INVESTIGADORES
FIORELLI lucas Ernesto
congresos y reuniones científicas
Título:
Sanagasta: record of a neosauropod nesting site in a Lower Cretaceous paleohydrothermal landscape
Autor/es:
LUCAS FIORELLI; GERALD GRELLET-TINNER; ELOISA ARGAÑARAZ; PABLO ALASINO; MARIANO LARROVERE
Lugar:
Heidelberg
Reunión:
Congreso; 22 Lateinamerika-Kolloquium; 2011
Institución organizadora:
Universität Heidelberg
Resumen:
Cretaceous dinosaur nesting sites have been
discovered on every continent, except Antarctica. Despite these discoveries, the factors that
influenced the choice of selected colonial nesting sites by Cretaceous dinosaur
still remained enigmatic. A recent study of the Sanagasta nesting site
demonstrated the relation between dinosaurs nesting behaviors and a specific
paleoenvironment: the Sanagasta neosauropod dinosaurs nested in an Early
Cretaceous geothermal paleosetting (Grellet-Tinner & Fiorelli, 2010).
Although the Los Llanos Formation outcrops throughout the La Rioja Province, the
new nesting site is geographically restricted to a relatively small area
(~300,000 m2) mostly located within the Sanagasta Geologic
Park boundaries, in the
central region of the Sierra de Velasco, La Rioja province, NW Argentina. There, the
neosauropods ovideposited clutches of 21cm sub-spherical eggs in dug out holes
systematically grouped nearby paleohydrothermal conduits, discharge channels,
fountain geysers, domal mounds, paleo-hot spring terraces, ponds, travertine
dams and mini-dams (Grellet-Tinner & Fiorelli, 2010). After detailed
microscopic characterizations the original ~7.5 mm thick eggshells are hypothesized as an adaptation to this specialized
geological paleoenvironment by compensating for the acidity of the hydrothermal
solutions during the necessary incubation period. The number and position of
the clutches combined with geological dating support colonial and nesting
fidelity behaviors, migrations for reproductive purposes, and adaptation to
soil moisture and thermoradiance for incubation, which for the latter had not
been suspected previously for extinct dinosaurs but still observed in modern
saurians. Indeed, several species, i.e. like the megapodes birds (Megapodius)
and the Galapagos land iguanas (Conolophos) (Werner, 1983; Göth &
Vogel, 1997) still rely on similar geological conditions to incubate their
eggs. Although most of the 80 recorded clutches in the Sanagasta Geologic Park
contain an average of 10 eggs, several displays up to 35 eggs with a maximum
axis of 220 cm. Thorough field and taphonomic observations and ensuing
statistical and geochemical analyses, coupled with microscopic
characterizations indicate that the reproductive behaviors of the Sanagasta
neosauropods was symbiotic and concomitant with the Early Cretaceous geothermal
activities dated by the Gondwanic geothermal cycle. This investigation resolves
longstanding geological issues related to the dating of the sedimentary basins
in the Sierras Pampeanas Orientales (central-west Argentina) and the Los Llanos
Formation by assigning them an Early Cretaceous date (Hauterivian to Aptian,
~134 and ~117 million years; Mutti et al., 2005; Grellet-Tinner &
Fiorelli, 2010). Furthermore, this research provides the first definitive
answer to the question to why neosauropod nesting sites were confined to a few
selected geographical localities during the Cretaceous times. As such, the
Cretaceous Sanagasta nesting site represents to date one of the most important
dinosaur nesting sites in the world, as, for the first time, it shed lights on
a particular reproductive behavior of neosauropods.