ArticleBMC ecology and evolution2023
Heads or tails first? Evolution of fetal orientation in ichthyosaurs, with a scrutiny of the prevailing hypothesis.
Article in BMC ecology and evolution, 2023. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 7 papers.
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Who cites it
7 citing papers in PubMed.
- Article
- Vertebral microstructure marks the emergence of pelagic ichthyosaurs soon after the End Permian Mass Extinction.Scientific reports · 2025Article
- A large new Middle Jurassic ichthyosaur shows the importance of body size evolution in the origin of the Ophthalmosauria.BMC ecology and evolution · 2024Article
- Special Issue: 100 years of scientific excavations at UNESCO World Heritage Site Monte San Giorgio and global research on Triassic marine Lagerstätten.Swiss journal of palaeontology · 2024Article
- Swiss ichthyosaurs: a review.Swiss journal of palaeontology · 2024Article
- The marine conservation deposits of Monte San Giorgio (Switzerland, Italy): the prototype of Triassic black shale Lagerstätten.Swiss journal of palaeontology · 2024Article
- Ontogenetic variation in the cranium ofSwiss journal of palaeontology · 2023Article
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Authors and funding
7 authors.
Funding
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Abstract
According to a longstanding paradigm, aquatic amniotes, including the Mesozoic marine reptile group Ichthyopterygia, give birth tail-first because head-first birth leads to increased asphyxiation risk of the fetus in the aquatic environment. Here, we draw upon published and original evidence to test two hypotheses: (1) Ichthyosaurs inherited viviparity from a terrestrial ancestor. (2) Asphyxiation risk is the main reason aquatic amniotes give birth tail-first. From the fossil evidence, we conclude that head-first birth is more prevalent in Ichthyopterygia than previously recognized and that a preference for tail-first birth likely arose in derived forms. This weakens the support for the terrestrial ancestry of viviparity in Ichthyopterygia. Our survey of extant viviparous amniotes indicates that fetal orientation at birth reflects a broad diversity of factors unrelated to aquatic vs. terrestrial habitat, further undermining the asphyxiation hypothesis. We propose that birth preference is based on parturitional mechanics or carrying efficiency rather than habitat.
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