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，牙齿排列成功能牙列。这些牙齿使得脊椎动物能够辐射成许多主要的类群，包括鲨鱼（软骨鱼目）和硬骨鱼（骨鱼目）。与这些一起出现的是各种各样的化石群，它们的牙列一直难以理解和解释。因为这些化石群更接近颌骨和牙齿的起源，所以我们试图更好地了解它们的牙齿是如何进化的至关重要。一种方法是研究生活群体的齿列是如何发展的，然后尽可能地将这些观察结果应用于化石分类群的齿列发展。骨鱼目包括著名的鱼类，如金枪鱼、鲑鱼、海马、腔棘鱼、肺鱼和四足动物。近年来，人们对骨鱼的牙齿进行了深入的研究，我们甚至了解了产生这些牙齿的基因。尽管如此，即使在这个群体中，我们对更原始的骨鱼目动物的牙齿发育也一无所知，比如白鲟和黄鳍鱼。同样，也许有些令人惊讶的是，我们对基因如何控制鲨鱼和鳐鱼牙齿的发育知之甚少。我们项目的目标是研究大范围软骨鱼的发育，以找到这些牙齿的共同发育特征，这些特征可以与骨鱼牙齿进行比较，并在未来与更原始，有问题的化石分类群进行比较。鲨鱼的牙齿在化石记录中有很多，它们所显示的特征对识别不同的物种很重要。软骨鱼显示出各种各样的牙齿，从大量沿着下颌几乎微小的牙齿（在滤食性鲨鱼中，如犀牛鲨，鲸鲨），到鳐鱼中像人行道一样的牙齿，再到牙齿沿着下颌从咬到咬的变化（异齿鲨，杰克逊港鲨）。这种多样性使得很难找到可以用来与上面提到的有问题的脊椎动物化石进行比较的牙齿发育的共同模式。鲨鱼和鳐鱼还拥有其他“齿状”结构，如滤食性姥鲨鲸头鲨的鳃耙，以及锯鱼和锯鲨的喙部的“牙齿”。我们的项目将研究各种不同生长阶段的现代鲨鱼和鳐鱼的标本，以研究颌内牙齿发育的模式，以及牙齿在生长过程中数量和形状的变化。一些保存非常完好的化石也将被研究，以便将现代形式置于更广泛的软骨鱼目环境中。此外，我们将研究鲨鱼、鳐鱼和基骨鱼的胚胎，并将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 control development 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 development that 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.