ANGIOSPERM TREE HEIGHTS DURING THE CRETACEOUS TERRESTRIAL REVOLUTION: EVIDENCE FROM THE UPPER CAMPANIAN JOSE CREEK FORMATION, SOUTH-CENTRAL NEW MEXICO

The Cretaceous terrestrial revolution changed the composition of forests. Slow-growing and low-transpiring gymnosperms and ferns were replaced by rapidly growing and fast transpiring dicots and monocots. The timing and geography of change are unclear, with some authors suggesting that large stature, dicot-dominated forests did not evolve until the Cenozoic.

Abundant fossil woods from the Upper Campanian Jose Creek Formation of south-central New Mexico indicate that tall dicot-dominated forests were present in regions of megathermal climate by the Late Campanian and that palms were also important trees. Allometric equations for modern forests that relate height to diameter at breast height (H:DBH) indicate that at least one lineage (Paraphyllanthoxylon) had reached the height of modern tropical canopy/emergent trees—over 50 m tall. The Forest of Giants, an in-situ assemblage consisting solely of dicot stumps and logs, comprises trunks up to 2 m in diameter and the oldest known dicot plank buttresses. Conifer stumps and logs occur at other localities; the largest is only 1.5 m in diameter. Conifer heights are dependent on the choice of allometric equation. Allometric equations for modern palms indicate that Jose Creek palms include trees, with at least one taxon taller than 10 m. Jose Creek woods add to growing evidence for angiosperm vegetation comparable to modern tropical forests by the Campanian and climatic/latitudinal gradients during the rise of angiosperms.