The macroevolutionary landscape of short-necked plesiosaurians

Area of Science:

• Paleontology
• Evolutionary Biology
• Marine Ecology

Background:

• Tetrapods have repeatedly colonized marine ecosystems, showcasing convergent evolution.
• Previous assessments of macroevolutionary landscapes have been largely qualitative.
• Short-necked plesiosaurians offer an ideal model for studying macroevolutionary dynamics due to repeated body plan evolution.

Purpose of the Study:

• To establish a protocol for visualizing trait space occupancy and testing macroevolutionary landscapes.
• To quantitatively assess trophic diversity in extinct marine reptiles using a new phenotypic dataset.
• To investigate macroevolutionary patterns in short-necked plesiosaurians over 135 million years.

Main Methods:

• Development of a protocol to visualize trait space occupancy density.
• Application of the protocol to a phenotypic dataset of short-necked plesiosaurian morphology.
• Phylogenetic analysis to reconstruct macroevolutionary landscapes.

Main Results:

• Identification of a bimodal craniodental macroevolutionary landscape separating latirostrine and longirostrine plesiosaurians.
• This bimodal pattern was established by the Middle Jurassic and persisted until the Late Cretaceous.
• A collapse to a unimodal landscape occurred in the Late Cretaceous (Turonian), with novel longirostrine morphologies.

Conclusions:

• The study provides the first phylogenetically-explicit quantitative assessment of trophic diversity in extinct marine reptiles.
• Macroevolutionary dynamics at the top of food chains can be significantly altered by severe environmental perturbations.
• Environmental changes profoundly impacted plesiosaurian evolution, leading to shifts in trophic diversity and morphology.