DINOWEB

FEATHER-LIKE STRUCTURES AND SCALES IN A JURASSIC NEORNITHISCHIAN DINOSAUR FROM SIBERIA

dinoweb — Sat, 12 Oct 2013 11:08:06 GMT

GODEFROIT, Pascal, Institut Royal des Sciences Naturelles de Belgique, Brussels,
Belgium; SINITSA, Sofia, Institute of Natural Resources, Ecology and Cryology, SB
RAS, Chita, Russia; DHOUAILLY, Danielle, Université Joseph Fournier, La Tronche,
France; BOLOTSKY, Yuri, Institute of Geology and Nature Management, FEB RAS,
Blagoveschensk, Russia; SIZOV, Alexander, Institute of the Earth’s Crust, SB RAS,
Irkutsk, Russia
Recent discoveries in Middle–Late Jurassic and Early Cretaceous deposits from
northeastern China have revealed that numerous theropod dinosaurs were covered by
feathers. Furthermore, filamentous integumentary structures were also recently described
in rare Early Cretaceous ornithischian dinosaurs from Liaoning Province in China.
Whether these filaments can be regarded as epidermal and therefore part of the
evolutionary lineage towards feathers remains controversial. Here we describe a new
basal neornithischian dinosaur, based on isolated bones and partial skeletons collected in
two monospecific bonebeds from the Middle–Late Jurassic Kulinda locality in the
Transbaikal region (Russia). Varied integumentary structures were found directly
associated with skeletal elements, supporting the hypothesis that simple filamentous
feathers, as well as compound feather-like structures comparable to those in theropods,
were widespread amongst the whole dinosaur clade. Moreover, scales along the distal
tibia and on the foot closely resemble the secondarily-appearing pedal scales in extant
birds. More surprisingly, dorso-ventral movements of the tail were prevented by large
imbricated scales on its dorsal surface. It is hypothesized that, at the same time early
feathers evolved within the whole dinosaur clade, genetic mechanisms limiting the
growth of long epidermal structures on the distal portion of the hind limb and on the tail
were selected as they facilitate bipedal terrestrial locomotion.
http://dinoweb.ucoz.ru/forum/29-1790-1

New Study of Anshunsaurus huangnihensis Cheng, 2007 (Reptilia:Thalattosauria): Revealing its Transitional Position in Askeptosauridae

dinoweb — Tue, 16 Jul 2013 18:48:17 GMT

The skull of Anshunsaurus huangnihensis Cheng, 2007, especially the skull roof, is described in detail in this paper. Compared to other genera and species of Askeptosauroidea, Anshunsaurus huangnihensis has some important transitional characters from Askeptosaurus italicus to Anshunsaurus huangguoshuensis: the rostral length related to the skull length between Askeptosaurus italicus and Anshunsaurus huangguoshuensis; the postfrontal existing but distinctly reduced; the posterolateral process relatedly short and overlapping the parietal. The phylogenetic analysis weakly supports the evolutional progress from Anshunsaurus huangnihensis to Anshunsaurus huangguoshuensis. The skeletal ratios indicated that the node among the Askeptosauridae ingroup. The evolutional direction of Askeptosauridae should be from Askeptosaurus italicus to Anshunsaurus huangguoshuensis. The skeletal ratios indicated that the evolutional progress is Askeptosaurus italicus – Anshunsaurus huangnihensis – Anshunsaurus huangguoshuensis. In biogeography provinces, the Askeptosauroidea taxa from south China have a close relationship with those from western Tethys; however, Xinpusaurus from the Late Triassic is more related to those from the eastern Pacific.

Cheng Long Chen Xiaohong Zhang Baomin Cai Yongjian,2011 New Study of Anshunsaurus huangnihensis Cheng, 2007 (Reptilia:Thalattosauria): Revealing its Transitional Position in Askeptosauridae. Acta Geologica Sinica,85(6):1231-1237

The Braincase of the Basal Sauropod Dinosaur Spinophorosaurus and 3D Reconstructions of the Cranial Endocast and Inner Ear

dinoweb — Tue, 16 Jul 2013 18:46:27 GMT

Background: Sauropod dinosaurs were the largest animals ever to walk on land, and, as a result, the evolution of their

remarkable adaptations has been of great interest. The braincase is of particular interest because it houses the brain and inner ear. However, only a few studies of these structures in sauropods are available to date. Because of the phylogenetic position of Spinophorosaurus nigerensis as a basal eusauropod, the braincase has the potential to provide key evidence on the evolutionary transition relative to other dinosaurs.

