131209139
Troodontidae (Dinosauria: Theropoda) from the Upper Cretaceous of Uzbekistan
Abstract To date three taxa of troodontid theropod dinosaurs have been recognized from Upper Cretaceous strata in two regions of the Kyzylkum Desert in Uzbekistan. The Cenomanian Khodzhakul Formation in the southwestern Kyzylkum Desert has yielded isolated serrated teeth and some postcranial bones of an indeterminate troodontid. In the central Kyzylkum Desert troodontids are known from the Cenomanian Dzharakuduk Formation ( Urbacodon itemirensis ) and the Turonian Bissekty Formation ( Urbacodon sp.). Urbacodon itemirensis is known from a single dentary whereas Urbacodon sp. is represented by isolated teeth, maxilla and dentary fragments, a partial braincase, and some postcranial bones. The troodontid affinities of Urbacodon are supported by several synapomorphies: presence of a subotic recess; reduced basal tubera placed directly under the occipital condyle; maxilla participating in the margin of the external naris; nutrient foramina on dentary situated within a deep lateral groove; dentary without distinct interdental plates; large number of small dentary and maxillary teeth; teeth constricted between root and crown; anterior dentary teeth smaller, more numerous, more closely spaced than those in the middle of the tooth row, and implanted in a groove; posterior dorsal vertebrae with tall and posterodorsally tapering neural spines; and presence of a midline sulcus on the neural arches of distal caudals. Among Troodontidae, Urbacodon resembles Byronosaurus , Gobivenator , and Xixiasaurus in the absence of serrations on the tooth crowns and having premaxillary teeth that are D-shaped in cross-section. However, phylogenetic analysis did not recover a clade of Asiatic troodontids with unserrated teeth.
131103354
Cranial anatomy of Stenonychosaurus inequalis (Saurischia, Theropoda) and its bearing on the origin of birds
The discovery in recent years of additional skull material of the rare carnivorous dinosaur Stenonychosaurus inequalis prompts the first thorough description of this animal. This species, known only from the Upper Cretaceous strata of North America, is closely related to, but distinct from, the two described species of Saurornithoides from Mongolia. A derived characteristic, an inflated parasphenoid capsule, is found in both the saurornithoidids and ornithomimids, strongly suggesting shared ancestry. The middle ear cavity is well defined and is connected to at least two systems of sinuses in the skull bones. Periotic sinuses like these have not been described in theropods, and their presumed absence has been used as evidence against theropod ancestry of birds. Although these and other cranial characteristics of Stenonychosaurus do not prove that birds descended from theropods, they strengthen the claim that small carnivorous dinosaurs are more plausible bird ancestors than either pseudosuchians or crocodiles:
4313286
Nest and egg clutches of the dinosaur Troodon formosus and the evolution of avian reproductive traits
Living archosaurs (crocodilians and birds) share several reproductive features, including hard-shelled eggs1, parental care2,3, assembly-line oviducts4 and luteal morphology5. Nevertheless, crocodilians produce many small eggs that they ovulate, shell and deposit en masse, and incubate within sediments or vegetation mounds2,4,6, whereas birds produce fewer but larger eggs7, usually from a single ovary and oviduct3. Further, birds ovulate, shell and lay one egg at a time and incubate eggs directly with body heat3. New discoveries from the Upper Cretaceous of Montana allow re-evaluation of the transition from basal archosaurian to avian reproductive behaviour in the Coelurosauria8,9, the thero-pod dinosaur clade that includes birds. Egg clutches and nests (Figs 1–3) suggest that the small coelurosaurian Troodon formosus (weight, about 50kg) produced two eggs simultaneously at daily or longer intervals and incubated eggs using a combination of soil and direct body contact. Non-avian coelurosaurians thus possess several primitive features found in crocodilians (two functional ovaries and oviducts, lack of egg rotation and chalazae, partial burial of eggs, precocial young) and several derived features shared with birds (relatively larger and potentially asymmetric eggs, one egg produced per oviduct at a time, loss of egg retention, open nests, brooding) (Fig. 4).
