Article: Allometry and heterochrony in the growth of the neck of Triassic prolacertiform reptiles

The functional morphology of the elongated neck of Tanystropheus longobardicus (Bassani) has long been controversial. It is suggested here, that the neck was not very flexible because the elongated cervical ribs are bundled along the ventrolateral margin of the vertebrae. The result, a stiffened neck, is advantageous in an aquatic environment. The ontogenetic development of the neck in T. longobardicus and Macrocnemus bassanii Nopcsa, both included within the Prolacertiformes, is another point of interest. During ontogeny, the neck exhibits constant, positive allometric growth with differing growth parameters for the two taxa. This difference most likely resulted from heterochronic processes. The marked elongation of the neck in T. longobardicus was primarily caused by hypermorphic growth. Additional factors, modifying the growth pattern, include predisplacement of growth and an increased number of cervical vertebrae.