Enigmatic teeth of small theropod dinosaurs from the Upper Cretaceous (Cenomanian–Turonian) of Uzbekistan 1 (original) (raw)
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Theropod teeth from the Lower Cretaceous Ilek Formation of Western Siberia, Russia
Trudy Zoologičeskogo instituta, 2019
A sample of 136 isolated theropod teeth from nine vertebrate localities within the Lower Cretaceous (Barremian-Aptian) Ilek Formation in West Siberia, Russia, can be separated into five dental morphotypes referred to five or six theropod taxa based on morphological characters. The Morphotype A includes small to large lateral teeth with relatively large distal denticles and smaller mesial denticles. Some of these teeth can be attributed to the Dromaeosauridae, while other teeth may belong to a basal member of the Tyrannosauroidea. The distinctly smaller lateral teeth referred to the Morphotype B are similar with Morphotype A in most respects but differ in the lack of mesial denticles and mesial carina, or having a lingually displaced mesial carina. These teeth may belong to juvenile individuals of the same dromaeosaurid taxon. The teeth belonging to Morphotype C also lack mesial denticles and differ from Morphotype B by a flattened area on the lingual side, which is also often present on the labial side. These teeth may belong to either Troodontidae or Microraptorinae, or to both groups. The mesial and lateral teeth of Morphotype E are characterized by unserrated mesial and distal carinae. These teeth most likely belong to a distinct taxon of Troodontidae with unserrated dentition. The teeth of the Morphotype D include mesial teeth with the mesial carina displaced lingually at various extent and denticles present on both carinae. The teeth with moderately displaced lingual carina can be referred to the same dromaeosaurid taxon, which lateral teeth represented by Morphotype A. The teeth with more displaced mesial carina and deeply U-shaped basal crown section belong to an indeterminate Tyrannosauroidea.
A proposed terminology of theropod teeth (Dinosauria, Saurischia)
Theropod teeth are typically not described in detail, yet these abundant vertebrate fossils are not only frequently reported in the literature, but also preserve extensive anatomical information. Often in descriptions, important characters of the crown and ornamentations are omitted, and in many instances, authors do not include a description of theropod dentition at all. The paucity of information makes identification of isolated teeth difficult and taxonomic assignments uncertain. Therefore, we here propose a standardization of the anatomical and morphometric terms for tooth anatomical subunits, as well as a methodology to describe isolated teeth comprehensively. As a corollary, this study exposes the importance of detailed anatomical descriptions with the utilitarian purpose of clarifying taxonomy and identifying isolated theropod teeth.
A Functional Explanation for Denticulation in Theropod Dinosaur Teeth
The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 2009
The serrated, or denticulated, ziphodont teeth of theropod dinosaurs display variability in their extent of denticulation. The functional model proposed here tests the hypothesis that denticles will not exist in areas that do not frequently contact the substrate. This area, defined as the ''dead-space,'' is determined by the direction the tooth moves through the fleshy substrate. The extent of denticulation, as well as the dead-space dimensions, is measured from photographs of 235 isolated and in situ theropod teeth, to determine a meaningful relationship between the two variables. Both Euclidean and geometric morphometric methods are employed, and the data are expressed in bivariate and ordination plots. The model predicts the direction of tooth movement through the curvature of the tip/apex. Tooth position and taxon are considered. The results show that the mesial margin is usually partially denticulated, while the distal margin is usually totally denticulated. Curved teeth have large dead-spaces, and tend to be less denticulated mesially. Straighter teeth are more extensively denticulated, to the point where they became symmetrical. The mesial denticulation is determined by the dead-space, and dictated by the substrate contact. The dead-space almost always predicted less extensive denticulation; a consequence of the model's limitations. Tooth curvature increases with a more distal position, due to rotation based on the proximity to the hinge. Denticulation indicates that theropods used a distally oriented puncture to modify the substrate, similar to modern analogues. Although there is little taxonomic variation, Troodontidae show unique and extreme degrees of mesial denticulation. Anat Rec, 292:1297Rec, 292: -1314Rec, 292: , 2009. V V C 2009 Wiley-Liss, Inc.
The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology, 2005
Isolated theropod teeth are common Mesozoic fossils and would be an important data source for paleoecology biogeography if they could be reliably identified as having come from particular taxa. However, obtaining identifications is confounded by a paucity of easily identifiable characters. Here we discuss a quantitative methodology designed to provide defensible identifications of isolated teeth using Tyrannosaurus as a comparison taxon. We created a standard data set based as much as possible on teeth of known taxonomic affinity against which to compare isolated crowns. Tooth morphology was described using measured variables describing crown length, base length and width, and derived variables related to basal shape, squatness, mesial curve shape, apex location with respect to base, and denticle size. Crown curves were described by fitting the power function Y ϭ a ϩ bX 0.5 to coordinate data collected from lateral-view images of mesial curve profiles. The b value from these analyses provides a measure of curvature. Discriminant analyses compared isolated teeth of various taxonomic affinities against the standard. The analyses classified known Tyrannosaurus teeth with Tyrannosaurus and separated most teeth known not to be Tyrannosaurus from Tyrannosaurus. They had trouble correctly classifying teeth that were very similar to Tyrannosaurus and for which there were few data in the standard. However, the results indicate that expanding the standard should facilitate the identification of numerous types of isolated theropod teeth. 2005 Wiley-Liss, Inc.
