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Anatomy of Sinosauropteryx prima from Liaoning, Northeastern China

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Abstract

A spectacular pair of Sinosauropteryx skeletons from Jurassic–Cretaceous strata of Liaoning in northeastern China attracted worldwide notoriety in 1996 as the first dinosaurs covered with feather-like structures. Sinosauropteryx prima is important not only because of its integument, but also because it is a basal coelurosaur and represents an important stage in theropod evolution that is poorly understood. Coelurosauria, which includes (but is not limited to) dromaeosaurids, ornithomimosaurs, oviraptorosaurs, troodontids, and tyrannosaurids, formed the most important radiation of Cretaceous carnivorous dinosaurs in the Northern Hemisphere. It also includes Aves. Sinosauropteryx prima has a number of characters that were poorly preserved in known specimens of the closely related Compsognathus longipes from Europe. These include the longest tail known for any theropod and a three-fingered hand dominated by the first digit, which is longer and thicker than either of the bones of the forearm. Both specimens have a thick coat of feather-like structures, which seem to be simple branching structures. The claim that one skeleton of Sinosauropteryx has preserved the shape of the liver is unsupportable, if only because the fossil had collapsed into a single plane, which would have distorted any soft, internal organs.

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... In this regard, the semilunate carpal of Megaraptor and Australovenator differs from the Figure 1. Humerus in lateral (C-I) and medial (A-B,J) views of: A, Megaraptor proximodistally shallower semilunate carpal of basal tetanurans (e.g., Allosaurus, Acrocanthosaurus) and basal coelurosaurs, such as Tanycolagreus (Carpenter et al., 2005), Sinosauropteryx (Currie and Chen, 2001), Scipionyx (Dal Sasso and Maganuco, 2011), Coelurus, and ornithomimosaurs (Kobayashi and Lü, 2003). In sum, megaraptorids retained a carpal morphology diagnostic at the level of Tetanurae. ...
... The proximal concavity on metacarpal I and its associated proximomedial process are less well developed in basal coelurosaurs (e.g., Scipionyx; Dal Sasso and Maganuco, 2011), basal tyrannosauroids (e.g., Tanycolagreus; Carpenter, Miles and Cloward, 2005), and paravians (e.g., Deinonychus; Ostrom, 1976), in which the proximal margin of metacarpal I is almost straight and a proximomedial process is lacking. The only possible exception among basal coelurosaurs is the compsognathid Sinosauropteryx, which appears to posseses a metacarpal I that is proximally notched and bears an associated proximomedial process (Figure 6; Currie and Chen, 2001). In the Australian megaraptorids Australovenator and " Rapator " the lateral margin of metacarpal I is straight (in dorsal and ventral views), and the lateral surface for articulation with metacarpal II is slightly faced dorsally (fig. ...
... Furthermore, in the megaraptorans Australovenator and Fukuiraptor, the ungual of digit I is much shorter than the ulna, representing approximately half of its length. Basal tetanurans that evolved an enlarged ungual in manual digit I are the compsognathid Sinosauropteryx (Currie and Chen, 2001), and the megalosauroids Baryonyx and Torvosaurus (Galton and Jensen, 1979; Charig and Milner, 1997). In the original description of Megaraptor (Novas, 1998), it was remarked that the ungual phalanx bore a sharp longitudinal ventral keel. ...
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Novas, F.E., Aranciaga Rolando, A.M. and Agnolín, F.L. 2016. Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy. Memoirs of Museum Victoria 74: 49–61. General comparisons of the manual elements of megaraptorid theropods are conducted with the aim to enlarge the morphological dataset of phylogenetically useful features within Tetanurae. Distinctive features of Megaraptor are concentrated along the medial side of the manus, with metacarpal I and its corresponding digit being considerably elongated. Manual ungual of digit I is characteristically enlarged in megaraptorids, but it is also transversely compressed resulting in a sharp ventral edge. We recognize two derived characters shared by megaraptorans and coelurosaurs (i.e., proximal end of metacarpal I without a deep and wide groove continuous with the semilunar carpal, and metacarpals I and II long and slender), and one derived trait similar to derived tyrannosauroids (i.e., metacarpal III length <0.75 length of metacarpal II). However, after comparing carpal, metacarpal and phalangeal morphologies, it becomes evident that megaraptorids retained most of the manual features present in Allosaurus. Moreover, Megaraptor and Australovenator are devoid of several manual features that the basal tyrannosauroid Guanlong shares with more derived coelurosaurs (e.g., Deinonychus), thus countering our own previous hypothesis that Megaraptora is well nested within Tyrannosauroidea.
... Compsognathidae were not included in the cladistic analysis due to lack of information of the quadrate morphology and bad preservations of this bone. Indeed, the quadrates of all compsognathids such as Compsognathus corallestris (Ostrom, 1978; Peyer, 2006), Juravenator starki (Chiappe and Göhlich, 2010), Scipionyx samniticus (Dal Sasso and Signore, 1998; Dal Sasso and Maganuco, 2011), Huxiagnathus orientalis (Hwang et al., 2004), Sinocalliopteryx gigas (Ji et al., 2007) and Sinosauropteryx prima (Currie and Chen, 2001) have been flattened by post mortem deformation and are either poorly preserved or obscured by other bones. The data matrix encompasses 98 equally weighted discrete morphological characters related to the quadrate (Appendices 1 & 2) and allowing to test and propose several quadrate synapomorphies for the 56 taxa coded (Appendix 3.1;Figure S5). ...
... beneath the quadrate head (Molnar, 1991; Brochu, 2003, figure 7). CNJ 79; Ostrom, 1978; Peyer, 2006); Scipionyx samnicicus (Dal Sasso and Maganuco, 2011); Juravenator starki (Chiappe and Göhlich, 2010); Sinosauropteryx prima (Currie and Chen, 2001). The quadrate anatomy of compsognathids is one of poorest known among nonavian theropods. ...
... The quadrate anatomy of compsognathids is one of poorest known among nonavian theropods. A thorough description of the bone was only given by Dal Sasso and Maganuco (2011) for Scipionyx samnicicus, and the quadrate of other Compsognathidae was either briefly described, as in Compsognathus longipes (Ostrom, 1978; Peyer, 2006), Juravenator starki (Chiappe and Göhlich, 2010), and Sinosauropteryx prima (Currie and Chen, 2001), or not described at all, as in Huxiagnathus orientalis (Hwang et al., 2004) and Sinocalliopteryx gigas (Ji et al., 2007). Although most of compsognathid specimens with cranial material tend to be extremely well preserved and almost complete, their remains are found in two dimensions on slabs of fine grained limestone, usually in articulations with other cranial PrePrints bones, or associated with them. ...
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The skull-bone quadrate in nonavian theropods is very diverse morphologically alongside the disparity of the group as a whole. However this disparity has been underestimated for taxonomic purposes. In order to evaluate the phylogenetic potential and investigate the evolutionary transformations of the quadrate, we conducted a Catalano-Goloboff phylogenetic morphometric analysis as well as a cladistic analysis using 98 discrete quadrate related characters. The cladistic analysis provides a fully resolved tree mirroring to some degree the classification of nonavian theropods. The quadrate morphology by its own provides a wealth of data with strong phylogenetic signal and allows inference of major trends in the evolution of this bone. Important synapomorphies include: for Abelisauroidea, a lateral ramus extending to the ectocondyle; for Tetanurae, the absence of the lateral process; for Spinosauridae, a medial curvature of the ventral part of the pterygoid ramus occurring just above the mandibular articulation; for Avetheropoda, an anterior margin of the pterygoid flange formed by a roughly parabolic margin; and for Tyrannosauroidea, a semi-oval pterygoid flange shape in medial view. The Catalano-Goloboff phylogenetic morphometric analysis reveals two main morphotypes of the mandibular articulation of the quadrate linked to function. The first morphotype, characterized by an anteroposteriorly broad mandibular articulation with two ovoid/subcircular condyles roughly subequal in size, is found in Ceratosauria, Tyrannosauroidea and Oviraptorosauria. This morphotype allows a very weak displacement of the mandible laterally. The second morphotype is characterized by an elongate and anteroposteriorly narrow mandibular articulation and a long and parabolic/sigmoid ectocondyle. Present in Megalosauroidea, Carcharodontosauridae and Dromaeosauridae, this morphotype permits the lower jaw rami to be displaced laterally when the mouth opened.
... Alternatively, conspicuous face markings could serve as a warning of a physical deterrent, such as a weapon or armor [17,22,23]. Although the theropod had an enlarged claw on each hand [24], the animal's small size makes it unlikely that it posed any real threat to its likely much larger theropod predators, making this function of the bandit mask unlikely. ...
... Banded tails have been proposed as a way of confusing predators or drawing attention away from more vital body parts [18]. The tail of Sinosauropteryx was the longest of any known theropod relative to body length [24]. Due to this length, it is unlikely that the animal could hold it in a perfectly horizontal position consistently, which would be necessary for a countershaded pattern to be effective. ...
... Several tyrannosauroids are contemporaneous with Sinosauropteryx [26]. Although these tyrannosauroids were small for the clade [26], they would likely have been more than capable of tackling the diminutive compsognathid, which appears to have not reached sizes much greater than a meter in length [24]. Modern avian predators rely heavily on their exceptional vision to hunt, and as such it is likely that their forebears, the theropods, also had excellent visual capabilities [27]. ...
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Countershading is common across a variety of lineages and ecological time. A dark dorsum and lighter ventrum helps to mask the three-dimensional shape of the body by reducing self-shadowing and decreasing conspicuousness, thus helping to avoid detection by predators and prey. The optimal countershading pattern is dictated by the lighting environment, which is in turn dependent upon habitat. With the discovery of fossil melanin, it is possible to infer original color patterns from fossils, including countershading. Applying these principles, we describe the pattern of countershading in the diminutive theropod dinosaur Sinosauropteryx from the Early Cretaceous Jehol Biota of Liaoning, China. From reconstructions based on exceptional fossils, the color pattern is compared to predicted optimal countershading transitions based on 3D reconstructions of the animal’s abdomen, imaged in different lighting environments. Reconstructed patterns match well with those predicted for animals living in open habitats. Jehol is presumed to have been a predominantly closed forested environment ], but our results indicate a more heterogeneous range of habitats. Sinosauropteryx is also shown to exhibit a “bandit mask,” a common pattern in many living vertebrates, particularly birds, that serves multiple functions including camouflage. Sinosauropteryx therefore shows multiple color pattern features likely related to the habitat in which it lived. Our results show how reconstructing the color of extinct animals can inform on their ecologies beyond what may be obvious from skeletal remains alone.
... The dentary and maxillary teeth have the same denticle density, about 7 denticles/mm. The first two dentary teeth are almost cylindrical and resemble the premaxillary teeth, while the more posterior dentary teeth look like the maxillary teeth, as in Sinosauropteryx (Currie & Chen 2001). The first dentary tooth has a FABL of 1.54 mm and a crown height of 5.30 mm, while the fourth visible dentary tooth has a FABL of 4.58 mm and a crown height of 8.16 mm. ...
... The first dentary tooth has a FABL of 1.54 mm and a crown height of 5.30 mm, while the fourth visible dentary tooth has a FABL of 4.58 mm and a crown height of 8.16 mm. Unfortunately, because their edges are covered by matrix, it is not possible to tell whether the anterior dentary teeth and the premaxillary teeth are completely unserrated as in Sinosauropteryx (Currie & Chen 2001), Compsognathus (Ostrom 1978) and many other coelurosaurs. The posterior dentary teeth of Huaxiagnathus are sharply bent posteriorly, as in Sinosauropteryx. ...
