Reconstruction and Growth of the Early Tree Calamophyton (Pseudosporochnales, Cladoxylopsida) Based on Exceptionally Complete Specimens from Lindlar, Germany (Mid-Devonian): Organic Connection of Calamophyton Branches and Duisbergia Trunks

Abstract

Middle Devonian Pseudosporochnales (Cladoxylopsida) are among the earliest tree-sized plants in the fossil record. We describe here new and spectacular complete specimens of Calamophyton primaevum Kräusel et Weyland from Lindlar (Eifelian, early Mid-Devonian), Germany. These demonstrate for the first time roots, trunk bases, trunks, trunk apices, and crowns of attached digitate branches in organic connection for multiple specimens of one taxon of pseudosporochnaleans from the same horizon. Completely preserved trunks are between 0.8 and 2.0 m long. Middle portions of the trunks demonstrate that the branches were abscised a short distance from the trunk surface, leaving branch bases of consistent length superficially similar to leaves. Such trunks and “leaves” were previously named Duisbergia mirabilis Kräusel et Weyland. Trunk diameter decreases distally in the lower half of the trunk but usually increases distally below the top. Some trunks may have divided dichotomously. The trunk apex is domed and takes up the entire width of the top of the trunk, up to 100 mm in diameter. Overall, the new evidence is not consistent with existing models of pseudosporochnalean growth. The suite of specimens suggests that the upward-growing primary body of the trunk increased in diameter, reaching a mature diameter ∼1–2 m from the ground. Lower parts of the plant are therefore likely to have increased in diameter by a process of secondary growth.