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A Semionotid Fish from the Crato Formation (Aptian, Lower Cretaceous) of Brazil: Palaeoecological Implications

A Semionotid Fish from the Crato Formation (Aptian, Lower Cretaceous) of Brazil: Palaeoecological Implications

ORYCTOS,Vol. 1 :37 - 42 Octobre1998

A SEMIONOTIDFISH FROMTHE CRATOFORMATION (, LOWER )OF : PALAEOECOLOGICALIMPLICATIONS

Paulo M. BRITO1 , David M. MARTILL, and SvtvieWENZ3

tDepartmento Biologia e Vegetal, Universidade do Estado do Rio de Janeiro, R. J. Brazil & Laboratoire Ichthyologie, Museum national d'Histoire naturelle, Paris, France. '?Departmentof Geology, University of Portsmouth, Portsmouth,pOl 3eL, UK. 3 Laboratoire de Paléontologie- URA 12 CNRS, 8 Rue Buffon, F-75005 Paris, France.

Abstract : A partial example of an articulated cf. Araripelepidotes sp. from the Nova Olinda Member of the (Aptian, Lower Cretaceous,, Bra\zil) is the first record of this taxon from this for- mation. other than spp. are extremely rare in the erato Formation and we consider the implications in terms of the overall ichthyofauna diversity and palaeoecology.

Key words: Pisces,Lower Cretaceous,Brazil

Un poissonsemionotidé de la Formation Crato (Aptien, Crêtacéinférieur) du N. E. du Brésil: implications paléoécologiques

Résumé : Un exemplaire incomplet, articulé, d'un poisson semionotidé,provenant du Membre Nova Olinda de la Formation Crato (Aptien du Bassin d'Araripe, Brésil) est identifié comme étant un cf . Araripelepidotes sp. C'est la première fois que ce type de poisson est signalé dans ce niveau. A l'exception de Dastilbe spp. les poissons sont extrêmementrares dansla Formation Crato. Le problème de la diversité de I'ichthyofaune et les implications paléo- écologiquesde cette découvertesont abordées.(traduit par la rédaction).

Mots clés: Pisces, Crétacé inférieu4 Brésil

INTRODUCTION thoughts on the palaeoenvironment, especially with regard to the palaeosalinity. Although the Nova The Crato Formation of the Araripe Basin, north Olinda Member of the Crato Formation (Aptian, east Brazll is one of the most important Meso zoic Lower Cretaceous,Araripe Basin, north east Brazll) conservation lagerstâtte, and is particularly is well known for its exceptional preservation and well-known for yielding abundant, diverse and well abundanceof , the ichthyofauna is of very low preservedinsects and plants (Martill, 1993).As of yet, diversity (only two genera so far being recorded) and no detailed palaeoecological analysis of the forma- only the gonorhynchiform Dastilbe elongatus tion has been published and questions remain as to (Silva Santos, 1947) occurs abundantly.On the other the exact nature of the palaeoenvironment. The pur- hand, winged are extremely abundant and pose of this paper is to document the first discovery include a wide range of orders. Other verte- of a semionotid fish; cf. Araripelepidotes sp., from brates such as birds, , crocodiles, lizards the Crato Formation and consider the palaeoecologi- and frogs have all been reported (Martill & Filgueira, cal implications of this fossil in the light of current 1994; Maisey, I99I). Perhaps remarkably, if one

37 ORYCTOS,VOL.1,1998 excludesDastilbe spp. pterosaursappear to be more THE NEW SPECIMEN abundantthan fish (seeMartill & Frey, this volume). Very rare examples of the ichthyodectiform fish The presentstudy is basedon a single specimen Cladocyclussp. from the Crato Formation were first (PMB.VP-I44) housedin the Departmentof Biology reportedby Wenzand Campos (1985) from Barbalha, of the State University of Rio de Janeiro (UERJ). Cearâ.More recently Maisey (1996) claimed that Although the new specimenis incomplete,it is an specimensof Cladocyclusfrom the Crato articulatedexample of a semionotidfish on a slab of representeda freshwater speciesof this taxon. We creamcoloured typical of the Nova Olinda discussthis considerationbelow. Memberof the CratoFormation (Figs . l, 2).It lacks the skull and anterior trunk region, thus preventing accurategeneric and specificidentification. SYSTEMATICS