... The posterior cervicals have low neural spines that are about twice as long than they are tall. The postzygapophyses in the anterior cervicals are stout and rounded , with small epipophyses as in Sinosauropteryx (Currie & Chen 2001). The postzygapophyses become more elongate and dorsoventrally slender in the posterior cervicals. ...
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A new, large compsognathid theropod, Huaxiagnathus orientalis gen. et sp. nov., from the Early Cretaceous Yixian Formation deposits of Liaoning Province, People's Republic of China is described. The holotype specimen is nearly complete, lacking only the distal portion of the tail. It is the second largest theropod taxon discovered from Jehol Group sediments. Like all compsognathids, Huaxiagnathus has short forelimbs and a relatively unspecialised coelurosaur body plan. Previously, fairly complete skeletons existed for only two small‐bodied taxa of compsognathids, Compsognathus longipes from the Late Jurassic of Western Europe and Sinosauropteryx prima, also from the Yixian. The phylogenetic position of Huaxiagnathus orientalis was analysed using an extensive matrix of theropod characters from many taxa. Huaxiagnathus orientalis fell out at the base of the Compso‐gnathidae, as it lacks the forelimb adaptations of more derived compsognathids. The addition of Huaxiagnathus and the two other compsognathid species to our data matrix resulted in the placement of Compsognathidae near the base of Maniraptora. Furthermore, Alvarezsauridae, Paraves, and a monophyletic Therizinosauroidea + Oviraptorosauria clade fall out in an unresolved trichotomy in the strict consensus of our most parsimonious trees.
... Comparison of the foot skeletons of the small Jehol dinosaurs Caudipteryx sp. (IVPP V 12430) (Zhou et al., 2000) and Sinosauropteryx prima (NIGP 127587) (Currie and Chen, 2001) with Grallator isp. (NGMC V2115B) shows (Xing et al., 2009) that it is more similar to the former. ...
... The best preserved YMZ-T13-L2 shows consistency with Sinosauropteryx prima (NIGP 127587) pedal morphology (Fig. 8). Sinosauropteryx and Compsognathus are similar (Currie and Chen, 2001) and based on computer simulations, Compsognathus appears to have been able to run very fast reaching maximum speeds up to nearly 64 km/h (=17.8 m/s) (Sellers and Manning, 2007). The high running speed estimated at up to 22.5 km/h (= 6.2 m/s) for the Minisauripus trackmaker from the YMZ sample is at least consistent with rapid movement by these small theropod trackmakers (Table 2 ). ...
... The histological analysis is corroborated by the lack of complete fusion of any of the neural arches to the centra in the vertebral column, which suggests that IVPP V15709 is an immature individual, although neural arch fusion is not necessarily a good indicator of developmental stage in archosaurs (Brochu 1996; Irmis 2007). Additionally, the cortical bone preserved on the lower jaw, metatarsus, tibia and femur has the striated, 'scarred' texture (Fig. 22) seen on these bones in many immature archosaurs, including extant crocodilians and birds (Dal Sasso & Maganuco 2011), sauropodomorph embryos (Reisz et al. 2005; Salgado et al. 2005 ), and the presumed early juvenile theropods Scipionyx (Dal Sasso & Maganuco 2011), Juravenator (Göhlich et al. 2006) and Sinosauropteryx (Currie & Chen 2001). This texture diminishes with increasing ontogenetic age. ...
... The gracile hand of Aorun with particularly thin metacarpals III and IV is more similar to the hands of derived non-avian coelurosaurs (Gishlick & Gauthier 2007) than to the hands of more basal theropods, where digit III is generally robust and proximally expanded (Rauhut 2003a). Metacarpal II is mediolaterally wider than the other metacarpals, and its first phalanx has a diameter greater than that of the radius, as in alvarezsauroids (Choiniere et al. 2010b ) and compsognathids (Currie & Chen 2001; Hwang et al. 2004; Dal Sasso & Maganuco 2011). Manual ungual II-2 is much larger than the other manual unguals, a feature characteristic of all alvarezsauroids (Choiniere et al. 2010b). ...
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We describe the anatomy of a new coelurosaurian theropod Aorun zhaoi gen. et sp. nov., from the Middle–Late Jurassic of Xinjiang, China. Histological analysis of the holotype and only known specimen shows that the new taxon is represented by the skeleton of a juvenile individual aged no more than one year. A phylogenetic analysis of theropod relationships places Aorun as a basal member of the Coelurosauria. Although the sole use of a sub-adult ontogenetic exemplar is potentially problematic for phylogenetic reconstruction, we show that the phylogenetic position of Aorun as a member of Coelurosauria is robust to the exclusion of characters known to change during theropod ontogeny. Aorun is the seventh theropod taxon, and temporally oldest coelurosaur, known from the Shishugou Formation, which has one of the most taxonomically diverse Jurassic coelurosaurian theropod faunas in the world.http://zoobank.org/urn:lsid:zoobank.org:pub:5CC73577-9EB3-47AB-9983-1677B278EFFD
... The claw morphology of Juravenator is characteristic in being very high proximally and tapering abruptly around the midpoint (Chiappe and G€ ohlich, 2010). The claws in Sinosauropteryx and Tanycolagreus (Currie and Chen, 2001;Carpenter et al., 2005) are significantly less curved than in spinosaurids. Tyrannosaurids (e.g., Tyrannosaurus, Albertosaurus) differ in having a flexor tubercle reduced to a small convexity (Porfiri et al., 2014: character 143) and shallower vascular grooves . ...
... Nevertheless, the function of manual unguals has received less interest (Lautenschlager, 2014). Ostrom (1969) and Currie and Chen (2001), for example, proposed that Deinonychus and Sinosauropteryx used their claws for grasping their prey. Lautenschlager (2014) pointed out that some therizinosaur taxa used their claws in a generalist fashion, whereas other taxa were functionally adapted for using the claws as grasping hooks during foraging. ...
Article
An enlarged theropod manual ungual (CSC1-4) from the Weald facies of Spain is described. The claw was found in the fossil locality of Caña Seca 1, Teruel province, within the El Castellar Formation of early Barremian (Early Cretaceous) in age. CSC1-4 is morphologically closer to megalosauroids than to any other theropod clade bearing enlarged manual claws and shows the greatest similarity to the manual ungual of digit I of Baryonyx walkeri. Both CS1-4 and this taxon share a particularly enlarged, elongated and transversely wide manual claw. CSC1-4, however, differs from Baryonyx´s ungual in having less curvature, a straight dorsal edge in the proximal part, slightly more width above the grooves than below, and a certain asymmetry, with the lateral face more flattened. Taking into account the paleogeographic and temporal context, these considerations suggest that they are closely related but distinct spinosaurid taxa. The presence of an enlarged manual claw in spinosaurids has been invoked as an anatomical feature typically associated with scavenging and hunting habits, as well as digging behaviour. The spinosaurid record from the Barremian of the Iberian Peninsula shows that members of this clade favored freshwater environments with some marine influence in this part of Europe.
... Among neotheropods, the position of the last caudal vertebra bearing a distinct neural spine is variable, and is not necessarily related to the total number of caudal vertebrae. In Dilophosaurus the 22 nd caudal vertebra is the last one bearing a neural spine (Welles, 1984); in Allosaurus it occurs between the 35 th and the 38 th position (Madsen, 1976); in Tyrannosaurus the neural spines reduce after the 13 th and the last one is at the 27 th position (Brochu, 2003); in Harpymimus (Kobayashi, 2004) and Nomingia (Barsbold et al., 2000) the neural spines become low crests after the 15 th position; in Sinosauropteryx, which has the highest known number of caudals (Rauhut, 2003), the neural spines reduce after the 10 th position and disappear at the 18 th (Currie & Chen, 2001); whereas in paravians there are usually no more than 9 proximal caudals bearing distinct neural spines (Ostrom, 1969; Forster et al., 1998; Mayr et al., 2007). Transverse processes -The absence of transverse processes shows that MSNM V6408 must have come from the part of the tail distal to the transition point (Russell , 1972; Gauthier, 1986; Tykoski, 2005). ...
... MSNM 6408 differs from coelophysid distal caudals in the relatively less elongate centra and in the presence of spinal laminae (Wilson et al., 2003, Appendix ), and from Dilophosaurus and several basal (non-coelurosaurian) tetanurans in the shape and robustness of the neural spine and in the relatively less elongate prezygapophyses (Madsen, 1976; Rauhut, 2003; Welles, 1984). It differs from the distal caudals of most coelurosaurs in the presence of a robust neural spine (Brochu, 2003; Currie & Chen, 2001; Kobayashi, 2004; Ostrom, 1969), and from oviraptorosaurs in the relatively narrower and more elongate centrum (Makovicky & Sues, 1998; Barsbold et al., 2000). Among known theropod middle and distal caudals, the combination of features observed in MSNM V6408 resembles that of some ceratosaur middle and distal caudals: namely, the caudal vertebrae have transversely wide neural spines (Coria & Salgado, 2000: fi g. 9A; Madsen & Welles, 2000; Novas et al., 2004; O&apos;Connor, 2007), and possess distinct neural spines and coalesced postzygapophyses (Bonaparte, 1996; Coria & Salgado, 2000). ...
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We describe a near-complete distal caudal vertebra from an Upper Cretaceous theropod, discovered in the Kem Kem Beds (Cenomanian) of Tafi lalt, Morocco. The specimen exhibits an extremely unusual combination of features , and we herein erect a new species, Kemkemia auditorei gen. et sp. nov. The specimen differs from other theropod distal caudal vertebrae in the presence of a relatively infl ated neural canal, strongly reduced zygapophyses, a low but very robust neural spine bearing shallow lateral fossae, a mediolaterally concave dorsal surface of the neural spine, and coalescence of the postzygapophyses in a position more proximal than the region where neural spines are absent. Although Kemkemia shares some derived features with neoceratosaurs, we provisionally refer it to Neotheropoda incertae sedis, pending the discovery of more complete material. Several distal caudal vertebrae from the Maastricthian of India are similar to Kemkemia, and may belong to a closely related taxon.
... In this respect Megaraptor differs from Aerosteon riocoloradensis (MCNA-PV-3137) in which most of the available cervicals bear a broad and flat ventral keel. The hemispherical cranial articular surface of the cervical centra resemble those of Monolophosaurus, Allosaurus, Sinraptor, Acrocanthosaurus, Torvosaurus, spinosaurids, and the basal coelurosaurs Compsognathus and Ornitholestes (Rauhut, 2003), whereas the cervical centra are slightly biconcave in tyrannosaurids, Sinosauropteryx, Scipionyx and Coelurus, among other coelurosaurs (Currie and Chen, 2001;Dal Sasso and Maganuco, 2011;Carpenter et al., 2005). Hemispherical cranial articular surface of centrum is present at least up to Cv9 (the centrum of Cv10 is lost), and D1 exhibits a flat cranial articular surface. ...
