Palaeontologia Africana Vol. 25; 181-201. The type and only species is A. plemmyridon and is represented by teeth and several dentary bones.
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The sixth species, A. rattoides, was found in the Kem Kem Beds of the Sahara in a similar location to the specimens of A. wegeneri found by Sereno and Larsson, and is known only from parts of dentary bones, up to the fourteenth alveolus. It was described in the same paper as Kaprosuchus, Laganosuchus and Anatosuchus; the four were therefore popularized by the authors as 'RatCroc', 'BoarCroc', 'PancakeCroc' and 'DuckCroc' respectively.
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Ambedus is a small diadectid known only from maxillae and dentary bones. It is considered the most primitive diadectid because unlike other forms it had a small, shallow lower jaw and many simple, conical teeth. It was also smaller than the later, rather bulky diadectids. Later diadectids have deep jaws with few teeth and forward-projecting incisiforms at the tips of the jaws for consuming plant material, and a corresponding greater girth.
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In mammals, the articular bone evolves to form the malleus, one of the mammalian ossicles of the middle ear. This is an apomorphy of the mammalian clade, and is used to determine the fossil transition to mammals. It is analogous to, but not homologous to the articular process of the lower jaw. After the loss of the quadrate-articular joint, the squamosal and dentary bones form the new jaw joint in mammals.
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The mandibles (lower jaws) are straight and slender, formed by the tooth-bearing dentary bones at the front and the splenial and angular bones at the back. The front tip of the mandibles curves very slightly downwards and inwards. The teeth of Jesairosaurus are pointed and very slightly curved, although they are also conical (particularly so in the maxilla) and only slightly flattened from the side. In addition, the teeth are subthecodont (also known as pleurothecodont).
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A pair of crests runs between the quadrate and the pterygoid on each lateral side of the braincase. The lower jaw is U-shaped, to match the upper jaw; the dentary bears twenty-one teeth on each side. The dentary becomes broader transversely than dorsoventrally as it turns the corners of the U-shape, due to wide and vascularised dentary shelves and alveolar margins. The two dentary bones are interdigitating at their symphysis, meaning that the lower jaw is entirely inflexible.
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Russian Academy of Sciences, Palaeontological Institute, Special Issue: 1-50. However, it was later discovered that N. valifanoi was actually a new misidentified specimen of Gobipteryx minuta. The mistake was, at least in part, due to a misidentification of the maxilla and dentary bones of the skull. In 1994, an expedition to the Gobi Desert was conducted by the American Museum of Natural History and the Mongolian Academy of Sciences, where a well preserved Gobiptetyx minuta skull was found in the Nemegt Basin.
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The size of the teeth varies greatly along the length of the jaws, lending Dimetrodon its name, which means "two measures of tooth" in reference to sets of small and large teeth. One or two pairs of caniniforms (large pointed canine-like teeth) extend from the maxilla. Large incisor teeth are also present at the tips of the upper and lower jaws, rooted in the premaxillae and dentary bones. Small teeth are present around the maxillary "step" and behind the caniniforms, becoming smaller further back in the jaw.
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Colosteids were unique compared to most stegocephalians in the fact that a pair of palatal fangs were present on the premaxillary bones at the tip of the snout. In conjunction with the forward position of these fangs, the dentary bones of the lower jaw developed a notch on either side near the symphysis (chin). The symphysis itself is formed by a rough area of bone on the left and right dentaries. This rough patch is formed by a complex system of ridges, which have been described as "brassicate" (textured like a cauliflower).
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Each side of the mouth bore 24 teeth, relatively evenly spaced save for the sixth and seventh, the dental alveoli of which have merged. Each side of these jaws is gently bowed outwards horizontally, curving more strongly towards the symphysis of the two dentary bones from the seventh alveolus forwards. The symphysis itself is relatively small and weak compared to other crocodyliforms, suggesting a very weak bite, although the bones are fully fused. The jaws are also bowed slightly, curving downwards from the articular facet and then back upwards to the symphysis of the jaws.
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Although the dentary bones assigned are nearly complete anteriorly, their morphology cannot confirm the entire depth or height of the lower jaw at the symphysis. This is because the dentary contributes only to the dorsal half of the symphysis in caseids, and the splenial most likely contributed to the symphysis, as it formed the lower part of the symphyseal region of the mandible. The assignment of these dentaries to Arisierpeton is based mainly on dental features, and to some extent on the labial surface characteristics of the bone. The teeth of these dentaries are identical to those found on the maxillae.
