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.[1] Meridiolestidans were morphologically diverse, containing both small insectivores such as the "sabretooth-squirrel" Cronopio,[2] as well as the clade Mesungulatoidea/Mesungulatomorpha, which ranged in size from the shrew-sized Reigitherium to the dog-sized Peligrotherium. Mesungulatoideans had highly modified dentition with
bunodont (low and rounded) teeth, and were likely herbivores/omnivores.[3]
Meridiolestidans are generally classified within
Cladotheria, more closely related to living
marsupials and
placental mammals (
Theria) than to
monotremes, barring one study recovering them as the sister taxa to
spalacotheriid "
symmetrodonts".[4] However, more recent studies have stuck to the cladotherian interpretation.[5][6] Within Cladotheria, they have often been placed in a group called Dryolestoidea together with
Dryolestida, a group of mammals primarily known from the Jurassic and Early Cretaceous of the Northern Hemisphere. However, some analyses have found this group to be
paraphyletic, with the meridiolestidans being more or less closely related to therian mammals than dryolestidans are.[6][7] Meridiolestidans differ from dryolestidans in the absence of a parastylar hook on the
molariform teeth and the lack of a
Meckelian groove.
Lakotalestes from the Early Cretaceous of North America, originally identified as a dryolestid, was noted in one paper to have a tooth morphology closer to that of meridiolestidans.[8] A possible meridiolestidan is known from a tooth fragment, now lost, found in the
La Meseta Formation from the Eocene of the
Antarctic Peninsula.[9] The latest surviving meridiolestidan was the mole-like burrowing insectivore Necrolestes from the
Miocene of Patagonia.[6]
^Averianov, Alexander O.; Martin, Thomas; Lopatin, Alexey V. (2013). "A new phylogeny for basal Trechnotheria and Cladotheria and affinities of South American endemic Late Cretaceous mammals". Naturwissenschaften. 100 (4): 311–326.
Bibcode:
2013NW....100..311A.
doi:
10.1007/s00114-013-1028-3.
PMID23494201.
S2CID18504005.
^
abcO’Meara, Rachel N.; Thompson, Richard S. (2014). "Were There Miocene Meridiolestidans? Assessing the Phylogenetic Placement of Necrolestes patagonensis and the Presence of a 40 Million Year Meridiolestidan Ghost Lineage". Journal of Mammalian Evolution. 21 (3): 271–284.
doi:
10.1007/s10914-013-9252-3.
S2CID880380.
^Martin, T.; Goin, F. J.; Schultz, J. A.; Gelfo, J. N. (2022). "Early Late Cretaceous mammals from southern Patagonia (Santa Cruz province, Argentina)". Cretaceous Research. 133: 105127.
doi:
10.1016/j.cretres.2021.105127.
S2CID245549530.
^
abRougier, G. W.; Turazzinni, G. F.; Cardozo, M. S.; Harper, T.; Lires, A. I.; Canessa, L. A. (2021). "New Specimens of Reigitherium bunodontum from the Late Cretaceous La Colonia Formation, Patagonia, Argentina and Meridiolestidan Diversity in South America". Journal of Mammalian Evolution. 28 (4): 1051–1081.
doi:
10.1007/s10914-021-09585-2.
S2CID254704047.