Abstract

The ichnosite of Ouro (Araraquara, São Paulo State) is one of the richests tetrapod ichnologic area of Jurassic age in South America. The ichnofossils are found in eolian sandstones, reddish colored in lithofacies considered to be dune and interdune deposits. These sandstones are named as Botucatu Formation, and originally covered a surface estimated in at least 1,300,000 km², constituting the largest known fossil desert in the world.

The tetrapod tracks from the Ouro quarries comprise bipedal dinosauroids of relatively large and smaller types; theromorphoid and mammaloid forms. This ichnofauna seems to be completely endemic and, therefore, quite new to science. Also occur invertebrate trace fossils produced by insects and earthworms.

Seventheen ichnosites analogous to that of Ouro site have been discovered along the strip of nearly 2,500 km where the Botucatu Formation sandstones outcrops at Paraná Basin. A complete and detailed study of this ichnofauna is in its initial phase.

Resumo

O jazigo icnofossilífero do Ouro (Araraquara, Estado de São Paulo) uma das mais ricas regiões icnológicas do Jurássico da América do Sul. Os icnofósseis são encontrados em arenitos eólicos avermelhados, em litofácies consideradas como depósitos de dunas e interdunas. Estes arenitos são designados como Formação Botucatu, e originalmente recobriam uma superfície estimada em pelo menos 1.300.000 km², constituindo o maior deserto já existente na superfície da Terra.

As pistas de tetrápodes das pedreiras da região do Ouro compreendem formas dinossauróides bípedes, além de formas teromorfóides e mamaliformes. Esta icnofauna parece ser completamente endêmica. Também ocorrem icnofósseis de invertebrados que são interpretados como pistas e escavações de insetos e anelídeos.

Dezessete sítios icnofossilíferos análogos à localidade do Ouro têm sido descobertos ao longo de uma faixa de 2.500 km em afloramentos da Formação Botucatu, Bacia do Paraná. O estudo detalhado desta importante icnofauna encontra-se apenas em sua fase inicial.

1. Introduction

The tetrapod ichnological site of Ouro is situated in the State of São Paulo, in the Municipality of Araraquara, 4 kilometers E of the Ouro railway station on the railway line from São Carlos to Araraquara, approximately 8 km ESE from the center of the town of Araraquara. There were there several quarries: São Bento - Corpedras (code: ARSB); Califórnia (ARCA); Cerrito Velho (ARCE); Cerrito Novo (ARCN); Santa Águeda (ARSA); Chibarro (ARCH). Presently only the São Bento - Corpedras quarry is open. The sandstones are quarried and used as a source of building material, particularly as flagstones for paving of sidewalks and for facing walls and pillars. The coordinates of the site (mean) are 21^o49'S; 48^o05'W.

The sandstones that present the tetrapod footprints are named as Botucatu Formation. This lithostratigraphic unit embodies Mesozoic eolian sandstones that extends along a stretch of Brazilian territory comprised between the states of Minas Gerais and Rio Grande do Sul, appearing also in the states of Mato Grosso and Goiás, on the west border of Paraná Basin (Figure 1).

The Botucatu Formation lithofacies are considered to be the dune (foreset and interdune facies) deposits. These are interpreted as great dunes climbing, in an inland

Figure 1 - Geological map of Paraná Basin and distribution area of Botucatu Formation ( modified from Mapa Geológico da Bacia do Paraná, 1981 ).

desert with high sand supply. In this way there was the construction of an erg, that overpass the freatic level changes, allowing that the interdunes areas keep always dry (Caetano-Chang, 1997). Despite this environmental condition of the Botucatu desert, some small lakes should have existed, especially in areas where the tetrapod ichnofauna is abundant.

2. Geology

The Botucatu Formation comprises Mesozoic aeolian sandstones, reddish colored, that originally covered a surface estimated in at least 1,300,000 km², constituting the largest known fossil desert in the world. From the paleontological point of view, the sandstones in the Botucatu Formation are void of body fossils, which have been interpreted as a consequence of the desert environment.

