Khosla, A. and Lucas, S.G., eds., 2016, Cretaceous Period: Biotic Diversity and Biogeography. New Mexico Museum of Natural History and Science Bulletin 71. 91 IMPORTANT CONTRIBUTIONS OF THE SOUTH AMERICAN RECORD TO THE UNDERSTANDING OF DINOSAUR REPRODUCTION MARIELA SOLEDAD FERNÁNDEZ Instituto de Investigaciones en Biodiversidad y Medioambiente, (INIBIOMA–CONICET), Quintral 1250, 8300, San Carlos de Bariloche, Río Negro, Argentina. e-mail: [email protected] Abstract—South American fossil eggs display a very rich record in the Cretaceous, which permits an understanding of dinosaur reproduction. In this paper I review all dinosaur ootaxa described at the moment and discuss their relationships and geographical distribution. Macro characters of eggshells were studied and interpreted as a possible source of paleobiological knowledge, whereas several other macro characters are questioned or discussed. Three megaloolithid oospecies have been described for North Patagonia, and they have been compared with worldwide materials revealing the Gondwana distribution. Two fusioolithid eggshells were described, and one of them, Fusioolithis baghensis, was synonymized with Indian, French and Spanish materials, indicating that this widespread oospecies was laid by titanosaurs because they share the same features as the Auca Mahuevo eggs. Faveoloolithid eggs have been compared from La Rioja, La Pampa, Uruguay and Patagonia, reflecting that one kind of dinosaur was reproducing in all Argentina and Uruguay with this kind of eggshell. Theropod eggs have been described from Río Negro province, and ornithothoracean eggs have been compared from Neuquán city with those of Brazil, and apparently the same group was reproducing in both areas during the Late Cretaceous. INTRODUCTION Formation, from Brazil (Price, 1951). These materials have been The amniotic egg was a great novelty in the evolution of related to the French sauropod Hypselosaurus. In fact, those dinosaur tetrapods. These complex structures allowed those animals to conquer eggs found in the Danian of the Provence region of France look similar new environments. Thus, its structure allowed them to reproduce in to them (Price, 1951). This Brazilian egg is spherical in shape, with a regions remote from bodies of water, so they were able to conquer 15 cm diameter, but the external surface has not been preserved, and diverse terrestrial environments (McFarland et al., 1979; Curtis and the egg just preserves its radial structural section. On the other hand, Barnes, 1993; Carpenter, 1999). The development of extra-embryonic the taxon Hypselosaurus (actually a nomen dubium) is not recorded in membranes gave to the embryo the aquatic environment for their correct Brazil, so because of that the egg was merely reassigned to the family development, so amniotic tetrapods could eliminate their larval stages, Titanosauridae, the sauropod family that includes Hypselosaurus so vulnerable to predation. The hard eggshells, composed of calcite (Price, 1951; Upchurch et al., 2004). or aragonite, provided to animals the protection from mechanical and The first fossil egg found in Argentina was collected from the physiological impediments, delimiting an isolated space with suitable basal part of the “rocanense” bed, a few kilometers from General conditions for the life of the embryo (McFarland et al., 1979; Curtis Roca city (Río Negro province). These fossils suffered a lithogenetic and Barnes, 1993). Dinosaurs, like most reptiles, reproduced by eggs, transformation, leaving only the external mold (Frengüelli, 1951). which are often preserved as fossils (Carroll, 1997; Chiappe et al., In Uruguay, dinosaur eggshells were collected from the Upper 2001; García, 2009). Cretaceous Ascencio Formation. Those materials were studied in detail South America dinosaurs have been successfully studied and by Erben in 1975, who determined that they belonged to at least two have a wide record from rocks of Cretaceous age. In this paper, I different taxa, cf. Ornithischia, family indet., genus Tacuaremborum and present a summary of all dinosaur egg taxa found in South America, Order Saurischia, cf. family Titanosauridae, genus Sphaerovum. Those more precisely in Argentina, and I will undertake a short discussion materials are silicified, so it is impossible to study their microstructure. of the reproductive biology of dinosaurs from the Late Cretaceous, Two genera and two species were identified from these eggshells, based on what we know so far. In South America, three megaloolithid Sphaerovum erbeni and Tacuaremborum oblongum (Mones, 1980). oospecies have been recorded to date (Megaloolithus jabalpurensis CHRONOLOGICAL CONTRIBUTIONS TO EACH OOFAMILY Khosla and Sahni, 1995, Megaloolithus cylindricus Khosla and