Document Type

Article

Department

​​Biology

Publication Date

4-18-2023

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.

Comments

Published version available at:https://bmcecolevol.biomedcentral.com/articles/10.1186/s12862-023-02110-4

Publication Title

BMC Ecol Evol

Volume

23

Issue

1

First Page

12

Last Page

12

ISSN

2730-7182

DOI

10.1186/s12862-023-02110-4

PubMed ID

37072698

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