ClassOsteichthyes Subclass Figure 1. cf . ' Araripelepidotes sp. from the Nova Olinda InfraclassNeopterygii Member of the Crato Formation (Aptian, Lower Cretaceous) Order Semionotiformes of the Araripe Basin, n.e. Brazll. Scale bar in centimetres. entire Family Semionotidae Specimennumber PMB.VP-I44. Photographshowing specimen on slab of typical Crato limestone. Note that the Genuscf . AraripelepidotesSilva Santos,1985 skull and anterodorsal part of the trunk appears to have (seealso Silva Santos, 1990) decayedaway prior to preservation.

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38 BRITO, MARTILL & WENZ- SEMIONOTID FROM BRAZIL

As preserved the specimen is approximately 250 caudal fin is slightly forked (Fig.2). mm in length, and represents a fish with an original The body is subcylindrical with a moderate ele- estimated length of between 240 mm and 300 mm vation anterior to the dorsal fin. Dorsal and anal fins (this estimate obtained by comparing the length bet- are situated in the posterior part of the body. All the ween base of the ventral lobe of the caudal fin and fins are preceded by strongly developed fulcra. The base of pectoral fins with that reconstructed by body is coveredby rhombic, smooth, isometric scales Maisey (I99I, p. 118) for Araripelepidotes). The covered by a thick layer of ganoin. The scales differ body measuresapproximately 180 mm from the pec- depending on their position in the body. The most toral girdle to the caudal pedicle. The anomaly bet- dorsal anterior scales are larger with serrated poste- ween the actual length of the specimen and the esti- rior edges; the mid and posterior scales are diamond mated length of the complete fish is due to the tapho- shaped and lack serration. nomic forward flexure of the right pectoral fin. The It is difficult to place the Crato specimen preci- anteroventral region of the trunk shows some disrup- sely in a taxonomic position, as it lacks the skull tion, and the missing skull is due to post mortem loss bones and the body shows only the most generalised during drifting. The paired pectoral fins are present, characters' of the Semionotidae. Semionotids are as is the anal fin and parts of the dorsal fin. The cau- common in the Mesozoic rift and pre-rift basins in dal fin is entire, although the dorsal and ventral lobes the north-east of BrazII, and are known by at least 4 have "closed" slightly to give the caudal region a nar- of , and one species of row appearance.A slight taper of the distal portions Araripelepidotes in the SantanaFormation. of the caudal fin suggest that in this specimen the

