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Fig. 5 | BMC Ecology and Evolution

Fig. 5

From: Heads or tails first? Evolution of fetal orientation in ichthyosaurs, with a scrutiny of the prevailing hypothesis

Fig. 5

Simplified phylogenetic bracketing of five ichthyopterygians on the basis of recent phylogenetic analyses and their preferred birth orientation. Early-diverging forms such as Chaohusaurus and Cymbospondylus both have one gravid specimen with head-first birth, Mixosaurus has a 66%/33% based on three specimens, and Merriamosauria (phylogenetic node denoted with M) likely have a slight preference for tail-first birth based on the sample of Stenopterygius and the fact that all other Merriamosauria show tail-first birth or are inconclusive (note: the relative phylogenetic position of Cymbospondylus and Mixosaurus is debated; compare e.g., [30, 31] (silhouettes adapted from: Chaohusaurus [2]; Cymbospondylus [87]; Mixosaurus [29]; Besanosaurus [84]; Stenopterygius [89]

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