Sauropod dinosaurs were quadrupedal herbivores with a highly specialised body plan
that attained the largest masses of any terrestrial vertebrates. Recent discoveries have
shown that key traits associated with sauropod gigantism appeared stepwise during
the Late Triassic and Early Jurassic in evolutionary ‘cascades’ of associated changes,
in which a ‘head and neck’ cascade has been suggested as an important module. Here,
we investigate the evolutionary transformation of the sauropodomorph braincase,
using discrete anatomical characters, prompted by the reanalysis of a Middle Jurassic
(Bathonian) sauropodiform braincase from England. Our analysis shows that
sauropod braincases are highly distinct, and occupy a different region of morphospace
than their evolutionary relatives. This resulted from anatomical transformations
including a set of changes in the surface attachments of craniocervical musculature,
which may indicate integrated evolution between neck elongation and transformation
in braincase anatomy. Neck elongation in Late Triassic and Early/Middle Jurassic
taxa is potentially associated with episodes of skull reduction, indicating that the
‘head and neck’ cascade was activated more than once in the evolutionary history of
Sauropodomorpha. The re-activation of this cascade in the Jurassic may have
impacted on the differential survival of sauropodomorph lineages through the Early-
Middle Jurassic