Journal of Vertebrate Paleontology, 2019
Richardoestesia is an enigmatic theropod dinosaur originally described on the basis of a pair of dentaries (holotype of R. gilmorei Currie et al., 1990) and isolated distinctive teeth, which are abundant in the Upper Cretaceous of North America. Richardoestesia asiatica (Nesov, 1995) is represented by numerous isolated teeth from the Upper Cretaceous Khodzhakul, Bissekty, and Aitym formations of Uzbekistan. Richardoestesia asiatica shows the typical features of the genus, including small mesial and distal denticles (on average 28.4 and 34.5 denticles per 5 mm, respectively), rectangular or knob-like denticles, and an apically convex distal margin of the tooth crown. The sample of R. asiatica has a large proportion of straight teeth (morphotype A) and includes several types of recurved teeth related to their position in the jaws (morphotypes BE). This species differs from R. gilmorei in the presence of straight teeth and fully serrated mesial carinae. Richardoestesia asiatica cannot be distinguished from R. isosceles Sankey, 2001, which we consider a nomen dubium due, in part, to the imperfect nature of its holotype. Discriminant function analysis (DFA) of dental measurements found no distinction between the samples from Khodzhakul and Bissekty formations. In DFA including North American samples, the morphospace of R. asiatica completely overlaps that of the sample from the Lance Formation (Maastrichtian) of Wyoming and only partly overlaps with that of the sample from the Milk River Formation (Santonian) of Alberta.
Small theropod teeth from the Upper Jurassic coal mine of Guimarota (Portugal)
Paläontologische Zeitschrift, 1998
With 8 figures and 1 table Kurzfassung: Isolierte Z~ihne theropoder Dinosaurier aus dem Oberen Jura der Kohlengrube Guimarota (bei Leiria, Portugal) werden beschrieben und abgebildet. Die h~tufigsten Zahnfunde ~ihneln morphologisch den Bezahnungen der oberjurassischen Theropoden Archaeopteryx und Compsognathus. Ein Morphotyp deutet auf das Vorhandensein eines Allosauriden hin. Sechs weitere Morphotypen von Theropoden-Z~ihnen zeigen grol3e Ahnlichkeiten mit kreidezeitlichen Formen, wie Dromaeosauriden, Troodontiden, Tyrannosauriden, Richardoestesia und Paronychodon. Fiir diese Gruppen wird ein spatjurassischer Ursprung diskutiert, wie er von einigen Autoren bereits vermutet wurde.
Journal of Vertebrate Paleontology, 2019
Richardoestesia is an enigmatic theropod dinosaur originally described on the basis of a pair of dentaries (holotype of R. gilmorei Currie et al., 1990) and isolated distinctive teeth, which are abundant in the Upper Cretaceous of North America. Richardoestesia asiatica (Nesov, 1995) is represented by numerous isolated teeth from the Upper Cretaceous Khodzhakul, Bissekty, and Aitym formations of Uzbekistan. Richardoestesia asiatica shows the typical features of the genus, including small mesial and distal denticles (on average 28.4 and 34.5 denticles per 5 mm, respectively), rectangular or knob-like denticles, and an apically convex distal margin of the tooth crown. The sample of R. asiatica has a large proportion of straight teeth (morphotype A) and includes several types of recurved teeth related to their position in the jaws (morphotypes BE). This species differs from R. gilmorei in the presence of straight teeth and fully serrated mesial carinae. Richardoestesia asiatica cannot be distinguished from R. isosceles Sankey, 2001, which we consider a nomen dubium due, in part, to the imperfect nature of its holotype. Discriminant function analysis (DFA) of dental measurements found no distinction between the samples from Khodzhakul and Bissekty formations. In DFA including North American samples, the morphospace of R. asiatica completely overlaps that of the sample from the Lance Formation (Maastrichtian) of Wyoming and only partly overlaps with that of the sample from the Milk River Formation (Santonian) of Alberta.
The dentition of Megalosauridae (Theropoda: Dinosauria)
Acta Palaeontologica Polonica, 2014
Theropod teeth are particularly abundant in the fossil record and frequently reported in the literature. Yet, the dentition of many theropods has not been described comprehensively, omitting details on the denticle shape, crown ornamentations and enamel texture. This paucity of information has been particularly striking in basal clades, thus making identification of isolated teeth difficult, and taxonomic assignments uncertain. We here provide a detailed description of the dentition of Megalosauridae, and a comparison to and distinction from superficially similar teeth of all major theropod clades. Megalosaurid dinosaurs are characterized by a mesial carina facing mesiolabially in mesial teeth, centrally positioned carinae on both mesial and lateral crowns, a mesial carina terminating above the cervix, and short to well-developed interdenticular sulci between distal denticles. A discriminant analysis performed on a dataset of numerical data collected on the teeth of 62 theropod taxa reveals that megalosaurid teeth are hardly distinguishable from other theropod clades with ziphodont dentition. This study highlights the importance of detailing anatomical descriptions and providing additional morphometric data on teeth with the purpose of helping to identify isolated theropod teeth in the future.