Comparative and parataxonomic studies of dinosaur eggshells belonging to oofamily Megaloolithidae from the Upper Cretaceous of Argentina

FERNÁNDEZ, MARIELA S.; KHOSLA, ASHU

Fukui

Simposio; Dinosaur Reproduction; 2016

Dinosaur Research Institute, Fukui Prefectural University and Fukui Prefectural Dinosaur Museum, Japan.

The dinosaur eggs and eggshells belonging to the oofamily Megaloolithidae from Argentina are similar in microstructural and magascopic characters to India, France and Spain. In this work we are presenting here a detailed review of Argentinean oospecies. The different eggshells look like each other in having a compactituberculate ornamentation and evidently arched growth lines of the spheroliths. The characteristic feature of these megaloolithid eggshells shows the presence of sharply separated fan shaped spheroliths. A detailed comparison between the eggshells from Argentina and India divulge the three groupings which shows the resemblance flanked by megaloolithids of both countries: (1) Megaloolithus jabalpurensis, M. matleyi and M. patagonicus. Megaloolithus jabalpurensis differs from M. cylindricus in being thinner and in having small and large, fan-shaped spheroliths of variable width and shapes. The pores are circular to elongate as compared to subcircular shape in M. cylindricus. (2) The oospecies M. cylindricus, M. rahioliensis and Tipo 1d are similar in micro and ultrastructural characteristics. The oospecies Megaloolithus cylindricus shows a lot of microstructural variations such as variation in the thickness of M. cylindricus (1.7?3.5 mm); long, slim, stretched out, cylindrical and compressed spheroliths with straight pore canals. M. cylindricus has publication priority as it was published in 1995 whereas the oospecies M. rahioliensis published afterward in 1998 by Mohabey and Type 1d more recently by Fernández (2013). The third grouping includes M. megadermus and Tipo 1e. Spherical-shaped eggs of M. megadermus are well known from the freshwater Late Cretaceous Lameta Formation of Paori and Dholidhanti in Dohad area (Panchmahal District) and Daulatporia (Kheda District), Gujarat (Mohabey 1998). The materials found in Argentina are inadequate. Fernández (2013) recognized eggshells with large thickness and an unknown egg diameter, and assigned as Tipo 1e. The other two types of eggshell oospecies recorded from India and Argentina show partly coalesced/fused outer nodes and spheroliths. Therefore, growth lines penetrate into the contiguous spheroliths with a clear concavity. Detailed microstructural studies of hundreds of eggshells recovered from both countries further shows the necessity of the creation of a new oogenus Fusioolithus . The oogenus have been erected due to fusion between spheroliths, belonging to tubospherulitic morphotype, which comprise two new oospecies F. baghensis and F. berthei. The oospecies F. baghensis was included formerly in the oofamily Megaloolithidae (Khosla and Sahni 1995). We consider the diagnosis of the oofamily Megaloolithidae which was erected originally by Zhao (1979); this author evidently avowed, ?Eggshell is composed of circular cones with clearly demarcated boundary lines?. The main purpose of this work is to include the new oofamily Fusioolithidae which has been characterized by spherical shaped eggs and fan shaped spheroliths of discretispherulitic morphotype. The oospecies of these eggs have been related with sauropod dinosaur in Auca Mahuevo and incorrectly related with Megaloolithus patagonicus (Chiappe et al. 1998, 2001, Grellet-Tinner & Zaher 2007) and F. berthei which is a new oospecies from Argentina. Up till now, morphostructurally, a total of 15 eggshell oospecies belonging to different oofamilies have been recorded from India and seven oospecies from Argentina. Palaeobiogeographically, the present study suggests close phyletic associations, as well as the likely presence of a terrestrial link of dinosaur fauna between India and Europe during the Upper Cretaceous, and between the three Gondwanan areas Africa, India and Patagonia (Vianey-Liaud et al. 2003; Chassagne-Manoukian et al. 2013).