Fingers zipped up or baby mittens? Two main tetrapod strategies to return to the sea

BUONO, MÓNICA R.; STERLI, JULIANA; FERNÁNDEZ, MARTA S.; ALZUGARAY, LUCIA; HERRERA, YANINA; VLACHOS, EVANGELOS; CAMPOS, LISANDRO; PAOLUCCI, FLORENCIA

BIOLOGY LETTERS

ROYAL SOC

Año: 2020 vol. 16 p. 1 - 6

1744-9561

The application of network methodology in anatomical structures offers newinsights on the connectivity pattern of skull bones, skeletal elements andtheir muscles. Anatomical networks helped to improve our understandingof the water-to-land transition and how the pectoral fins were transformedinto limbs via their modular disintegration. Here, we apply the same methodology to tetrapods secondarily adapted to the marine environment. Wefind that these animals achieved their return to the sea with four types ofmorphological changes, which can be grouped into two different main strategies. In all marine mammals and the majority of the reptiles, the fin isformed by the persistence of superficial and interdigital connective tissues,like a ?baby mitten?, whereas the underlying connectivity pattern of thebones does not influence the formation of the forefin. On the contrary,ichthyosaurs ?zipped up? their fingers and transformed their digits intocarpal-like elements, forming a homogeneous and better-integrated forefin.These strategies led these vertebrates into three different macroevolutionarypaths exploring the possible spectrum of morphological adaptations.