新しく発見された恐竜Ianiは、変化する惑星における種の「最後の斑点」だったかもしれません

アーティストの再構成 ヤニ・スミス。 最近発見されたこの初期の彫刻類恐竜は、約9,900万年前に白亜紀中期の地球気候温暖化期間中に種の最後の立場を代表することができ、これにより恐竜個体数に急激な変化が発生しました。 クレジット: Jorge Gonzalez

新たに発見された恐竜、 ヤニ・スミス中期の気候激変に住んでいました。[{” 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.

白亜紀中期は、恐竜個体数に大きな影響を与えた大きな変化の時期でした。 この期間中、大気中の二酸化炭素の増加により地球が暖かくなり、海面が上昇し、ますます小さな土地に恐竜が集まりました。 暖かすぎて熱帯雨林が極地で繁栄しました。 開花植物は海岸地域を占領し、草食動物の正常な食糧供給源を置き換えた。

北米では巨大な植物を食べる竜脚類（かつて風景の巨人）がアロサウルス捕食者と共に消えていました。 同時に、初期のオリブリーやホーン恐竜のような小さな草食動物、ティラノサウルスや巨大なオビラブトロサウルスのような羽毛のある獣脚類がアジアから到着しました。

入力する ヤニ・スミス新しく発見されただけでなく、北米の化石記録で珍しい恐竜の歴史で占める場所のためにユニークです。

「発見 いいえ 幸運の連続だった。 孤立した歯があちこちに集められたので、私たちはそれがこの生態系に住んでいるのと同じことを知っていましたが、特に地球の歴史のこの時期からこのような美しい骨格を偶然発見するとは予想していませんでした。 ほぼ完全な頭蓋骨を持つことは物語をつなぐために非常に重要でした。」とLindsay Zanno副教授は言います。[{” 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.