The age of these deposits have been traditionally considered as belonging to the Triassic. Therefore, Leonardi & Oliveira (1990) recognized that the date is not known with any precision. The reason for this is the environment: it represents a hot, dry, continental interior desert, where body fossils of animals and plants do not occur, nor pollens. There is only radiometric dating (120 - 140 Ma) on the flood basalts of the Serra Geral Formation that capped the Botucatu Formation. The ichnological analysis presented by Leonardi & Oliveira (1990) postulated that the Botucatu Formation, at least in outcrops of São Paulo State, and particularly in the Araraquara area could be considered between the Rhaetian and Middle Jurassic, with greater probability for the Lower Jurassic or the lower most section of Middle Jurassic.

3. History of the Site

In 1911, the Brazilian mining engineer Joviano Pacheco discovered the first slab from the Botucatu Formation with a tetrapod trackway, as a flagstone in a sidewalk in the town of São Carlos, 39 km SW of Araraquara, where very probably it originated. The original flagstone was deposited by Pacheco, along with some slabs with invertebrate trails, in the Geographic and Geological Commission Museum of São Paulo, presently called the Geological Institute of São Paulo, and appears to be the first tetrapod trackway discovered and collected in South America. However, it was only much later published by Friedrich von Huene (1931).

Shortly after arriving in Brasil, Leonardi started inquiries about the origin of the Pacheco's flagstone and discovered in July 1976 in the municipality of Araraquara, region of Ouro, an abundant and varied ichnofauna consisting mainly of vertebrate tracks and secundarily invertebrate trails, in the above said quarries, then actively worked, as well as in the sidewalks of the town of Araraquara (Leonardi, 1980). These findings have both ichnological and petrographic characteristics similar to those of the Geological Institute flagstone. Other Leonardi's expeditions followed (11 altogether, cfr. Leonardi, 1994, p. 169), by means of grants from the CNPq (The Nacional Council for Research of Brazil). Between 1976 and 1986 natural exposures, quarries and town pavements throughout the eastern outcrop of the Botucatu Formation, from Minas Gerais (North) to Rio Grande do Sul (South) was explored by Leonardi and collaborators, especial attention being paid to those of the São Paulo State. The recovery of fossils was startling: vertebrate tracks were discovered in five Brazilian states, at Sacramento (Minas Gerais), Rifaina, Franca, Brodósqui, Analândia, Araraquara, São Carlos and Botucatu (São Paulo); Jacarezinho (Paraná), Serra do Rio do Rasto (Santa Catarina), Taquari, Tramandaí and Santa Cruz do Sul (Rio Grande do Sul) a belt 2500 km long (Leonardi, 1977; 1981a-b; 1989; Leonardi & Sarjeant, 1986; Leonardi & Godoy, 1980). Later, two sites were discovered by Leonardi in the western side of the Paraná basin, in Murtinho (Mato Grosso) and Asunción (Paraguay) (Leonardi, 1992, 1994).

From the first visit in 1976, it was realized that the most important track bearing outcrop of the Botucatu Formation was not in any quarry or natural exposure, but in the streets of Araraquara. This is an agricultural and industrial city situated near the geographical center of the state of São Paulo. Here there are over 300 linear kilometers of sidewalks, courtyard paving and other pedestrian ways, all made from flagstones of pink or red sandstone. Such is the frequency of tetrapod tracks that any average stretch of flags, 100 metres long (a mean block) by 2.5 metres wide can be expected to contain between five and ten trackways or isolated footprints all in all, an enormous bonanza for the paleoichnologists! Whilst any paleontologist would, of course, prefer to find his fossils in situ, the fact that all those flagstones came from a restricted area of outcrop means that their source is known with sufficient accuracy for most practical purpose. Indeed, all the quarries from which the flagstones were procured (with the exception of the Chibarro quarry) are within an area of only 0.75 km². In many instances, the precise colour and consistency of the slab and the nature of its sedimentary structures enable the very horizon from which it came to be identified with confidence (Leonardi & Sarjeant, 1986).

