The mountain horned dragon, Acanthosaura capra

Photo by Tom Oates, 2010, CC3.0

A continental collision

2500万年前，印度构造板与欧亚大陆相撞。碰撞 - 印度与印度分手后的1亿年旅程的高潮Gondwanaland super-continent—had an outsize impact on the region. It reshaped the geology of south-east Asia, with the creation of the Himalayan Mountains just the most notable effect. The impact was not just geological: the mixing of two very different groups of plants and animals, separated for hundreds of millions of years, had dramatic effects on the evolution of life in the region.

传统的观点是，后崩溃后的变化主要是由于印度次大陆进化的物种对欧亚大陆的入侵而产生的，这种观点是由现代热带亚洲许多冈瓦南血统的存在所支持的。最近，许多研究表明，从亚洲到印度的相反方向的物种流对许多现代印度血统的起源产生同样的显着影响。

在这种纠结的进化关系中，揭示了该地区现代群体的起源，继续证明具有挑战性。

Dragon origins

The Draconinae, commonly known as dragon lizards, are a large subfamily of almost 200 species that today range widely over Southeast Asia. Their origins, like those of so many groups in the region, remain unclear.

Two previous studies were unable to provide a clear answer as to how the Indian-Eurasian collision affected the group. These studies, one a 1980 PhD thesis by S.M Moody, the other published byMacey等。in 2000，had to work with limited data and, while they broadly supported a Eurasian origin of dragon lizards, exactly how and when they invaded India remained unclear.

自从这些早期研究以来，已经发现了新的Draconinae物种（甚至是整个属），并从几种稀有物种中收集了第一批样品。拥有这些新数据，并受益于DNA测序技术的最新进展，这是一组新的研究人员，由Jesse Grismer和Rafe Brownat the University of Kansas, have taken a fresh look at Draconinae evolution.

Their study,最近出版inBMC Evolutionary Biology，reinterprets the biogeographic origins of both Indian and Southeast Asian draconine lineages and provides the best answer yet to the question of how these dragons originated.

在影响之前

事实证明，前所未有的抽样和新的遗传标记结合在解决了德拉科尼亚种类之间的许多以前有问题的进化关系方面成功。结果证实了印度龙蜥蜴的东南亚起源，并暗示亚洲物种通过两个不同的殖民化侵入印度。

也许更令人惊讶的是，结果表明这些菌落发生了beforethe final collision between India and Asia. While this occurred approximately 25 million years ago, both lizard invasions took place during the preceding Eocene geological period (34-56 million years ago). While the more recent Macey study had suggested a post-collision origin for Indian lizards, this pre-collision hypothesis was predicted by Moody in his original 1980 work on this group; 35 years later, modern-day techniques now support this theory.

The first invasion of dragon lizards from Asia to India happened approximately 50-55 million years ago, the results of which are today represented by the genusSalea，found only in India. The second invasion then occurred in the middle Eocene (around 35-50 million years ago) and eventually resulted in the fan-throated lizards andOtocryptis;再次,属今天只发现在印度。

跨越鸿沟

Previous research提出，在始新世时期，亚洲和即将接近的印度次大陆之间存在陆桥。Grismer等。建议这样的陆桥为亚洲龙蜥蜴如何两次入侵印度提供了最好的解释，而它仍然是一个单独的地块（请参阅地图）。

这增加了越来越多的工作，这表明印度与欧亚大陆之间的许多动植物之间发生了始新世期间发生的许多动植物和动物的交流，这是在数百万年后的两次土地上的“严重碰撞”之前。许多这些物种的生态 - 特别是它们不喜欢弄湿 - 使过水的散布事件不太可能。而是格里斯特等。suggest that land bridges between Asia and India existed for much of the Eocene, leading to broad scale patterns of faunal exchanges.

They term this idea the “Eocene Exchange Hypothesis” and suggest it could account for the substantial disagreements over Indian vs. Asian origins of many modern groups; that is, focusing on eventsafterthe collision has blinded us to the importance of interchange of species between the continentsbefore碰撞。尽管印度对亚洲的雷鸣般的影响无疑引起了今天的转变，但当今印度仍处于海上寂静的态度时，可能发生了一些最重要的发展。