ABSTRACT

Baenidae are the most diverse clade of turtles from the latest Cretaceous and earliest Paleogene of North America. Palatobaena species have a distinctive cranial bauplan within baenid turtles and we herein describe a new species, P. knellerorum, based on a complete cranium from the lower Paleocene Denver Formation in the Denver Basin, Colorado. Palatobaena knellerorum differs from other Palatobaena species in the extreme degree of its dorsally oriented orbits, as well as the presence of a broad pentagonal midline crest formed by the supraoccipital and parietals. It can be further diagnosed from other species of Palatobaena by the following unique combination of characters: having a broadly rounded cranium, presence of upper temporal emargination that extends well anterior to the otic chamber, a broad exposure of the supraoccipital on the dorsal skull roof, a broadly rounded ‘tongue groove’ between the maxillae and premaxillae, and a deeply emarginated nasal region that exposes the underlying premaxillae in dorsal view. Palatobaena knellerorum most closely resembles the Maastrichtian/Danian taxon Palatobaena cohen and the Danian taxon P. bairdi. A phylogenetic analysis places P. knellerorum as sister to P. bairdi, and these taxa are sister to P. cohen. Palatobaena knellerorum overlaps in time with P. cohen, but the two are separated geographically with P. knellerorum restricted to the Denver Basin and P. cohen restricted to the Williston Basin. Cranial anatomical data and sedimentological data suggest Palatobaena spp. were bottom dwelling turtles living in shallow water environments that used a putative proboscis to prey upon freshwater-shelled invertebrates.

摘要

Baenidae 是北美洲最晚白垩纪和最早古近纪最多样化的海龟进化枝。Palatobaena物种在 baenid 龟体内具有独特的颅骨 bauplan，我们在此描述了一个新物种P. knellerorum，它基于来自科罗拉多州丹佛盆地的下古新世丹佛组的完整颅骨。Palatobaena knellerorum与其他Palatobaena物种的不同之处在于其背向轨道的极端程度，以及存在由上枕骨和顶骨形成的宽阔的五边形中线嵴。可以从其他种类的帕拉托巴纳进一步诊断通过以下独特的特征组合：具有宽阔的圆形颅骨，存在延伸至耳腔前方的上颞骨外缘，颅背顶上的枕上骨广泛暴露，上颌骨之间有一个宽阔的圆形“舌沟”和前上颌骨，以及从背侧看暴露下面的前上颌骨的深切鼻区域。Palatobaena knellerorum与马斯特里赫特/达尼亚分类群Palatobaena cohen和达尼亚分类群P. bairdi最相似。系统发育分析放在P. knellerorum为妹妹P. bairdi，这些类群是姐妹P.科恩。Palatobaena knellerorum与P. cohen在时间上重叠，但两者在地理上是分开的，P. knellerorum仅限于丹佛盆地，而P. cohen仅限于威利斯顿盆地。颅骨解剖数据和沉积学数据表明Palatobaena spp。是生活在浅水环境中的底栖海龟，它们使用假定的长鼻来捕食淡水有壳的无脊椎动物。