Between 1976 and 1983, all the sidewalks and other pavements - an extent of 308 km, or 0.77 km² - were surveyed by Leonardi, in one expedition being aided by a group of students from the School of Geology of the Federal University of Paraná at Curitiba. Some thousands of tracks were recorded, many of them were filed, photographed, measured, and sketched. Of these, some sixty trackways or isolated footprints were of such quality as to merit special attention. After two unsuccessful attempts to convince two successive mayors of Araraquara that these slabs were of scientific importance, the chosen sixty flagstones were successfully collected and substituted with the permission and the logistic assistence of the City Council in 1983, in a rare urban palaeoichnology exploit (Ibidem). In the meanwhile, the continuation of the stope on the working faces of the São Bento quarry of the Corpedras firm was periodically assisted by Leonardi. Altogether, more than 200 slabs exhibiting tetrapod footprints have been collected from the urban sidewalks as well as from the quarries, for lodgement either in the Museu Nacional at Rio de Janeiro (Federal University of Rio de Janeiro), palaeontological collection of the Departamento Nacional da Produção Mineral at Rio de Janeiro (Ibidem) and Federal University of Paraná (Curitiba).

Many flagstones with tetrapod tracks produced almost certainly from the Ouro ichnosites were found in the urban pavements of other towns within the São Paulo state, including the capital of São Paulo, e.g. in the pavements outside the airport of Congonhas and the Zoo.

Nowadays there is a continuous prospection and collection of new slabs that have been lodged at Universidade Estadual Paulista (UNESP - Rio Claro) and Rio de Janeiro Federal University (Geology Department).

4. The Ichnofauna of the Ouro Ichnosite

The tetrapod tracks from the Ouro quarries (and from the sidewalks of the town) are almost always (90-95%) of poor quality, the footprints being simply a rounded or elliptical cavity (convexity in the counterprints or natural casts) furnishing no morphological details. Characteristically this cavity is accompanied by a crescentic sandstone ridge, always in the direction of foreset dip, representing the sand displaced by the animal's foot during its progression across the slopes of a dune. However, the parameters of such tracks frequently enable them to be classified, despite their poor quality, provided that a good specimen of the same type has been found also. Firm identifications and descriptions depend necessarily on the better specimens, and it is on the basis of these, in the last analysis, that the comments below are made (Ibidem).

The classification is always difficult due to the poor quality of the material and due to the uncertainty as to the age of the formation, because of lack of associated body fossils and because of the endemicity of the ichnofauna.

Presently it appears that the ichnofauna of Ouro covers (Figure 2,3).

a) Eight dinosauroid forms, all bipedal, digitigrade and tridactylous, with an elevated pace angulation (up to 180^o). These tracks are relatively rare. This group includes two or three types of relatively large dinosaurs (within this dwarf desert fauna), with footprints 12 cm long and strides up to 2 meters; some medium-sized animals, with a stride of 1-1.5 metres; and some smaller types. One small form is trydactylous but frequently appears monodactylous in the running gait.

b) At least seven theromorphoid forms that are rarely encountered in the sidewalks and very rarely found in the quarries. It is difficult to recognize the parameters of the trackways (stride, pace, pace angulation etc.) because they are represented mainly by isolated footprints. By the morphology of the footprints, they are attributable to highly specialized quadrupedal animals, with advanced gait. The footprints are plantigrade and their outline points to rounded or elliptical paws, with the transverse axis larger than the antero-posterior. The digits are always very short, pointing to a probable phalangeal formula 2-3-3-3-3 (osteologic or functional). The claws are partially or completely separated from the palm or sole and are sometimes modified into small hooves. The stride is between 15 and 50 cm. The trackway is relatively narrow for a quadrupedal animal and the pace angulation is up to 160^o.

c) At least nine forms, because of their advanced gait, the shape of their autopodia (rounded or elliptical paws, with the transverse axis larger than the antero-posterior, the digits always very short, pointing to a probable phalangeal formula 2-3-3-3-3) and because of their small dimensions can be morphologically defined as mammaloid. Almost all of these forms appears to be new; some at the ichnogenus level, others at the morphofamily level. This group includes some rare and interesting trackways with hopping and gallopping gaits. Among these tracks, the most abundant form was classified Brasilichnium elusivum Leonardi, 1981. This form has a strong heteropody, with the forefeet extremely small.

d) Height to ten forms of invertebrate trails, mainly attributable to arthropods. The invertebrate trails are remarkably rarer than the tetrapod tracks.

The statistical composition of the Ouro icnhnofauna, in a sample of the first 100 collected slabs, is as follows: it includes a small number of therapsid individuals but a large

Figure 2 - Fossil footprints from Botucatu Formation. (A),(B),(C) Theromorphoid footprints attributed to ? Tritylodontoidea Flagstones from the sidewalks of Araraquara; (D),(E) Small theropod trackway ( ? coelurosaur ) collected from the sidewalks of Araraquara (D) and (E) Cerrito Velho Quarry, Araraquara; (F) Mammaloid trackway with galloping gait. São Bento Quarry, Araraquara.

