Appendix 1.Analytical trait types according to Lovejoyet al [11]
Type 1: A trait that differs in two taxa (1) because its presence and/or expression are downstream consequences of differences in the positional information of its cells and their resultant effects on local pattern formation (2). Type 1 traits are fixed by directional and/or stabilizing selection because their primary functional features have a real effect on fitness and result largely from a direct interaction between genes expressed during field deployment and the functional biology of their adult product; eg, the superoinferior shortening of the ilium in hominids.
Type 2: A trait that is a collateral byproduct of other field changes. Type 2 traits differ in two taxa because of differences in pattern formation (like in Type 1) but have no functional consequences. Unlike Types 4 and 5, they represent true field-derived pleiotropy (3). Type 2A traits are those whose primary antecedent shift was the product of natural selection. Type 2B traits are those whose “parent” changes were not under selection. They are likely to result from minor fluctuations in morphogenetic fields, and differences in their expression among demes (4) arise by stochastic processes such as genetic drift.
Type 3: A trait that differs in two taxa because of modification of a systemic growth factor that affects multiple elements such as an anabolic steroid; eg,body size and its allometric (5)effects. Allometric shifts probably usually reflect slight changes of systemic control factors during development; eg, small modulations of growth hormone and/or its related factors can generate fully coordinated morphological change.
Type 4: A trait that differs between taxa because its presence/absence and/or “grade” are attributable exclusively to phenotypic effects of the interaction of “systematic assembly mechanisms” such as cartilage modeling and environmental stimuli. Such traits have no antecedent differences in pattern formation and therefore have no value in phyletic analysis. They are epigenetic (6) and are not pleiotropic. However, they can provide significant behavioral information and are therefore of expository or evidentiary value in interpreting fossils. They result from habitual behaviors during development; eg, the bicondylar angle of the femur.
Type 5: Traits arising by the same process as Type 4 but which have no reliable diagnostic value with respect to significant behavior. Such traits are not consistently expressed within species and often show marked variation of expression within individuals and demes; eg, femoral anteversion.
1 = taxa plural of taxon: group of one or more populations of organisms.
2 = pattern formation: the process by which cells in a developing embryo acquire identities that lead to well-ordered spatial patterns of cell activities.
3 = pleiotropy: the production of two or more unrelated effects in the phenotype.
4 = demes plural of deme: a local population of closely related organisms.
5 = allometric: pertaining to the relative growth of a part relative to a whole body.
6 = epigenetic: resulting from external rather than genetic influences.