... The gastral elements are represented by several medial components that are paddle-like medially. The shape of the gastralia is very similar to those of Australovenator (Hocknull et al., 2009), tyrannosaurids (Claessens, 2004) and carcharodontosaurids , being different from the stick-shaped condition present in compsognathids, ornithomimids, allosaurids, sinraptorids, and dromaeosaurids (Norell and Makovicky, 1997;Currie and Chen, 2001;Brusatte and Sereno, 2008). In Sinocalliopteryx the medial gastralia are large and similar in shape to those of Megaraptor (Xing et al., 2012). ...
... In this respect Megaraptor differs from Aerosteon riocoloradensis (MCNA-PV-3137) in which most of the available cervicals bear a broad and flat ventral keel. The hemispherical cranial articular surface of the cervical centra resemble those of Monolophosaurus, Allosaurus, Sinraptor, Acrocanthosaurus, Torvosaurus, spinosaurids, and the basal coelurosaurs Compsognathus and Ornitholestes (Rauhut, 2003), whereas the cervical centra are slightly biconcave in tyrannosaurids, Sinosauropteryx, Scipionyx and Coelurus, among other coelurosaurs (Currie and Chen, 2001;Dal Sasso and Maganuco, 2011;Carpenter et al., 2005). Hemispherical cranial articular surface of centrum is present at least up to Cv9 (the centrum of Cv10 is lost), and D1 exhibits a flat cranial articular surface. ...
... The gastral elements are represented by several medial components that are paddle-like medially. The shape of the gastralia is very similar to those of Australovenator (Hocknull et al., 2009), tyrannosaurids (Claessens, 2004) and carcharodontosaurids , being different from the stick-shaped condition present in compsognathids, ornithomimids, allosaurids, sinraptorids, and dromaeosaurids (Norell and Makovicky, 1997;Currie and Chen, 2001;Brusatte and Sereno, 2008). In Sinocalliopteryx the medial gastralia are large and similar in shape to those of Megaraptor (Xing et al., 2012). ...
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Megaraptorids are a group of predatory dinosaurs that inhabited Gondwana from Cenomanian to Santonian times (Late Cretaceous). Phylogenetic relationships of megaraptorids have been matter of recent debate, being alternatively interpreted as basal coelurosaurs, carcharodontosaurian allosauroids, megalosauroids, and basal tyrannosauroids. One of the main reasons for such different interpretations is the incomplete nature of most available megaraptorid skeletons and, in particular, the scarce information about their cranial anatomy. Here we describe a partially preserved skeleton of a juvenile specimen of Megaraptor namunhuaiquii that provides substantial new information about the cranial morphology of this Patagonian taxon. The specimen comes from the Upper Cretaceous (TuronianeConiacian) of the Portezuelo Formation, northwestern Patagonia, Argentina. The anatomy of the new specimen bolsters the recently proposed hypothesis that megaraptorids are nested within Coelurosauria, and possibly within Tyrannosauroidea. The most relevant features that megaraptorans share with tyrannosauroids include several foramina on the premaxillary body, extremely long and straight prenarial process of the premaxilla, incisiviform premaxillary teeth with a D-shaped cross-section, and cranially expanded supratemporal fossae separated from each other by a sharp sagittal median crest on frontals, which was presumably extended caudally above the parietals (not preserved). Information gathered from the present specimen allows to make for the first time a reconstruction of the skull of Megaraptor and hypothesize about evolutionary trends within Tyrannosauroidea.
... Metrische und morphologische Vergleiche mit dem Holotypus von Sinosauropteryx (Exempl. NIGP 127586; vgl.CHEN et al. 1998;CURRIE & CHEN 2001), dem einzigen bekannten Compsognathiden mit einem fast vollständigen Schwanz, bestehend aus 64 Wirbeln, legen nahe, dass die 44 bei Juravenator erhaltenen Schwanzwirbel wohl nur } der Gesamtlänge des Schwanzes ausmachen. Diese Vergleichsuntersuchungen lassen erahnen, dass der Schwanz von Juravenator wohl sehr lang war – vielleicht der proportional längste von allen bisher bekannten Theropoden. ...
... " This kind of major scientific failing goes back at least 15 years in this field e.g. when Currie and Chen (2001) produced subjective inky outlines of integumental structures that are meant to represent no less important structures than branched feathers. Most deserving of censure, however, in that same study was, " [u]nder magnification, the margins of the larger structures arc darker along the edges but light medially, which suggests that they may have been hollow. ...
... Importantly, there is no ulnare in the most bird-like dinosaurs (Oviraptorosauria, Dromaeosauridae, Troodontidae [71][72][73][74][75]), which are known from several well-preserved, articulated specimens ( Figure 9). In many theropods, the ulnare was mistakenly considered present, having been confused with other elements, such as the intermedium [56], distal carpal 2 [76][77][78], and the posterior-distal dc3, which in modern adult birds fuses to the carpometacarpus [79,80]. In early dinosaurs, some bird-like dinosaurs, and Mesozoic birds, dc3 is observable as a separate bone (blue in Figure 9) that has been variably labelled as the ulnare, ''element x'' [81][82][83][84], or dc3 [85]. ...
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From early dinosaurs with as many as nine wrist bones, modern birds evolved to develop only four ossifications. Their identity is uncertain, with different labels used in palaeontology and developmental biology. We examined embryos of several species and studied chicken embryos in detail through a new technique allowing whole-mount immunofluorescence of the embryonic cartilaginous skeleton. Beyond previous controversy, we establish that the proximal-anterior ossification develops from a composite radiale+intermedium cartilage, consistent with fusion of radiale and intermedium observed in some theropod dinosaurs. Despite previous claims that the development of the distal-anterior ossification does not support the dinosaur-bird link, we found its embryonic precursor shows two distinct regions of both collagen type II and collagen type IX expression, resembling the composite semilunate bone of bird-like dinosaurs (distal carpal 1+distal carpal 2). The distal-posterior ossification develops from a cartilage referred to as "element x," but its position corresponds to distal carpal 3. The proximal-posterior ossification is perhaps most controversial: It is labelled as the ulnare in palaeontology, but we confirm the embryonic ulnare is lost during development. Re-examination of the fossil evidence reveals the ulnare was actually absent in bird-like dinosaurs. We confirm the proximal-posterior bone is a pisiform in terms of embryonic position and its development as a sesamoid associated to a tendon. However, the pisiform is absent in bird-like dinosaurs, which are known from several articulated specimens. The combined data provide compelling evidence of a remarkable evolutionary reversal: A large, ossified pisiform re-evolved in the lineage leading to birds, after a period in which it was either absent, nonossified, or very small, consistently escaping fossil preservation. The bird wrist provides a modern example of how developmental and paleontological data illuminate each other. Based on all available data, we introduce a new nomenclature for bird wrist ossifications.
... The small vertebrae herein described have strongly elongated prezygapophyses, extending more than half of the centrum length, as is typical of most coelurosaurs. The presence of a bifurcated neural spine is a character shared by many theropods including tetanurans as Allosaurus or Acrocanthosaurus and coelurosaurs as Sinosauropteryx (Currie and Chen, 2001; Currie and Carpenter, 2000; Madsen, 1976). Although, a similar bifurcated neural spine was not reported in compsognathids as Compsognathus (Peyer, 2006). ...
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The Andrés fossil-site is one of the most noteworthy examples of an association of multiple vertebrate taxa preserved in the same quarry from the Late Jurassic of the Portuguese Lusitanian Basin. The quarry is known since the 90s decade when it was described a specimen assigned to Allosaurus fragilis, which constituted the first evidence of this species of tetanuran theropods out of the North American Late Jurassic (Pérez-Moreno et al., 1999). Posteriorly, several systematic fieldworks were conducted, resulting on the discovery of a great amount of vertebrate remains. The fossils collected represent a diverse vertebrate fauna, including fishes, sphenodonts, crocodylomorphs, pterosaurs, and several dinosaur forms (Malafaia et al., 2010). Dinosaur elements, particularly those assignable to Allosaurus, are the most abundant fossils. The collection of Allosaurus remains from Andrés includes abundant cranial and post-cranial remains of at least two individuals, which constitutes the most complete evidence of this tetanuran dinosaur known at the moment in the Portuguese record. Other dinosaur groups are represented mainly by isolated elements belonging to theropods, sauropods and ornithopods. Among these are scarce teeth recognized as dromaeosaurid theropods. Herein, we report some caudal vertebrae of small sized theropods collected in Andrés with morphology compatible with some coelurosaurs.
... With the most active maggot decomposition of the cadaver from the centre of the cadaver outward it seems reasonable to expect the feathers to be predominantly preserved in the final stages along the margins of the cadavers. This has been an argument used to account for the preservation of integumental structures in fossil birds and non-avian dinosaurs as a halo around the fossils (Currie & Chen, 2001). However, a few points are noteworthy. ...
Article
Fresh ostrich cadavers were exposed in a natural environment (two on land and one in a shallow pool of water) to investigate decomposition and possible opisthotonus. The decomposition followed through to skeletonization of the ostrich cadavers by maggots, the primary agents of decay. During ostrich decomposition, tissue was consumed sequentially from the soft matrix tissue of muscles to fibrous and ligamentous tissue (both comprising collagen). The feathers (comprising β-keratin) were not consumed. The entire decomposition process was completed in 5 days. Towards the latter stages of the experiment, the cadavers on land showed stages of strong upward arching of the neck which fell short of the opisthotonic posture, while the cadaver in the pool showed the classic form of opisthotonus, strongly supporting the post-mortem hypothesis of the phenomena. Comparisons are made with opisthotonus in the theropod dinosaur, Sinosauropteryx.
... pages of supplementary material). Moreover, the pace of discovery and description of new fossil specimens has steadily increased across a variety of journals and the appearance of in-depth papers on early birds and closely related non-avian theropods (many with feathers) is ever more frequent (Chiappe et al. 1999, 2014, Currie and Chen 2001, Clarke and Norell 2002, Hwang et al. 2002, Norell and Xu 2005, Clarke et al. 2006, Lamanna et al. 2006, Li et al. 2012, 2014a, O'Connor et al. 2012, Chinsamy et al. 2013). Undoubtedly, studies on the diversity of non-avian dinosaurs and early birds from the Daohugou and Jehol Biotas have resulted in a wealth of novel information about the anatomy of these animals and its relevance for understanding the origin of birds and of their flight. ...
Article
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Birds are maniraptoran theropod dinosaurs. The evidence supporting the systematic position of Avialae as a derived clade within Dinosauria is voluminous and derived from multiple independent lines of evidence. In contrast, a paucity of selectively chosen data weakly support, at best, alternative proposals regarding the origin of birds and feathers. Opponents of the theory that birds are dinosaurs have frequently based their criticisms on unorthodox interpretations of paleontological data and misrepresentation of phylogenetic systematic methods. Moreover, arguments against the nested position of Avialae in Dinosauria have often conflated the logically distinct questions of avian origins, the evolution of flight, and the phylogenetic distribution of feathers. Motivated by a Perspectives article with numerous factual inaccuracies that recently appeared in The Auk, we provide a review of the full complement of facts pertaining to the avian origins debate and address the misplaced criticisms raised in that opinion paper.
... An independent assessment cannot be made of van der Reest et al.'s interpretive drawings without adequate photos or, it becomes an " appeal to authority. " This kind of major scientific failing goes back at least 15 years in this field e.g. when Currie and Chen (2001) produced subjective inky outlines of integumental structures that are meant to represent no less important structures than branched feathers. Most deserving of censure, however, in that same study was, " [u]nder magnification, the margins of the larger structures arc darker along the edges but light medially, which suggests that they may have been hollow. ...