Figure 3 - Fossil footprints from Botucatu Formation. (A) Probable theromorphoid track ( ? Tritylodontoidea ) from São Bento Quarry, Araraquara; (B) ? Coelurosauria footprint, Cerrito Novo Quarry, Araraquara; (C) Bipedal dinosaur track. Flagstone from the sidewalks of Araraquara; (D), (E) Brasilichnium elusivum trackways referred to early mammals. (D) São Bento Quarry, Araraquara; (F) Flagstone from the sidewalks of Araraquara.

number of forms ( 7.7% of the individuals and 29.2% of the forms ); a good percentual of dinosauroid tracks as for the individuals (27,9%) and the forms (33.3%); the mammal percent is high as for the individuals (64.4%), not so for the forms (37.5%). Sixty three tracks and 14 forms are quadrupedal; 41 tracks and 10 forms are bipedal. In this ichnofauna, where a number of mammaloid tracks present bipedal hopping gait, bipedalism is rather common (39.4% of the individuals and 41,7% of the forms). The sprawling tracks are completely absent. The therapsidian/archosaurian ratio is 0.28; the mammalian/archosaurian ratio is 2.31; the theropsidian = (therapsids + mammals)/archosaurian ratio is 2,58. These results are significant; however, they were probably biased in the picking up of the slabs, in favour of the dinosauroid and theromorphoid tracks.

The trackwakers, at Ouro site and especially at the São Bento quarry, preferred certain directions. Indeed, 76% of the trackways examined in situ are oriented in both ways to directions within the 2nd and 4th quadrants of the compass. As a whole, the animals have crossed most frequently (and diagonally) a large transverse dune. The motives that explain this special direction are not known at present. One could express the working hypothesis that this direction could correspond to a track connecting two watering points or oases.

The ichnofauna seems to be completely endemic. This factor causes problems in the classification and interpretation of the tracks, but adds greatly to their interest. As noted earlier, this was a very arid environment, a desert and/or semi-desert highland and it is known that arid and highland environment ichofaunas and faunas are relatively rare. Unfortunately, a complete and detailed study of this ichnofauna was not so far issued.

5. The Trackmakers

We start from the presumption that the Botucatu Formation be Lower Jurassic, as it seems more probable from the ichnological point of view (Leonardi & Lima, 1990). If this is the correct datation, then the small and medium dinosauroid tracks with clawed digits may most probably be attributed to ceratosaurid theropods and the largest dinosauroid tracks, sometimes with hoofed digits, to the ornithopods. The theromorphoid tracks are attributed to therapsids and, in the Liassic hypothesis, to the Tritylodontoidea, the only group of therapsids present after the end of the Triassic. The mammaloid forms probably belong to true early mammals.

6. Other Ichnosites of the Botucatu Formation

A number of ichnosites analogous to that of Ouro site were discovered by Leonardi, along the strip of nearly 2,500 km where the Botucatu Formation sandstones outcrop along the eastern side of the Paraná Basin and more rarely along the western side. The sites are the following, clockwise:

Eastern side:

a) Sacramento (Minas Gerais) - flagstones of some sidewalks; undetermined tetrapods.

b) Frutal (Minas Gerais) - flagstones of some sidewalks; undetermined tetrapods.

c) Rifaina (São Paulo) - flagstones of some sidewalks; isolated footprints and trackways of the theromorphoid and coelurosauroid kind.

d) Franca (São Paulo) - flagstones of some sidewalks; isolated footprints and trackways of the theromorphoid and coelurosauroid kind on the flagstones of some sidewalks; these probably proceed from the Brodósqui quarries.

e) Brodósqui (São Paulo) - isolated footprints and trackways of the theromorphoid and coelurosauroid kind.

f) São Carlos (São Paulo) - in a quarry, a short trackway attributed to a mammal or to a theriodont. Tracks on flagstones of some sidewalks and on the facing of the cathedral pillars. These probably proceed from Araraquara quarries.

g) Analândia (São Paulo) - some trackways of the mammaloid kind, one of them with the ricochet gait.

