Fig. 4.

Sutural morphospace defined by cross-sectional sutural measurements in Eusthenopteron, Acanthostega, and Phonerpeton. The volumes defined by suture morphologies in the extant fish Polypterus known to experience tension, compression, or a combination of tension and compression that reflects more complex loading conditions (such as shearing or bending) are shown in pink, blue, and green, respectively. The locations of the fossil data points within these volumes are used to infer the loading conditions experienced by the fossil sutures. Taxa: Polypterus, purple; Eusthenopteron, blue; Acanthostega, red; Phonerpeton, green. Sutures: IF, ●; IP, ■; IPP, ♦; left frontoparietal (LFP), ◀; right frontoparietal (RFP), ▶; left nasofrontal (LNF), ▴; right nasofrontal (RNF), ▾. (Scale bars: 1 mm.)