Article
We confirm the presence of pigmented keratinized integumentary structures attributable to feathers in the Late Cretaceous Ornithomimus specimen UALVP 52531. We falsify the hypothesis that these features represent collagen fibers and address additional criticisms of our paper made by Lingham-Soliar (2016).
... In one of these shown here (Fig. 2), despite the skull and anterior portion of the neck being firmly glued to the hard ground by the proteinaceous material of the head (darkened area), release of the stored tensile forces was powerful enough for part of cervical region (still articulated) to be forced upward into a deep dorsal loop (Fig. 2). Post mortem opisthotonus in Sinosauropteryx has in effect acted as a dissection of several layers of the integument , (1) the epidermis, (2) the dermal fibres from the opposite side of the tail embedded on the matrix (distinctive cross-fibre pattern), and (3) the structural fibres (Lingham-Soliar et al. 2007; Lingham-Soliar 2011) interpreted by other workers as protofeathers (Chen et al. 1998; Currie and Chen 2001). ...
Article
The epidermis and dermis are exposed in the tail region of the theropod dinosaur Sinosauropteryx. The specimen under study, like many others of the genus and other air-breathing vertebrates discovered in the Jehol biota, shows strong opisthotonus (i.e., recurvature of the spine) that includes the neck and tail. Here, recurvature of the tail upwards is considered to have aided the separation of the dermal and epidermal elements of the skin. Addressing a somewhat controversial question, the sequence of events in which this apparently occurred also suggests that the development of opisthotonus may have occurred post mortem rather than perimortem in this specimen. Crucially, epidermal structures considered to be scales are preserved overlying the posterior part of the tail and alongside it. They are approximately 2.0–2.5 mm in diameter and have distinctive papillae radiating around a central point, comparable to scales in some modern day lizards. Some of these scales overlie thick structural fibres external to the body outline, extending posteriorly at steep angles to the body's long axis, considered by many workers to be protofeathers. Intervening between the epidermal scales and the deeper structural fibres are preserved traces of a dermal fibre meshwork with two layers of oppositely oriented fibres.
... Este pequeño terópodo está representado por cinco ejemplares y posiblemente tenía un comportamiento gregario (Martínez & Novas, 2006;Ibiricu et al., 2013b). Además, representaría durante el Cretácico Superior un superviviente de una radiación celurosauriana basal pobremente documentada hasta el momento (Martínez & Novas, 2006Currie & Chen, 2001); Nqwebasaurus thwasi del BerriasianoValanginiano de Sudáfrica (de Klerk et al., 2000); Sinraptor heping del Jurásico Superior de China (Currie & Zhao, 1993) y Allosaurus, Ornitholestes hermanni y Tanycolagreus topwilsoni estos tres últimos del Jurásico Superior de Estados Unidos (Osborn, 1903;Gilmore, 1920;Carpenter et al., 2005).Novas et al. (2012), dieron a conocer un nuevo celurosaurio basal de la Formación Candeleros, Bicentenaria argentina. Este pequeño dinosaurio terópodo representaría otro de los linajes basales de celurosaurios que habitaron Patagonia durante el Cenomaniano. ...
Article
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The Chubut Group, central Patagonia, Argentina, is characterized by a lacustrine and fluvial-lacustrine system with variable participation of volcanic ash. This group includes the Bajo Barreal Formation (Cenomanian-Turonian) and a recently nested new lithostratigraphic unit, the Lago Colhue Huapi Formation (Coniacian-Maastrichtian). The Lago Colhue Huapi Formation overlies the Bajo Barreal Formation. These sedimentary units preserve a rich and diverse vertebrate fossil record including, among others, representatives of Crocodylomorpha, Testudines, Pterosauria and abundant Dinosauria. Nevertheless, the stratigraphic position of several of its taxa has been historically controversial. The unclear stratigraphic provenance of these taxa difficults the correct interpretation of the relationships with other Patagonian and South American basins. In this context, we present a detailed stratigraphic study to clarify the position of the vertebrate fossils of both Late Cretaceous formations. We also discuss the implications of this faunistic arrangement in terms of vertebrate evolution and paleobiogeography. Finally, this study broadens our knowledge on the fossil fauna of these units and therefore the vertebrate assemblages of central Patagonia.
... Taxa in bold were specimens without preserved forelimb remegies for whom feather lengths were estimated based on closely related taxa or other members of the same genus. For Jianchangosaurus we based our estimate on the longest preserved body feather traces, this is defensible as this clade is not know to have pennaceous remegies (Foth, Tischlinger & Rauhut, 2014) and in other maniraptorans without remegies the integument on the distal cervicals are similar in size, if not longer, than those on the forelimbs (Currie & Chen, 2001). CF indicates mass estimated based on Christiansen & Fariña (2004), Liu indicates avian mass estimates based on Liu, Zhou & Zhang (2012), Fe for avian mass estimates based on Field et al. (2013). ...
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Background: Powered flight is implicated as a major driver for the success of birds. Here we examine the effectiveness of three hypothesized pathways for the evolution of the flight stroke, the forelimb motion that powers aerial locomotion, in a terrestrial setting across a range of stem and basal avians: flap running, Wing Assisted Incline Running (WAIR), and wing-assisted leaping. Methods: Using biomechanical mathematical models based on known aerodynamic principals and in vivo experiments and ground truthed using extant avians we seek to test if an incipient flight stroke may have contributed sufficient force to permit flap running, WAIR, or leaping takeoff along the phylogenetic lineage from Coelurosauria to birds. Results: None of these behaviours were found to meet the biomechanical threshold requirements before Paraves. Neither was there a continuous trend of refinement for any of these biomechanical performances across phylogeny nor a signal of universal applicability near the origin of birds. None of these flap-based locomotory models appear to have been a major influence on pre-flight character acquisition such as pennaceous feathers, suggesting non-locomotory behaviours, and less stringent locomotory behaviours such as balancing and braking, played a role in the evolution of the maniraptoran wing and nascent flight stroke. We find no support for widespread prevalence of WAIR in non-avian theropods, but can't reject its presence in large winged, small-bodied taxa like Microraptor and Archaeopteryx. Discussion: Using our first principles approach we find that "near flight" locomotor behaviors are most sensitive to wing area, and that non-locomotory related selection regimes likely expanded wing area well before WAIR and other such behaviors were possible in derived avians. These results suggest that investigations of the drivers for wing expansion and feather elongation in theropods need not be intrinsically linked to locomotory adaptations, and this separation is critical for our understanding of the origin of powered flight and avian evolution.
... The branched feathers have a weak pennaceous arrangement of barbs consistent with non-avialan coelurosaurs, particularly paravians. Although the feathers are somewhat pennaceous, none of the observed osteological features preclude a compsog- nathid [28] affinity. The presence of pennaceous feathers in pairs down the length of the tail may point toward a source within Pen- naraptora [9] , placing a lower limit on the specimen's phylogenetic position. ...
Article
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In the two decades since the discovery of feathered dinosaurs [1-3], the range of plumage known from non-avialan theropods has expanded significantly, confirming several features predicted by developmentally informed models of feather evolution [4-10]. However, three-dimensional feather morphology and evolutionary patterns remain difficult to interpret, due to compression in sedimentary rocks [9, 11]. Recent discoveries in Cretaceous amber from Canada, France, Japan, Lebanon, Myanmar, and the United States [12-18] reveal much finer levels of structural detail, but taxonomic placement is uncertain because plumage is rarely associated with identifiable skeletal material [14]. Here we describe the feathered tail of a non-avialan theropod preserved in mid-Cretaceous (∼99 Ma) amber from Kachin State, Myanmar [17], with plumage structure that directly informs the evolutionary developmental pathway of feathers. This specimen provides an opportunity to document pristine feathers in direct association with a putative juvenile coelurosaur, preserving fine morphological details, including the spatial arrangement of follicles and feathers on the body, and micrometer-scale features of the plumage. Many feathers exhibit a short, slender rachis with alternating barbs and a uniform series of contiguous barbules, supporting the developmental hypothesis that barbs already possessed barbules when they fused to form the rachis [19]. Beneath the feathers, carbonized soft tissues offer a glimpse of preservational potential and history for the inclusion; abundant Fe(2+) suggests that vestiges of primary hemoglobin and ferritin remain trapped within the tail. The new finding highlights the unique preservation potential of amber for understanding the morphology and evolution of coelurosaurian integumentary structures.
... In the compsognathid Compsognathus the long, thin anterior process of the jugal reaches the antorbital fenestra, the dorsal process is subvertical, and the posterior process is rod-like and bears a longitudinal groove for reception of the quadratojugal (Peyer, 2006). The jugal is similarly slender and triradiate in other compsognathids (Currie and Chen, 2001;Hwang et al., 2004). In the probable compsognathid Juravenator the dorsal process of the jugal is posteriorly inclined, and the posterior process relatively short (Chiappe and G€ ohlich, 2010). ...
Article
In dinosaurs, as in other reptiles, the homologue of the mammalian zygomatic bone is the jugal. The dinosaurian jugal was primitively triradiate, with posterior, dorsal and anterior processes that respectively contacted the quadratojugal, the postorbital, and the maxilla and lacrimal. However, the jugal evolved along different lines in the three major dinosaurian clades. In theropods this cranial element remained relatively conservative in morphology, apart from being reduced to a rod-like structure in most birds and a few non-avians. In sauropodomorphs the jugal eventually became small, plate-like and nearly restricted to the area below the orbit, even being excluded from the ventral margin of the skull in many derived taxa. Among ornithischians the jugal was highly variable, but in many cases became large and/or adorned with ornamental features such as horns, flanges, and rugosities. The jugal does not appear to have been a site of muscle attachment in most non-avian dinosaurs, but represented an important structural element in the akinetic dinosaurian skull. The conspicuous jugal ornaments seen in many ornithischian dinosaurs, like the less striking ones documented in some saurischians, may have played an important role in the social behavior of the species that possessed them. In many cases they have a weapon-like aspect suggesting use in aggressive displays, if not actual combat, adding to the evidence that agonistic behavior was likely widespread among ornithischians in particular. Anat Rec, 300:30–48, 2017.
... The prezygapophyses of the mid-and posterior caudals are proportionally longer in Ornitholestes than in Coelurus, but even the longest do not extend to mid-centrum (Fig. 3.6B' ); in Coelurus the prezygapophyses are shorter than in Tanycolagreus . The neural spines are damaged in both taxa, but from their remnants they appear to have been longer and lower in Coelurus than in Ornitholestes; neither show the bifid spines seen in Sinosauropteryx (Currie and Chen 2001). The distal chevrons of Ornitholestes are elongate, being about as long anteriorly as posteriorly. ...
... Tyrannosaurids do not, therefore, exhibit the widely distributed filamentous feathers present in Dilong and Yutyrannus, where scales are unknown[1,8]. In fact, within Coelurosauria, where feathers are present, they cover virtually the entire body[13,14]. On the other hand, the co-occurrence of epidermal scales and filamentous structures has only been reported in some neornithischians[15], although the homology of these filamentous structures with theropod feathers has been questioned[7]. ...
