- 學位論文
台灣更新世馬來鱷類化石的形態與親緣分析
Morphological and Phylogenetic Analyses of A Tomistomine Fossil from the Pleistocene of Taiwan
摘要
馬來鱷亞科(Tomistominae)，一個包含許多長吻部鱷類的亞科，是個多樣且廣布於全世界的支系，但目前只有一個現生種馬來長吻鱷(Tomistoma schlegelii)生存於東南亞。對於馬來鱷類多樣性的衰亡仍所知甚少。在本論文中，我描述一件從澎湖和台灣之間海底所打撈的馬來鱷類標本。這件標本的地層層位不明，但根據先前研究很有可能來自中至晚更新世。該標本屬於頭骨的後部，並保留了馬來鱷類的獨特特徵組合，像是後結節凸起可見於背側、方骨的內側半球踝膨大、額骨頂骨縫合線可完全見於頭蓋骨表面等。此外，該標本的其他特徵，包括外枕骨的腹側突粗壯且參與枕骨結節形成、基蝶骨前後較長且暴露於腹側等，表明其分類與豐玉姬鱷(Toyotamaphimeia)相近。最有趣的是，該標本的幾個特徵與迄今唯一所知的物種待兼豐玉姬鱷(Toyotamaphimeia machikanensis)不同：頭蓋骨表面向腹側傾斜、頸外側開孔高於基蝶骨的側面暴露、上顳窩開孔的後緣與側緣等寬。為了進一步檢驗這件標本在鱷目中的親緣關係位置，我選擇了74個分類群和254個形態特徵，並使用最大簡約法進行親緣關係分析。結果顯示其與豐玉姬鱷形成姊妹群。結合其獨特的形態、親緣關係位置以及較為年輕的地質年代(中至晚更新世)，該標本不僅揭示豐玉姬鱷支系所隱藏的多樣性，還突顯了馬來鱷亞科在歐亞大陸東緣較為近期的生存。此外，這個台灣更新世豐玉姬鱷可能新種的出現有望提供相關後續研究，來闡述相當大體型的豐玉姬鱷的滅絕，並可望提供新證據來解決馬來鱷亞科在鱷類演化中的親緣關係難題。
並列摘要
Tomistominae, a subfamily of longirostrine crocodiles, is a speciose lineage globally but currently only includes one extant species: Tomistoma schlegelii (the false gharial) in Southeast Asia. The demise of the tomistomine diversity remains poorly known. In this thesis, I described a tomistomine specimen dredged from the sea bottom between Penghu Islands and Taiwan. The geological horizon of this specimen is uncertain but likely from Middle to Late Pleistocene based on previous studies. The specimen preserves the posterior part of the cranium and shows the unique morphological combination of Tomistominae, such as posterior tuberosity of the supraoccipital visible in dorsal view, quadrate with expanded medial hemicondyle, and frontoparietal suture entirely on skull table. Besides, this specimen exhibits exoccipital ventral process robust and participating in occipital tubera, basisphenoid anteroposteriorly long and exposed ventrally, suggesting its taxonomic affinity to Toyotamaphimeia. Most interestingly, this specimen differs from the only known Toyotamaphimeia (T. machikanensis): skull table surface sloping ventrally and inclined, the opening of the lateral carotid foramen dorsal to the basisphenoid lateral exposure, and posterior edge of the supratemporal fenestra as thick as the lateral margin. To further test its position within Crocodylia, I chose 74 crocodile taxa and 254 characters to perform the phylogenetic analysis under the maximum parsimony, resulting in the sister group with Toyotamaphimeia. Given its unique morphology, phylogenetic position, and young geological age (Middle to Late Pleistocene), this new specimen not only unveils a hidden diversity of the Toyotamaphimeia lineage but also highlights the late survival of Tomistominae along the eastern margin of Eurasia. In addition, the presence of a possibly new Toyotamaphimeia from the Pleistocene of Taiwan promises in-depth research to elucidate the extinction of the fairly large Toyotamaphimeia and might lend new evidence to resolve the phylogenetic conundrum of Tomistominae in the evolution of Crocodylia.