Gnathostome dental pattern and the evolution of chondrichthyan dentitions

脊椎动物最重要的创新之一是颌骨的进化，在这些颌骨上，牙齿排列成功能性的牙列。这些牙列使脊椎动物可以辐射成许多主要的类群，包括鲨鱼(软骨鱼)和硬骨鱼(骨鱼)。随之而来的是各种化石群体，它们的牙齿特征一直难以理解和解释。由于这些化石类群更接近颌骨和牙齿的起源，我们试图更好地了解它们的牙齿是如何进化的是至关重要的。要做到这一点，一种方法是研究活着的类群的牙齿是如何发育的，然后尽可能地将这些观察结果应用于化石类群中牙齿的发育。骨鱼类包括众所周知的鱼类，如金枪鱼、鲑鱼、海马、腔棘鱼、肺鱼和四足动物。近些年来，人们对硬骨鱼的牙齿进行了深入的研究，我们甚至了解了是什么基因参与了这些牙齿的形成。尽管如此，即使在这一组中，我们对更原始的硬骨鱼的牙齿发育也一无所知，例如白鳍鱼和白鲨。此外，也许有些令人惊讶的是，我们对基因如何控制鲨鱼和射线牙列的发育知之甚少。我们项目的目标是研究范围广泛的软骨动物的发育，以找到这些牙列的共同发育特征，这些特征可以与骨鱼的牙列以及未来更原始、更有问题的化石分类群进行比较。鲨鱼的牙齿在化石记录中很丰富，它们所显示的特征对识别不同的物种很重要。软骨动物表现出各种各样的牙列，从沿下巴的大量几乎微小的牙齿(在滤食性鲨鱼，如鲸鲨Rhincodon)，到在射线中的人行道状的牙列，再到牙齿沿下巴从咬合到挤压的牙列(异齿鲨，杰克逊港鲨)。这种多样性使人们很难找到可以用来与上述有问题的脊椎动物化石进行比较的牙齿发育的共同模式。鲨鱼和射线也有其他类似牙齿的结构，比如滤食性姥鲨的颧骨，以及锯鱼和锯鲨嘴上的“牙齿”。我们的项目将研究不同生长阶段的各种现代鲨鱼和射线的标本，以研究颌骨内牙齿的发育模式以及牙齿数量和形状在生长过程中的变化。还将研究一些保存异常完好的化石，以便将现代形态置于软骨类更广泛的背景下。此外，我们还将研究鲨鱼、银鱼和基本硬骨鱼的胚胎，并记录控制它们牙齿发育的基因，这将使我们能够比较所有脊椎动物牙齿形成的潜在机制。

One of the most significant vertebrate innovations was the evolution of jaws, and on these jaws, teeth arranged into functional dentitions. These dentitions allowed vertebrates to radiate into a number of major groups, including sharks (Chondrichthyes) and bony fishes(Osteichthyes). Along with these are a variety of fossil groups whose dentitions have been difficult to understand and interpret. Because these fossil groups are closer to the origin of jaws and teeth, it is crucial that we try to better understand how their dentitions evolved.One way to do this is to study how the dentitions of living groups developed and then apply these observations, as far as possible, to the development of dentitions in fossil taxa. The group Osteichthyes includes well-known fish such as the tuna, salmon, seahorse, coelacanth, lungfish and also tetrapods. Osteichthyan dentitions have been intensely studied in recent years, and we even understand what genes are involved in producing these dentitions. Despite this, even within this group we know nothing about tooth development of more primitive osteichthyans, such as the paddlefish and gar. As well, and perhaps somewhat surprisingly, we know very little about how genes controldevelopment of shark and ray dentitions. The goal of our project is to study development in a broad range of chondrichthyans to find common developmental characters of these dentitions that can be compared to osteichthyan dentitions and in the future, to the more primitive, problematic fossil taxa. Shark teeth are plentiful in the fossil record and features they show are important in identifying different species. Chondrichthyans show a wide variety of dentitions, ranging from large numbers of almost microscopic teeth along the jaw (in filter-feeding sharks such as Rhincodon, the Whale shark), to the pavement-like dentition in rays, to a dentition in which teeth change along the jaw from biting to crushing (Heterodontus, the Port Jackson shark). This diversity has made it difficult to find common patterns of dentition developmentthat could be used to compare to the problematic fossil vertebrates mentioned above. Sharks and rays also possess other 'tooth-like' structures such as the gill rakers in the filter-feeding basking shark Cetorhinus and 'teeth' along the rostrum of sawfish and sawsharks. Our project will study specimens of a wide range of modern sharks and rays of different growth stages in order to investigate the patterns of tooth development within the jaws and changes in the number and shape of teeth during growth. A number of exceptionally well-preserved fossils will also be studied in order to place the modern forms within a wider context within the Chondrichthyes. Additionally, we will study embryos of a shark, ray and a basal bony fish and will record the genes controlling their tooth development that will allow us to compare underlying mechanisms of the formation of teeth in all vertebrates.