Article
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Recent evidence for feathers in theropods has led to speculations that the largest tyrannosaurids, including Tyrannosaurus rex, were extensively feathered. We describe fossil integument from Tyrannosaurus and other tyrannosaurids (Albertosaurus, Daspletosaurus, Gorgosaurus and Tarbosaurus), confirming that these large-bodied forms possessed scaly, reptilian-like skin. Body size evolution in tyrannosauroids reveals two independent occurrences of gigantism; specifically, the large sizes in Yutyrannus and tyrannosaurids were independently derived. These new findings demonstrate that extensive feather coverings observed in some early tyrannosauroids were lost by the Albian, basal to Tyrannosauridae. This loss is unrelated to palaeoclimate but possibly tied to the evolution of gigantism, although other mechanisms exist.
... In some Compsognathus specimens, the teeth are confluent between the crown and the root and not constricted as occur in morphotype 5, but mesial denticles are not present in mesial or lateral teeth (Zinke 1998;Peyer 2006). However, compsognathid teeth like those of Compsognathus (Peyer 2006), Scipionyx (Dal Sasso and Maganuco 2011), Juravenator (Göhlich and Chiappe 2006), and Sinosauropteryx (Currie and Chen 2001) are typically very elongated, with few relatively large denticles. Beside, most compsognathid teeth, with the exception of Juravenator, have an unserrated mesial carina and interdenticular sulci are generally absent. ...
Article
Purpose Isolated theropod teeth are abundant in the Upper Jurassic of the Lusitanian Basin and are an important source to reconstruct the diversity of this group as well as its geographic and stratigraphic distribution. However, reliably identification of isolated teeth is complex, especially for those morphotypes related to poorly represented groups. Herein a set of isolated theropod teeth collected in different sites from the Upper Jurassic of the Lusitanian Basin ranging from the late Kimmeridgian to late Tithonian in age are described and discussed. Methods These teeth were grouped in seventeen distinct morphotypes based first on morphology and comparative anatomy. Multivariate statistical analyses were performed in order to assign each morphotype to a certain taxon. Results The current analysis shows the presence of several groups of theropods such as Ceratosaurus, Torvosaurus, and Allosaurus beside morphotypes identified as belonging to indeterminate Megalosauroidea and Allosauroidea and morphotypes tentatively assigned to Tyrannosauroidea, Dromaeosauridae, and Richardoestesia. This faunal composition, namely the presence of a non-megalosaurid megalosauroid possibly related to the piatnitzkysaurid Marshosaurus, indicates a higher diversity of theropods in the Late Jurassic of the Lusitanian Basin than previously known, based on more complete specimens. Results obtained from this analysis partially agree with previous studies of other collections with isolated theropod teeth from the Upper Jurassic of Portugal such as those of the Guimarota coal mine. However, the presence of velociraptorine dromaeosaurids, compsognathids, and troodontids reported from this site could not be confirmed in the sample herein analyzed. This analysis also indicates a great similarity of the theropod faunas from the Late Jurassic of the Lusitanian Basin and other European chronocorrelative localities such as those from Spain and Germany.
... Sinosauropteryx prima (Figura 18), com o tamanho aproximado de uma galinha, está primorosamente preservado (Chen et al., 1998). Muitos paleontólogos acreditam que as estruturas eriçadas em seu pescoço, dorso, flancos e cauda sejam simplesmente penas (Chen et al., 1998;Unwin, 1998;Currie & Chen, 2001 (Ji et al., 2001;Sues, 2001;Xu et al., 2001;Prum & Brush, 2002). ...
Chapter
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Nada faz sentido em biologia exceto à luz da evolução. Essa frase, frequentemente citada, é título de um famoso trabalho de Theodosius Dobzhansky – que foi um dos biólogos evolucionistas mais eminentes do século XX - e resume bem a importância dos conceitos evolutivos para as ciências biológicas. A teoria da evolução por seleção natural é, sem dúvida alguma, a generalização mais importante até agora feita no campo das ciências naturais e pode ser testada cientificamente em todas essas áreas de conhecimento. Ela é uma das ideias mais poderosas em todas as áreas da ciência e é a única teoria que pode seriamente reivindicar a condição de unificar a biologia. Neste material irei abordar como o pensamento evolucionista foi se modificando e se aprimorando ao longo do tempo, e como essa ciência sempre foi cercada por aspectos religiosos e culturais, tanto que encontra barreiras para o seu entendimento até nos dias de hoje. Veremos como a publicação de A Origem das Espécies por Charles Darwin, em 1859, influenciou o estudo evolucionista e os pesquisadores a partir de então, por ter feito mais do que qualquer outro indivíduo, antes ou depois dele, para modificar a atitude e a visão do homem em relação ao fenômeno da vida. Os conceitos evolutivos forneceram à biologia um arcabouço científico coerente de ideias, em vez de uma abordagem composta de mitos e superstições, fazendo com que a evolução por seleção natural se tornasse um fato inegável, compreensível como processo e abrangente como conceito. A emergência do darwinismo e o avanço tecnológico, principalmente na genética, permitiram o desenvolvimento de novas teorias e o aprimoramento de antigas. Veremos como a seleção natural, o isolamento reprodutivo e as barreiras geográficas e ecológicas são os principais mecanismos que atuam nas populações naturais, impulsionando-as a divergências evolutivas que contribuíram ao longo do tempo para a diversificação e estabelecimento da majestosa biodiversidade de nosso planeta. Uma das principais conclusões que espero é que o estudo deste módulo possa despertar em cada aluno a ideia de que somente em um contexto evolutivo o ser humano é capaz de olhar a Natureza com humildade e vislumbre, colocando-se não mais no centro de uma visão antropocêntrica para compreender a diversidade das formas de vida da atualidade. E isso só se é possível quando aplicamos os princípios das teorias evolutivas para interpretar, criticar e debater diferentes versões da origem e evolução das espécies. Assim, os temas são aqui divididos em oito unidades que abordarão, respectivamente, (1) as principais teorias que buscam respostas sobre a origem das espécies; (2) as evidências da ação da evolução por seleção natural; (3) os princípios e perspectivas da ação da evolução; (4) os tipos de evolução; (5) a origem da Terra e da vida; (6) as vias evolutivas das plantas; (7) as vias evolutivas dos animais e, por fim, (8) a origem e evolução do ser humano. Os conteúdos dentro de cada unidade serão distribuidos em diversas lições, com a finalidade de dividir temporal e coerentemente os principais conceitos para estudo.
Chapter
The plight of the tetrapod forebears at the closing stages of the Carboniferous was quite dire. They had become the unfortunate victims of a change in the earth’s climate that irrevocably reversed their earlier good fortune. The lush swamps were drying up completely or being reduced in size, heralding more arid conditions and areas of desert and near-desert (DiMichele et al. 2006). The rich life afforded to the large numbers of early tetrapod forebears living in the aquatic and semi-aquatic environment was under extreme stress (Fig. 6.1). Those vertebrates, the “amphibians,” that survived were restricted to the small areas of lakes and rivers that remained. They were ill-equipped for dry conditions and tightly bound to the water. Their skin, the epidermis in particular, was extremely thin to allow gaseous and nutrient exchange whereas out of water for any measure of time highly prone to rapid dehydration. The mucous glands would only help to stall drying up over short periods of time (Fig. 6.2). Hence, the generally arid conditions in the Carboniferous proved catastrophic for most of the “amphibians” with only a few groups surviving. However, their misfortune would force one of the most successful radiations on land, that of the reptiles, which includes the dinosaurs and the mammal-like reptiles, the latter would ultimately give rise to our own forebears (Chap. 8). Later, we will look at how a major change in the structure of the skin would allow the conquest of land. But first we will look at another remarkable development.
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Middle Jurassic to Early Cretaceous deposits from northeastern China have yielded varied theropod dinosaurs bearing feathers. Filamentous integumentary structures have also been described in ornithischian dinosaurs, but whether these filaments can be regarded as part of the evolutionary lineage toward feathers remains controversial. Here we describe a new basal neornithischian dinosaur from the Jurassic of Siberia with small scales around the distal hindlimb, larger imbricated scales around the tail, monofilaments around the head and the thorax, and more complex featherlike structures around the humerus, the femur, and the tibia. The discovery of these branched integumentary structures outside theropods suggests that featherlike structures coexisted with scales and were potentially widespread among the entire dinosaur clade; feathers may thus have been present in the earliest dinosaurs.
Article
The origin of birds and of bird flight has drawn scientific interest since the inception of evolutionary thinking. Though early investigations were hampered by a paucity of fossils, new discoveries have filled in many gaps and provided unprecedented detail into morphological changes that attended the evolutionary appearance of birds and bird flight. Birds are now widely regarded as the descendents of theropod dinosaurs. In contrast, form–function relationships and behaviours that might have facilitated the evolutionary acquisition of flight remain widely debated. Given the versatility of extant birds, we should not expect to find only one solution to this problem. Nevertheless, much debate seems to stem not from looking for multiple plausible functions and behaviours, but rather from traditional ‘ground up’ versus ‘trees down’ assumptions and a general lack of experimental and ecological support for inferred form–function relationships. Many researchers have therefore called for more rigorous hypothesis testing, and a plethora of new techniques and perspectives are up to the challenge.
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Theropod dinosaurs form a highly diversified clade, and their teeth are some of the most common components of the Mesozoic dinosaur fossil record. This is the case in the Lourinhã Formation (Late Jurassic, Kimmeridgian-Tithonian) of Portugal, where theropod teeth are particularly abundant and diverse. Four isolated theropod teeth are here described and identified based on morphometric and anatomical data. They are included in a cladistic analysis performed on a data matrix of 141 dentition-based characters coded in 60 taxa, as well as a supermatrix combining our dataset with six recent datamatrices based on the whole theropod skeleton. The consensus tree resulting from the dentition-based data matrix reveals that theropod teeth provide reliable data for identification at approximately family level. Therefore, phylogenetic methods will help identifying theropod teeth with more confidence in the future. Although dental characters do not reliably indicate relationships among higher clades of theropods, they demonstrate interesting patterns of homoplasy suggesting dietary convergence in (1) alvarezsauroids, therizinosaurs and troodontids; (2) coelophysoids and spinosaurids; (3) compsognathids and dromaeosaurids; and (4) ceratosaurids, allosauroids and megalosaurids. Based on morphometric and cladistic analyses, the biggest tooth from Lourinhã is referred to a mesial crown of the megalosaurid Torvosaurus tanneri, due to the elliptical cross section of the crown base, the large size and elongation of the crown, medially positioned mesial and distal carinae, and the coarse denticles. The smallest tooth is identified as Richardoestesia, and as a close relative of R. gilmorei based on the weak constriction between crown and root, the "eight-shaped" outline of the base crown and, on the distal carina, the average of ten symmetrically rounded denticles per mm, as well as a subequal number of denticles basally and at mid-crown. Finally, the two medium-sized teeth belong to the same taxon and exhibit pronounced interdenticular sulci between distal denticles, hooked distal denticles for one of them, an irregular enamel texture, and a straight distal margin, a combination of features only observed in abelisaurids. They provide the first record of Abelisauridae in the Jurassic of Laurasia and one of the oldest records of this clade in the world, suggesting a possible radiation of Abelisauridae in Europe well before the Upper Cretaceous.