Methodology/Principal Findings: The only known braincase of Spinophorosaurus (‘Argiles de l’Irhazer’, Irhazer Group;

Agadez region, Niger) differs significantly from those of the Jurassic sauropods examined, except potentially for Atlasaurus imelakei (Tilougguit Formation, Morocco). The basisphenoids of Spinophorosaurus and Atlasaurus bear basipterygoid processes that are comparable in being directed strongly caudally. The Spinophorosaurus specimen was CT scanned, and 3D renderings of the cranial endocast and inner-ear system were generated. The endocast resembles that of most other sauropods in having well-marked pontine and cerebral flexures, a large and oblong pituitary fossa, and in having the brain structure obscured by the former existence of relatively thick meninges and dural venous sinuses. The labyrinth is characterized by long and proportionally slender semicircular canals. This condition recalls, in particular, that of the basal non-sauropod sauropodomorph Massospondylus and the basal titanosauriform Giraffatitan.

Conclusions/Significance: Spinophorosaurus has a moderately derived paleoneuroanatomical pattern. In contrast to

what might be expected early within a lineage leading to plant-eating graviportal quadrupeds, Spinophorosaurus and

other (but not all) sauropodomorphs show no reduction of the vestibular apparatus of the inner ear. This characterstate

is possibly a primitive retention in Spinophorosaurus, but due the scarcity of data it remains unclear whether it is also the case in the various later sauropods in which it is present or whether it has developed homoplastically in these taxa. Any interpretations remain tentative pending the more comprehensive quantitative analysis underway, but the size and morphology of the labyrinth of sauropodomorphs may be related to neck length and mobility, among other factors.

Knoll F, Witmer LM, Ortega F, Ridgely RC, Schwarz-Wings D (2012) The Braincase of the Basal Sauropod Dinosaur Spinophorosaurus and 3D Reconstructions of the Cranial Endocast and Inner Ear. PLoS ONE 7(1): 1-12.

Homology and Architecture of the Caudal Basket of Pachycephalosauria (Dinosauria: Ornithischia): The First Occurrence of Myorhabdoi in Tetra

dinoweb — Tue, 16 Jul 2013 18:45:38 GMT

Background: Associated postcranial skeletons of pachycephalosaurids, most notably those of Stegoceras and Homalocephale, reveal enigmatic osseous structures not present in other tetrapod clades. The homology and functional

significance of these structures have remained elusive as they were originally interpreted to be abdominal ribs or gastralia, and more recently have been interpreted as de novo structures in the tail.

Principal Findings: Analysis of these structures in nearly all pachycephalosaurid skeletons has facilitated a complete

description of their architecture, and the establishment of patterns consistent with those of myorhabdoid ossifications —

ossifications of the myoseptal tendons associated with myomeres. The presence and structure of myorhabdoid ossifications are well established for teleost fish, but this marks their first recognition within Tetrapoda. These elements are both structurally and histologically distinct from the deep, paraxial ossified tendon bundles of other ornithischian clades, although they may have performed a similar function in the stiffening of the tail.

Conclusions/Significance:These myorhabdoi are not de novo structures, but are instead ossifications (and therefore more amenable to fossilization) of the normally unossified plesiomorphic caudal myosepta of vertebrates. The ubiquitous ossification of these structures in pachycephalosaurids (all specimens preserving the tail also exhibit myorhabdoid ossifications) suggests it is a likely synapomorphic condition for Pachycephalosauria.

Brown CM, Russell AP (2012) Homology and Architecture of the Caudal Basket of Pachycephalosauria (Dinosauria: Ornithischia): The First Occurrence of Myorhabdoi in Tetrapoda. PLoS ONE 7(1): 1-12.

Re-examination of Chuanjiesaurus anaensis (Dinosauria: Sauropoda) from the Middle Jurassic Chuanjie Formation, Lufeng County, Yunnan Provinc

dinoweb — Tue, 16 Jul 2013 18:42:21 GMT

The present study re-evaluates Chuanjiesaurus anaensis Fang et al., 2000 from the Middle Jurassic of Lufeng,Yunnan, Southwest China. The holotype and a new referred specimen are described in detail, and re-examined osteologically and phylogenetically. In this report, the author proposes several emended diagnoses based on close observations and comparisons of the specimens. Some osteological features reveal that Chuanjiesaurus belongs to Mamenchisauridae. Compared to other mamenchisaurid dinosaurs, C. anaensis possesses relatively primitive characters. The phylogenetic position of C. anaensis was determined according to the present analysis. In addition,the data sets of some taxa of Mamenchisauridae from southwestern China are modified in the present research. The present analysis reveals that C. anaensis, Mamenchisaurus, Tienshanosaurus and Yuanmousaurus constitute a monophyletic group that belongs to relatively derived Eusauropoda. This suggests that Mamenchisauridae could be positioned at a more derived part of Eusauropoda than previously thought. This study confirms that C. anaensis is a member of Mamenchisauridae.

T. Sekiya. 2011. Re-examination of Chuanjiesaurus anaensis (Dinosauria: Sauropoda) from the Middle Jurassic Chuanjie Formation, Lufeng County, Yunnan Province, southwest China. Memoir of the Fukui Prefectural Dinosaur Museum 10:1-54