EVOLSONIA,A NEW GENUS OF GIGANTOPTERIDACEAE FROM THE LOWER PERMIAN VALE FORMATION,NORTH-CENTRAL TEXAS

Evolsonia is a new gigantopterid genus (type-species: E. texana), based on leaf impressions from 3 widely separated localities in north-central Texas. The leaves are associated with terrestrial vertebrates in floodplain sediments of the Vale Formation in the Clear Fork Group, of late Leonardian (Early Permian) age. Evolsonia leaves are simple, with very large elliptic laminae reaching 27 cm in width and 80 cm, possibly more, in length. Leaf margins are sinuate to crenate, with mostly shallow concavities. Venation is pinnate, in 4 orders; all but the ultimate veins are very thick and protrude below the lamina, creating deep impressions in the matrix. The secondary and tertiary veins form a precise herringbone pattern, with the secondaries and exmedial tertiaries ending at the leaf margin between concavities. The other tertiary veins are either simple or divided into 2 nearly equal divisions; they produce simple or variously divided quaternary veins that end at a thin sutural vein, forming a dense reticulum; some of the terminally branched tertiaries delimit areolelike areas that enclose several quaternaries and meshes. One of 6 presently known American gigantopterids, Evolsonia most closely resembles the younger Delnortea in gross architecture; with its sutures and dichotomously divided veins, however, Evolsonia is architecturally intermediate between Delnortea and the older American gigantopterids with forked leaves. Sedimentary features indicate deposition under alternating periods of flooding and drought. Their huge size invites comparison of Evolsonia leaves with those of modern tropical plants, whereas their thick veins and preservational features suggest thick, coriaceous texture.