Shape analysis using the thin-plate spline: Neanderthal cranial shape as an example

This paper describes a new geometric method for illustrating and quantifying biological shape difference. The technique is discussed in some detail, and is illustrated by applying it to the problem of characterizing Neanderthal cranial shape. The method of thin-plate splines uses a mathematical model based on the bending of a hypothetical steel plate in order 1) objectively to generate a D'Arcy Thompson-style deformed grid that illustrates the shape contrast between two forms, and 2) to quantify the shape difference by breaking it down into a series of components based on scale. Results confirm the presence of some features traditionally attributed to Neanderthals, but some “classic” Neanderthal features do not in fact characterize the Neanderthal sample. Traits may have been misidentified because of failure to take into account differences in absolute size, use of a misleading frame of reference, and interpretation of one aspect of a large-scale change as a localized feature. In particular, the important Neanderthal “specialization” midfacial prognathism, defined as forward displacement of the nasal region and the tooth row relative to more lateral facial structures, does not appear to be a typical Neanderthal trait. The uniqueness of Neanderthals appears to have been exaggerated, and may be related to Boule's peculiar, flawed reconstruction of the skull of La Chapelle-aux-Saints. The method of thin-plate splines is a powerful technique, capable of providing a new and insightful perspective on morphological problems in physical anthropology. © 1996 Wiley-Liss, Inc.