interior of pedicle valve, x 1.5, note the fonn of the muscle field posteriorly (damaged anteriorly)and the short dental lamellae; 6, impression of exterior of brachial valve, x 1.5, note the form of the costellae and the medial, broadly sulcate form; 7, impression of interior of brachial valve, x 3, note the fonn of the cardinalia.

Two samples were wllected from the Vargas Peíía Shale. One of these bears impressions of Calymene boettneri Hanington, and the other a small number of generically indeterminate brachiopods (probably chonetids). Clarkeia is also recognized in Europe (Bouwt, 1990) from the Pridoli of Brittany, and possibly from the basal Silurian of the Carnic Alps (Jaeger et al., 1975). An aileged Afiican occurrence (Cocks', 1972, reassignment of Aratanea Schmidt to Clarkeia) was rejected by Drot et al. (1979) and by Boucot (in Laubacher et ai., 1982). Drot et al. (1979) have described Clarkeia and Heterorthella (the specimens iliustrated by them as Salopina may be early growth stages of Heterorthella) from eastem Senegal that they initiaily assigned to the Silurian, but which Racheboeuf and Villeneuve (1 989) wnsidered to be more likely of lochkovian, i.e., earliest Devonian, age. Heterorthella is recognized widely from the South American Malvinokaffric Realm Siiurian. Localities include the area from northem Argentina to southem Peru (Berry and Bouwt, 1972), to the north of the Amazon in Brazil on the Rio Trombetas, and in the Disa SiitstoneMember, CedarbergFormation, Table Mountain Group in South Afiica (Cocks, 1972). Boucot (in Berry and Bouwt, 1972) considered the Disa lowest Silurian, say G. persculptus Zone. Comparison of the figures provided here of Paraguayan Clarkeia with other South American specimens can be made fiom the figures in Laubacher et al. (1982). The Heterorthella figures provided here from Paraguayan material may be w m pared with the typicai Andean Silurian material figured in Harper et al. (1969). BIOGEOGRAPHY

Neither Clarkeia nor Heterorthella had previously been recognized within the wnfines of the vast Paraná Basin of eastem South America. When one considers how littie sheily Silurian has been recognized to date within the Paraná Basin, this situation is not puuiing. Shelly Silurian previously had only been rewgnized in the northeastern part of the Basin, in the Branlian State of Goiás (Gray et al., 1985), where only Benthic Assem-

blage 1 nuculoid bivalves, orbiculoid brachiopods, and plectonotid gastropods occur. The Goiás occurrence is too shallow an environment for either Clarkeia or Heterorthella. Shelly Silurian was also recognized in centrai Paraguay, the area in which the new occurrence is situated. Despite the smaii size of the samples, there is iittie doubt that the dominante of Clarkeia, in association with some Heterorthella, is adequate basis for recognition of the Clarkeia antisiensis Community (see Boucot et al., in press, for a discussion and description of the Clarkeia Community.) The Clarkeia Community is a typicai Benthic Assemblage 2, subtidal, normal turbulence level, low diversity, Malvinokaffiric Realrn, level bottom community. Similar material is widespread in the Siiurian of Bolivia, nearby Argentina, and southem Peru. While considering this new information from the uppermost Ayala Sandstone, consider that the famas from the overlying Vargas Peíía Shale, discussed by Hanington (1972), also suggest a Benthic Assemblage 2 assignrnent. Owing to the scattered nature of the fossils, however, it is di5cult to define communities, although when individual beds have been studied one might be able to decide on the wmmunity or wmmunities present. Individual specimens wllected hither and yon in a large quarry do not provide a reliable basis for community analysis. Harrington's (1972) still younger Cariy Sandstone also yields fossilssuggesting Benthic Assemblage 2, and possibly 1 as weil. The authors are indebted to geologist F. Wiens (San Luka Oriente SRL Mineral, Asunción) for having kindly provided assistance and field guidance to PETROBRAS staff in the weste m Paraná Basin. The -wllaboration of other members of the field party (PETROBRAS geologists E. J. Milani, W. Guazelli, and A. B. Franca, and the Paragmyan geologists C. A. Figueredo and J. Adorno) is also acknowledged. J. H.G. Melo, E. V. Santos Neto, and S. Wolff thank PETROBRAS (Petróleo Brasileiro S.A.) for permission to publish this note.

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REFERENCES BABCOCK, L. E., J. GRAY,A. J. BOUCOT, G. T. HIMES,AND P. K. SIEGEL. 1990. First Silunan conulanids from Paraguay. Joumal of Paleontology, 64997-902. BERRY,W. B. N., AND A. J. BOUCOT(eds). 1972. Correlation of the South Amencan Silunan rocks. Geological Society of Amenca Special Paper 133, 59 p. B o u c o ~ A. , J. 1975. Reclassification of Australostrophia mesembria (Brachiopoda, Devonian). Journal of Paleontology, 49:633-637. -, 1990. silunan biogeography, p. 191-196. W, S. M ~ and C, R, scotese (eds,), palaeozoic palaeogeography and ~ i raphy. Geological Society Memoir No. 12. -, y, G-, AND J. H, G. ME^, press, south ~~~n~~~rnanne Silunan communities. In A. J. Boucot and J. D. Lawson (e&.), Final Report of Project Ecostratigraphy. Cambndge University Press, Cambridge. cocKs, L. R. M. 1972. ~h~ o,-igin ofthe silunan clarkeia shelly fauna of South America, and its extension to West Africa. Palaeontology, 15:623-630. DROT,J., H. L ~AND A. ~LE pAGE,~ 1979, sur ~ la découverte , de silunen supé.ieur au sommet de la séne de Y~~~~~~~~~~ au oriental: implications paléogeographiquies et stmcturales, société Géologique et Mineralogique de Bretagne, Bulletin, Série C, Tome X, Fascicle 1, 1978:7-30. G ~ J,, G. ~ K., cOLBATH,A. DE FARI~,AND D. M. ROHR, 1985. Silunan-age fossils from the Paleozoic Paraná Basin, southern Brazil. Geology, 13521-525. HARPER, C. W., JR., ANDA.J. BOUCOT.1978. The Stropheodontacea, Pt. I, Leptostrophiidae, Eostropheodontidae and Strophonellidae. Palaeontographica, Abteilung A, 16155-118. -, -, AND V. G. WALMSLEY.1969. The rhipidomellid brachio-

