New Material of Beelzebufo, a Hyperossified Frog (Amphibia: Anura) from the Late Cretaceous of Madagascar

The extant anuran fauna of Madagascar is exceptionally rich and almost completely endemic. In recent years, many new species have been described and understanding of the history and relationships of this fauna has been greatly advanced by molecular studies, but very little is known of the fossil history of frogs on the island. Beelzebufo ampinga, the first named pre-Holocene frog from Madagascar, was described in 2008 on the basis of numerous disarticulated cranial and postcranial elements from the Upper Cretaceous (Maastrichtian) Maevarano Formation of Madagascar. These specimens documented the presence of a hyperossified taxon that differed strikingly from extant Malagasy frogs in its large size and heavy coarse cranial exostosis. Here we describe and analyse new, articulated, and more complete material of the skull, vertebral column, and hind limb, as well as additional isolated elements discovered since 2008. μCT scans allow a detailed understanding of both internal and external morphology and permit a more accurate reconstruction. The new material shows Beelzebufo to have been even more bizarre than originally interpreted, with large posterolateral skull flanges and sculptured vertebral spine tables. The apparent absence of a tympanic membrane, the strong cranial exostosis, and vertebral morphology suggest it may have burrowed during seasonally arid conditions, which have been interpreted for the Maevarano Formation from independent sedimentological and taphonomic evidence. New phylogenetic analyses, incorporating both morphological and molecular data, continue to place Beelzebufo with hyloid rather than ranoid frogs. Within Hyloidea, Beelzebufo still groups with the South American Ceratophryidae thus continuing to pose difficulties with both biogeographic interpretations and prior molecular divergence dates.马达加斯加现存无尾目（anuran）动物群异常丰富，且几乎完全为该岛特有类群。近年来，诸多新物种被正式描述，分子研究极大推进了学界对该动物群演化历史与亲缘关系的认知，但关于这座岛屿上蛙类的化石记录，我们仍知之甚少。 魔鬼蛙（Beelzebufo ampinga）是首个被命名的马达加斯加全新世前蛙类，2008年研究者基于采自马达加斯加上白垩统（Upper Cretaceous）马斯特里赫特阶（Maastrichtian）马埃瓦拉诺组（Maevarano Formation）的大量分散脱节的颅部与颅后骨骼标本，对其进行了正式描述。这些标本证实了一种骨化过度类群的存在：该类群体型庞大，颅部带有厚重粗糙的外生骨疣，与现存马达加斯加蛙类差异显著。 本文中，我们对2008年后新发现的关联保存、且更为完整的头骨、脊柱与后肢标本，以及额外的孤立骨骼元素展开描述与分析。显微CT（μCT）扫描使得我们能够详细解析其内外形态，并实现更为精准的三维重建。新标本显示，魔鬼蛙的怪异程度远超此前的认知——其头骨后外侧带有宽大的翼状结构，脊柱棘突表面具雕刻状纹饰。 该类群似乎不存在鼓膜，加之发达的颅部外生骨疣与脊柱形态特征，暗示其可能在季节性干旱环境中进行穴居。这一环境特征已通过独立的沉积学与埋藏学证据，在马埃瓦拉诺组的相关研究中得到证实。 本次整合了形态学与分子数据的全新系统发育分析结果显示，魔鬼蛙仍被归入雨蛙总科（Hyloidea），而非蛙总科（Ranoid）。在雨蛙总科内部，魔鬼蛙仍与南美洲角蛙科（Ceratophryidae）聚类，这一结果依然对生物地理学解释以及此前的分子分化时间估算提出了挑战。