83798981
Paleoecological implications of Alaskan terrestrial vertebrate fauna in latest Cretaceous time at high paleolatitudes
The latest Cretaceous cool temperate environment of the Alaskan North Slope included dinosaurs (some species represented by both juveniles and adults) and mammals, all probably endothermic, and freshwater fish among its terrestrial vertebrate fauna. No traces have been found of amphibians or nondinosaurian reptiles, ectothermic vertebrates that are abundantly represented in approximately contemporaneous faunas of North American middle paleolatitudes. A geologically brief period of intense cold and darkness has been hypothesized as the primary cause of terminal Cretaceous extinctions. However, the extinction of the lineages of Alaskan dinosaurs and mammals, in contrast to the survival of most lineages of amphibians and nondinosaurian reptiles into the Tertiary, contradicts this hypothesis.
130766946
THEROPOD TEETH FROM THE PRINCE CREEK FORMATION (CRETACEOUS) OF NORTHERN ALASKA, WITH SPECULATIONS ON ARCTIC DINOSAUR PALEOECOLOGY
Abstract Theropod teeth are taxonomically diagnostic components of dinosaur assemblages. Seventy teeth have been recovered from six different localities in the Kogosukruk Tongue of the Prince Creek Formation (Upper Cretaceous) of the North Slope of Alaska. This assemblage of teeth shows slightly less diversity compared to well documented assemblages of teeth from the slightly older Judith River Formation of south-central Montana, the Aguja Formation of west Texas, and the Hell Creek Formation of eastern Montana. In addition, in contrast to the Judith River Formation assemblage of teeth in south-central Montana, the teeth assigned to Troodon dominated the Alaskan assemblage. The dominance of Troodon is attributed to adaptation by this theropod to low light conditions while over-wintering at a high paleolatitude.
9743271
A NEW TROODONTID (DINOSAURIA: THEROPODA) FROM THE CENOMANIAN OF UZBEKISTAN, WITH A REVIEW OF TROODONTID RECORDS FROM THE TERRITORIES OF THE FORMER SOVIET UNION
Abstract Based on a review of troodontid specimens from the territories of the former Soviet Union, including new discoveries from Uzbekistan, two dental morphotypes can be distinguished among Troodontidae from the Cretaceous of Asia: (1) unserrated teeth, present in Mei from Lujiatun (China; Early Cretaceous: Hauterivian-Barremian), an unnamed taxon from Hövöör (Mongolia; Early Cretaceous: Aptian-Albian), Urbacodon itemirensis, gen. et sp. nov. from Itemir and Urbacodon sp. from Dzharakuduk (Uzbekistan; Late Cretaceous: Cenomanian and Turonian, respectively), and Archaeornithoides from Bayn Dzak and Byronosaurus from Ukhaa Tolgod (Mongolia; Late Cretaceous: Campanian); and (2) serrated teeth, present in Sinornithoides from Huamuxiao (China; Early Cretaceous) and Sinornithoides-like taxa from Khamryn Us (Mongolia; Early Cretaceous: Aptian-Albian), Shestakovo (Russia; Early Cretaceous: Aptian-Albian), and Sheikhdzheili (Uzbekistan; Late Cretaceous: Cenomanian); Troodontidae indet. from Kansai (Tajikistan; Late Cretaceous: Santonian) and Alymtau (Kazakhstan; Late Cretaceous: Campanian), Saurornithoides (Mongolia and China; Late Cretaceous: Campanian-Maastrichtian), and Troodon from Kakanaut and Blagoveshchensk (Russia; Late Cretaceous: Maastrichtian).