39 ORYCTOS,VOL.1,1998

In the Araripe basin, Lepidotes sp. is known only the anatomy of Dastilbe from the Crato Formation by disarticulated material from the Missao Velha and considers that two species may occur; a small Formation. From the Romualdo Member of the species with a dorsal fin ray count of 10 and larger SantanaFormation is known Araripelepidotes temnu- examples with a fin ray count of 13. In the Nova rus (Agassiz, 1841), a smaller and more slender Olinda Member specimens of both large and small semionotid, as well as a possible distinct semionotid Dastilbe spp. occur in abundance;smaller individuals taxon, âS yet undescribed (Brito &. Wenz in prep.). in super abundance, whereas examples of Recently, Wenz & Brito (1992) described two primi- ate extremely tate, and usually represent tive gar fishes; Obaichthys decoratus and O? laevis, small individuals (size range 150 to 300 mm) compa- also from the Romualdo Member. red with examples of Cladocyclus from the The new Crato specimen can be distinguished Romualdo Member of the Santana Formation where from all other Lepidotes known in Brazllby its body lengths of over 1 m are recorded (Maisey, I99I: p. shape (subcylindrical), the absenceof a pronounced 190). The new specimen described here with pro- hump in front of the dorsal fin and the dimensions of bable affinities to Araripelepidotes indicates that its body. other fish species were entering the Crato Formation It can be distinguished from Obaichthys by the water body, but only very rarely. presence of large scales in the front part of the body The low diversity of the Crato Formation ich- (Obaichthys spp. have similar sized scales throu- thyofauna is in marked contrast to the high diversity ghout), and the absenceof opisthocoelous vertebrae. Santana Formation ichthyofauna which has to date In addition, the vertebrae of the new specimen are not yielded some twenty genera (Maisey I99I; Martill fully ossified, whereas in gars the vertebrae are well 1993). Of those recorded from the Crato Formation, ossified throughout. Araripelepidotes and Cladocyclus are also well Although no single synapomorphycan be poin- known from the Romualdo Member of the Santana ted out, we can separatethe Crato specimen from all Formation, but the gonorhynchiform Dastilbe elon- other Brazllian semionotifoffns sensu Olson and gatus has yet to be recorded. This anom aly has McCune I99I (theseauthors combine Semionotidae, important implications for any reconstruction of the Macrosemiidae and Lepisosteidae in the palaeoenvironment of the Crato Formation water Semionotiformes), except Araripelepidotes . body. The Santana Formation ichthyofauna probably However, the absenceof the skull makes any identi- represents a mixed salinity assemblage with both fication tenuous. The new specimen is certainly more marine, freshwater and brackish forms. No certain similar to Araripelepidotes (e.g. shape of the body, marine fossils (ammonites, brachiopods, etc.) have shape and dimension of the scales) than to any other been found commonly in the Santana Formation known semionotiform. We here treat it as cf. although rare echinoids occur just a few metres above Araripelepidotes sp. Araripelepidotes temnurus the fish bearing concretions, as do marine gastropods. (Agassiz, 1841) is well-known from the slightly younger Romualdo Member of the Santana Formation which occurs in the same basin just a few PALAEOENVIRONMENT metres above the Crato Formation; for descriptions of its anatomy seeMaisey, l99I and Thies, 1996. The palaeoenvironment of the Crato Formation has only been discussed briefly (Martill, 1993; Maisey, I99I; Viana, 1992). In reality, the Crato THE NOVA OLINDA Formation represents many environments ranging MEMBER ICHTHYOEAUNA from lacustrine (sensu lato) to fluvial and terrestrial. Of particular importance is the palaeoenvironment of So far only the teleost fish Dastilbe elongatus the suite of laminated limestones of the basal Nova Silva Santos I94l and very rare Cladocyclus sp. have Olinda Member which are the source of so many been recorded from the Nova Olinda Member of the exquisitely preserved fossils. This environment, wha- Crato Formation. Blum (1991, pp. 274-283) discusses tever its nature and complexity, persisted without 40 BRITO, MARTTLL & WENZ- SEMIONOTID FROM BRAZIL apparent intemrption in the