Ancient teeth reveal surprising diversity of Cretaceous reptiles at Argentina fossil site

Paleoambiental reconstruction at Cerro Fortaleza of the Upper Cretaceous faunal group, including a nodosaurid and a few notosuchian perirosaurids. Credit: Jorge Gonzlez.
According to a study by Ariana Paulina Carabajal (Instituto de Investigaciones en Biodiversidad y Medioambiente), and CONICET, Argentina (Consejo Nacional de Investigaciones Cientficas y Tcnicas), isolated teeth can help us understand ancient reptile-dominated ecosystems in areas where skeletons are scarce.

South America is home to some of the most important fossil sites in the world for studying the history of Mesozoic reptiles. The Cerro Fortaleza, a Late Cretaceous Cerro Fortaleza location in Santa Cruz, Argentina, is however, surprisingly, sparse. While other sites nearby preserve diverse reptile assemblages too, the Cerro Forteza location's skeletal remains are almost exclusively restricted to one type dinosaur: the Dreadnoughtus giant sauropod. Researchers expanded the reptile diversity at this site by using teeth.

The fossil excavations at Cerro Forteza in December 2016 revealed 13 teeth and 9 small osteoderms (armorlike skin bones), which were representative of a variety ancient reptiles. These remains were identified as belonging to at least three types dinosaurs: armored ankylosaurs (carnivorous abelisaurs), long-necked titanosaurs (carnivorous), and armored ankylosaurs (armored ankylosaurs). The majority of the teeth were found to be from land-dwelling relatives of crocodiles, known as peirosaurs. Although these tiny fossils aren't able to identify specific species, they do indicate that there is a greater variety of reptiles than previously thought.

Ankylosaur osteoderm. Thin sections. Credit: Dr. I. Cerda.

These remains provide important insights into the geographical ranges of some animals. Ankylosaurs (armored dinosaurs) are found at this site. This is a link between records from further north in Patagonia, and farther south in Antarctica. The southernmost record of this group is the peirosaurs, or croc-cousins, found at this site. This study shows the value of small fossil remains such as teeth to help us understand ancient environments and patterns of dispersal at fossil sites with few skeletal remains.

The authors also mention that sometimes the skeletons don't appear. The tiny fossils of teeth and dermal oilicles reveal the variety of dinosaurs and other crocodiles in this region. These discoveries reveal a new faunal association. The records of ankylosaur dinosaurs, and peirosaurid noosuchians are some of the most austral for South America.

More information: Paulina-Carabajal A, Barrios FT, Mndez AH, Cerda IA, Lee Y-N (2021) A Late Cretaceous dinosaur and crocodyliform faunal associationbased on isolate teeth and osteodermsat Cerro Fortaleza Formation (Campanian-Maastrichtian) type locality, Santa Cruz, Argentina. PLoS ONE 16 (9): e0256233. Journal information: PLoS ONE Paulina-Carabajal A, Barrios FT, Mndez AH, Cerda IA, Lee Y-N (2021) A Late Cretaceous dinosaur and crocodyliform faunal associationbased on isolate teeth and osteodermsat Cerro Fortaleza Formation (Campanian-Maastrichtian) type locality, Santa Cruz, Argentina.16(9): e0256233. https://doi.org/10.1371/journal.pone.0256233

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