Monday, 1 April 2019
PALEO PARENTING: NOTHOSAURS
Previous studies have successfully applied an extant squamate model to sauropterygian life‐history traits. In extant squamates, oviparity and viviparity are associated with differences in life‐history trait combinations.
A paper released in March 2019, in the journal Palaeontology, sheds light on this view. Griebeler et al. have establish growth curves for Nothosaurus specimens based on their humeral histology.
They analyzed life‐history traits derived from these curves and compared inferred traits to those of modern squamates and pachypleurosaurs to assess their reproduction mode.
Their data shows birth to adult size ratios (i.e. birth size divided by the mother's size) provides a good estimate of clutch sizes in extant squamates and in viviparous extinct marine reptiles, but these ratios cannot discriminate viviparous and oviparous squamates.
Thus, large ratios do not indicate viviparity in fossil taxa to which the extant squamate model is applicable.
Applying differences in birth size, age at maturation, and maximum longevity that are observed between extant viviparous and oviparous squamates to our Nothosaurus sample, they identified 7 out of 24 specimens as being potentially viviparous.
Conversely, they suggested oviparity for many nothosaurs but also for many pachypleurosaur samples.
Under the assumption that the entire clade Pachypleurosauria was viviparous, the majority of nothosaurs would also have been viviparous as they comprised trait combinations similar to those seen in pachypleurosaurs.
Overall, this suggests that within nothosaurs and pachypleurosaurs both reproduction modes existed in different taxa.