Abstract:

Over the past decades, an increasing number of reptiles have been described from the Middle Triassic of southern parts of China. Marine reptiles such as thalattosaurs, ichthyosaurs and sauropterygians dominated these paleofaunas and are known to have had a Tethys-wide distribution. Indeed, several species have been described from both the eastern and western margins of that ancient ocean. The last addition to this list was a less common terrestrial reptile, Macrocnemus fuyuanensis, first discovered in Yunnan Province. The species was also tentatively inferred to be represented by a single disarticulated specimen in the paleofauna from the World Heritage Site of Monte San Giorgio in southern Switzerland (as Macrocnemus aff. fuyuanensis). The initial referral was mainly based on limb proportions and ratios rather than on discrete osteological characters, partially due to a limited anatomical description of the holotype specimen of M. fuyuanensis. Here we provide a re-description of the anatomy of the complete skeleton of the holotype and compare it with the available referred specimens. Our re-analysis shows that the pectoral girdle of the holotype specimen is more complete than previously reported, revealing the shape of the interclavicle, which is only partially exposed in the only referred specimen from China but well-preserved in the specimen from Europe. The interclavicle of M. fuyuanensis can be distinguished from M. bassanii by its short and fusiform posterior process and anterior facing rod-like processes that extend from a common base enclosing a narrow V-shaped median notch, among other features, and is here inferred to be the most important bone for discriminating species of Macrocnemus, apart from the limb ratios. We further document in detail the cranial anatomy of the holotype, which is virtually identical to that of the crania of M. bassanii, and due to its exquisite preservation and preparation, it adds important information on the palate, which was previously poorly known for Macrocnemus.

Key words: Tethys, Triassic, Ladinian, Falang Formation, terrestrial reptile, archosauromorph, tanystropheid

摘要：

过去数十年里,中国西南地区的中三叠统产出了越来越多的爬行动物化石。以海龙类、鱼龙类和鳍龙类为主的海生爬行动物,广泛分布于整个特提斯洋周边。甚至有一些物种在这古海洋的东、西两侧,即现在的中国和欧洲都有报道。最近发现的富源巨胫龙(Macrocnemus fuyuanensis)是较为罕见的陆生物种,该种最初发现于云南中三叠统。瑞士南部的世界遗产地圣乔治山动物群中发现的一零散标本也曾被初步推断属于该物种(作为归入种：Macrocnemus aff. M. fuyuanensis)。由于最初对富源巨胫龙模式标本的解剖学记述有限,这一归入仅基于肢骨比例而不是骨骼特征。本文对富源巨胫龙的模式标本进行了重新描述,并与已知归入标本进行了比较。研究发现,富源巨胫龙模式标本的肩带保存比从前报道的更加完整,间锁骨形态可以被明确,而这一结构在中国唯一归入标本中只是部分暴露,但在欧洲归入标本中保存完好。在区别巨胫龙属的不同种时,推测除了肢骨比例之外,间锁骨的形态特征最为重要：富源巨胫龙间锁骨的后突短且呈纺锤状,间锁骨前缘有一对棒状的突起,从前缘中间的V形凹槽处延伸而出,以此可与巴氏巨胫龙(Macrocnemus bassanii)相区别。此外,进一步详细研究了富源巨胫龙模式标本的颅骨解剖特征,发现与巴氏巨胫龙完全相同。以往对巨胫龙的腭部知之甚少,保存精美和精心修理的标本为了解该部形态特征增加了重要的信息。

关键词: 特提斯, 三叠纪, 拉丁期, 法郎组, 陆生爬行动物, 主龙型类, 长颈龙类