The largest Silurian vertebrate and its palaeoecological implications

Area of Science:

• Paleontology
• Vertebrate Evolution
• Early Osteichthyan Biology

Background:

• The perceived absence of large Silurian fishes (>0.5m) suggested limited gnathostome size and diversity before the Devonian.
• This assumption has influenced palaeoatmospheric models, linking lower oxygen levels to physiological size constraints in early vertebrates.

Purpose of the Study:

• To describe the largest known pre-Devonian vertebrate, Megamastax amblyodus gen. et sp. nov.
• To re-evaluate the size and trophic capabilities of early osteichthyans and challenge existing evolutionary constraints.

Main Methods:

• Fossil discovery and description of Megamastax amblyodus from the Silurian Kuanti Formation, China.
• Analysis of dentition to infer diet and trophic specialization.
• Estimation of body size based on fossil evidence.

Main Results:

• Description of Megamastax amblyodus, an osteichthyan approximately 1 meter in length, from the late Ludlow (~423 Ma).
• Unusual dentition suggests a durophagous diet, indicating significant trophic specialization.
• This finding demonstrates the presence of large-bodied vertebrates in the Silurian, contradicting previous assumptions.

Conclusions:

• The discovery of Megamastax amblyodus refutes the notion that pre-Emsian vertebrates were uniformly small.
• Early osteichthyans exhibited considerable size and trophic diversity during the Silurian period.
• This challenges the use of size limitations in palaeoatmospheric and evolutionary modeling.