''Necrolestes'' ("grave robber" or "thief of the dead") is an extinct genus of mammals, which lived during the

Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages: the Aquitanian age, Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 annum, Ma to ...

in what is now Argentine

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

. It is the most recent known genus of Meridiolestida, an extinct group of mammals more closely related to therians (marsupials and placentals) than to

monotremes Monotremes () are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals (Eutheria), and marsupials ( Metatheria). Monotremes are typified by structural differences in their br ...

that dominated South America during the Late Cretaceous. It contains two species, ''N. patagonensis'' and ''N. mirabilis,'' The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

''N. patagonensis'' was named by Florentino Ameghino in 1891 based on remains found by his brother,

Carlos Ameghino Carlos Ciriaco Ameghino (16 June 1865 – 12 April 1936) was an Argentine paleontologist and explorer who accompanied his brother Florentino Ameghino throughout Argentina searching for fossils. Scientific career Carlos Ameghino was educated ...

in Patagonia. Fossils of ''Necrolestes'' have been found in the Sarmiento and Santa Cruz Formations.''Necrolestes''
at Fossilworks.org Its morphology suggests that is was a digging, subterranean dwelling mole-like mammal that fed on invertebrates.

Description

Necrolestes patagonensis lower jaw (holotype)

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 and

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

bones, which is unknown in therian 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 The olecranon (, ), is a large, thick, curved bony eminence of the ulna, a long bone in the forearm that projects behind the elbow. It forms the most pointed portion of the elbow and is opposite to the cubital fossa or elbow pit. The 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 moles and golden moles, 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

apomorph In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

ic and having an

anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...

unlike any other known mammal, living or extinct. It was thought to be a

theria Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes. ...

n mammal; placement within either the

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

lineage (

Metatheria Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as wel ...

) or as a member of

Eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distinguished from noneutherians by various phenotypic tra ...

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 An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...

with ''Cronopio'', ''Leonardus'' and the clade containing all other meridiolestidans while Averianov ''et al.'' (2013) recovered ''Cronopio'', ''Necrolestes'' and ''Leonardus'' as forming a

grade Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also ref ...

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 A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

follows the paper of Rougier, Wible, Beck and Apesteguía of 2012:

References

{{Taxonbar, from=Q75630 Dryolestida Miocene mammals of South America Santacrucian Neogene Argentina Fossils of Argentina Fossil taxa described in 1894 Taxa named by Florentino Ameghino Prehistoric mammal genera Golfo San Jorge Basin Sarmiento Formation