Necrolestes ("grave robber" or "thief of the dead") is an extinct genus of , which lived during the Miocene in what is now Argentina Patagonia. It is the most recent known genus of Meridiolestida, an extinct group of mammals more closely related to Theria (marsupials and placentals) than to monotremes, which were the dominant mammals in South America during the Late Cretaceous. It contains two species, N. patagonensis and N. mirabilis; the type species N. patagonensis was named by Florentino Ameghino in 1891 based on remains found by his brother, Carlos Ameghino in Patagonia. Fossils of Necrolestes have been found in the Sarmiento and Santa Cruz Formations.[ Necrolestes at Fossilworks.org] Its morphology suggests that it was a digging, subterranean-dwelling mole-like mammal that fed on invertebrates.
Description
About one-third of the skeleton of
N. patagonensis—including most of the skull— has been found as disassociated bones of several individuals. The snout bends upwards at its end. The opening of the nasal fenestra has a septomaxilla separating the
Nasal bone and
premaxilla bones, which is unknown in
Theria mammals, with the nasal fenestra also appearing to have ossified external nasal cartilage.
The forelimbs have numerous characters in common with those of
fossorial mammals, including a medially curved
olecranon process of the ulna, and a mediolaterally compressed head of the humerus.
Ecology
Necrolestes was probably a subterranean mole-like mammal that fed on invertebrates. The morphology of the snout suggests that it dug by lifting its snout upwards, similar to modern
Marsupial mole and
Golden mole, as well as by using its forelimbs. The high volume of the middle ear suggests that it had enhanced hearing of low-frequency sounds.
Classification
Its classification was historically unclear due to it being highly
and having an
anatomy unlike any other known mammal, living or extinct. It was thought to be a
mammal; placement within either the
marsupial lineage (
Metatheria) or as a member of
Eutheria would have been possible given that South America as an island had extensive lineages of both marsupial and placental mammals. However, phylogenetic analyses conducted by Rougier
et al. (2012), Chimento, Agnolin and Novas (2012) and Averianov, Martin and Lopatin (2013) recovered
Necrolestes in an unexpected phylogenetic position as a nontherian mammal that belonged to the clade
Meridiolestida;
if confirmed this would make
Necrolestes the youngest known member of the group. Within Meridiolestida, Rougier
et al. (2012) found
Necrolestes to be particularly closely related to the genera
Cronopio and
Leonardus;
Chimento
et al. (2012) found it to be in unresolved
polytomy with
Cronopio,
Leonardus and the clade containing all other meridiolestidans
while Averianov
et al. (2013) recovered
Cronopio,
Necrolestes and
Leonardus as forming a grade at the base of Meridiolestida rather than a clade.
A subsequent 2017 monograph of the skull anatomy further supported a placement within Meridiolestida.
Phylogeny
This
cladogram follows the paper of Rougier, Wible, Beck and Apesteguía of 2012:
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