Description and Classification

Lessemsaurus was a quadrupedal dinosaur, meaning it walked on all four legs. It was one of the earlier large sauropodomorphs, showing some features that would later become common in giant sauropods like Brachiosaurus or Apatosaurus. It had a long neck for reaching high vegetation, a bulky body, and a long tail that likely helped with balance. Estimates suggest Lessemsaurus could grow up to 9 meters (about 30 feet) long and weigh several tons, making it a significant herbivore in its ecosystem.

Lessemsaurus belongs to the group Sauropodomorpha, which includes the long-necked, plant-eating dinosaurs. More specifically, it is considered a basal (early) sauropod or a very sauropod-like sauropodomorph. Scientists often place it in a family called Lessemsauridae, along with other early large-bodied sauropodomorphs like Antetonitrus and Ingentia. These dinosaurs are important because they show the evolutionary steps sauropodomorphs took to become the massive sauropods of the Jurassic and Cretaceous periods. They were more heavily built than earlier sauropodomorphs like Plateosaurus and always walked on four legs, unlike some earlier relatives that might have been able to walk on two legs at times.

Distinguishing Features

Lessemsaurus had several features that help paleontologists identify it and understand its place in dinosaur evolution:

• Unusually tall neural spines: The bony projections extending upwards from its vertebrae (backbones), especially in the back and hip regions, were very high. This would have given its back a distinctive, somewhat raised profile and provided strong attachment points for powerful back muscles.
• Robust build: For a Triassic sauropodomorph, Lessemsaurus was quite heavily built, with strong, sturdy limb bones suited for supporting a large body.
• Large size for its time: It was significantly larger than many of its contemporary sauropodomorph relatives, indicating an early trend towards gigantism in this lineage.
• Specialized vertebral articulations: Its vertebrae had additional interlocking joints (hyposphene-hypantrum articulations) that helped to stiffen the spine, which was important for supporting its increasing body mass.

Paleoenvironment and Diet

Lessemsaurus lived in what is now the Los Colorados Formation in northwestern Argentina. During the Late Triassic, this area was a semi-arid environment. It featured seasonal rivers that created floodplains, alongside open woodlands. The climate likely had distinct wet and dry seasons. Lessemsaurus shared this habitat with other early dinosaurs, such as the common sauropodomorph Riojasaurus, the predatory theropod Zupaysaurus, and various early crocodylomorphs (relatives of crocodiles) and cynodonts (relatives of mammals).

As a sauropodomorph, Lessemsaurus was a herbivore, feeding on plants. Its long neck would have allowed it to browse on leaves from taller plants available in its environment, such as conifers, cycads, and large ferns. Its size suggests it needed to consume substantial amounts of vegetation each day to sustain itself.

Significance and Ongoing Research

Lessemsaurus is a significant dinosaur because it provides valuable insights into the early evolution of sauropods, the group that includes the largest land animals ever to have lived. It represents an early stage of the trend towards “gigantism” – growing to enormous size – within the sauropodomorph lineage. The discovery of Lessemsaurus and related dinosaurs like Ingentia has shown that some sauropodomorphs achieved very large body sizes much earlier in their evolutionary history than previously understood, already during the Triassic period.

Ongoing research on Lessemsaurus and its kin, the Lessemsauridae, focuses on refining their exact position within the sauropodomorph family tree. Scientists study its anatomy in detail to learn more about how these early giants moved, grew, and interacted with their environment. Understanding Lessemsaurus helps clarify the important evolutionary transition from smaller, often bipedal, sauropodomorphs to the massive, fully quadrupedal sauropods. Future fossil discoveries in the Los Colorados Formation and other Triassic rock layers worldwide could reveal even more information about Lessemsaurus and the rise of giant dinosaurs.