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A shift in ontogenetic timing produced the unique sauropod skull
Matteo Fabbri1,2, Guillermo Navalón3,4, Nicolás Mongiardino Koch1,2
1Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, 06511.
Evolution; International Journal of Organic Evolution
|February 12, 2021
Summary
Sauropod dinosaur skulls evolved through developmental timing shifts, with key features appearing early in juveniles, enabling feeding adaptations and gigantism. This study analyzed Anchisaurus cranial ontogeny to understand these evolutionary changes.
Area of Science:
- Paleontology
- Developmental Biology
- Evolutionary Biology
Background:
- Sauropod dinosaurs exhibit extreme cranial modifications linked to their massive size.
- Previous hypotheses on sauropod skull evolution involved feeding adaptations and paedomorphosis.
- Limited ontogenetic data for early sauropodomorphs hindered testing these hypotheses.
Purpose of the Study:
- To investigate the cranial ontogeny of the early sauropodomorph Anchisaurus.
- To determine the developmental mechanisms behind sauropod-like cranial features.
- To explore the relationship between developmental timing shifts and sauropod evolution.
Main Methods:
- Phylogenetic analysis to establish Anchisaurus's relationship to sauropods.
- Digital reconstruction of μCT-scanned juvenile and adult Anchisaurus skulls.
- Cranial shape analysis and allometric studies.
Main Results:
- Anchisaurus displays a mix of ancestral and derived sauropod-like cranial features.
- Sauropod-like braincase and adductor chamber traits emerge late in Anchisaurus ontogeny (terminal addition).
- Sauropod embryos and juveniles exhibit these derived traits early, indicating a predisplacement shift.
Conclusions:
- A developmental shift in timing (predisplacement) facilitated the evolution of novel skull morphologies in sauropods.
- This shift relaxed developmental constraints, enabling feeding apparatus specialization and contributing to gigantism.
- Cranial evolution in sauropods was integrated with innovations in physiology and locomotion.
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