Sahni, 1995, Megaloolithus megadermus Mohabey, 1998), two Fusioolithidae Megaloolithid eggs: Calvo et al. (1997) described the first oospecies (Fusioolithus baghensis (Khosla and Sahni, 1995) and oospecies from Neuquén, Megaloolithus patagonicus. In Neuquén Fusioolithus berthei Fernández and Khosla, 2015)), one faveoloolithid province, one of the most impressive nesting sites in the world, the oospecies (Paquiloolithus rionegrinus Simón 2002), one theropod Auca Mahuevo locality, was found. It encompasses hundreds of nests oospecies (Arriagadoolithus patagoniensis Kundrát, Novas, Agnolin in the Anacleto Formation, Campanian, Upper Cretaceous (Chiappe and Powell, 2012) and one enanthiornithine egg (referred to oofamily et al., 1998; Coria et al., 2007). In this locality the sedimentological Laevisioolithidae) are known. structure of six nests was studied. According to Chiappe et al. (2004), The oofamilies Megaloolithidae, Fusioolithidae and the dinosaurs used their fore limbs to dig their nests. Faveoloolithidae have been related to titanosaur sauropods (Chiappe Grellet-Tinner et al. (2007) described megaloolithid egg and et al., 1998; Grellet-Tinner et al., 2006; Salgado et al., 2007; Grellet- eggshells in Minas Gerais, Brazil (Baurú Basin, Upper Cretaceous). Tinner and Fiorelli, 2011; Fernández and Khosla, 2015). The oofamily These authors compared them with the Auca Mahuevo eggs, concluding Megaloolithidae has also been related to hadrosaurs (Grigorecu, 1994). that the Baurú eggshells are similar to those assigned to the Titanosauria. On the other hand, the only oospecies that have been described in Simón (1999) described eggshells of the Oofamily Megaloolithidae. Argentina and have been related to their producers are: Arriagadoolithus Salgado et al. (2007, 2009) published two articles describing two types patagoniensis to alvarezsaurid theropods, laevisioolithid eggs from of megaloolithid eggs that range in diameter between 10-12 cm. The Neuquén city have been related to ornithothoraces birds and Fusioolithus most important contribution of these works was that megaloolithid baghensis from Auca Mahuevo has been related with titanosaurs. On eggshells are associated with other kinds of eggshells in their nesting the other hand, in this report I will analyze the macrocharacters of the areas (Salgado et al., 2009; Coria et al., 2010). eggshells to interpret patterns of reproduction of these dinosaurs. The Coria et al. (2010) described two clutches from Bajo de Santa characters analyzed were: eggshell thickness, water vapor conductance, Rosa, where both clutches appear at the same level; the clutches are ornamentation and egg size. different in that they are integrated by eggs of different oofamilies: Megaloolithidae and Faveoloolithidae. Fernández and Khosla (2015) FIRST STUDIES IN SOUTH AMERICA described all of the megaloolithid materials from Salitral Ojo de Agua In 1951, a dinosaur egg was found in the Upper Cretaceous Baurú and Bajo de Santa Rosa, comparing them with the worldwide record. 92 These authors found that four of these oospecies are common in South pointed end downwards, a position that would have exposed the pole America, India, Africa and Europe. The oospecies in common are M. containing the air cell, and precluded egg turning, although there is no jabalpurensis, M. cylindricus, M. megadermus and F. baghensis. In evidence for nesting structures. This egg position is not seen in living addition, these authors described a new oospecies apparently endemic birds, with the exception of the basal galliform megapodes that place to South America, F. berthei. their eggs within mounds of vegetation or burrows (Garcia et al., 2008). Recently, a new oospecies, Pseudomegaloolithus atlasi This accumulation reveals a novel nesting behavior in Mesozoic Aves (Chassagne-Manoukian et al.. 2013) from Morocco was erected, that was perhaps shared with avian theropods and more basal troodontid and these authors have related megaloolithid materials from South theropods (Fernández et al., 2014). America to those from India (Chassagne-Manoukian et al., 2013). Otherwise, in 2014, the first avian fossil egg from Brazil were The fossil record of megaloolithids in Morocco indicates an ancient described, which were discovered in Upper Cretaceous deposits Gondwana ancestry for this group, and even is informative on the of the Vale do Rio do Peixe Formation in the Bauru Group of São relationship between these three areas during the Upper Cretaceous. Paulo in the southeastern part of the country. These eggshells of It indicates that megaloolithid producers, the titanosaur dinosaurs, 125.5-μm-thickness show three structural layers with both prismatic lived in Auca Mahuevo (Neuquén province), Bajo de Santa Rosa and aprismatic