In the Cretaceous Period , dinosaur were big , and mammals were pocket-sized . At least , that ’s been the universal sentiment – until very recently , when a heap of turgid ancient fuzzies started turn up in the fossil disc . None , however , come anywhere close to the sizing ofPatagomaia chainko : a steel - young belated Cretaceous mammalian reckoned to have possibly consider as much as 26 kg ( 57 hammering ) .
discover in southernPatagonia , South America , the Modern species is represented by just fragment of its hindlimb and pelvis . Nevertheless , that ’s enough for expert to reckon its sizing and likely general appearance : “ Estimates of the trunk mass ofPatagomaiawere made by taking measurements of the postcranial stiff , ” the researchers write , “ using fixation that have already been used in other fossil mammalian . ”
The verdict : the stiff “ belong to a intermediate - sized mammal , corresponding in size to [ … ] the canidLycalopex culpaeus , ” the team determined . That ’s the Latin name for the culpeo , or Andean fox – though it ’s actually more closely related to a savage or a Canis aureus than a substantial fox – or to put it another way : P. chainkowas large than a red Charles James Fox , but smaller than a brush wolf .
Cladogram showing the phylogenetic affinities of Patagomaia chainko, geographic location, and paleohistological images; Map showing the fossil locality; Transverse section of the femur (left); tibia (right) in polarized light with lambda compensator.Image Credit: Chimento, N.R., Agnolín, F.L., García-Marsà, J. et al., Scientific Reports, (CC BY 4.0)
That may seem at betting odds with the 26 - kilo estimation . There ’s a good intellect for that : it ’s a maximum weight , rather than an average or likely one for the specie . In fact , the team write , “ we estimated a dead body pot of ~ 14 kg [ 30.8 Pound ] for the holotype specimen , ” which they think “ likely represents the maximal ace that this animal could have reached . ”
That , however , is still highly noteworthy . Most Northern Hemisphere mammals from the era have a body bulk below 100 grams ( 0.22 Irish pound ) , they place out , with 99 percentage not even reaching 1 kg ( 2.2 dog pound ) . Even the heavy previously known species from the period – the Early CretaceousRepenomamusand the Late CretaceousVintana – clear out at roughly 10 and 8.9 kilogram ( 22 and 19.6 pounds ) severally .
Based on the specimen ’s femoris , tibia , pelvic girdle , and hip joint socket , the researchers were also able to gather a few clues about the beast ’s potential figure . It does n’t seem to have much in common with monotremes such as theplatypus , for example , though it shares some law of similarity withbadgersand porcupines .
In total , the creature is doubtlessly a therianmammal : its clay show a broad range of features that practically always bend up in other know examples of the class , and virtually never outside of it . Overall , however , the creature is fairly unique , even for its time – and not only because of its size .
“ AlthoughPatagomaiareveals therian affinities , it differs from Paleogene South American representatives of this clade , ” the researchers notice . “ In sum , Patagomaiadoes not exhibit morphologic feature that may ally it with any of the mammalian clade [ … ] frequently recorded in Cretaceous and early Paleogene beds from South America . ”
“ This new find demonstrates that Late Cretaceous mammalian faunas from South America were taxonomically diverse , not only including gondwanatherians , dryolestoids and monotremes , but also former therians , ” the squad reason out . “ Patagomaiaalso reveals that the evolution of large body size among Late Cretaceous mammals was more complex than previously understood . ”
The paper is published in the journalNature Scientific Reports .
