Modularity and developmental patterning in the evolution of early jawed vertebrates

大约5.4亿年前，所有有颅类的祖先，产生了今天的八目鳗、七鳃鳗、软骨鱼（鼠鱼、鳐和鲨鱼）和硬骨鱼（鳍鱼、腔棘鱼、肺鱼和四足动物），获得了独特的胚胎学特征-神经嵴和表皮基板（在器官形成早期形成的专门胚胎细胞群）。这两个发展的新奇是负责许多解剖特征的颅，如大脑和颅面软骨和骨骼。没有其他的发展新奇已经与有颌脊椎动物的早期进化，或颚口动物（棘皮动物，盾皮动物，软骨和硬骨鱼）。因此，基颚口的相互关系解决不好。最有可能的是，识别新的发育特征，如发育模块（一个相互作用的元素网络，表现为相对独立的发育单元）和模式（这些元素的形成顺序），可以帮助解决颚口畸形。所有先前提出的解剖模块，将被编译重建的理论模型gnathostome模块化。这些基本模块的存在将通过观察（1）它们的内部变异模式和（2）它们的形成模式在活的有颌动物中进行测试。这些模块和模式将在化石分类群中进行评估，随后用于重建化石发生。换句话说，我们将解决三个问题的模块化和模式化的进化在有颌脊椎动物的历史：（1）什么是模块化组织的有颌动物在其起源？(2)我们还能在活的和化石的有颚类中识别出这些模块及其相关的形成模式吗？(3)我们能否根据新的模块化和模式化特征重建有颌类的生命树？这项研究计划将有助于理解负责有颌脊椎动物进化的发育机制，我们属于分类组，我们继承了基本的解剖和发育特征。

Approximately 540 million years ago, the ancestor of all craniates, which gave rise to today's hagfishes, lampreys, cartilaginous (ratfishes, skates and sharks) and bony fishes (ray-fined fishes, coelacanths, lungfishes and tetrapods), acquired distinctive embryological features - the neural crest and the epidermal placodes (specialized groups of embryonic cells forming early during organogenesis). These two developmental novelties are accountable for numerous anatomical characteristics of craniates, such as the brain and craniofacial cartilages and bones. No other developmental novelties have been associated to the early evolution of jawed vertebrates, or gnathostomes (acanthodians, placoderms, cartilaginous and bony fishes). As a result, basal gnathostome interrelationships are poorly resolved. Most likely, the recognition of new developmental features such as developmental modules (a network of interacting elements behaving as relatively independent units of development) and patterning (the order of formation of these elements) can help solving gnathostome phylogeny. All anatomical modules that have been previously proposed will be compiled to reconstruct a theoretical model of gnathostome modularity. The presence of these fundamental modules will be tested in living gnathostomes by looking at (1) their internal pattern of variation and (2) their pattern of formation. These modules and patterning will be evaluated in fossil taxa and subsequently used to reconstruct phylogeny. In other words, we will be addressing three questions about the evolution of modularity and patterning in jawed vertebrate history: (1) What was the modular organization of gnathostomes at their origin? (2) Can we still recognize these modules and their associated patterns of formation in living and fossil gnathostomes? (3) Can we reconstruct the gnathostomes' tree of life based on new modular and patterning characters? This research program will help understanding developmental mechanisms that have been responsible for the evolution of jawed vertebrates, the taxonomic group we belong to and from which we inherited fundamental anatomical and developmental characteristics.