Reconstrução artística Ianni Smithy. Este dinossauro ornitópode recém-descoberto pode representar a última posição da espécie durante o período de aquecimento global no meio do período Cretáceo, cerca de 99 milhões de anos atrás, o que levou a mudanças drásticas nas populações de dinossauros. Crédito: Jorge González

dinossauro recém-descoberto, Ianni SmithyEle viveu durante as convulsões climáticas do meio[{” attribute=””>Cretaceous era and might be the last of its lineage, replaced by duckbill dinosaurs. This dinosaur, found in Utah, represents a critical transitional period in dinosaur history, affected by rising CO2 levels, global warming, and shifting dinosaur populations.

A newly discovered plant-eating dinosaur may have been a species’ “last gasp” during a period when Earth’s warming climate forced massive changes to global dinosaur populations.

The specimen, named Iani smithi after Janus, the two-faced Roman god of change, was an early ornithopod, a group of dinosaurs that ultimately gave rise to the more commonly known duckbill dinosaurs such as Parasaurolophus and Edmontosaurus. Researchers recovered most of the juvenile dinosaur’s skeleton – including skull, vertebrae and limbs – from Utah’s Cedar Mountain Formation.

Iani smithi lived in what is now Utah during the mid-Cretaceous, approximately 99 million years ago. The dinosaur’s most striking feature is its powerful jaw, with teeth designed for chewing through tough plant material.

A metade do período Cretáceo foi uma época de grandes mudanças, que tiveram grandes impactos nas populações de dinossauros. O aumento do dióxido de carbono na atmosfera durante esse período fez com que a temperatura da Terra subisse e o nível do mar aumentasse, fazendo com que os dinossauros ocupassem áreas cada vez menores. Era tão quente que as florestas tropicais floresciam nos pólos. A floração da vida vegetal tomou conta das áreas costeiras e substituiu as fontes naturais de alimento para os herbívoros.

Na América do Norte, os saurópodes herbívoros gigantes – outrora titãs da paisagem – estavam desaparecendo, junto com seus predadores alossauros. Ao mesmo tempo, herbívoros menores, como os antigos dinossauros com bico de pato e chifres, e terópodes emplumados, como tiranossauros e enormes oviraptorossauros, também chegavam da Ásia.

entra Ianni Smithyé único não apenas por ter sido descoberto recentemente, mas também por sua raridade no registro fóssil norte-americano e seu lugar na história dos dinossauros.

“Encontrar meu Foi um golpe de sorte. Sabemos que algo parecido viveu neste ecossistema porque dentes isolados foram coletados aqui e ali, mas não esperávamos tropeçar em um esqueleto tão bonito, especialmente desta época da história da Terra. Ter um crânio quase completo foi inestimável para juntar as peças da história”, diz Lindsey Zano, professora de pesquisa associada da[{” attribute=””>North Carolina State University, head of paleontology at the North Carolina Museum of Natural Sciences, and corresponding author of the work.

The lower jaw and teeth of new dinosaur Iani smithi. Credit: National Geographic, Mark Thiessen and Becky Hale

Zanno and her team used the well-preserved skeleton to analyze the evolutionary relationships of Iani and were surprised – and a bit skeptical – of the results.

“We recovered Iani as an early rhabdodontomorph, a lineage of ornithopods known almost exclusively from Europe,” Zanno says. “Recently, paleontologists proposed that another North American dinosaur, Tenontosaurus – which was as common as cattle in the Early Cretaceous – belongs to this group, as well as some Australian critters. If Iani holds up as a rhabdodontomorph, it raises a lot of cool questions.”

Key among these is, could Iani be a last gasp, a witness to the end of a once successful lineage? Zanno thinks that studying this fossil in the context of environmental and biodiversity changes during the mid-Cretaceous will give us more insight into the history of our planet.

Iani smithi is named for Janus, the two-faced god who symbolized transitions – an apt name, given its position in history.

“Iani may be the last surviving member of a lineage of dinosaurs that once thrived here in North America but were eventually supplanted by duckbill dinosaurs,” Zanno says. “Iani was alive during this transition – so this dinosaur really does symbolize a changing planet.

“This dinosaur stood on the precipice,” she says, “able to look back at the way North American ecosystems were in the past, but close enough to see the future coming like a bullet train. I think we can all relate to that.”

Reference: “An early-diverging iguanodontian (Dinosauria: Rhabdodontomorpha) from the Late Cretaceous of North America” by Lindsay E. Zanno, Terry A. Gates, Haviv M. Avrahami, Ryan T. Tucker and Peter J. Makovicky, 7 June 2023, PLOS ONE.
DOI: 10.1371/journal.pone.0286042

The work appears in PLOS ONE and was supported by the National Science Foundation. Zanno is lead author as well as corresponding. Terry Gates and Haviv Avrahami, both of NC State and the North Carolina Museum of Natural Sciences, along with Ryan Tucker of Stellenbosch University and Peter Makovicky of the University of Minnesota, also contributed to the work.