region of Nova Olinda Some sedimentological considerations suggest and Santana do Cariri for some time as the unit is that salinities may have been elevated.A general lack continuous at the same millimetrically laminated of bioturbation is difficult to interptet, although it scale for up to 6 m. Martill (1993) considered that the may have been a result of elevated salinities of bot- environment was that of a saline lake or lagoon over tom water, it may also have been a result of bottom which extended a thin and probably temporary fresh- water anoxia. If Viana ( 1992) is correct that the mil- water tongue of water, the volume and extent of limetric lamination is a type of stromatolite, anoxia which would have been controlled by seasonalfluc- could be ruled out if the organism responsible for the tuations in fluvial input. Similarly, Viana (1992) lamination could be shown to have been an obligate considered that the fauna and flora representeda ter- aerobe. Perhaps more convincingly, the widespread restrial and freshw ater assemblage,but that the water occurrence of hopper faced halite pseudomorphs body may have been saline. On the other hand, suggest that the Nova Olinda Member was deposited Maisey (1996) considers that the Crato Formation under mainly saline conditions. These probably for- limestones represent a freshwater sequence,and sup- med in high salinities developed at the wateilair posed that the Cladocyclus specimens in the unit interface during hot and dry seasonsand sank when must have been a freshwater species. the surface waters were disturbed by winds. They From a palaeogeographical viewpoint the Crato then left impressions in the bottom sediments, but Formation water body was certainly situated in an probably redissolved in the slightly lower benthic internal basin, and any link with marine waters must salinities. have been through elongate, probably restricted, fault-bounded grabens to the south, north and possi- bly west (Berthou, 1990; Maise], I99I; Martill, 1993). From a palaeontological perspective, the LINKS TO MARINE WATERS fauna is dominated by a single fish species,usually found in mass mortality assemblages,and by winged Although the Araripe Basin is currently situated insects. Terrestrial invertebrates are also known, some 600 km inland from the Atlantic Ocean, during 'What including scorpions, spiders and centipedes. is Cretaceous high sea stands, this distance was proba- notably absent is a normal freshwater invertebrate bly reduced considerably. No firm evidence exists for assemblage. Only one choncostracan specimen a direct route to a particular marine sedimentary (Cyzicus sp.) was reported by Viana (1992) in what basin, but it has been suggestedthat links may have was an extensive period of work collecting assem- existed between the Araripe Basin and the Potiguar blages from all levels within the Nova Olinda Basin to the north, the Parnaiba Basin to the west and Member. Freshwater molluscs are unknown from the to the Jatoba-Reconcavo-TucanoBasin complex to unit and freshw ater insect larvae ate rare (larvae of a the south (Berthou, 1990), all of which are known to number of ephemeropterans are commor, and possi- have fully marine Lower Cretaceous sediments. bly represent pelagic larval forms). Also missing That marine waters entered the Araripe Basin is from the limestones are ostracodes,which ate extre- unequivocably demonstratedby the presenceof mari- mely abundant in other parts of the Crato Formation ne dinoflagellate cysts, foraminifera and echinoids in sequence.Thus the fossil assemblagedoes not repre- the upper parts of the Santana Formation and possi- sent that of a normal freshw ater body. This raises a bly by the presence of elasmbobranchs in the number of important issues with regard to interpre- Romualdo Member nodules of the Santana ting the autecology of those organisms that do occur Formation. It is thus possible that marine waters may within the Nova Olinda Member and, in particular, similarly have entered the basin during Crato those that only occur very rarely. Does an isolated Formation times to give mixohaline conditions. example of a fish represent a freshw ater example washed in from a river system draining into the basin, or does it represent a marine species that came in through one of the restricted links to the sea ?

