An elephant-sized Late Triassic synapsid with erect limbs

Area of Science:

• Paleontology
• Vertebrate Evolution
• Mesozoic Ecosystems

Background:

• Dicynodonts were a diverse group of synapsids prevalent during the Triassic period.
• Previous understanding suggested that only dinosaurs achieved massive terrestrial herbivore body sizes in the Late Triassic.
• The upper size limits for non-dinosaurian terrestrial tetrapods in the Triassic were considered to be significantly smaller than those of large dinosaurs.

Purpose of the Study:

• To describe the newly discovered gigantic dicynodont, Lisowicia bojani, from the Late Triassic of Poland.
• To analyze the paleobiology and evolutionary implications of Lisowicia bojani's size and growth patterns.
• To reassess the role of synapsids, particularly stem-group mammals, in the Triassic megaherbivore radiation.

Main Methods:

• Fossil description and osteological analysis of Lisowicia bojani.
• Estimation of body size (length, height, mass) based on fossil remains.
• Histological examination of limb bone cortex and analysis of lines of arrested growth (LAGs) to infer growth rates.

Main Results:

• Lisowicia bojani is described as a gigantic synapsid, reaching an estimated 9 tons, 4.5 meters in length, and 2.6 meters in height.
• It represents the youngest known undisputed dicynodont and the largest non-dinosaurian terrestrial tetrapod from the Triassic.
• Evidence suggests permanently rapid growth, similar to dinosaurs and mammals, indicated by the lack of LAGs and highly remodeled bone cortex.

Conclusions:

• The discovery of Lisowicia bojani overturns the notion that only dinosaurs achieved megaherbivore status in the Triassic.
• It demonstrates that stem-group mammals (dicynodonts) were capable of reaching body sizes not seen again in mammalian evolution until the Eocene.
• This finding significantly expands our understanding of Triassic megaherbivore diversity and the evolutionary capabilities of synapsids.