2026-06-07 ノースカロライナ州立大学(NCState)
◆イアニ・スミシティは中生代白亜紀の約9900万年前、現在のユタ州に生息していました。この恐竜の最も特徴的な点は、堅い植物質を咀嚼するために適応した強力な顎と歯です。研究者たちは、この化石を使ってイアニの進化的な関係を分析しました。
◆イアニが北米で発見されることは稀であり、恐竜の歴史上の位置においても特異です。これは、イアニが成功した系統の終焉の証人である可能性があります。この化石を中生代白亜紀の環境変動や生物多様性の変化と結びつけて研究することで、地球の歴史に関するさらなる洞察が得られると考えられています。
<関連情報>
- https://news.ncsu.edu/2023/06/new-dino-iani-was-face-of-a-changing-planet/
- https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0286042
北米白亜紀後期の早期分岐型イグアノドン類(Dinosauria: Rhabdodontomorpha)の一種 An early-diverging iguanodontian (Dinosauria: Rhabdodontomorpha) from the Late Cretaceous of North America
Lindsay E. Zanno ,Terry A. Gates,Haviv M. Avrahami,Ryan T. Tucker,Peter J. Makovicky
PLOS ONE Published: June 7, 2023
DOI:https://doi.org/10.1371/journal.pone.0286042
Abstract
Intensifying macrovertebrate reconnaissance together with refined age-dating of mid-Cretaceous assemblages in recent decades is producing a more nuanced understanding of the impact of the Cretaceous Thermal Maximum on terrestrial ecosystems. Here we report discovery of a new early-diverging ornithopod, Iani smithi gen. et sp. nov., from the Cenomanian-age lower Mussentuchit Member, Cedar Mountain Formation of Utah, USA. The single known specimen of this species (NCSM 29373) includes a well-preserved, disarticulated skull, partial axial column, and portions of the appendicular skeleton. Apomorphic traits are concentrated on the frontal, squamosal, braincase, and premaxilla, including the presence of three premaxillary teeth. Phylogenetic analyses using parsimony and Bayesian inference posit Iani as a North American rhabdodontomorph based on the presence of enlarged, spatulate teeth bearing up to 12 secondary ridges, maxillary teeth lacking a primary ridge, a laterally depressed maxillary process of the jugal, and a posttemporal foramen restricted to the squamosal, among other features. Prior to this discovery, neornithischian paleobiodiversity in the Mussentuchit Member was based primarily on isolated teeth, with only the hadrosauroid Eolambia caroljonesa named from macrovertebrate remains. Documentation of a possible rhabdodontomorph in this assemblage, along with published reports of an as-of-yet undescribed thescelosaurid, and fragmentary remains of ankylosaurians and ceratopsians confirms a minimum of five, cohabiting neornithischian clades in earliest Late Cretaceous terrestrial ecosystems of North America. Due to poor preservation and exploration of Turonian–Santonian assemblages, the timing of rhabdodontomorph extirpation in the Western Interior Basin is, as of yet, unclear. However, Iani documents survival of all three major clades of Early Cretaceous neornithischians (Thescelosauridae, Rhabdodontomorpha, and Ankylopollexia) into the dawn of the Late Cretaceous of North America.