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Coelurosauria is the most diverse clade of theropod dinosaurs. Much of this diversity is present in Paraves—the clade of dinosaurs containing dromaeosaurids, troodontids, and avialans. Paraves has over 160 million years of evolutionary history that continues to the present day. The clade represents the most diverse living tetrapod group (there are over 9000 extant species of Aves—a word used here as synonomous with “bird”), and it is at the root of the paravian radiation, when dromaeosaurids, troodontids, and avialans were diverging from one another, that we find the morphology and soft tissue changes associated with the origin of modern avian flight. Within the first 15 million years of known paravian evolutionary history members of this clade exhibited a difference of nearly four orders of magnitude in body size, a value that is similar to the extreme body size disparity present today in mammalian carnivorans, avians, and varanoid squamates. In this respect, Paraves is an important case study in characterizing the patterns, processes, and dynamics of evolutionary size change. This last point is of particular interest because of the historical significance placed on the role of body size reduction in the origin of powered avian flight.Our study reviews and revises the membership of Dromaeosauridae and provides an apomorphy-based diagnosis for all valid taxa. Of the currently 31 named dromaeosaurid species, we found 26 to be valid. We provide the most detailed and comprehensive phylogenetic analysis of paravians to date in order to explore the phylogenetic history of dromaeosaurid taxa. The general pattern of paravian relationships is explored within the broader context of Coelurosauria with an emphasis on sampling basal avialans, because of their importance for character optimizations at the base of Paraves.A large dataset was constructed by merging two datasets, one examining coelurosaur relationships broadly (based on previous TWiG datasets) and the other examining avialan relationships specifically (Clarke et al., 2006). This merged dataset was then significantly revised and supplemented with novel character analysis focusing on paravian taxa. During character analysis, particular attention was given to basal members of Dromaeosauridae, enigmatic basal paravians such as Jinfengopteryx elegans and Anchiornis huxleyi, and the incorporation of new morphological information from two undescribed troodontid species from the Late Cretaceous of Mongolia. A final dataset of 474 characters scored for 111 taxa was used to address paravian evolution. This dataset is important in that it bridges a phylogenetic gap that had persisted between studies on birds and studies on all other coelurosaurs. Most scorings in this matrix were based on the direct observation of specimens.All most parsimonious trees recovered in the cladistic analysis support the monophyly of Paraves, Troodontidae, Dromaeosauridae, and Deinonychosauria. A new clade of basal troodontids is discovered including two undescribed Mongolian troodontids and Jinfengopteryx elegans. Xiaotingia and Anchiornis form a clade at the base of Troodontidae. Recently proposed relationships within Dromaeosauridae are further supported and a succession of clades from Gondwana and Asia form sister taxa to a clade of Laurasian dromaeosaurids. Avialan monophyly is strongly supported with Archaeopteryx, Sapeornis, Jeholornis, and Jixiangornis forming the successive sister taxa to the Confuciusornis node. This topology supports a more basal position for Sapeornis than previous phylogenetic analyses and indicates a progressive acquisition of a fully “avian” shoulder morphology.
Article
Recent discoveries of more than ten new species of tyrannosauroid theropods are helping to understand the origin and evolution of colossal body size and other characteristic features of Tyrannosaurus rex and its terminal Cretaceous relatives. Particularly important has been the discovery and reinterpretation of Late Jurassic tyrannosauroids from Europe and North America, which are intermediate in size and phylogenetic position between small basal tyrannosauroids and the largest Late Cretaceous species. The fragmentary nature of these Jurassic specimens, however, has frustrated attempts to understand their systematics and phylogeny. A new specimen from the Late Jurassic of England was recently named as a new species (Stokesosaurus langhami) of the genus Stokesosaurus, which is known from several fragmentary fossils from North America. We review the systematics and phylogeny of these European and North American specimens and show that there are no unequivocal synapomorphies uniting them. Furthermore, a revised phylogenetic analysis does not recover them as sister taxa. This necessitates a taxonomic revision of this material, and we name a new genus (Juratyrant) for the British specimen.
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Since the 1969 description of Deinonychus antirrhopus Ostrom, cooperative pack hunting behavior for this species and, subsequently, for many other nonavian theropods, has attained wide acceptance. In this paper we assess the hypothesis of mammal-like cooperative pack hunting in D. antirrhopus and other nonavian theropods by examining the behaviors of extant diapsids. Through phylogenetic inference and character optimization, we conclude that this hypothesis is both unparsimonious and unlikely for these taxa and that the null hypothesis should therefore be that nonavian theropod dinosaurs were solitary hunters or, at most, foraged in loose associations. Moreover, we present new evidence from the D. antirrhopus type locality of probable intraspecific aggression in this species. Additionally, our study suggests that some evidence that has previously been proposed in support of highly gregarious, mammal-like behavior in nonavian theropods (e.g., certain theropod-dominated fossil assemblages, preserved bite-mark injuries on some specimens, and the preponderance of theropod trackways at some sites) may alternatively be interpreted as evidence that nonavian theropod behavior was more agonistic, cannibalistic, and diapsid-like than has been widely believed.
Article
The presence of feathers in Ornithomimus is questioned on poor evidence and a failure to observe scientific process and procedure.
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Identifying feather morphology in extinct dinosaurs is challenging due to dense overlapping of filaments within fossilized plumage and the fact that some extinct feather morphologies are unlike those of extant birds or those predicted from an ‘evo-devo’ model of feather evolution. Here, we compare a range of dinosaur taxa with preserved integumentary appendages using high-resolution photographs to better understand fossil feather morphology and gain insight into their function and evolution. A specimen of the basal paravian Anchiornis possesses contour feathers disarticulated from the plumage, revealing a novel feather type: a ‘shaggy’, open-vaned, bifurcated feather with long barbs attached to a short rachis, which is much simpler than the contour feathers of most extant birds. In contrast, it is likely that the contour feathers of Sinosauropteryx were simpler than those seen in Anchiornis; a ‘tuft’ morphology of multiple barbs connected at their bases (e.g. via a shared follicle), but lacking a rachis, is tentatively inferred. However, conclusive morphological descriptions await the discovery of isolated Sinosauropteryx contour feathers. Paravian wing feathers also show potentially plesiomorphic traits. Comparison with Confuciusornis suggests that Anchiornis wing feathers were at least partially open-vaned. Combined with the interpretation of Anchiornis contour feathers, this suggests that differentiated barbicels are relatively derived compared to pennaceous feathers and the appearance of wings. ‘Shaggy’ contour feathers probably influenced thermoregulatory and water repellence abilities, and, in combination with open-vaned wing feathers, would have decreased aerodynamic efficiency. Simplified, open-vaned wing feathers were also observed on the oviraptorosaur Caudipteryx, consistent with, but not necessarily diagnostic of, its suggested flightlessness. Taken together, these observations have broad implications for how we depict a wide variety of dinosaurs and how we view the function and evolution of feathers.
Article
To develop a widely applicable method to estimate body size in theropods, the scaling relationship between skull length, body length, and body mass was investigated using 13 strictly carnivorous, non-avialan theropod taxa ranging in size from the 1-m Sinosauropteryx prima to the 12-m Tyrannosaurus rex. Body length was obtained from the literature for complete to nearly-complete specimens and body mass was obtained from three-dimensional mathematical slicing of those same specimens to ensure accurate body length-body mass associations. Least-square regressions reveal a tight correlation between skull length and body length (SK-BL) and skull length and body mass (SK-BM). The SK-BL regression is negatively allometric, which indicates that skulls become longer relative to body length with increasing body size. In contrast, the SK-BM regression is positively allometric, indicating that body mass increases faster than skull length with increasing body size. These conclusions confirm that the common practice of scaling isometrically smaller relatives of a given taxon to obtain body length and body mass estimates is not valid. Although predictive equations derived from the regressions fail to predict accurately body size in abelisaurids and juvenile theropods due to their different head/body proportions, they produce accurate body size estimates for theropods of known body size, thus validating their applicability. Body size estimates for Carcharodontosaurus and Giganotosaurus, approaching 13 m and 14 tons, suggest that they may have surpassed Tyrannosaurus in size. A revised body size estimate for a large Spinosaurus specimen suggests a much shorter and heavier animal than recently suggested.
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Non-avian saurischian skulls underwent at least 165 million years of evolution and shapes varied from elongated skulls, such as in Coelophysis, to short and box-shaped skulls, such as in Camarasaurus. A number of factors have long been considered to drive skull shape, including phylogeny, dietary preferences and functional constraints. However, heterochrony is increasingly being recognized as a major factor in dinosaur evolution. In order to quantitatively analyse the impact of heterochrony on saurischian skull shape, we have analysed five ontogenetic trajectories using two-dimensional geometric morphometrics in a phylogenetic framework. This allowed for the evaluation of how heterochrony affected overall skull shape through both ontogenetic and phylogenetic trajectories and how it impacted modular changes within the skull. Using principal component analyses and multivariate regressions, it was possible to quantify different ontogenetic trajectories in light of heterochrony. The results recovered here indicate that taxa underwent a combination of local paedomorphosis and peramorphosis within the skull along individual ontogenies and phylogenies, but that either peramorphosis or paedomorphosis dominated when the skull was considered as a whole. We found that the hypothetical ancestor of Saurischia led to basal Sauropodomorpha mainly through paedomorphosis, and to Neotheropoda mainly through peramorphosis. Paedomorphosis then led from Orionides to Avetheropoda, indicating that the paedomorphic trend previously found in advanced coelurosaurs may extend back into the early evolution of Avetheropoda. Not only are changes in saurischian skull shape complex due to the large number of factors that affect shape, but heterochrony itself is complex, with a number of reversals throughout non-avian saurischian evolution. The sampling of ontogenetic trajectories is considerably lower than the sampling of adult species and the current study represents a first exploratory analysis. To better understand the impact of heterochrony on cranial evolution in saurischians, the data set we present must be expanded and complemented with further sampling from future fossil discoveries, especially of juvenile taxa.
Article
Full-text available
Non-avian saurischian skulls underwent at least 165 million years of evolution and shapes varied from elongated skulls, such as in Coelophysis, to short and box-shaped skulls, such as in Camarasaurus. A number of factors have long been considered to drive skull shape, including phylogeny, dietary preferences and functional constraints. However, heterochrony is increasingly being recognized as a major factor in dinosaur evolution. In order to quantitatively analyse the impact of heterochrony on saurischian skull shape, we have analysed five ontogenetic trajectories using two-dimensional geometric morphometrics in a phylogenetic framework. This allowed for the evaluation of how heterochrony affected overall skull shape through both ontogenetic and phylogenetic trajectories and how it impacted modular changes within the skull. Using principal component analyses and multivariate regressions, it was possible to quantify different ontogenetic trajectories in light of heterochrony. The results recovered here indicate that taxa underwent a combination of local paedomorphosis and peramorphosis within the skull along individual ontogenies and phylogenies, but that either peramorphosis or paedomorphosis dominated when the skull was considered as a whole. We found that the hypothetical ancestor of Saurischia led to basal Sauropodomorpha mainly through paedomorphosis, and to Neotheropoda mainly through peramorphosis. Paedomorphosis then led from Orionides to Avetheropoda, indicating that the paedomorphic trend previously found in advanced coelurosaurs may extend back into the early evolution of Avetheropoda. Not only are changes in saurischian skull shape complex due to the large number of factors that affect shape, but heterochrony itself is complex, with a number of reversals throughout non-avian saurischian evolution. The sampling of ontogenetic trajectories is considerably lower than the sampling of adult species and the current study represents a first exploratory analysis. To better understand the impact of heterochrony on cranial evolution in saurischians, the data set we present must be expanded and complemented with further sampling from future fossil discoveries, especially of juvenile taxa.
