Data from: Evolution of early Eocene Palaeosinopa (Mammalia, Pantolestidae) in the Willwood Formation of the Bighorn Basin, Wyoming

Species-level diversity and evolution of Palaeosinopa from the Willwood Formation of the Bighorn Basin is reassessed based on substantial new material from the Bighorn, Powder River, and Wind River basins. We recognize three species of Palaeosinopa in the Willwood Formation of the Bighorn Basin: P. lutreola, P. incerta, and P. veterrima. The late Wasatchian species P. didelphoides is not present in the Bighorn Basin. The Willwood species can be differentiated based only on size. P. veterrima is the most common and wide-ranging species and is the most variable in size and morphology: the stratigraphically lowest individuals are smaller, with narrower, more crestiform lower molars; whereas the highest are larger, with wider, more bunodont teeth. Although it could be argued that these represent distinct species, we demonstrate that this morphological evolution occurred as the gradual and mosaic accumulation of features, suggesting in situ anagenetic evolution. The two smaller species are present only low in the section (biochrons Wa0–Wa4) and show no discernable evolution in size or morphology. A new skeleton of Palaeosinopa veterrima from the Willwood Formation is described, and other new postcrania are reported. The skeleton is the oldest associated skeleton of Palaeosinopa known, yet it is remarkably similar to those of younger, more derived pantolestids, the primary disparities being minor differences in proportions of the innominate, femur, and tibia, and co-ossification of the distal tibia and fibula. Either P. incerta or P. lutreola was likely the ancestral population that gave rise to the other Wasatchian Palaeosinopa. Alternatively, P. veterrima may have migrated into the Bighorn Basin from the Powder River Basin.基于从大角盆地（Bighorn Basin）、鲍德河盆地（Powder River Basin）和风河盆地（Wind River Basin）采集的大量新标本，我们对大角盆地威尔伍德组（Willwood Formation）产出的古帕洛兽（Palaeosinopa）的物种级多样性与演化历程进行了重新评估。本次研究在大角盆地的威尔伍德组中识别出3种古帕洛兽：P. lutreola、P. incerta与P. veterrima。晚瓦萨奇期（late Wasatchian）物种P. didelphoides并未见于该盆地。威尔伍德组的古帕洛兽仅能通过体型差异进行区分。其中P. veterrima是最为常见且分布范围最广的物种，同时也是体型与形态变异程度最高的类群：地层层位最低的个体体型更小，下臼齿更窄且呈脊形（crestiform）；而层位最高的个体体型更大，牙齿更宽且呈丘形（bunodont）。尽管有观点认为这些类群可代表不同物种，但我们的研究证实，这些形态演化是特征逐步、镶嵌式积累的结果，暗示了原地发生的线系前进演化（anagenetic evolution）。另外两种体型较小的物种仅见于剖面下部（生物年代带Wa0–Wa4），未表现出可识别的体型或形态演化。本文描述了一件产自威尔伍德组的古帕洛兽（Palaeosinopa veterrima）的全新关联骨架标本，并报道了其他新发现的颅后骨骼（postcrania）。该骨架是目前已知最古老的关联保存的古帕洛兽骨架，但其形态与更年轻、更特化的潘诺兽类（pantolestids）骨架极为相似，仅存在细微差异：无名骨、股骨与胫骨的比例略有不同，且胫骨远端与腓骨发生了骨性愈合。P. incerta或P. lutreola大概率是演化出其他瓦萨奇期古帕洛兽的祖先类群。此外，P. veterrima也可能是从鲍德河盆地迁徙进入大角盆地的。