ABSTRACT

Paleocene deposits of the Tullock Member of the Fort Union Formation, Montana, U.S.A., have yielded several new specimens of †Polyodon tuberculata, a taxon previously described from the formation, as well as a new genus and species of sturgeon (Acipenseridae). The three new specimens of †P. tuberculata allow us to revise and to confirm previously reported features of the holotype, as well as to describe other features that were not preserved in the single specimen previously known. For example, we observe that (1) the left and right posttemporals overlie the left and right parietals to meet in the midline, (2) the posttemporal has a deep ventral flange, and (3) the parasphenoid extends farther posteriorly than the parietals. The new sturgeon is fairly small, and not well preserved. It can be distinguished from all other acipenserids by a combination of features, including kite-shaped dorsal scutes bearing a strong median ridge, lateral scutes that vary in shape from rhomboid to irregularly shaped elements, a large triangular scute behind the anal fin, and numerous small rhomboid scales covering the caudal skeleton. It cannot be included in any currently known genus and is here named †Engdahlichthys milviaegis, gen. et sp. nov.

摘要

美国蒙大拿州Fort Union组Tullock成员的古新世沉积物产生了† Polyodon tuberculata的几个新标本（以前从该组中描述过的分类单元），以及a鱼的一个新属和新种（Acipenseridae）。† P. tuberculata的三个新标本允许我们修改和确认先前报道的全型特征，并描述先前已知的单个样本中未保留的其他特征。例如，我们观察到（1）左侧和右侧后颞骨覆盖左，右顶骨以在中线相遇;（2）颞后骨具有较深的腹缘;（3）蝶骨比顶骨向后延伸得更远。新的urge鱼很小，并且保存得不好。它的特征可以与所有其他先人动物区分开，包括风筝形背侧背鳍，背负着强大的正中脊，形状从菱形到不规则形状的侧背背鳍，肛门鳍后方的大型三角形背鳍，以及众多小菱形鳞片覆盖尾骨。Engdahlichthys milviaegis，gen。等。十一月