Article
Within the past decade exceptional preservation of original organic components have been reported from several dinosaurian families, including members of Sauropodomorpha. Here we document the partial preservation of a vertebral ligament in the dorsal and sacral series of a titanosaur. Unlike other cases of tissue preservation, this structure does not represent biomineralization of the original organic components. Histology, morphology, and comparative anatomy from extant taxa as well as the preferential placement on the vertebral column suggests that it represents the partial preservation of the nuchal ligament. While preservation of other sauropod connective tissues are known, this case represents the first reported non-biomineralized tissue from a sauropod. In consideration of the location and external and internal morphologies compared to modern vertebral ligaments, we believe this structure to be the micritic replacement of the original tissue via microbially-mediated processes. Along with the suggestive external morphology, internally we interpret some of the unusual structures to represent the remnants of the collagen and elastin fascicles that are strongly overprinted by a clotted, thrombolytic-like fabric recording microbial activity and deposition of micrite prior to lithification. In consideration of the interpreted depositional history, we theorize that post-deposition, bacteria deposited the micrite as a byproduct of metabolization. Subsequently, the recognition of this structure as a vertebral ligament, the largest of such thus documented, substantiates previous findings on the morphological attributes of sauropod vertebral ligaments.
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The quadrate of reptiles and most other tetrapods plays an important morphofunctional role by allowing the articulation of the mandible with the cranium. In Theropoda, the morphology of the quadrate is particularly complex and varies importantly among different clades of non-avian theropods, therefore conferring a strong taxonomic potential. Inconsistencies in the notation and terminology used in discussions of the theropod quadrate anatomy have been noticed, including at least one instance when no less than eight different terms were given to the same structure. A standardized list of terms and notations for each quadrate anatomical entity is proposed here, with the goal of facilitating future descriptions of this important cranial bone. In addition, an overview of the literature on quadrate function and pneumaticity in non-avian theropods is presented, along with a discussion of the inferences that could be made from this research. Specifically, the quadrate of the large majority of non-avian theropods is akinetic but the diagonally oriented intercondylar sulcus of the mandibular articulation allowed both rami of the mandible to move laterally when opening the mouth in many of theropods. Pneumaticity of the quadrate is also present in most averostran clades and the pneumatic chamber—invaded by the quadrate diverticulum of the mandibular arch pneumatic system—was connected to one or several pneumatic foramina on the medial, lateral, posterior, anterior or ventral sides of the quadrate.
Chapter
For all creatures in the ecosystems, they strived to successfully carry out three main functions of life: to feed, to avoid being eaten; and to pass on their genes. Dilong paradoxus, a small tyrannosauroid dinosaur, is one of the earliest and most primitive known tyrannosauroids and has a covering of “proto‐feathers” in fossilized skin impressions from near the jaws and tail. Fossil bird specimens were found in 1994 in Jianshangou and Huangbanjigou of Shangyuan near Beipiao City. Monjurosuchus splendens is a medium‐sized choristoderan reptile found in Niuyingzi of the Lingyuan City of Liaoning Province in the Yixian Formation. Abundant and diverse plant fossils have been found from the Middle Jurassic to the Early Cretaceous in Northeastern China. Recent findings indicate that the first angiosperms (vascular flowering plants with seeds enclosed in an ovary) appeared in the eco‐system during the Early Cretaceous. Bennettitales are in the order Cycadophyta, commonly called cycads and cycadeoids.
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The inclination of the scapular blade and the resting pose of the forelimb in dinosaurs differ among reconstructions and among skeletal mounts. For most dinosaurian taxa, no attempt has previously been made to quantify the correct resting positions of these elements. Here, we used data from skeletons preserved in articulation to quantify the resting orientations of the scapula and forelimb in dinosaurs. Specimens were included in the study only if they were preserved lying on their sides; for each specimen the angle between forelimb bones at a given joint was included in the analysis only if the joint was preserved in articulation. Using correlation analyses of the angles between the long axis of the sacrum, the first dorsal centrum, and the scapular blade in theropods and Eoraptor, we found that vertebral hyperextension does not influence scapular orientation in saurischians. Among examined taxa, the long axis of the scapular blade was found to be most horizontal in bipedal saurischians, most vertical in basal ornithopods, and intermediate in hadrosauroids. We found that in bipedal dinosaurs other than theropods with semilunate carpals, the resting orientation of the elbow is close to a right angle and the resting orientation of the wrist is such that the hand exhibits only slight ulnar deviation from the antebrachium. In theropods with semilunate carpals the elbow and wrist are more flexed at rest, with the elbow at a strongly acute angle and with the wrist approximately at a right angle. The results of our study have important implications for correct orientations of bones in reconstructions and skeletal mounts. Here, we provide recommendations on bone orientations based on our results.
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A new theropod dinosaur, Lepidocheirosaurus natatilis gen. et sp. nov., from the Upper Jurassic (?Tithonian) deposits of the Kulinda locality (Transbaikal Area, Russia) is described based manus fragments, caudal vertebrae, and imprints of horn scales. The new form is similar in morphology to Nqwebasaurus thwazi de Klerk et al., 2000 from the Lower Cretaceous of South Africa and assigned to the family Nqwebasauridae fam. nov. (Ornithomimosauria, Theropoda). It is proposed that nqwebasaurids searched for relatively small prey in the water column.
Book
The emphasis in this volume is on the structure and functional design of the integument. The book starts with a brief introduction to some basic principles of physics (mechanics) including Newton’s Three Laws of Motion. These principles are subsequently used to interpret the problems animals encounter in motion. It is in only the last 40 or so years that we have begun to understand how important a role the integument plays in the locomotion of many marine vertebrates. This involves the crossed-fiber architecture, which was first discovered in a classic study on nemertean worms. As a design principle we see that the crossed-fiber architecture is ubiquitous in nature. Research on some of the most dynamic marine vertebrates of the oceans - tuna, dolphins and sharks, and the extinct Jurassic ichthyosaurs - shows precisely how the crossed-fiber architecture contributes to high-speed swimming and (in lamnid sharks) may even aid in energy conservation. However, this design principle is not restricted to animals in the marine biota but is also found as far afield as the dinosaurs and, most recently, has been revealed as a major part of the microstructure of the most complex derivative of the integument, the feather. We see that a variety of phylogenetically diverse vertebrates take to the air by using skin flaps to glide from tree to tree or to the ground, and present detailed descriptions of innovations developed in pursuit of improved gliding capabilities in both extinct and modern day gliders. But the vertebrate integument had even greater things in store, namely true or flapping flight. Pterosaurs were the first vertebrates to use the integument as a membrane in true flapping flight and these interesting extinct animals are discussed on the basis of past and cutting-edge research, most intriguingly with respect to the structure of the flight membrane. Bats, the only mammals that fly, also employ integumental flight membranes. Classic research on bat flight is reviewed and supplemented with the latest research, which shows the complexities of the wing beat cycle to be significantly different from that of birds, as revealed by particle image velocimetry. The book's largest chapter is devoted to birds, given that they make up nearly half of the over 22,000 species of tetrapods. The flight apparatus of birds is unique in nature and is described in great detail, with innovative research highlighting the complexity of the flight structures, bird flight patterns, and behavior in a variety of species. This is complimented by new research on the brains of birds, which shows that they are more complex than previously thought. The feather made bird flight possible, and was itself made possible by -keratin, contributing to what may be a unique biomechanical microstructure in nature, a topic discussed in some depth. A highly polarized subject concerns the origin of birds and of the feather. Alleged fossilized protofeathers (primal simple feathers) are considered on the basis of histological and taphonomic investigative studies in Chapter 6. Finally, in Chapter 7 we discuss the controversies associated with this field of research. Professor Theagarten Lingham-Soliar works at the Nelson Mandela Metropolitan University, Port Elizabeth and is an Honorary Professor of Life Sciences at the University of KwaZulu-Natal.
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Sigilmassasaurus brevicollis is an enigmatic theropod dinosaur from the early Late Cretaceous (Cenomanian) of Morocco, originally based on a few isolated cervical vertebrae. Ever since its original description, both its taxonomic validity and systematic affinities were contentious. Originally considered to represent its own family, Sigilmassasauridae, the genus has variously been suggested to represent a carcharodontosaurid, an ornithischian, and, more recently, a spinosaurid. Here we describe new remains referrable to this taxon and re-evaluate its taxonomic status and systematic affinities. Based on the new remains, a re-evaluation of the original materials, and comparisons with other spinosaurids, the holotype of Sigilmassasaurus brevicollis is identified as an anterior dorsal, rather than a cervical vertebra, and differences between elements referred to this taxon can be explained by different positions of the elements in question within the vertebral column. Many characters used previously to diagnose the genus and species are found to be more widespread among basal tetanurans, and specifically spinosaurids. However, the taxon shows several autapomorphies that support its validity, including the presence of a strongly rugose, ventrally offset triangular platform that is confluent with a ventral keel anteriorly in the mid-cervical vertebral centra and a strongly reduced lateral neural arch lamination, with no or an incomplete distinction between anterior and posterior centrodiapophyseal laminae in the posterior cervical and anterior dorsal vertebrae. We argue furthermore that Spinosaurus maroccanus, also described on the basis of isolated cervical vertebrae from the same stratigraphic unit and in the same paper as Sigilmassasaurus brevicollis, is a subjective synonym of the latter. Both a detailed comparison of this taxon with other theropods and a formal phylogenetic analysis support spinosaurid affintities for Sigilmassasaurus. However, we reject the recently
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Tyrannosaurids are a well-supported clade of very large predatory dinosaurs of Late Cretaceous Asiamerica. Traditional dinosaurian systematics place these animals within the infraorder Carnosauria with the other large theropods (allosaurids, megalosaurids). A new cladistic analysis indicates that the tyrannosaurs were in fact derived members of the Coelurosauria, a group of otherwise small theropods. Despite certain gross cranial similarities with the large predators of the Jurassic and Early Cretaceous, the Late Cretaceous tyrannosaurids are shown to be the sister group to ornithomimids and troodontids, which share a derived condition of the metatarsus. This clade is found to be nested within Maniraptora, which is a more inclusive taxon than previously recognized. The atrophied carpal structure found in tyrannosaurids and ornithomimids is derived from a maniraptoran condition with a large semilunate carpal, rather than from the plesiomorphic theropod morphology. The taxa “Carnosauria” and “Deinonychosauria” (Dromaeosauridae plus Troodontidae) are shown to be polyphyletic, and the Late Jurassic African form Elaphrosaurus is found to be the sister taxon to Abelisauridae rather than a primitive ornithomimosaur. Purported allosaurid-tyrannosaurid synapomorphies are seen to be largely size-related, present in the larger members of both clades, but absent in smaller members of the Tyrannosauridae. The remaining giant tetanurine theropods (Megalosaurus and Torvosaurus) were found to be progressively distant outgroups to an allosaurid-coelurosaur clade. The inclusion of the Tyrannosauridae within Maniraptora suggests a major adaptive radiation of coelurosaurs within Cretaceous Asiamerica comparable to contemporaneous radiations in various herbivorous dinosaurian clades.
