Fossilized bones unearthed in Japan’s northeastern region 20 years ago belong to one of the smallest iguanodont dinosaurs ever discovered in Japan’s Cretaceous marine rocks, a new researcher-led study reveals. University of Tsukuba.
Reconstruction of iguanodont dinosaurs from the Ashizawa Formation in Japan. The red bone is the right sternum. Image provided by: Masato Hattori
“iguanodontia Masami Kondo, a paleontologist at the University of Tsukuba, and his colleagues said they were a major group of small to large ornithopod dinosaurs that ranged in length from about 2 meters (6.6 feet) to more than 10 meters (33 feet) and existed from the late Jurassic period to the latest Cretaceous period.
“During this period, Iguanodonts achieved a worldwide distribution, and their remains are known on every continent.”
“Asia was an important region for dispersal across Laurasia, as dispersal occurred both between Asia and North America and between Asia and Europe.”
“A highly diverse group of iguanodont species has been discovered from the Cretaceous period of East and Central Asia.”
“The increase in the number of iguanodont fossil reports from Japan over the past 20 years is significant because this region corresponds to the easternmost tip of the Cretaceous Laurasia continent.”
In this study, Dr. Kondo and his co-authors reexamined an isolated right sternum plate excavated in 1999 near Iwaki, Fukushima Prefecture, Japan.
fossils come from Ashizawa layerIt is part of the Futaba Group, a layer of sandstone and mudstone that was deposited on an ancient ocean floor about 90 million years ago.
The specimen was tentatively named the skeleton of a hadrosaurid (duck-billed) dinosaur, but it remained unstudied for more than 20 years.
Paleontologists determined that the hatchet-like bone belonged to the indeterminate bones. Stilacostanana broad group within Iguanodontia that includes hadrosauroids and their relatives.
Its characteristics closely resemble those found in more derived iguanodontid species rather than primitive iguanodontids.
Based on comparisons with the sternums of related species, researchers estimate that this iguanodont dinosaur was only about 3 meters (10 feet) long, making it small by the standard classification system for these dinosaurs.
“This is significantly smaller than other iguanodont fossils previously excavated from the same formation,” the researchers said.
“Large iguanodonts, including hadrosaurs, are known to have existed in Japan during the Late Cretaceous, so this discovery suggests that iguanodonts of a wide range of body sizes lived in coastal environments in East Asia.”
“This discovery provides new insights that further support the diversity of ancient coastal ecosystems.”
of the team result Published in a magazine published on July 6th paleontological research.
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Masami Kondo others. 2026. An iguanodont sternum plate excavated from the Upper Cretaceous Ashizawa Formation (Futaba Group) in Fukushima Prefecture. paleontological research 30: 122-134;doi: 10.2517/prpsj.250042
Source: www.sci.news
