A new theropod eggsite in the Late Jurassic of Casal da Rola, Lourinhã, Portugal, and the nesƟng preferences of basal theropod dinosaurs Vasco Ribeiro & Femke Holwerda Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, Museu da Lourinhã (vascomsribeiro@gmail.com; f.m.holwerda@gmail.com) SEM; inner surface LPM; inner surface SEM, close-up of prism (radial view) LPM, close up of prisms (radial view) SEM, outer surface close-up of pore SEM, radial section outer surface inner surface mammillae pore Casal da Rola thick eggshell SEM, close up SEM, close up of pore SEM, radial of thin eggshell LPM, radial view inner surface outer surface mammillae Casal da Rola thin eggshell Eggshell Locality Casal da Rola Casal da Rola thin Paimogo Mean radius (mm) 57 (±16) 32 (±9) 57 (±12) Eggshell thickness (mm) 0.87 (±0.06) 0.30 (±0.03) 0.93 (±0.11) 139x103 87x54 135x105 Pore diameter ( m) 160 (±41) ~100 180 (±56) RelaƟve pore area to egg surface 0.55% - 0.52% Egg dimension (mm) 0.50% 0.06% Lourinhanosaurus antunesi Casal da Rola 1.00% Comparison between birds and dinosaurs eggs pore area / egg area ratio Geological map of Lourinhã area with straƟgraphical chart (adapted aŌer Manuppella et al. 1999) Theropods after Deeming (2006) Hypselosaurus egg 0.07 % Troodontid egg 0.55% 0.41% 1.16% Extant birds Lourinhanosaurus antunesi Paimogo 0.52% A new Late Jurassic (uppermost Late Kimmeridgian) dinosaur eggsite at Casal da Rola near Lou- rinhã, central-west Portugal is described. The eggshell macro- and microstructure are posiƟvely comparable with those from a nest as - signed to the basal theropod Lourinhanosaurus antunesi (Antunes et al. 1998, Mateus et al. 1998, 2001) from Paimogo eggsite, about 8km NNW of Casal da Rola, on coeval strata. Eggs from both sites share the following characters: Egg dimension, eggshell thickness, smooth outer surface, semi-round simple oblique pores, pore relaƟve area, dimensional relaƟons be - tween mammillary layer, prismaƟc layer and eggshell thickness (Table 1). These similariƟes, vi - sible under Scanning Electron Microscope (SEM) and Light Polarized Microscope (LPM), suggest that the eggshell type of Casal da Rola and Paimogo are assigned to a similar/ close taxon. A thinner type of eggshell was also found, as in Paimogo, which is idenƟfied as a crocodiloid egg - type. The high porosity of both type of eggshells implies a higher humidity in the nesƟng environ - ment. The eggs were laid in mud and silt characterisƟc to distal floodplain sediments, with carbonate concreƟons indicaƟng paleosol development already observed in three independent occur - rences, see geological map. These features are related with paleoenvironmental condiƟons indicaƟng marked seasonal drought and flooding (Myers et al. 2012), which leads us to believe that nesƟng is associated with seasonality in the case of basal theropod dinosaurs such as Lourinhanosaurus . GEOLOGICALSETTING CONCLUSIONS& IMPLICATIONS The Casal da Rola thick eggshell are related to Lourinhanosaurus antunesi A second, thinner eggshell type is associated with this eggsite This taxon would nest in alluvial plains in dry and soŌ mud and silt NesƟng is associated with seasonality The results lead us to suggest that: • The close water table would then provide the necessary moisture to success- fully incubate the eggs • The predicted paleotemperature (about 31ºc at soil level, Myers et al. 2012) would be ideal for incubaƟon • For the remainder dry season the juveniles should grow enough to leave the area before the rainy season REFERENCESCITED Antunes, M.T., Taquet, P. and Ribeiro, V., 1998. Upper Jurassic dinosaur and crocodile eggs from Paimogo nesƟng site (Lourinhã- Portugal): Memórias da Academia de Ciências de Lisboa, v. 37, p. 83-100. Deeming, D.C., 2006. Ultrastuctural and funcƟonal morphology of eggshells supports the idea that dinosaur eggs were incubated buried in a substrate. Palaeontology 49,171–185 Mateus I., Mateus H., Antunes M.T., Mateus O., Taquet P,. Ribeiro V. and Manuppella G., 1998. Upper Jurassic theropod dinosaur embryos from Lourinhã (Portugal): Memórias da Academia de Ciências de Lisboa, v. 37, p. 101-110. Mateus, O., Antunes, M.T. and Taquet, P., 2001. Dinosaur ontogeny: The case of Lourinhanosaurus (Late Jurassic, Portugal): Journal of Vertebrate Paleontology, v. 21 (Suppl. 3), p. 78A. Manuppella G., Antunes M., Pais J., Ramalho M.M., Rey J. 1999. Noƨcia explicaƟva da Folha 30-A Lourinha. Departamento Geolologia do InsƟtuto Geológico e Mineiro, Lisboa, pp 1–83 Myers, T. S., Tabor, N. J., Jacobs, L. L. and Mateus, O. 2012. Palaeoclimate of the Late Jurassic of Portugal: comparison with the Western United States. Sedimentology, 59: 1695–1717. doi: 10.1111/ j.1365-3091.2012.01322.x CASALDA ROLA EGGSITE RelaƟve pore area over egg surface area for different dinosaur eggs compared to Lourinhanosaurus (data from Deeming et al. 2006 and references therein) ACKNOWLEDGMENTS We would like to acknowledge Nuno Leal for the SEM images, João Russo and Emanuel Tschopp for their help during the field work, and also the team of Project DinoEggs. A special thanks to Octávio Mateus for his supervision. This work is part of Project Dinoeggs PTDC/BIA-EVF/113222/2009 financed by Fundação para a Ciência e Tecnologia, in collaboraƟon with the Centro de InvesƟgação em Ciência e Engenharia Geológica da Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa and Museu da Lourinhã. Table 1: eggshell dimensions