Cretaceous biota of the Triângulo Mineiro region ( Brazil ) : A review of recent finds Biota cretácica de la región del Triângulo Mineiro ( Brasil ) : Revisión de hallazgos recientes

The Bauru Group (Adamantina, Uberaba, and Marília Formations) crop out in the Triângulo Mineiro region, Minas Gerais State, Brazil, and yield a rich continental biota. Invertebrate and vertebrate taxa from underlying and overlying strata, as well as biostratigraphical correlations with other fossil sites in Argentina, suggest an Upper Cretaceous age for this biota. The diversity of the fossil assemblage recorded in these formations is summarized here and includes: frogs, lizards, crocodiles, titanosaurs, abelisaurid and carcharodontosaurid dinosaurs. This fossil assemblage provides important clues to understand faunas from other southern landmasses, particularly those from the Cretaceous of the African continent. Key-words: Upper Cretaceous, Triângulo Mineiro, Adamantina, Uberaba, and Marília Formations, biota, Brazil.

Vertebrate bones were first discovered in late 1940 near Uberaba Town; during the following decade, Llewellyn Ivor Price re-studied the vertebrate-bearing deposits of the Triângulo Mineiro region focusing on the Adamantina and Marília Formations.The Adamantina, Uberaba, and Marília Formations from Triângulo Mineiro have yielded abundant dinosaur bones, including partial skeletons, eggs, and teeth associated with remains of other macro and microvertebrate assemblages (Bertini et al., 1993;Dias-Brito et al., 2001).
The most common taxa is reptilian, and occurs in the Adamantina and Marília formations of Campina Verde, Monte Alegre, Prata, and Uberlândia municipalities.The Uberaba Formation, restricted to the Triângulo Mineiro region, includes only a few vertebrate taxa.In the Uberaba Formation scarce

Cretaceous biota of the Triângulo Mineiro region (Brazil):
A review of recent finds records of dinosaurs are represented mainly by eggs and isolated bones.
The intention of this work is to summarize the current knowledge of the stratigraphy of the Upper Cretaceous fossil-bearing units of the Bauru Group from Triângulo Mineiro, and the composition of fauna and flora inferred from their assemblages.

Geological and paleontological setting
The Bauru Group is an important fossil-bearing unit in the Triângulo Mineiro region that ranges in age from Turonian to late Maastrichtian (fig.2).According to Fernandes & Coimbra (1996) the group comprises a southeastward-thinning sucession of continental rocks nowadays exposed in modern drainages throughout South-Central Brazil, which conformably overlies magmatic rocks of the Jurassic-Cretaceous Serra Geral Formation (São Bento Group, Paraná Basin).The Bauru Group has been a source of dinosaur and other fossil vertebrates (figs.3A-K), invertebrates, and plants that have been discovered and collected since the early part of the 20th century.Fernandes & Coimbra (1996) included the Adamantina, Uberaba, and Marília formations (ascending order) in the Bauru Group; this stratigraphic arrangement is widely accepted and used in this study.

Adamantina Formation
This unit was established by Soares et al. (1980) referring to the continental deposits which unconformably overlie the Serra Geral Formation (São Bento Group, Paraná Basin).The Adamantina Formation crops in the States of Goiás, São Paulo and in the Triângulo Mineiro region, Minas Gerais State.Sediments are fluvial-lacustrine reddish clays and sands, deposited during warm and humid climatic events (Suguio & Barcelos, 1983).Based primarily on its vertebrate fossil contents, it is assumed that the Adamantina sediments were deposited during the Turonian-Santonian (Dias-Brito et al., 2001).The geology of the Adamantina Formation in Triângulo Mineiro region has been studied by several authors (Barcelos, 1984;Ferreira-Júnior, 1996;Goldenberg & Garcia, 2000).The formation's maximum thickness is close to 200m.; it is composed of medium-grained sandstones, shales, and conglomerates that are purple, dark red and brownish in color, deposited in a fluvial environment under braided regime (Barcelos, 1984).

Fossil content
The Adamantina Formation has a remarkable faunal record of essentially vertebrate taxa.Dinosaur remains are the most representative record.Among sauropods, specimens recovered include the eutitanosaurian Aeolosaurus (Almeida et al., 2004), isolated caudal vertebrae, and ribs of Titanosauria from the Prata area (Marinho, 2003;fig. 3J).Recently at the Prata Site was described a new titanosaur Maxakalisaurus topai by Kellner et al. (2006).Abelisaurid, carcharodontosaurid, and theropod indet.isolated attributed to teeth were reported by Marinho (2003), and Candeiro et al. (2003, 2006), from this unit near the Boa Vista Hill (Prata Town).The fossil-bearing horizons of the Adamantina Formation at Boa Vista Hill have yielded freshwater taxa including turtles and crocodyliforms (Marinho, 2003;Candeiro et al., 2003).

Uberaba Formation
This unit, defined by Barbosa (1934), is one of the most homogeneous and characteristic units of the Bauru Group.The formation has restricted exposures in Triângulo Mineiro region where interdigitates with the Adamantina Formation.Litholog-   Powell (1986Powell ( , 1987Powell ( , 2003)) ically, these strata are composed of freshwater limestones, sandstones, and basal conglomerate, all cemented by calcium carbonate and vulcanoclastic sediments (Barcelos, 1984); green sandstones with thin layers of light red sandstones are common within the succession.The formation's maximum thickness is close to 140 m (Fernandes & Coimbra, 1996), and is considered Coniacian-Santonian by Dias-Brito et al. (2001)

Fossil content
The Uberaba Formation has yielded only disarticulated dinosaur specimens.Santucci (2002) noted that sauropod remains from the Uberaba Formation represent possibly basal titanosaurs.One dinosaur nest was reported near the Peirópolis district of the Uberaba Town by Barbosa et al. (1970), which Campos & Bertini (1985) attributed to an ornithischian taxon (fig.3H-I).However, Kellner et al. (1998) attributed this record to a theropod dinosaur.

