Evolutionary contingency in lingulid brachiopods across mass extinctions

Area of Science:

• Paleontology and Evolutionary Biology
• Marine Ecology
• Geometric Morphometrics

Background:

• Lingulid brachiopods (order Lingulida) were abundant in the early Paleozoic but are now rare, often termed "living fossils."
• The reasons for their diversity decline and potential loss of morphological and ecological variation remain unclear.
• Morphological analysis is a key proxy for understanding functional ecology and macroevolutionary trends.

Purpose of the Study:

• To reconstruct the global morphospace occupation of lingulid brachiopods throughout the Phanerozoic.
• To investigate the impact of mass extinctions on lingulid shell morphology and ecological strategies.
• To determine if modern lingulid diversity reflects evolutionary contingency or deterministic evolutionary pathways.

Main Methods:

• Application of geometric morphometrics to analyze shell shape variation.
• Reconstruction of morphospace occupation across geological time (Phanerozoic).
• Integration of anatomical and ecological data with morphological analyses.

Main Results:

• Maximum morphospace occupation for lingulids occurred in the Early Ordovician, with early infaunal features present in sub-rectangular shelled forms.
• The End Ordovician extinction disproportionately affected rounded-shell linguloids, while sub-rectangular forms survived subsequent mass extinctions.
• Discinoids maintained consistent morphospace occupation and epibenthic strategies throughout the Phanerozoic.

Conclusions:

• The survival of sub-rectangular linguloids through major extinction events shaped the modern infaunal-dominated fauna.
• Consistent morphospace occupation in discinoids suggests stable ecological roles.
• The limited modern morphological and ecological diversity of lingulids is attributed to evolutionary contingency, not deterministic factors.