pod subfamily Heterorthinae and Platyorthinae (new). Journal of Paleontology343:74-92. H-GTON> H. J. 1950. Geoloda de1 Paraguay oriental. ~acultad de Ciencias Extactas, Universidad de Buenos Aires, Contnbuciones Cientificas, E$ 1:1-82. -. 1972. Silunan of Paraguay, p. 41-50. In W. B. N. Berry and A. J. Boucot (eds.), Correlation of the South Amencan Silunan Rocks. Geological Society 0f Amencan Special Paper 33. JAEGER> H., V. HAvL1cEK,AND H. P. ScHomuB. 1975. BiOstrati~aphie in den Sudalpen-Ein Beitrag K der Ordovizium/Silunan-Grenze ~ ~ ~ ~ um~ die Himantia-Fauna. Verhandlungen der Geo~ Diskussion ~ ~ ~ logischen Bundesanstalt, Jahrgang 1975, 4:271-289. LAUBACHER, G., A. J. BOUCOT,AND J. GRAY. 1982. Additions to Silunan stratigraphy, lithofacies, biogeography and paleontology of Bolivia and southern Peru. Journal 0f Paleontology, 56: 1138-1 170. MELO,J. H. G. DE,ANDA.J. BOUCOT.1990. Harringtonina is Anabaia (Brachiopoda, Silunan, Malvinokaffnc Realm). Journal of Paleontology, 64:363-366. RACHEBOEUF, P. R., AND M. VILLENEWE.1 989. Australostrophia senegalensis n. sp.: first chonostrophiid brachiopod (Chonetacea) from NW Afnca. Implications for the northwestem Gondwanaland margin. Neues Jahrbuch fur Geologie und Palaontologie Monatsheft, 12: 737-748. WOOD,G. D., M. A. MILLER,D. A. SAWICKI, AND C. L. SHINELDECKER. 1989. Chitinozoans and microplankton from the Silunan Vargas Pena Shale (Itacumbí G r o u ~ ) ,Chaco Basin, Paraguay. C.I.M.P. Newsletter 38:6 [abstract presented at the AASP Houston Meeting, NOV. 9881. A C C E ~ E10 D NOVEMBER i 990

J. Paleonl., 65(3), 1991, pp. 514-515 Copynght O 1991, The Paleontological Society 0022-3360/91/0065-O5 14103.00

THE VAN STRAELEN DECAPOD COLLECTION, INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE, BRUXELLES R O D N E Y M. FELDMANN AND ANNIE V. D H O N D T Department of Geology, Kent State University, Kent, Ohio 44242 and Institut Royal des Sciences Naturelles de Belgique, Department of Palaeontology, B- 1040 Brussels, Belgium THEREARE relatively few large collections of decapod crustacean fossils in the museums of the world. Most of them are well known and serve as depositories for numerous type and figured specimens that are documented in the literature. T h e purpose of this note is to cal1 attention to the extensive decapod crustacean collection in the Institut Royal des Sciences Naturelles d e Belgique, Brussels-a collection that is largely attnbutable t o the efforts of the late Dr. Victor Van Straelen. Van Straelen was Director of the Institut from 1925 until 1959. D u n n g that time he published extensively on a vanety of paleontological a n d stratigraphical problems. H e is perhaps best known for his contributions in the area of decapod paleontology. C o n n (1965) listed 118 papers published by Van Straelen, the overwhelming majority of which deal with crustaceans. Examination of his work in this area, however, would lead to the conclusion that most of the material basis for his work was that housed in other collections. Most of the type and figured specimens to which Van Straelen referred are deposited in other museums. Thus, the extent of the decapod collection a t the Institut is not well known and, because it contains material

that is potentially very useful t o researchers, it is important t o note its presence. Well over 1,000 specimens are deposited in this collection. Van Straelen accumulated a large collection of decapods, primarily brachyurans, from several Cretaceous and Cenozoic localities in Belgium and adjacent countries. These are curated with the museum's biostratigraphic collection and the specimens are readily accessible and available for examination. Notably, one single locality of the Rupelian (Oligocene) Boom Clay yielded several hundred superbly preserved specimens of Coeloma rupeliensis which would make excellent material for the study of biometry, intraspecific variation, and sexual dimorphism. Although many of the specimens are moderately well prepared, some would be enhanced by a more complete preparation of matrix, a task that would be fairly straightforward given the nature of the enclosing sediment. These specimens form a n extremely valuable collection. Van Straelen also amassed a large and extensive foreign collection from various classic localities around the world. Recent cataloguing of this material documented over 740 specimens