Patagorhynchus pascuali represents the first Cretaceous toothed monotreme from the supercontinent Gondwana.
Life reconstruction of Patagorhynchus pascuali. Image credit: Gabriel Lio.
Patagorhynchus pascuali lived in what is now Patagonia, southern Argentina, during the Late Cretaceous epoch, some 70 million years ago.
At the time, Argentina was part of Gondwana, an ancient supercontinent in the southern hemisphere.
Patagorhynchus pascuali belonged to Monotremata, a group of egg-lying mammals, represented by the living platypus and echidnas, which is endemic to Australia, and adjacent islands.
“Occurrence of early monotremes in the Early Cretaceous of Australia has led to the consensus that this clade originated on that continent, arriving later to South America,” said Dr. Nicolás Chimento, a paleontologist at the Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’ and CONICET, and his colleagues from Argentina, Japan, and Australia.
“The discovery of a Late Cretaceous monotreme from southern Argentina demonstrates that monotremes were present in circumpolar regions by the end of the Mesozoic, and that their distinctive anatomical features were probably present in these ancient forms as well.”
A second lower molar of Patagorhynchus pascuali was collected from the Puma Cave site of the Chorrillo Formation, cropping out in Santa Cruz province, Patagonia, Argentina.
“The discovery expands the list of mammals documented in the Chorrillo and equivalent Dorotea formations of southern South America,” the researchers noted.
Reconstruction of Patagorhynchus pascuali’s skull. Image credit: Santiago Miner Reconstruction / LACEV.
The new specimen was found in association with the fossilized remains of early mammals, frogs, turtles, snakes, ornithopod, sauropod and theropod dinosaurs, birds, aquatic plants, freshwater snails and abundant larvae of chironomid insects, with the latter two invertebrates constituting part of the food for the living platypuses.
“The possibility that Patagorhynchus pascuali had already acquired ecological and behavioral characteristics similar to those of the living platypus, which inhabits ponds and lakes, is congruent with sedimentological evidence suggesting that such environments were prevalent during deposition of the Chorrillo Formation,” the scientists said.
Patagorhynchus pascuali had unique features that are lacking in other monotremes, and may be considered autapomorphic (derived trait that is unique to a given species) among these creatures.
“Australia has yielded the most complete fossil record of monotremes, including an array of Barremian through Cenomanian taxa, as well as several species of the Oligocene-Pliocene monotreme Obdurodon,” the authors said.
“In this context, the presence of the toothed monotreme Monotrematum in the Early Paleocene of Patagonia was interpreted as the result of a single dispersal of monotremes from Australia to South America, before or during the Late Cretaceous or early Paleocene.”
“The discovery of Patagorhynchus pascuali clearly demonstrates that the monotremes had already attained a wide paleogeographic distribution, stretching across southern South America, Australia, and Antarctica, the later one as a connecting pathway (but fossil monotremes are still unknown from this landmass), constituting a clade characteristic of the Weddelian Paleobiogeographical Province,” they concluded.
A paper on the findings was published in the journal Communications Biology.
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N.R. Chimento et al. 2023. First monotreme from the Late Cretaceous of South America. Commun Biol 6, 146; doi: 10.1038/s42003-023-04498-7