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A detailed description ofthe holotype specimen of Mononykus olecranus, a basal flightless bird from the Late Cretaceous Nemegt Formation of Mongolia, is presented. The holotype comprises a fragmentary skull, most precaudal vertebrae, fore and hindlimbs, the thoracic girdle, and fragments of the pelvis and synsacrum. In the skull, caudal, dorsal, and rostral tympanic recesses are well developed. The maxilla is toothless, and the anterior margin of the antorbital fossa lacks accessory fe-nestrae. The only dental element found is a tiny isolated tooth that lacks serrations and has a constricted base. The axial skeleton is remarkable in having a biconvex posterior dorsal vertebra, and keeled posterior synsacral vertebrae. The forelimb is short and extremely robust. The humerus bears a prominent deltopectoral crest. The olecranon process of the ulna is hypertrophied. The carpo-metacarpus is very short, subquadrangular, and massive. The alular digit is extremely robust, bearing a robust ungual phalanx. The sternum is stout and carinate. In the pelvis, the ilium bears a strong antitrochanter and the pubis is retroverted. The hindlimb is gracile. In the femur the trochanteric crest is undivided, and the popliteal fossa is bounded distally by projections from both con-dyles. The tibia and proximal tarsals are partially fused. Two cnemial crests are present on the tibio-This is contribution number 4 of the Mongolian-American Museum Paleontological Project.
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The osteology and plumage of Confuciusornis sanctus and Changchengornis hengdaoziensis from the Chaomidianzi Formation (previously referred to as the lower section of the Yixian Formation) of western Liaoning Province (China) are described in detail. Confuciusornis sanctus and Changchengornis hengdaoziensis have toothless, beaked skulls (the tomial crest is straight in the former species and strongly curved in the latter) and retain the dorsal portion of the nasal process of the maxilla. The skull of Confuciusornis sanctus is of typical diapsid plan. It possesses a triradiate postorbital that with the squamosal forms a complete supratemporal arcade. Furthermore, a robust jugal-postorbital contact completely separates the infratemporal fenestra from the orbit. Although the postorbital region is not preserved in Changchengornis hengdaoziensis, it likely resembles that of Confuciusornis sanctus. Both species have abbreviated tails with long pygostyles, not the long, bony tail originally reconstructed in Confuciusornis sanctus. Scapulae and coracoids are fused to form scapulocoracoids. The coracoids are strutlike but much shorter than the scapulae. The furculae are robust and boomerang shaped. The sterna are long and nearly flat. A complete basket of gastralia follows the sternum caudally. The wing elements are short, and proportions among individual bones are primitive in that the hand is longer than either the humerus or the ulna and the ulna is shorter than the humerus. The pelvis is opisthopubic. The postacetabular wing of the ilium is much shorter than the preacetabular wing. Differences in plumage, namely the presence or absence of two very long tail feathers, are observed among several well-preserved specimens of Confuciusornis sanctus. This difference is likely the expression of sexual dimorphism, although other biological attributes known for extant populations (e.g., differential molting, correlation between sexual maturity and ornamental plumage) indicate that alternative explanations may also account for the observed plumage variation among specimens of Confuciusornis sanctus. Given the latest Jurassic-earliest Cretaceous age of the Chaomidianzi Formation, Confuciusornis sanctus and Changchengornis hengdaoziensis are surely among the oldest known birds after the Early Tithonian Archaeopteryx lithographica. Confuciusornis sanctus and Changchengornis hengdaoziensis thus furnish the earliest record of beaked birds. The fully diapsid skull of Confuciusornis sanctus, and presumably of Changchengornis hengdaoziensis, and the absence of a bending zone on the base of the snout suggest that earlier interpretations of the skull of Confuciusornis sanctus as prokinetic are incorrect. Confuciusornis sanctus probably had very limited cranial kinetic capabilities, if any. Optimization of the postorbital-jugal contact, a character intimately correlated with intracranial kinesis, in a phylogeny of basal avians indicates that the essentially akinetic condition of the skull of Confuciusornis sanctus is a reversal derived from forms possessing kinetic properties. Recent recognition of two additional species of Confuciusornis - Confuciusornis chuonzhous and Confuciusornis suniae - are based on anatomical misinterpretations. Thus, Confuciusornis suniae and Confuciusornis chuonzhous are regarded as junior synonyms of Confuciusornis sanctus. Confuciusornis sanctus is the sister-taxon of Changchengornis hengdaoziensis, and both are placed within the Confuciusornithidae. Some of the synapomorphies supporting this grouping include the presence of edentolous jaws, a rostrally forked mandibular symphysis, a reduced claw of manual digit II, and a V-shaped caudal margin of the sternum. The Confuciusornithidae is considered to be the sister-group of a clade composed of the Enantiornithomorpha and the Ornithuromorpha. This phylogenetic interpretation is far more parsimonious than previous systematic hypotheses placing the Confuciusornithidae as either within the Enantiornithes or as its sister-group. Purported climbing specializations of Confuciusornis sanctus are evaluated in light of the available anatomical evidence. We conclude that both Confuciusornis sanctus and Changchengornis hengdaoziensis were ill suited for tree climbing. The foot of Changchengornis hengdaoziensis, however, suggests a greater grasping ability than that of Confuciusornis sanctus. It is argued that both Confuciusornis sanctus and Changchengornis hengdaoziensis were able to fly and take off from the ground. The remarkable concentration of specimens of Confuciusornis sanctus from a relatively small quarry near the village of Sihetun (Liaoning Province) suggests several events of mass mortality and, perhaps, a gregarious behavior.
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SYNOPSIS. A number of hypotheses have been suggested for the origin of birds and feathers. Although distributions of functional complexes have frequently been used to test phylogenetic hypotheses, analysis of the origin of feathers remains hampered by the incomplete fossil record of these unmineralized structures. It is also complicated by approaches that confuse the origins of birds, feathers, and flight without first demonstrating that these relate to the same historical event. Functional speculation regarding the origin of feathers usually focuses on three possible alternatives: (1) flight; (2) thermal insulation; or (3) display. Recent fossil finds of Late Cretaceous feathered dinosaurs in China have demonstrated that feathers appear to have originated in taxa that retained a significant number of primitive nonavian features. Current evidence strongly suggests that birds are the- ropod dinosaurs, and that the most primitive known feathers are found on non- flying animals. This further suggests that feathers did not evolve as flight struc- tures. Thermoregulatory, display, and biomechanical support functions remain possible explanations for the origin of feathers. As the earliest function of feathers was probably not for aerial locomotion, it may be speculated that the transitional animals represented by the Chinese fossils possessed skin with the tensile properties of reptiles and combined it with the apomorphic characteristics of feathers.
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Until now, Syntarsus was based on a single species, S. rhodesiensis, known only from southern Africa. The discovery of Syntarsus in North America adds significantly to the increasingly detailed resemblance of African and North American Early Jurassic terrestrial vertebrate faunas. The new species, Syntarsus kayentakatae, is based on a complete skull and partial skeleton, and more fragmentary remains of at least 16 additional individuals, all from a narrow stratigraphie interval in the Kayenta Formation. Syntarsus kayentakatae is diagnosed by parasagittal cranial crests and fusion of the fibula to the calcaneum in adults. Syntarsus is the most derived member of the newly diagnosed theropod taxon Ceratosauria, possessing 22 apomorphies that arose subsequent to the divergence of ceratosaurs from other theropods. Syntarsus shares 20 of these with Coelophysis bauri, one of the earliest well-known theropods. By their first appearance, probably late Carnian, ceratosaurs already possessed a history involving considerable morphological transformation. A number of these characters arose convergently much later in time in ornithurine birds.
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Caudipteryx zoui Posed in courtship display a model depicts a creature nearly three feet long that stunned paleontologists when resurrected from its stony grave - a dinosaur with feathers. This plumage appears on the fossil (above) at the and of the tail, at top, and under the arm at lower left. More than 120 million years old. Caudipteryx zoui and three other new fossil species from China support the thinking of most scientists. Birds descended from dinosaurs, a lineage illustrated on pages 90-91.
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Scanning electron microscopy of feathers has revealed evidence that a bacterial glycocalyx (a network of exocellular polysaccharide fibers) played a role in promoting their fossilization in some cases. This mode of preservation has not been reported in other soft tissues. The majority of fossil feathers are preserved as carbonized traces. More rarely, bacteria on the surface are replicated by authigenic minerals (bacterial autolithification). The feathers of Archaeopteryx are preserved mainly by imprintation following early lithification of the substrate and decay of the feather. Lacustrine settings provide the most important taphonomic window for feather preservation. Preservation in terrestrial and normal-marine settings involves very different processes (in amber and in authigenically mineralized coprolites, respectively). Therefore, there may be a significant bias in the avian fossil record in favor of inland water habitats.
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Preliminary evidence suggests that during the Early Cretaceous there were separate dinosaur faunas in northern and southern Asia. The northern fauna, the Psittacosaurus fauna, is well known and based upon collections from numerous localities and formations throughout northern China and southern Mongolia. Although the southern fauna is still poorly known and based upon collections from only a small number of sites, it appears to be distinguished by the absence of psittacosaurs. The discovery of Psittacosaurus in Thailand suggests that the division is probably ecological in nature.
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A year ago, the so-called "feathered dinosaur" Sinosauropteryx made the front page of The New York Times, and was viewed by some as confirming the dinosaurian origins of birds. But at this year's vertebrate paleontology meeting in Chicago late last month, the verdict was a bit different: The structures are not modern feathers, say the roughly half-dozen Western paleontologists who have seen the specimens. But just what the structures are--and whether they link birds and dinosaurs--is still under debate.
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New discoveries of dinosaurs, together with cladistics procedures, have provided further insights into the morphological transition from nonavian dinosaurs to modern birds. Here we report the occurrence of growth rings in the Cretaceous birds Patagopteryx deferrariisi and Enantiornithes, which are phylogenetically intermediate between nonavian dinosaurs and ornithurine birds.
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DISCOVERY of avian remains close to the age of Archaeopteryx in the Liaoning Province of northeastern China provides the earliest evidence for a beaked, edentulous bird. The associated wing skeleton retains the primitive pattern found in Archaeopteryx, including a manus with unfused carpal elements and long digits. Two leg skeletons from the same site also show an Archaeopteryxlevel of morphology, and provide the earliest indisputable evidence for a covering of body contour feathers. These specimens provide evidence for either an undiscovered pre-Archaeopteryx or a rapid, post-Archaeopteryxevolution in birds. As the first Jurassic birds to be described from outside Germany, they show that birds with long fingers terminating in large recurved claws were widely distributed. They are not found in the Early Cretaceous sediments of the same region, where there is a diverse assemblage of more advanced flying birds with smaller fingers and claws. The postcran-ial structure of Archaeopteryx andConfuciusornis seems to be adapted for climbing tree trunks and may have disappeared near the end of the Jurassic.
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The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists' Union.
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Reptiles and birds possess septate lungs rather than the alveolar-style lungs of mammals. The morphology of the unmodified, bellowslike septate lung restricts the maximum rates of respiratory gas exchange. Among taxa possessing septate lungs, only the modified avian flow-through lung is capable of the oxygen–carbon dioxide exchange rates that are typical of active endotherms. Paleontological and neontological evidence indicates that theropod dinosaurs possessed unmodified, bellowslike septate lungs that were ventilated with a crocodilelike hepatic-piston diaphragm. The earliest birds (Archaeopteryx and enantiornithines) also possessed unmodified septate lungs but lacked a hepatic-piston diaphragm mechanism. These data are consistent with an ectothermic status for theropod dinosaurs and early birds.