Marília Formation
This is the youngest unit of the Bauru Group and was first named by Almeida & Barbosa (1953).The Marília Formation is exposed in the Goiás and São Paulo States and in the Triângulo Mineiro region.The Marília Formation consists in fine to medium sandstones intercalated by conglomerate levels.The sandstones are cemented and contain concretions of calcium carbonate (Fúlfaro & Barcelos, 1991).The formation thickness is estimated to be 180m in Minas Gerais State (Fernandes & Coimbra, 1996).Dias-Brito et al. (2001) suggested an Upper Maastrichtian age for the Marília Formation.Barcelos (1984) subdivided the Marília Formation into three members: two restricted in the Triângulo Mineiro region, the Ponte Alta & Serra da Galga Members, and the Echaporã Member that crops in the Goiás and São Paulo States.The Ponte Alta Member is characterized sedimentologically as a "calcareous white member" composed of thin and medium calcareous horizons with pebbles and calcareous nodules deposited in alkaline lakes ("playalake" type) oversaturated with calcium bicarbonate (Garrido et al., 1992).The upper Serra da Galga Member is characterized as a "member of white limestone and conglomerate" composed of conglomerate and thin to medium limestones, with a bleached coloration in a feldspar matrix (Garrido et al., 1992).According to Suguio (1973Suguio ( , 1980)), both members were formed in a moderately dry climate that would have favored fossil preservation.

Discussion
The Triângulo Mineiro biota is important for several reasons, principally in terms of stratigraphical interest, because it ranges in age from the Turonian to the late Maastrichtian.It is also historically important because of many early discoveries of Late Cretaceous vertebrates from Central Brazil, including the first dinosaur eggs ever found in Brazil.Crocodiles and dinosaurs are the most common vertebrates found in Triângulo Mineiro region.Titanosaurid dinosaurs are the most abundant, but abelisaurid and carcharodontosaurid theropods are also represented.Our knowledge of Triângulo Mineiro biota has been greatly improved in the last five years through the exploration of a number of rich localities at Uberaba and Prata municipalities and due to the identification or revision of interesting specimens: 39 taxa have been reported in recent years.New taxa include abelisaurid and carcharodontosaurid theropods, and the eutitanosaurian Aeolosaurus, from the Adamantina and Marília Formations.Additional dinosaur specimens have been re-described or revised in detail in recent years (Marinho, 2003;Powell, 2003;Marinho & Candeiro, 2005), including remains from Marília Formation, such as titanosaur osteoderms and caudal vertebrae, and "Megalolithidae" eggs.Most of the vertebrate material from Triângulo Mineiro is fragmentary, but specimens of Peirosaurus, Itasuchus, Aeolosaurus, Abelisauridae and Carcharodontosauridae have diagnostic features such as wrinkles on the crown tooth.For the ichnological record, dinosaur eggs of "Megalolithidae" are known from the sites of the Uberaba municipality.Finally, the Late Cretaceous mollusk and charophytae records of Uberaba are among the most representative in the Bauru Group and have yielded several species also known from Patagonia (Leanza et al., 2004).
The similarity between the biota contents of the Turonian-Maastrichtian units of the Triângulo Mineiro region to the Patagonian units (Bajo Barreal Formation, middle Cenomanian-Turonian; Angostura Colorada, Late Senonian; Bajo de La Carpa Formation, Santonian; Los Alamitos, Late Campanian; Allen Formation, middle Maastrichtian), suggests that by the early Late Cretaceous there was an interconnection between these realms.This is evidenced from the common presence of Carcharodontosauridae and Abelisauridae.The same geographical spreading pattern is evidenced by the crocodilian Peirosaurus tormini found both, in the Marília Formation in Brazil and in the Bajo de la Carpa Formation of Patagonia, where seems to appear as early as the Santonian stage.
It is difficult to determine whether this Brazilian biota is more related to African or Patagonian taxa from the middle Cretaceous.Comparison of the tetrapod assemblages from both areas is heavily biased.Most of the southern Patagonian ones well represented in the Triângulo Mineiro region (e.g.Aeolosaurus, Peirosaurus, ostracods) are currently considered as endemic.However, the similarity of carcharodontosaurid remains (from the Adamantina Formation, São Paulo State, Brazil) to the African biota may demonstrate their close relationship with African taxa.Another important implication concerns the distribution of the crocodile genus Itasuchus, which is found in the Santana Formation (Albian).The frequent occurrences of this genus in the Marília Formation indicate that this taxon was probably also extremely common during Upper Cretaceous.

Conclusions
The evaluation of the Triângulo Mineiro biota has revealed a wide diversity of taxa (e.g.mollusks, crocodilians, dinosaurs) and ostracods.This biota, discovered in the formations of the Bauru Group, spans from Turonian to late Maastrichtian.These sediments where deposited in eolian and fluviolacustrine environments.
The Triângulo Mineiro biota is similar to Argentinean Late Cretaceous faunal assemblages, such as those from Patagonian deposits.The Triângulo Mineiro biota also shares compositional features with Cretaceous continental tetrapod faunas from more distant Gondwanan localities (e.g.continental Africa), indicating a common Gondwanan origin.