Experts identify a new "aetosaur" that lived 200 million years ago

Aetosaurs, a group of heavily armored reptiles akin to modern crocodiles, dominated the landscapes of the Triassic era, long before the reign of dinosaurs. 

These ancient crocodile ancestors, which thrived approximately 200 million years ago, have left behind fossils scattered across all continents except Antarctica and Australia, revealing a rich diversity in form and function. 

Extensive bony armor 

Unlike the more celebrated dinosaurs, aetosaurs were characterized by their extensive bony armor, which has historically posed a significant challenge to scientists attempting to classify and understand these prehistoric beings due to the scarcity of complete fossilized skeletons.

In a groundbreaking study led by researchers from the University of Texas at Austin (UT), a remarkably preserved aetosaur armor provides new insights into the anatomy and evolutionary history of these ancient reptiles (image). 

Well-preserved specimen 

The study, centered around an aetosaur carapace that is around 70% complete, marks a significant departure from the norm, offering a comprehensive view of the creature’s protective bony plates spanning from the neck to the tail. 

“We have elements from the back of the neck and shoulder region all the way to the tip of the tail,” said lead author William Reyes, a doctoral student at the UT Jackson School of Geosciences, emphasizing the rarity of finding such well-preserved material.

Armadillo-like version of a crocodile

The study introduced Garzapelta muelleri, a new species of aetosaur named in honor of the area of its discovery (Garza County, Texas), the Latin word for shield (pelta), and the paleontologist who first unearthed it, Bill Mueller. 

Garzapelta’s appearance, heavily armored with bony plates and flanked by curved spikes for added defense, drew parallels to an armadillo-like version of a modern American crocodile, suggesting an omnivorous diet, in contrast to the carnivorous nature of today’s crocodiles.

Convergent evolution within the aetosaur lineage

The research highlights the significance of osteoderms, the bony plates embedded in the skin of aetosaurs, in species identification. These osteoderms, while crucial for protection, also serve as a key to understanding the evolutionary adaptations of aetosaurs. 

The study unveils the phenomenon of convergent evolution within the aetosaur lineage, with Garzapelta’s armor showcasing similarities to other species despite a distant genetic relationship, suggesting independent evolutionary paths leading to similar protective strategies.

Evolutionary relationships among aetosaurs 

Addressing Garzapelta’s placement within the aetosaur phylogenetic tree proved to be a complex endeavor, as the research team navigated the intricacies of convergent evolution. 

Depending on which armor features were emphasized, Garzapelta’s phylogenetic position varied, underscoring the challenges in disentangling evolutionary relationships within this group. 

“Convergence of the osteoderms across distantly related aetosaurs has been noted before, but the carapace of Garzapelta muelleri is the best example of it,” Reyes explained, highlighting the evolutionary dynamics at play and their implications for understanding phylogenetic relationships.

Importance of museum collections

Housed in the Texas Tech University fossil collections, Garzapelta spent decades on a shelf before catching the attention of Reyes. The study underscores the value of university and museum collections as repositories of untapped scientific knowledge, awaiting discovery and analysis by researchers. 

Bill Parker, an aetosaur specialist and park paleontologist at Petrified Forest National, who was not involved in the research, praised this study for bringing to light specimens that have languished in obscurity, emphasizing the importance of museum collections in advancing our understanding of prehistoric life.

Further exploration of aetosaur evolution

Further exploration of aetosaur evolution, including the influence of age or sex on armor characteristics, remains a focal point of ongoing research. Reyes’s continued examination of Jackson School’s aetosaur fossils, primarily excavated in the 1940s, promises to shed additional light on the complexities of these ancient reptiles. 

This research not only enriches the taxonomy of the aetosaur family but also deepens our comprehension of the ecological roles and evolutionary strategies of these Triassic giants, offering a glimpse into a world where armored crocodile-like creatures roamed the Earth long before the age of dinosaurs.

The study is published in the journal The Anatomical Record.

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