The cranial characters of a new specimen of Yunguisaurus from Middle Triassic Ladinian Xingyi fauna, Guizhou
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摘要:
产自欧洲、北美洲和中国三叠纪的纯信龙次亚目，是连接鳍龙类"干群"和"冠群"的关键分子，也是探讨侏罗纪—白垩纪"冠群"蛇颈龙类起源和早期演化的关键环节类群。李氏云贵龙是中国华南地区发现的纯信龙次亚目中较原始的属种，也是目前发现保存最完好、数量最多的纯信龙类，但对其头骨骨骼形态学的认识依然存在不足。贵州兴义中三叠世拉丁期法郎组竹杆坡段中新发现的一件云贵龙完整头骨化石补充了云贵龙的骨骼学信息，如额骨未愈合、枕部存在开放空间等。经详细比较，新材料可能代表了目前发现的5件李氏云贵龙标本中体长最大的个体，推断额骨未愈合这一特征为云贵龙特有的鉴定特征，而非个体成年与否的判断依据。新材料显示，云贵龙的鳞状骨没有后内侧支，存在开放式枕部，同蛇颈龙类相似，指示了三叠纪纯信龙类同蛇颈龙类密切的亲缘关系。
Abstract:The Triassic Pistosauroidea from Europe, North America and China is the key to link the "stem-group" and "crown-group" Sauropterygia, and is important to reveal the origin and the early evolution of Jurassic-Cretaceous "crown-group" Sauropterygia, Plesiosaurus. Yunguisaurus is one of the most primitive genera of Pistosauroidea discovered in South China, with the most well-preserved specimens. However, the cranial osteology of Yunguisaurus is still lack of understanding. A new material of Yunguisaurus, excavated from the Zhuganpo Member(Ladinian) of Falang Formation, Xingyi Fauna in Guizhou Province, provides new detailed cranial information, such as the unfused frontals and the existence of an open space in the occipital region. Detailed comparison shows that the new material is the longest one among the five specimens of Yunguisaurus reported so far, indicating the unfused frontals should be a diagnosis of Yunguisaurus, rather than an ontogenic difference. There is no inner-posterior branch in squamosal of this new material, forming an open occipital part, which is similar to that of Plesiosaurus, indicating a close relationship with this genus.
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Key words:
- Middle Triassic /
- Pistosauroidea /
- Yunguisaurus /
- Guizhou Province
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图 1 鳍龙超目谱系关系(据Ma et al., 2015修改)
Figure 1.
图 2 兴义动物群地理位置(a)与泥麦古剖面照片(b) (据Lu et al., 2017修改)
Figure 2.
表 1 云贵龙新材料(GMPKU-P-1528)头骨测量数据
Table 1. Measurements of the skull of the new specimen (GMPKU-P-1528)
测量项 长度/mm 头骨长(吻端-鳞状骨后缘) 238 下颌骨长(齿骨前缘-关节骨后缘) 254 吻端-外鼻孔前缘 80 吻端-眼眶前缘 107 吻端-上颞孔前缘 147.9 吻部宽(垂直于鼻孔中线) 45.8 额骨中间宽 11 眼眶长(左) 32.9 眼眶宽(左) 32.8 眼眶后缘-鳞状骨后缘 103 外鼻孔长轴(左/右) 8.3/8.5 外鼻孔短轴(左/右) 5.5/5.2 上颞孔长(左/右) 83/83.7 上颞孔中间宽(左/右) 35/18 顶骨后部高 15.8 
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表 2 5件云贵龙标本解剖学数据对比
Table 2. Measurements of the five specimens of Yunguisaurus
对比项 正型标本*
NMNS 004529/F003862参考标本
ZMNH M8738参考标本
IVPP V 14993参考标本
XNGM XY-2013-R1新材料
GMPKU-P-1528头长/吻端-外鼻孔前缘 — 2.8 — 3.31 3.0 头长/吻端-眼眶最前缘 2.17 2.3 — 2.39 2.22 头长/上颞孔长 — 2.55 — 2.8 2.87 上颞孔长/眼眶长 — 1.95 — 2.3 2.52 额骨是否愈合 未愈合 未愈合 未愈合 — 未愈合 注：*数据据Sato et al.(2010)，其他为实际测量数据
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