h) Rio Claro (São Paulo) - flagstones of some sidewalks; undetermined tetrapods.

i) Botucatu range (São Paulo) - two isolated footprints, relatively large size, perhaps attributable to ornithopods.

j) Jacarezinho (Paraná) - tracks of undetermined tetrapods on flagstones found in other Paraná towns were procured in quarries near this town.

k) Ponta Grossa and Curitiba (Paraná) - flagstones of some sidewalks; undetermined tetrapods. The flagstones probably come from the Jacarezinho quarries.

l) Serra do Rio do Rasto (Santa Catarina) - record of a tetrapod trackway, not seen.

m) Taquari (Rio Grande do Sul) - record of tetrapod trackways, not seen.

n) Santa Cruz do Sul (Rio Grande do Sul)- a flagstone with two parallel trackways, one of a small theropod, the other of Brasilichnium elusivum.

o) Tramandaí (Rio Grande do Sul) - one theropod isolated track, on a flagstone in the town sidewalks.

Western side:

a) Assunción (Paraguay) - flagstones of some sidewalks; theropods and tritylodonts; Missiones Formation, probably Lower Jurassic.

b) Murtinho (Mato Grosso do Sul) - flagstones of the platforms of the railway station; undetermined tetrapods.

7. Invertebrate Tracks

The first description of invertebrate trace fossils was presented by Pacheco (1913) that recognized "worm tunnels" in the sandstones of Botucatu Formation. Later, Almeida (1954), Bjornberg & Tolentino (1959) also identified new "worm trails" in threse sandstones. Paraguassu (1970) proposed that these ichnofossils were produced by conchostraceans. Leonardi (1980, 1984), Leonardi & Godoy (1980) and Leonardi & Sarjeant (1986) considered them as "worm" and arthropod tracks.

The following localites with invertebrate ichnofossils in Botucatu Formation was presented by Fernandes et alii (1990):

a) Quarry 3 - 4 km from São Carlos (São Paulo) - worm tunnels (Pacheco, 1913).

b) Botucatu Range (São Paulo) - worm tunnels (Almeida, 1950).

c) Pacaembu, São Carlos (São Paulo) - worm trails (Bjornberg & Tolentino, 1959).

d) Quarry of São Tomás Farm, Ibaeté county (São Paulo) - conchostraceans trails (Paraguassu, 1970).

e) Quarries of Araraquara (São Paulo) - worm trails and arthropod tracks (Leonardi, 1980).

f) São Bento Quarry, Araraquara (São Paulo) - arthropod trails (Leonardi, 1984).

g) São Bento Quarry, Araraquara (São Paulo) - trails and invertebrate burrows (Leonardi & Godoy, 1980).

h) Quarry of Itaguaçu Farm, São Carlos (São Paulo) - worm trails (Leonardi & Godoy, 1980).

The study presented by Fernandes et alii (1990) classified the trace fossils of Botucatu Formation as Taenidium satanassi D’Alessandro & Bromley, 1987 and Taenidium serpentinum Heer, 1897, besides "U" shaped burrows. Ethological interpretation of Taenidium trails attributes them as feeding traces, whose burrow fills could be considered as faecal material or the packets of surrounding sediments by earthworms and insects; the "U" - shaped burrows are probably evidence of insect or earthworms dwelling tubes.

8. Protection

The tetrapod ichnofossils from Ouro site have been collected and housed in Museums and Universities of Paraná, São Paulo and Rio de Janeiro states. There is any kind of protection in the quarry were these material are found. Generally the more conspicuous tracks are selected by the workers of the Corpedras (Ouro Site) and then foward to universities.

The flagstones with ichnofossils from the sidewalks of São Carlos (São Paulo State) have been filed by Marconoto & Bertini (1999) aiming the educational use of this material integrated in the daily of the São Carlos citizens. The sidewalks with fossil footprints are an open museum, that can be used in the future in regional tourism projects.

9. Acknowledgments

Mr. Tim Halley of the Zoology Department of the Queensland University Brisbane (Austrália) for its critical review. Professor Maria Rita Caetano-Chang (Universidade Estadual Paulista - UNESP/Rio Claro) for her collaboration with the bibliographic material. The family Grosso (CORPEDRAS) for the collaboration.

This study was support by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) and Fundação Universitária José Bonifácio (FUJB/UFRJ).

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