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，牙齿排列成功能性牙列。这些齿系使脊椎动物能够辐射成许多主要群体，包括鲨鱼（软骨鱼）和硬骨鱼（硬骨鱼）。沿着的还有各种各样的化石群，它们的齿系一直难以理解和解释。由于这些化石群更接近颌骨和牙齿的起源，因此我们必须更好地了解它们的齿系是如何进化的，方法之一是研究现存化石群的齿系是如何发展的，然后尽可能地将这些观察结果应用于化石分类群中齿系的发展。硬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。近年来，人们对硬骨鱼的齿系进行了深入的研究，我们甚至了解了哪些基因参与了这些齿系的产生。尽管如此，即使在这个群体中，我们对更原始的硬骨鱼类（如白鲟和雀鳝）的牙齿发育也一无所知。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牙齿的发育知之甚少。我们的项目的目标是研究在广泛的软骨鱼类的发展，以找到这些齿系的共同发展特征，可以比较硬骨鱼类的齿系，并在未来，更原始的，有问题的化石类群。鲨鱼牙齿在化石记录中非常丰富，它们所显示的特征在识别不同物种方面非常重要。软骨鱼类的齿系种类繁多，从沿着颚部的大量几乎是微小的沿着牙齿（在滤食性鲨鱼如鲸鲨中），到鳐的铺路状齿系，再到牙齿沿着颚部从沿着咬合到压碎的齿系（Heterodontus，港口杰克逊鲨鱼）。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齿系发育的共同模式。鲨鱼和鳐也有其他“牙齿状”结构，如滤食性姥鲨Cetorhinus的鳃耙，以及锯鳐和锯鲨喙部的沿着“牙齿”。我们的项目将研究不同生长阶段的各种现代鲨鱼和鳐的标本，以研究颌骨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。还将研究一些保存非常完好的化石，以便将现代形式置于软骨鱼纲更广泛的背景下。此外，我们还将研究鲨鱼、鳐鱼和基底硬骨鱼的胚胎，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 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.