INVESTIGADORES
POL Diego
congresos y reuniones científicas
Título:
Taphonomy of a dinosaur breeding colony in southern Patagonia
Autor/es:
SMITH, R.; POL, D.; MANCUSO, A.C.; MARSICANO, C.A.
Lugar:
Los Angeles
Reunión:
Congreso; 73° Annual Meeting of the Society of Vertebrate Paleontology; 2013
Resumen:
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The Late Triassic?Early Jurassic Laguna
Colorada Formation of Patagonia contains a unique fossil assemblage dominated
by the basal sauropodomorph Mussaurus
patagonicus. This taxon was originally described from several
well-preserved post- hatching specimens associated with egg remains found at
the Laguna Colorada type section. Our recent expeditions to this locality have
yielded 25 new specimens of this taxon, comprising skeletons of six different
ontogenetic stages along with several complete ?nests? of un-hatched eggs.
Detailed sedimentological investigation
shows the skeletal remains and eggs occur in three distinct horizons within a 3
m- thick bed of mottled light reddish- brown/olive- grey massive siltstone. The
bones are encrusted in brown weathering calcareous siltstone similar to the
numerous spherically-shaped calcareous nodules that occur in the same horizons.
The latter are interpreted as palustrine carbonate precipitated in loessic
parent material around a floodplain pond under a seasonally warm climate.
The first Mussaurus hatchlings described from this site comprise 8 closely
associated and notably small individuals (femoral length 3 cm). Their proximity
to unbroken eggs and eggshell fragments clearly suggests an aggregation of
nestlings rather than unhatched embryos, as their body size largely exceeds
that of all the associated eggs, and the lack of size variation among them
suggests they are from the same brood. A new aggregation of at least 11
articulated juvenile skeletons (femoral length 12 cm) was found in the vicinity
of the type hatchlings. Taphonomic assessment of this aggregation rules out any
post-mortem transport of the carcasses and suggests these are the result of
synchronous death and burial of behaviorally aggregated individuals. These
specimens are all the same size and histological data indicates that these
individuals died together before reaching the first year of life.
Our latest field studies located
several clusters of up to 24-27 unhatched dinosaur eggs close to the Mussaurus juvenile and nestling
aggregations in the same horizons. The egg clusters lie in two layers within
elongate depressions or tunnels that appear to have been deliberately excavated
in the loess. We propose that the fertilized but unhatched eggs (at least one
with an ossified embryo) were all laid at the same time, possibly by more than
one female Mussaurus, and left half exposed to incubate. The unhatched clutches appear to have
been asphyxiated by rapid deposition of a thick layer of aeolian silt loaded
with volcanic ash.