INVESTIGADORES
CASSINI Guillermo Hernan
congresos y reuniones científicas
Título:
New data on the neuroanatomy of Adinotherium ovinum (Notoungulata, Toxodontidae, Nesodontinae) from virtual cranial endocast
Autor/es:
HERNANDEZ DEL PINO, SANTIAGO; CASSINI, GUILLERMO HERNÁN; CERDEÑO, MARÍA ESPERANZA; VIZCAINO, SERGIO FABIÁN
Lugar:
Mendoza
Reunión:
Congreso; 4th International Palaeontological Congress The history of life: A view from the Southern Hemisphere; 2014
Institución organizadora:
International Palaeontological Association
Resumen:
Toxodontids
were endemic South American ungulates, characteristic of the Cenozoic faunas.
Although variable in size, their skulls present a conservative morphology.
Among them, Adinotherium
ovinum is a rather small basal taxon characteristic of the early Miocene Santacrucian Age (Santa Cruz
Province, Argentina). The primary objective of this contribution is to provide
a detailed anatomical description of the endocranial morphology of A. ovinum, an approximation of the brain and
associated soft-tissue structures, and considerations about the relative brain
size in this species. For the present study we reconstructed a virtual cranial
endocast of an adult specimen (MPM PV-3532) based on CT scans and estimated the
encephalization quotient (EQ=brain mass/0.055 × body mass0.74) for a sample of eight
genera of Santacrucian South American native ungulates. The obtained virtual
endocast is almost complete, showing only a slight lateral deformation due to
lithostatic pressure, allowing the description from all views and obtaining
linear and volumetric measurements. The general morphology is in agreement with
previous anatomical data on the endocranial cavity of Adinotherium
documented by Patterson in the 1930s (i.e., the high, arched and upwardly
inclined cerebrum, the dorsal exposure of the cerebellum sloping downward, and
the enormous hypophysis) and also shows a more complex pattern of sulci for the
neopallium than that registered in previous works. The EQ
(from an endocast volume of 116 mm3 and estimated body mass of 56.35 kg) is 0.61 and
represents a lower value than that previously reported by Radinsky (EQ=0.78)
for Adinotherium in his work about brain evolution in South American
native ungulates, who also estimated a lower body mass (40.31 kg). The EQ obtained
in our estimation is around the mid values when compared with EQs obtained for
other Santacrucian ungulates: the interatheriid Protypotherium (0.86;
the highest value) and the toxodontid Nesodon (0.34; the lowest one)
among Notoungulates, and the astrapothere Astrapotherium (0.43). Our
results indicate that A. ovinum has a higher relative brain size than the larger well-known and
coeval nesodontine toxodontid Nesodon (body mass of 308.93
kg). This agrees with previous ontogenetic studies on nesodontine skulls, which
revealed that cranial measurements related to the neurocranium
show higher allometric coefficients in A. ovinum
than in the larger Nesodon, resulting in a proportionally greater brain in the former. This kind
of description constitutes a base for broader studies, with a larger sample, on the ontogenetic
development of the cranial cavity and the brain in both nesodontine genera.