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道虎沟化石层分布于内蒙古宁城县道虎沟以及毗邻的河北北部和辽宁西部等地,已报道4种有尾类、1个无尾类蝌蚪、1个幼年蜥蜴、3种带原始羽毛的兽脚类恐龙、2种翼龙、3种哺乳动物以及双壳类、叶肢介、昆虫和植物等化石(有学者称之为“前热河生物群”)。该层位比热河群义县组低,但地层划分存在争议:中侏罗统九龙山组、上侏罗统道虎沟组和下白垩统热河群均有报道。本文研究的道虎沟蜥蜴是该地点发现的第2个蜥蜴化石,其身体细长,为一幼年个体;前颌骨、顶骨和额骨均成对;上颌骨的面突高;后额骨和后眶骨不愈合;后额骨较大,但可能未进入上颞孔;后眶骨具宽的后突;牙齿小而尖锐,结构简单且可能为侧生;头骨的眶前区较长;具27个荐前椎;虽然未成年但个体较大;未见真皮骨板;手掌和四肢较长。上述特征组合区别于所有现生蜥蜴类,四肢比例也与其他蜥蜴有较大区别。欧美中侏罗世-早白垩世的小盗蜥(Parviraptor)和蒙古早白垩世的一个幼年个体(可能属于壁虎型类)与道虎沟标本比较相似。头骨特征和较大的荐前椎数目显示道虎沟标本可能属于硬舌蜥类(scleroglossan)。但因标本为幼年个体,本文暂将它归入有鳞类属种未定(Squamata gen.et sp.indet.)。测量数据显示,道虎沟标本的手掌和前肢相对较长;该特征常见于适应攀爬的蜥蜴种类,似可显示攀爬习性。但肢体比例可能会随身体增长而发生变化,所以此生活习性并非定论。
The Daohugou fossil layer is distributed in Dahuogou, Ningcheng County, Inner Mongolia, adjacent to northern Hebei and western Liaoning. There are four species of tailed foxtail, one tailed albino tadpole, one juvenile lizard, and three species of primitive feathers Two species of pterosaurs, three species of mammals, and fossils such as bivalves, leaves, insects and plants (some scholars call them “exothermic biota”). This horizon is lower than that of Jixian Formation of Rehe Group, but stratigraphic division is controversial: Jiulongshan Formation, Upper Jurassic Dahuogou Formation and Lower Cretaceous Rehe, both of Middle Jurassic, have been reported. The Daohugou lizard studied in this article is the second lizard fossil found at this site. Its body is slender and is an infant. The front jaw, parietal bone and frontal bone are paired. And posterior orbital nonunion; large posterior facet, but may not enter the upper temporal foramen; posterior orbital bone with a broad kyphosis; small and sharp teeth, simple structure and may be lateral; long anterior orbital skull ; With 27 pre-recommended vertebrae; although juvenile but larger individuals; no dermal bone plate; palms and limbs longer. The above feature combination is different from all current lizards, and the proportions of the limbs are also greatly different from other lizards. The European and American Middle Jurassic-Early Cretaceous Parviraptor and Early Cretaceous Mongolian individuals (possibly belonging to gecko type) are similar to Daohugou specimens. Skull characteristics and the larger number of pre-vertebrae suggest that the Daohugou specimens may belong to the genus Scleroglossan. However, because the specimens are juvenile individuals, this article tentatively classified it as Squamata gen.et sp.indet. Measurement data show that the Daohu ditch specimens have relatively long palms and forelimbs; this feature is commonly found in climbing lizard species and may show climbing habits. However, the proportion of the limbs may change as the body grows, so this lifestyle is not conclusive.