4T ORYCTOS,VOL.1,1998

CONCLUSIONS dans le cadre de 1'ouverture de l'Atlantique équatorial. Comparisonavec les bassinsouest-africains situés dans le même contexte:pp. Palaeoenvironmental indicators in the Nova 113-134.InCANIPOS, D. A.; VIANA, M. S. S.; BRITO, P. M. & BEURLEN, G. (eds). Atas do simposio sobre a Olinda Member of the Crato Formation suggest that it Bacia do Araripe e Bacias Interiores do Nordeste, Crato, 14-16 was deposited under saline conditions, although fre- de Junho de 1990. shwater tongues of surface waters may have been pre- BLIIM, S. 1991.Dastilbe Jordan,1910 ; pp. 214- 283. InMAISEX sent during wet seasonsin front of river mouths and J. G. (ed.) Santana fossils: an illustrated atlas. T. F. H. deltas. Elevated salinities are indicated by abundant Publications,Inc., New York. MAISEY, salt pseudomorphs on many bedding planes throu- J. G. 1991. Santanafossils : an illustrated atlas. T. F. H. Publications,Inc., New York : l-459. ghout the sequence.Mass mortalities of Dastilbe may -1 996. Non-marine occurrence of ichthyodectiforms also be due to elevated salinity. Negative evidence for in the Lower Cretaceous of Brazll. Journal of Vertebrate elevatedsalinities include the lack of normal freshwa- Palaeontology, 16,, 3, suppl., Abstracts of the 56th Annual ter invertebrates, such as ostracods, gastropods and Meeting, New York. bivalves. , usually good indicators of fre- MARTILL, D. M. 1993. Fossils of the Santana and Crato Formations, shwater are known from only two examples of frogs, Brazll. Palaeontological Association Field Guides toFossils.5:1-159. both of which are probably allochthonous. and FILGUEIRA. J. B. M. 1994.A new feather The large amounts of drifted terrestrial plant from the Lower Cretaceousof Brazll. Palaeontology,3T: 483-487. material in the Crato Formation might imply that and FREX E. 1998. The Crato Formation Dastilbe too was washed into the lagoon, perhaps (Aptian, Lower Cretaceous) of Brazil : a new during periods of high freshw ater input during lagerstâtte.Oryctos, | : 79 - 85. floods . Later overturn or mixitrg of a stratified water oLSoN, P. E. & McCUNE, A. M. 199r. Morphology of Semionotus elegans a species group from the Early part of the column resulted in mass deaths of a drifted alloch- Newark Supergroup of Eastern North America with comments thonous biota. While the presence of cf. on the family Semionotidae.Journal of VertebratePaleontology, Araripelepidotes in this formation may also be an 11 (3) : 269- 292. example of a freshw ater fish washed into the basin, SILVA SANTOS, R. daI947. Umarediscricaode Dastilbe elongatus, we cannot rule out that it is a marine fish that entered com algumas consideracoes sobre o genero Dastilbe. the basin during a brief normal salinity excursion. D.G.M./D.Ir{.PM.,Notas prelim. Estudos,2g : 1-13. 1985. Nova conceituaçâo taxonomica do Thus we urge caution when trying to interpret Lepidotes temnurus Agassiz, do Cret âceoInferior da Form açâo palaeoecologieson rare specimensfrom sedimentary Santana, Nordeste do Brasil. Sociedade Brasileira de systems where the ambient conditions ate unclear Paleontologia, IX Congresso Brasileiro de Paleontologia, and may fluctuate widely. Resumosdas Communicaçôes: 16. 1990. Nova conceituaçâogenérica do Lepidotes temnurus Agassiz, 1841 (Pisces - Semionotidae).Annais da Academia ACKNOWLEDGEMENTS Brasileira de Ciencias, 62 : 239-249. THIES, D. 1996. The jaws of Araripelepidotes temnurus (Agassiz, 1841) (Actinopterygia, Semionotiformes) from the early we thank valeria G. Silva (Rio) for her helpful Cretaceousof Brazil Journal of VertebratePaleontology,16 (3) : criticism and Dr BetimarFilgueira, D.N.P.M. Cearâ, 369-373. for his assistancein the field. Thanks also to Mr VIANA, M. S. S. 1992. Um perfil paleoecoldgico no Membro Crato RobertLoveridge for help with photographyand Dr da FormaçâoSantana. 2nd Simposiosobre as Bacias Cretacicas Brasileiras, Rio Claro, SP,Brasil :71-73. Mike Barker for commentson the manuscript.DMM WENZ, S. &. BzuTo, P. M. 1992. Découverte de Lepisosreidae Fieldwork supported by NERC grant number (PiscesActinopterygii) dans Ie Crétacé infét'reur de la Chapada GRg/02505. do Araripe (N-E du Brésil): systématique et phylogénie. Comptes-rendusde l'Académie des Sciencesde Paris, 3L4, Ser REFERENCES II: 1519-1525. AGASSIZ,L. 1841. On the fossil fishes found by Mr Gardnerin the -& CAMPOS, D. A. 1985. Ensaio sobre a distribuiçâo Province of Cearâ, in the north of Brazll. Edinburgh New estratigrâfica de Cladocyclus (Pisces, ) do Philosophical Journal, 30 : 82-84. Cretâceo do Nordeste Brasileiro. Sociedade Brasileira de BERTHOU, P.-Y. 1990. Le bassin d'Araripe et les petits bassins Paleontologia, IX Congresso Brasileiro de Paleontologia, resu intracontinentaux voisins (NE du Brésil): formation et évolution mos das Comunicaçôes,Fortaleza, 1-7 September1985 : 10.

42 Note reçue Ie 3I-07-1997 acceptéeaprès révision le 15-01-1998

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