140657219
On the Occurrence of Exceptionally Large Teeth of Troodon (Dinosauria: Saurischia) from the Late Cretaceous of Northern Alaska
Abstract Exceptionally large teeth attributable to the theropod genus Troodon are abundant in Upper Cretaceous rocks (Campanian–Maastrichtian) of northern Alaska. The dominance of low-angle light in this Cretaceous high-latitude environment seems to have selected for an abundance of Troodon. The population of these Alaskan specimens— morphologically the same as teeth attributable to this taxon in other regions—show a mean approximately twice the size of those found in such southern latitudes as southern Alberta and Montana. Microwear patterns on the teeth of this taxon in Alaska and Montana suggest that these animals were eating similar food items. There appears to be good correlation between tooth size and body size in theropods, thereby allowing the inference that the increase in the size of Alaskan Troodon teeth equates to an increase in body size. The increased body size for Alaskan Troodon is likely related to increased availability of food resources as a result of decreased numbers of other predatory dinosaurs, particularly tyrannosaurids, in the ecosystem.
162697
The last polar dinosaurs: high diversity of latest Cretaceous arctic dinosaurs in Russia
A latest Cretaceous (68 to 65 million years ago) vertebrate microfossil assemblage discovered at Kakanaut in northeastern Russia reveals that dinosaurs were still highly diversified in Arctic regions just before the Cretaceous–Tertiary mass extinction event. Dinosaur eggshell fragments, belonging to hadrosaurids and non-avian theropods, indicate that at least several latest Cretaceous dinosaur taxa could reproduce in polar region and were probably year-round residents of high latitudes. Palaeobotanical data suggest that these polar dinosaurs lived in a temperate climate (mean annual temperature about 10°C), but the climate was apparently too cold for amphibians and ectothermic reptiles. The high diversity of Late Maastrichtian dinosaurs in high latitudes, where ectotherms are absent, strongly questions hypotheses according to which dinosaur extinction was a result of temperature decline, caused or not by the Chicxulub impact.
129893055
A nesting trace with eggs for the Cretaceous theropod dinosaur Troodon formosus.
ABSTRACT An unusual trace containing eggs of the 50 kg-plus theropod dinosaur, Troodon formosus, represents one of the best preserved dinosaur nests. This unique specimen (MOR 963) represents the actual nest structure and the direct product of Troodon behavior. The trace comes from the Campanian, Late Cretaceous Two Medicine Formation of Montana, and consists of a bowl-shaped depression with an internal area of ~1m2 surrounded by a distinct rim. A clutch of 24 tightly-placed eggs sat in the center and both nest and clutch show bilateral symmetry about a north–south axis. The trace occurs within a moderately well-developed micritic paleosol. A physically and chemically distinct mudstone covered the nest and represents overbank deposition. The nest protected the eggs by creating a suitable micro-environment during the lengthy egg-laying and incubation periods. Clutch and nest size, shape, and symmetry and low organic carbon of the overlying mudstone suggests brooding rather than incubation with vegetative c...
51824767
Osteology and Relationships of Byronosaurus jaffei (Theropoda: Troodontidae)
Abstract The troodontid Byronosaurus jaffei is known from two specimens from adjacent localities in the Nemegt basin, Ömnögov Aimag, Mongolia. These specimens are composed of well-preserved cranial material and fragmentary postcrania. All of these elements are described here. Byronosaurus jaffei is included in a comprehensive phylogenetic analysis of Coelurosauria to ascertain its relationships. Several interesting characters of Byronosaurus jaffei have implications both for theropod relationships and for understanding patterns of variation within coelurosaurian theropods. These include the position of a foramen that marks the exit of the supra-alveolar canal (which we suggest is homologous with the subnarial foramen), the flattened internarial bar, the unusual interfenestral bar, and the unserrated teeth. Additionally, the well-preserved braincase allows detailed comparison with other troodontid taxa.
