New early Jurassic tetrapod assemblages constrain Triassic-Jurassic tetrapod extinction event

Area of Science:

• Paleontology
• Geochronology
• Extinction Event Studies

Background:

• The Triassic-Jurassic extinction event marks a significant biotic turnover.
• Previous studies suggested a global extinction at the Triassic-Jurassic boundary.
• The precise timing and duration of tetrapod extinctions remain debated.

Purpose of the Study:

• To reevaluate the duration of the Triassic-Jurassic tetrapod extinction event.
• To establish the precise age of the earliest Jurassic tetrapod assemblage from the Fundy basin.
• To investigate the pattern of tetrapod family disappearances and introductions across the Triassic-Jurassic boundary.

Main Methods:

• Discovery and analysis of a definitively correlated earliest Jurassic tetrapod assemblage.
• Stratigraphic correlation using pollen and spores.
• Radiometric and geochemical dating of fossil assemblages.
• Comparative analysis of faunal composition with Late Triassic and Jurassic records.

Main Results:

• The Fundy basin assemblage represents an early Hettangian (earliest Jurassic) age.
• The assemblage includes diverse tetrapods: mammal-like reptiles, dinosaurs, crocodylomorphs, sphenodontids, and fishes.
• All constituent families are known from earlier strata, with no new families appearing in this earliest Jurassic assemblage.
• Typical Triassic forms are absent, indicating extinctions occurred prior to the early Hettangian.

Conclusions:

• The majority of Triassic-Jurassic tetrapod extinctions occurred before the early Hettangian, without the introduction of new families.
• This pattern supports a global extinction event at the Triassic-Jurassic boundary, consistent with marine invertebrate studies.
• The Manicouagan impact event, dated broadly to the Triassic-Jurassic boundary, is a potential causal factor for the extinction.