''Reigitherium'' was a

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

that lived during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

, in the (Late

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

). Its fossils have been found in the Los Alamitos and the La Colonia

Formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

s of

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

Description

The original specimen of ''Reigitherium'' was a fragmentary single molar tooth, with a lot of the surface detail damaged. It was mistakenly identified as an upper left molar, but new material - including a whole tooth row of this species - clarifies that it was a lower right tooth. ''Reigitherium'' was a small mammal with simple premolars that increased in size along the tooth row to an enlarged fourth premolar. The molar teeth them decreased in size along the tooth row.

Taxonomy

''Reigitherium'' has proven difficult to classify until recently, because the original fossil material was sparse, damaged, and difficult to identify. It was initially thought to be a

dryolestid Dryolestidae is an extinct family of Mesozoic mammals, known from the Middle Jurassic to the Early Cretaceous of the North Hemisphere. The oldest known member, '' Anthracolestes'', is known from the Middle Jurassic Itat Formation of Western Siber ...

mammal when described in 1990. Ten years later, Pascual et al. argued that it was a

docodont Docodonta is an order of extinct mammaliaforms that lived during the Mesozoic, from the Middle Jurassic to Early Cretaceous. They are distinguished from other early mammaliaforms by their relatively complex molar teeth, from which the order get ...

based on the wear patterns they interpreted on the teeth.Pascual R., Goin F.J., Gonzalez P., Ardolino A. & Puerta P.F. (2000) A highly derived docodont from the Patagonian Late Cretaceous Geodiversitas 22 (3
Documento pdf
. In 2011, Rougier ''et al.'' argued again for it being a dryolestoid, within

Meridiolestida Meridiolestida is an extinct clade of mammals known from the Cretaceous and Cenozoic of South America and possibly Antarctica. They represented the dominant group of mammals in South America during the Late Cretaceous. Meridiolestidans were morp ...

, an order of

Gondwanan Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

dryolestoids.Supplementary information
/ref> More complete fossils have now supported this analysisHarper T, Parras A, Rougier GW. 2018. ''Reigitherium'' (Meridiolestida, Mesungulatoidea) an enigmatic Late Cretaceous mammal from Patagonia, Argentina: morphology, affinities, and dental evolution. ''Journal of Mammalian Evolution''. A recent phylogenetic study finds it to be the sister taxon to ''

Peligrotherium ''Peligrotherium'' is an extinct meridiolestidan, and the sole member of the family Peligrotheriidae, from the Paleocene of Patagonia, originally interpreted as a stem-ungulate (though it did co-exist with early meridiungulates). Its remains have ...

''. Although the latter is much larger than ''Reigitherium'', they share many tooth and skull characteristics that indicate they are closely related.

References

Dryolestida Prehistoric mammal genera Late Cretaceous mammals Campanian life Maastrichtian life Cretaceous mammals of South America Late Cretaceous tetrapods of South America Cretaceous Argentina Fossils of Argentina Los Alamitos Formation Cañadón Asfalto Basin Fossil taxa described in 1990 Taxa named by José Bonaparte {{cretaceous-mammal-stub