INVESTIGADORES
MARSICANO Claudia Alicia
congresos y reuniones científicas
Título:
THE EARLY DIVERSIFICATION OF AMNIOTES ON LAND: THE ROL OF ICHNOLOGY IN THE GONDWANAN CONUNDRUM
Autor/es:
MARSICANO, CLAUDIA; KRAPOVICKAS, VERONICA
Reunión:
Congreso; 4th International Palaleontological Congress; 2014
Resumen:
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It has long been known
that during the Permian a major transition occurred in terrestrial tetrapod
faunas, the radiation of amniotes on land. The Early Permian faunas, dominated
by temnospondyl amphibians together with early amniotes, changed during the
Middle-Late Permian with the onset of much diverse and complex terrestrial amniote
faunas. These changes in diversity and occupancy of continental environments are
fully documented by the well-known paleotropical Laurasian faunas. In contrast,
little is known about the early history of amniotes in the Southern Hemisphere.
Basically all the information available comes from Permian beds at several high
latitude localities in southern Africa and South America, where some clades of terrestrial
synapsids along with parareptiles are well documented as early as the Middle
Permian (Wordian-Capitanian). Before that time, the evolutionary history of amniotes
in Gondwana remains elusive, as their skeletal record is very scarce. The only
exception is a group of aquatic parareptiles, the mesosaurids, known from Artinskian
(Early Permian) levels from southwestern Gondwana (southern Africa, Uruguay,
Brazil). The mesosaurids has recently proved to be the earliest viviparous
reptiles, an evolutionary novelty related to their fully aquatic mode of life.
In this context, our current knowledge of the Gondwanan amniote fossil record
suggests their sudden appearance by the Early Permian in high latitudes represented
by an endemic group of specialized aquatic parareptiles. This is followed by a
gap of information of ca. 10 Ma until the Middle Permian, when amniotes suddenly
became diversified and abundant in the region,
occupying different terrestrial ecological roles. Nevertheless, if the known amniote
ichnological record is considered, a substantial different scenario is
depicted. In the last years, levels containing tetrapod
footprints have been described from putative Early Permian (Sakmarian-Artinskian)
beds of Argentina (Patquia and Yacimiento Los Reyunos formations). In all
cases, the footprints were preserved in sandstone levels associated with dune
field environments (dune and interdune deposits) revealing the presence of
different groups of small-to-medium sized desert
dwellers. Accordingly, the combination of the ichnological and
skeletal record suggests that amniotes were already widespread in the high
latitudes of Gondwanan by the beginning of the Permian with a complex ecological
structure, including the colonization of deserts as well as the aquatic habitats.
This new scenario also implies that amniotes evolved in Gondwana significantly
earlier than previously thought, probably in coincidence with the establishment
of amniote-dominated land habitats in the Northern Hemisphere.