4417515
A basal troodontid from the Early Cretaceous of China
Troodontid dinosaurs form one of the most avian-like dinosaur groups. Their phylogenetic position is hotly debated, and they have been allied with almost all principal coelurosaurian lineages. Here we report a basal troodontid dinosaur, Sinovenator changii gen. et sp. nov., from the lower Yixian Formation of China. This taxon has several features that are not found in more derived troodontids, but that occur in dromaeosaurids and avialans. The discovery of Sinovenator and the examination of character distributions along the maniraptoran lineage indicate that principal structural modifications toward avians were acquired in the early stages of maniraptoran evolution.
55220748
A New Troodontid Theropod from the Late Cretaceous of Central China, and the Radiation of Asian Troodontids
A new troodontid dinosaur, Xixiasaurus henanensis gen. et sp. nov., from the Upper Cretaceous Majiacun Formation of the Xixia Basin, Henan Province, is erected, based on a partial skull. It is characterized by bearing 22 maxillary teeth, a distinct opening on the lateral surface of the base of nasal process of the premaxilla, the rostral end of the upper jaw forming a tapered U-shape, and the mandibular symphyseal region slightly inflected medially. Xixiasaurus is most closely related to the Mongolian Byronosaurus among troodontids. Byronosaurus, Urbacodon, and Xixiasaurus may form a new clade, suggesting an endemic radiation of troodontids across Asia, including multiple taxa without dental serrations. The discovery of Xixiasaurus in the Xixia Basin may imply that the Xixiasaurus-bearing Majiacun Formation is Campanian in age.
54705292
A New Dromaeosaurid Theropod from Ukhaa Tolgod (Ömnögov, Mongolia)
Abstract We describe a new dromaeosaurid theropod from the Upper Cretaceous Djadokhta Formation of Ukhaa Tolgod, Mongolia. The new taxon, Tsaagan mangas, consists of a well-preserved skull and cervical series. This specimen marks only the second dromaeosaurid taxon from a formation that has otherwise yielded numerous specimens of Velociraptor mongoliensis, and Tsaagan mangas is the only dromaeosaurid known from Ukhaa Tolgod beyond sporadic occurrences of isolated teeth. Tsaagan mangas differs from other dromaeosaurids in the possession of a straight, untwisted, and pendulous paroccipital process, a large and anteriorly located maxillary fenestra, and a jugal–squamosal contact that excludes the postorbital from the margin of the infratemporal fenestra. The phylogenetic affinities of Tsaagan mangas are determined through a comprehensive phylogenetic analysis of Coelurosauria, confirming its position within Dromaeosauridae. This new specimen, coupled with CT imaging, provides new information on the skull and braincase anatomy of dromaeosaurids.
2502021
A New Troodontid Theropod, Talos sampsoni gen. et sp. nov., from the Upper Cretaceous Western Interior Basin of North America
Background Troodontids are a predominantly small-bodied group of feathered theropod dinosaurs notable for their close evolutionary relationship with Avialae. Despite a diverse Asian representation with remarkable growth in recent years, the North American record of the clade remains poor, with only one controversial species—Troodon formosus—presently known from substantial skeletal remains. Methodology/Principal Findings Here we report a gracile new troodontid theropod—Talos sampsoni gen. et sp. nov.—from the Upper Cretaceous Kaiparowits Formation, Utah, USA, representing one of the most complete troodontid skeletons described from North America to date. Histological assessment of the holotype specimen indicates that the adult body size of Talos was notably smaller than that of the contemporary genus Troodon. Phylogenetic analysis recovers Talos as a member of a derived, latest Cretaceous subclade, minimally containing Troodon, Saurornithoides, and Zanabazar. MicroCT scans reveal extreme pathological remodeling on pedal phalanx II-1 of the holotype specimen likely resulting from physical trauma and subsequent infectious processes. Conclusion/Significance Talos sampsoni adds to the singularity of the Kaiparowits Formation dinosaur fauna, which is represented by at least 10 previously unrecognized species including the recently named ceratopsids Utahceratops and Kosmoceratops, the hadrosaurine Gryposaurus monumentensis, the tyrannosaurid Teratophoneus, and the oviraptorosaurian Hagryphus. The presence of a distinct troodontid taxon in the Kaiparowits Formation supports the hypothesis that late Campanian dinosaurs of the Western Interior Basin exhibited restricted geographic ranges and suggests that the taxonomic diversity of Late Cretaceous troodontids from North America is currently underestimated. An apparent traumatic injury to the foot of Talos with evidence of subsequent healing sheds new light on the paleobiology of deinonychosaurians by bolstering functional interpretations of prey grappling and/or intraspecific combat for the second pedal digit, and supporting trackway evidence indicating a minimal role in weight bearing.