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By contrast, the long and slender dentary bones of the lower jaw curved slightly upwards towards the front. Unlike modern crocodilians, the eye of Terrestrisuchus was supported by a ring of bony ossicles, the sclerotic ring. Skeletal restoration showing known remains The body was relatively short and shallow, and the spine was topped by paired rows of osteoderms running down from its neck down its back. These osteoderms are described as "leaf-shaped", being relatively longer than wide with a prominent spur at the front that slides under and interlocks with the scute in front of it.
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The name Euteleostomi was coined as a monophyletic alternative that unambiguously includes the living tetrapods and is widely used in bioinformatics. The term Euteleostomi comes from Eu-teleostomi, where "Eu-" comes from the Greek εὖ meaning well or good, so the clade can be defined as the living teleostomes. Euteleostomes originally all had endochondral bone, fins with lepidotrichs (fin rays), jaws lined by maxillary, premaxillary, and dentary bones composed of dermal bone, and lungs. Many of these characters have since been lost by descendant groups, however, such as lepidotrichs lost in tetrapods, and bone lost among the chondrostean fishes.
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It may have consisted of connective tissue and skin, rather than muscle fibers, which meant that the tongue was used to move food that had accumulated between the teeth and the cheek, back to the tongue side of the cheek so that it could be further broken down by the teeth. The ornithischian cheek is absent or only weakly developed in Lesothosaurus, which supports its placement as a sister group to Genasauria. In Genasauria, the mandibular symphysis is shaped like a spout and forms at an acute angle. The mandibular symphysis is the point of fusion between the two lateral dentary bones.
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They are positioned closer to the midlines of the upper and lower jaws than are the incisors due to an inward expansion of the maxilla and dentary bones. Microgomphodon is very similar in appearance to Bauria, but differs in having a small hole called a pineal foramen at the top of the skull behind the eye sockets, a complete postorbital bar enclosing the eye sockets from behind, fewer postcanine teeth, and canines located farther back along the upper jaw. Additionally, the two taxa can be distinguished by many subtle differences relating to the shape of the skull. For example, Microgomphodon has a deeper snout, slightly larger eyes, and a sharper angle to the zygomatic arches than does Bauria.
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Each of the dentary bones is very slender, only about 22 mm wide even at the slightly thickened 'chin' of the symphysis. While L. thaumastos has a small crest running along the lingual side of the dentary to thicken it, this feature is not present in L. maghrebensis. The splenial is a very thin sheet of bone in both species; it stretches much of the way along the lower jaws, but does not participate in the symphysis as the dentary does. The anterior end of the splenial differs between the two species; in L. thaumastos it is bifurcated, whereas in L. maghrebensis the anterior end of the splenial comes to a simple point.
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A 2013 study by Lü and colleagues found that oviraptorids appear to have retained their hind limb proportions throughout ontogeny (growth), which is also a pattern mainly seen in herbivorous animals. In 2017, the Canadian palaeontologist Gregory F. Funston and colleagues suggested that the parrot- like jaws of oviraptorids may indicate a frugivorous diet that incorporated nuts and seeds. Diagrams showing the hands of specimen MPC-D 107/15 and 107/16 In 1977 Barsbold suggested that oviraptorids fed on molluscs, but Longrich and colleagues rejected the idea that they practised shell-crushing altogether, since such animals tend to have teeth with broad crushing surfaces. Instead, the shape of the dentary bones in the lower jaws of oviraptorids suggests they had a sharp-edged beak used for shearing tough food, not for cracking hard food items such as bivalves or eggs.
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Hadrocodium, whose fossils date from approximately 195 million years ago, in the early Jurassic, provides the first clear evidence of a jaw joint formed solely by the squamosal and dentary bones; there is no space in the jaw for the articular, a bone involved in the jaws of all early synapsids. Fossil of Thrinaxodon at the National Museum of Natural History The earliest clear evidence of hair or fur is in fossils of Castorocauda and Megaconus, from 164 million years ago in the mid-Jurassic. In the 1950s, it was suggested that the foramina (passages) in the maxillae and premaxillae (bones in the front of the upper jaw) of cynodonts were channels which supplied blood vessels and nerves to vibrissae (whiskers) and so were evidence of hair or fur; it was soon pointed out, however, that foramina do not necessarily show that an animal had vibrissae, as the modern lizard Tupinambis has foramina that are almost identical to those found in the nonmammalian cynodont Thrinaxodon. Popular sources, nevertheless, continue to attribute whiskers to Thrinaxodon.
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