Testing the inhibitory cascade model in Mesozoic and Cenozoic mammaliaforms

Area of Science:

• Evolutionary developmental biology (Evo-Devo)
• Paleontology
• Mammalian evolutionary history

Background:

• Evolutionary development studies link developmental pathways to morphological evolution.
• Tooth morphology is a valuable model for evo-devo due to its fossil record and phylogenetic utility.
• The Inhibitory Cascade (IC) Model proposes a developmental mechanism for mammalian lower molar size evolution.

Purpose of the Study:

• To test the predictions of the Inhibitory Cascade (IC) Model across diverse mammalian taxa.
• To investigate the evolutionary constraints on mammalian tooth size.
• To determine the ancestral state of molar size regulation in mammals.

Main Methods:

• Analysis of tooth morphology in a wide range of extant and fossil mammalian groups.
• Comparison of observed molar size patterns with predictions from the IC Model.
• Statistical analysis of taxon distribution based on diet and phylogenetic relationships.

Main Results:

• Approximately 65% of tested taxa conform to the IC Model's predictions for molar size.
• Extinct groups, particularly 'condylarths', and some Mesozoic mammals showed deviations from the IC Model.
• Taxon distribution was significantly influenced by diet and phylogenetic clustering.

Conclusions:

• The IC Model is supported as a plesiomorphic (ancestral) developmental system for Mammalia.
• Mammalian tooth size has been under this developmental constraint since at least 180 million years ago.
• Deviations from the IC Model likely represent secondary evolutionary changes rather than alternative ancestral models.