129032671
New information on Cretaceous troodontids (Dinosauria, Theropoda) from the People's Republic of China
Troodontid specimens were recovered from three localities in China by the Sino-Canadian expeditions between 1987 and 1990. These include a Lower Cretaceous form (Sinornithoides youngi), which is the most complete troodontid skeleton ever found, isolated bones from the Iren Dabasu Formation (?Turonian), and partial skeletons of Saurornithoides mongoliensis from Djadokhta-equivalent beds (?Campanian). These, and other specimens recently described from North America, allow a better assessment of the phylogenetic position of troodontids than has been possible before. Although troodontids have autapomorphies that eliminate them from consideration as bird ancestors, they are nevertheless one of the closest avian outgroups within the Theropoda.
129108134
Stenonychosaurus inequalis(Saurischia: Theropoda) from the Judith River (Oldman) Formation of Alberta: new findings on metatarsal structure
A partial foot of Stenonychosaurus from the Judith River (Oldman) Formation, Dinosaur Provincial Park, Alberta, shows features in the metatarsus that have not previously been recognized. These include compression of metatarsal II and exclusion of the proximal half of metatarsal III from the anterior (= dorsal) surface of the metatarsus. Exclusion from the anterior surface of metatarsal III to this extent is unprecedented among theropods and further underscores the distinctiveness of the Sauromithoididae.
12612087
A Second Soundly Sleeping Dragon: New Anatomical Details of the Chinese Troodontid Mei long with Implications for Phylogeny and Taphonomy
A second nearly complete, articulated specimen of the basal troodontid Mei long (DNHM D2154) is reported from the Early Cretaceous (Hauterivian-Valanginian) lower Yixian Formation, Liaoning Province, China. New diagnostic features of Mei long are identified, including: a uniquely shaped maxilla, low with small, low maxillary fenestra; sacrum with an extremely wide caudal portion and elongate 4th and 5th sacral processes; and a large distal articular surface on the tibiotarsus which continues caudally on the tibia. A phylogenetic analysis including new data from the second specimen recovered Mei as a basal troodontid, in keeping with previous analyses. Although the skeleton exhibits several juvenile-like features including free cervical ribs, unfused frontals and nasals, and a short snouted skull, other attributes, full fusion of all neurocentral synostoses and the sacrum, and dense exteriors to cortical bone, suggest a small, mature individual. Microscopic examination of tibia and fibula histology confirms maturity and suggests an individual greater than two years old with slowed growth. Despite being one of the smallest dinosaurs, Mei long exhibits multi-year growth and cortical bone consisting largely of fibro-lamellar tissue marked by lines of arrested growth as in much larger and more basal theropods. This Mei long specimen lies in a similar but mirrored sleeping position to that of the holotype, strengthening the hypothesis that both specimens were preserved in a stereotypical life position. Like many Liaoning specimens, the new specimen also lacks extensive taphonomic and stratigraphic data, making further behavioral inference problematic.
