Early Cretaceous Archivi

New dinosaur species from Utah lived at a time of major transition: Iani smithi provides insights into how dinosaurs weather mid-Cretaceous ecological change.

Iani smithi from Utah lived at a time of major transition — Location of holotype locality for Iani smithi. (A) Global map showing location of Mussentuchit Member outcrop in central Utah, western North America, and a stratigraphic section at the quarry with dated ash horizons; and (B) graphical representation of preserved skeletal elements of the holotype specimen. Preserved elements are colored on the left facing skeletal whether they derive from the right or left side of the body. Exact positions of chevrons and ribs unknown due to poor preservation. Credits: Zanno et al., 2023, PLoS ONE, CC-BY 4.0

A new species of dinosaur from Utah sheds light on major North American ecological changes around 100 million years ago, according to a study published June 7, 2023 in the open-access journal PLoS ONE by Lindsay Zanno of the North Carolina Museum of Natural Sciences and colleagues.

The boundary between the Early and Late Cretaceous Period saw major reassembly of global ecosystems associated with a peak in global temperatures. In the fossil record of western North America, this ecological shift has been well-documented for marine habitats, but less study has been done regarding terrestrial life. In this study, Zanno and colleagues identify a new dinosaur from the early Late Cretaceous Cedar Mountain Formation of Utah.

The new dinosaur, named Iani smithi, lived around 100 million years ago and is known from a single fossil specimen including a well-preserved skull and parts of the spine and limbs. The name derives from Ianus, a Roman deity who presided over transitions, referencing the changing world of the mid-Cretaceous.

Iani is a member of an early branch of the ornithopod dinosaurs, a group of mostly bipedal herbivores that also includes famous examples like Iguanodon and Tenontosaurus. Iani is the first early-diverging ornithopod known from the Late Cretaceous of North America.

This discovery, along with other recent reports from the same geologic formation, indicates that several major groups of dinosaurs survived into the early Late Cretaceous despite the ecological changes of the time, but exactly what these survivors were doing and how long they lasted is still unclear. Since Iani and its closest cousins are typically found in ancient coastal habitats along the shores of the now-vanished Western Interior Seaway, the authors suggest that more investigation into coastal deposits of similar age might yield further evidence to address these lingering questions.

The authors add: “Early ornithopods were once a common part of North American ecosystems, but we did not know they survived into the Late Cretaceous. The discovery of Iani helps us link their extinction on the continent with a major interval of global warming, one with striking similarities to our current climate crisis.”

Bibliographic information:

Zanno LE, Gates TA, Avrahami HM, Tucker RT, Makovicky PJ (2023) An early-diverging iguanodontian (Dinosauria: Rhabdodontomorpha) from the Late Cretaceous of North America, PLoS ONE 18(6): e0286042. https://doi.org/10.1371/journal.pone.0286042

Press release from the Public Library of Science.

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New species of stegosaur is oldest discovered in Asia, and possibly the world

Bashanosaurus primitivus roamed the earth around 168 million years ago during the Middle Jurassic period, suggesting that stegosaurs may have originated in Asia

Bashanosaurus primitivus species Stegosaurs Asia — Bashanosaurus primitivus – the newest and oldest species of stegosaur in Asia. *Bashanosaurus primitivus* roamed the earth around 168 million years ago during the Middle Jurassic period, suggesting that stegosaurs may have originated in Asia. Credits: Credit Banana Art Studio

Relatively small, but fearsome-looking stegosaur measured about 2.8 metres (9 feet) from nose to tail—but scientists can’t tell whether the remains are those of an adult or juvenile.

A new species of one of the most recognisable types of dinosaur is the oldest stegosaur ever found in Asia, and one of the earliest unearthed anywhere in the world, according to research published today in the peer-reviewed Journal of Vertebrate Paleontology.

Remains of the stegosaur, which included bones from the back, shoulder, thigh, feet, and ribs, as well as several armour plates, date to the Bajocian stage of the Middle Jurassic period – much earlier than most known stegosaurs.

A team from the Chongqing Bureau of Geological and Mineral Resource Exploration and Development in China and London’s Natural History Museum named it Bashanosaurus primitivus – “Bashan” in reference to the ancient name for the area of Chongqing in China where the dinosaur was found, and the Latin for ‘first’ – primitivus.

The new dinosaur, which roamed the planet 168 million years ago, plays a part in uncovering how the stegosaurs evolved – of which, to this day, little is known.

It has a smaller and less developed should blade, narrower and thicker bases to its armour plates and other features that are different from all other Middle Jurassic stegosaurs discovered so far. However, it does have similarities with some of the first armoured dinosaurs, which are over 20 million years older.

“All these features are clues to the stegosaurs’ place on the dinosaur family tree”, says Dr Dai Hui from Chongqing Bureau of Geological and Mineral Resource Exploration and Development who led the research. “Bashanosaurus can be distinguished from other Middle Jurassic stegosaurs, and clearly represents a new species.

“What’s more, our analysis of the family tree indicates that it is one of the earliest-diverging stegosaurs along with the Chongqing Lizard (Chungkingosaurus) and Huayangosaurus. These were all unearthed from the Middle to Late Jurassic Shaximiao Formation in China, suggesting that stegosaurs might have originated in Asia”, adds Hui.

Instantly recognisable by the huge back plates, long tail spikes and tiny head, stegosaurs were four-legged, plant-eating dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaur fossils have been found on all continents except for Antarctica and Australia, and 14 species of stegosaur have been identified so far.

Well-known members of Stegosauria include Huayangosaurus (one of the most primitive stegosaurs), Gigantspinosaurus, notable for its enormous shoulder spines, and Miragaia for its extremely long neck. However, the fragmentary fossil material has hindered attempts to understand how the stegosaurs evolved and how they relate to one another.

With the discovery of this new species the mystery has started to clear up. Bashanosaurus primitivus has several primitive features that are similar to the earliest stegosaurs like Huayangosaurus and Gigantspinosaurus and early-branching thyreophorans (armoured dinosaurs). These include longer tail vertebrae, a shoulder blade that is narrower and flares out, and features of the back vertebrae that are similar to the early armoured dinosaur Scelidosaurus, which lived during the Early Jurassic.

The fossilised remains of Bashanosaurus also reveal a host of features that make it unique from other known stegosaurs. For example, the bony point at the end of the shoulder blade is small and less well developed than in other stegosaurs; a bony projection of the thighbone (fourth trochanter) is positioned below the middle of the shaft; and the bases of the armour plates curve outwards and are thicker than the plates on the backs of its later relatives.

“The discovery of this stegosaur from the Middle Jurassic of China adds to an increasing body of evidence that the group evolved in the early Middle Jurassic, or perhaps even in the Early Jurassic, and as such represent some of the earliest known bird-hipped dinosaurs,” says Dr Susannah Maidment, co-author and palaeontologist at London’s Natural History Museum.

“China seems to have been a hotspot for stegosaur diversity, with numerous species now known from the Middle Jurassic right the way through until the end of the Early Cretaceous period.”

New stegosaurs from the Middle Jurassic Lower Member of the Shaximiao Formation of Chongqing, China, Journal of Vertebrate Paleontology (4/03/2022), DOI: 10.1080/02724634.2021.1995737

Press release from Taylor & Francis Group.

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