†Pycnodonts (Neopterygii, †Pycnodontiformes) from the Del Rio Formation (Early Cenomanian, Cretaceous) of Waco Lake, Texas (U.S.A.)

The author provides the first report of the presence of pycnodonts in the clays of the Del Rio Formation, outcropping on the East bank of the Waco Lake, in central Texas, U.S.A. These fossils were found in association with a rich malacofauna, echinoderms, bryozoans and foraminifera, that were characteristic of coastal marine environments. The findings on which this indication is based are both isolated teeth as well as three dental apparati (one vomer and two prearticulars). Most of these fossils shown the characteristic random disposition of the anterior teeth, which are, moreover, exclusively for pycnodonts pertaining to the genus Anomoeodus. The detailed anatomical study of the sample allows the identification of a new genus and species, namely Globanomoeodus dentespassim gen. and sp. nov., as well a new species, namely Anomoeodus wolfi sp. nov. The new genus (Globanomoeodus) seem to be closely related to Anomoeodus, with which it differs for three substantial characters: (i) the circular profile and the semi-spherical shape of the teeth, (ii) their totally unorganized spatial arrangement, and (iii) the presence of teeth also on the oral border (upper edge) of the prearticular. The new species (A. wolfi) is characterized by the presence of vomerine teeth that exhibit a very unique sculpture of the occlusal surface, and are arranged in seven parallel rows. Finally, the presence of pycnodont remains in the Waco pit clays, demonstrate the deposition environment of the Del Rio Formation was connected with another, different environment, that of the cliff and the backcliff of the Cenomanian sea, in which the pycnodonts lived together with other organisms, such as the molluscs of the genera Gryphaea, Inoceramus, Ostrea, etc.

本文作者首次报道了美国德克萨斯州中部沃科湖东岸露头的德尔里奥组（Del Rio Formation）黏土层中褶齿鱼（pycnodonts）的存在记录。这些化石与丰富的软体动物群（malacofauna）、棘皮动物（echinoderms）、苔藓虫（bryozoans）及有孔虫（foraminifera）伴生产出，上述类群均为海岸海洋环境的典型生物标志。本研究依托的化石标本既包括孤立牙齿，也包含三件齿器（dental apparati）：一件犁骨（vomer）与两件前关节骨（prearticular）。多数这类化石展现出前齿特有的随机排布特征，且这类前齿仅隶属于异齿鱼属（Anomoeodus）的褶齿鱼类。通过对标本的详细解剖学研究，本次发现包含一个新属新种——Globanomoeodus dentespassim gen. et sp. nov.，以及另一个新种Anomoeodus wolfi sp. nov.。新属Globanomoeodus与异齿鱼属（Anomoeodus）亲缘关系密切，但存在三项显著差异：（i）牙齿呈圆形轮廓与半球形形态；（ii）牙齿的空间排布完全无规律；（iii）前关节骨的口缘（上缘）亦分布有牙齿。新种A. wolfi的特征为其犁骨牙齿的咬合面（occlusal surface）带有极为独特的纹饰，且牙齿以七列平行的方式排布。沃科坑黏土层中褶齿鱼残骸的发现，证明德尔里奥组的沉积环境与另一处不同环境存在连通：即森诺曼期海洋（Cenomanian sea）的崖壁及崖后环境，该环境中褶齿鱼与格氏蛤属（Gryphaea）、叠瓦蛤属（Inoceramus）、牡蛎属（Ostrea）等其他生物类群伴生共存。