13920021
An exquisitely preserved troodontid theropod with new information on the palatal structure from the Upper Cretaceous of Mongolia
Troodontidae is a clade of small-bodied theropod dinosaurs. A new troodontid, Gobivenator mongoliensis gen. et sp. nov., is described based on the most complete skeleton of a Late Cretaceous member of this clade presently known, from the Campanian Djadokhta Formation in the central Gobi Desert. G. mongoliensis is different from other troodontids in possessing a pointed anterior end of the fused parietal and a fossa on the surangular in front of the posterior surangular foramen. The skull was superbly preserved in the specimen and provides detailed information of the entire configuration of the palate in Troodontidae. Overall morphology of the palate in Gobivenator resembles those of dromaeosaurids and Archaeopteryx, showing an apparent trend of elongation of the pterygoid process of the palatine and reduction of the pterygopalatine suture toward the basal Avialae. The palatal configuration suggests that the skull of Gobivenator would have been akinetic but had already acquired prerequisites for later evolution of cranial kinesis in birds, such as the loss of the epipterygoid and reduction in contact areas among bones.
4362560
A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers
Recent coelurosaurian discoveries have greatly enriched our knowledge of the transition from dinosaurs to birds, but all reported taxa close to this transition are from relatively well known coelurosaurian groups. Here we report a new basal avialan, Epidexipteryx hui gen. et sp. nov., from the Middle to Late Jurassic of Inner Mongolia, China. This new species is characterized by an unexpected combination of characters seen in several different theropod groups, particularly the Oviraptorosauria. Phylogenetic analysis shows it to be the sister taxon to Epidendrosaurus, forming a new clade at the base of Avialae. Epidexipteryx also possesses two pairs of elongate ribbon-like tail feathers, and its limbs lack contour feathers for flight. This finding shows that a member of the avialan lineage experimented with integumentary ornamentation as early as the Middle to Late Jurassic, and provides further evidence relating to this aspect of the transition from non-avian theropods to birds.
83974628
The Evolution of the Antorbital Cavity of Archosaurs: A Study in Soft-Tissue Reconstruction in the Fossil Record with an Analysis of the Function of Pneumaticity
ABSTRACT The most commonly cited apomorphy of Archosauriformes is an opening in the snout known as the antorbital cavity. Despite the ubiquity and prominence of the antorbital cavity, its function and importance in craniofacial evolution have been problematic. Discovering the significance of the antorbital cavity is a two step process: first, establishing the function of the bony cavity (that is, its soft-tissue relations), and second, determining the biological role of the enclosed structure. The first step is the most fundamental, and hence is examined at length. Three hypotheses for the function of the antorbital cavity have been advanced, suggesting that it housed (1) a gland, (2) a muscle, or (3) a paranasal air sinus. Thus, resolution is correctly viewed as a “soft-tissue problem,” and is addressed within the context of the extant phylogenetic bracket (EPB) approach for reconstructing the unpreserved features of fossil organisms. The soft-anatomical relations of the antorbital cavity (or any bony st...
4362745
A new troodontid dinosaur from China with avian-like sleeping posture
Discovering evidence of behaviour in fossilized vertebrates is rare. Even rarer is evidence of behaviour in non-avialan dinosaurs that directly relates to stereotypical behaviour seen in extant birds (avians) and not previously predicted in non-avialan dinosaurs. Here we report the discovery of a new troodontid taxon from the Early Cretaceous Yixian Formation of western Liaoning, China. Numerous other three-dimensionally preserved vertebrate fossils have been recovered recently at this locality, including some specimens preserving behavioural information. The new troodontid preserves several features that have been implicated in avialan origins. Notably, the specimen is preserved in the stereotypical sleeping or resting posture found in extant Aves. Evidence of this behaviour outside of the crown group Aves further demonstrates that many bird features occurred early in dinosaurian evolution.
84158904
Bird-like characteristics of the jaws and teeth of troodontid theropods (Dinosauria, Saurischia)
ABSTRACT The discovery of a new dentary of “Stenonychosaurus inequalis” with six germ teeth prompted a critical examination of all jaws and teeth attributed to Troodon, Stenonychosaurus, and Pectinodon. It is concluded that Troodon is the senior synonym of these genera, and that the name Troodontidae has priority over Saurornithoididae. Troodontid dentaries are unique amongst the Theropoda in that they lack interdental plates. Previous reports that Dromaeosaurus, Deinonychus, and Saurornitholestes do not have interdental plates are erroneous. Premaxillary, maxillary, anterior dentary and dentary teeth can be distinguished from each other. Each troodontid tooth has a constriction between the crown and root that is more comparable with birds and crocodiles than with other theropods.
83572446
A Review of Dromaeosaurid Systematics and Paravian Phylogeny
Abstract 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.
14744914
A Short-Armed Troodontid Dinosaur from the Upper Cretaceous of Inner Mongolia and Its Implications for Troodontid Evolution
Background The Troodontidae represents one of the most bird-like theropod groups and plays an important role in our understanding of avian origins. Although troodontids have been known for over 150 years, few known derived troodontid specimens preserve significant portions of both the forelimb and the hindlimb. Methodology/Principal Findings Here, we report a new troodontid taxon, Linhevenator tani gen. et sp. nov., based on a partial, semi-articulated skeleton recovered from the Upper Cretaceous Wulansuhai Formation of Wulatehouqi, Inner Mongolia, China. L. tani has an unusual combination of primitive and derived character states, though our phylogenetic analysis places it in a derived clade within the Troodontidae. As a derived taxon, L. tani has a dromaeosaurid-like pedal digit II, and this species also possesses a humerus that is proportionally much shorter and more robust than those of most other troodontids. Conclusion/Significance The combination of features present in Linhevenator indicates a complex pattern of character evolution within the Troodontidae. In particular, the discovery of Linhevenator suggests that derived troodontids have independently evolved a highly specialized pedal digit II and have significantly shortened the forelimb over the course of their evolution.
87063912
THE TAXONOMY OF THE TROODONTID IVPP V 10597 RECONSIDERED
The partial troodontid hindlimb IVPP V 10597 was originally described as a juvenile Saurornithoides mongoliensis.The present study reconsiders the taxonomic placement of this interesting specimen,given the significant advances in understanding of the Troodontidae that have taken place since it was first described.Morphological comparisons and numerical phylogenetic analyses indicate that V 10597 is more closely related to the sympatric Linhevenator tani than to Saurornithoides mongoliensis,raising the possibility that V 10597 might be a juvenile L.tani.However,V 10597 differs significantly from other troodontids,including L.tani,in numerous hindlimb features and particularly in the proportions of various hindlimb elements.These differences are likely to be taxonomic,and suggest that V 10597 represents a new troodontid.Furthermore,histological analysis indicates that V 10597 is unlikely to be a juvenile of L.tani or any other large troodontid.Based on the available morphological and histological information,we propose the erection of a new taxon,Philovenator curriei gen.et sp.nov.,based on V 10597.This new find increases the known taxonomic diversity and morphological disparity of Late Cretaceous troodontids.
83516867
A Successive Approximations Approach to Character Weighting
Abstract Fa~ris, J. S. (Dept. Biol. Sci., State Uniu., Stony Brook, New York 11790) 1969. A successive approximations approach to charaaer weighting. Syst. Zool., 18:374385.-Characters that are reliable for cladistic inference are those that are consistent with the true phyletic relationships, that is, those that have little homoplasy. A set of cladistically reliable characters are correlated with each other in a particular non-linear fashion here referred to as hierarchic correlation. Cladistically unreliable characters can be hierarchically correlated only by chance. A technique that infers cladistic relationships by successively weighting characters according to apparent cladistic reliability is suggested, and computer simulation tests of the technique are described. Results indicate that the successive weighting procedure can be highly successful, even when cladistically reliable characters are heavily outnumbered by unreliable ones. [Evolutionary taxonomy. Cladistics. Char-acter weighting.]