[Paleontology • 2017] A New Phylogeny of Stegosauria (Dinosauria, Ornithischia)

DOI:  10.1111/pala.12291 

Abstract

The stegosaurs are some of the most easily recognizable dinosaurs, but are surprisingly rare as fossils. Consequently much remains unknown about their palaeobiology, and every new stegosaurian find contributes to our understanding of the evolution of the clade. Since the last attempt to examine the evolutionary relationships of Stegosauria, new specimens have come to light, including the most complete individual of Stegosaurus ever found, new taxa have been described and, perhaps most importantly, new methods for analysis of cladistic datasets have been produced. In the light of these new data and technological advances, the phylogenetic relationships of the stegosaurs and basal armoured dinosaurs are investigated. The inclusion of continuous data results in much better resolution than was previously obtained, and the resulting single most parsimonious tree supports re-erection of the genera Miragaia and Hesperosaurus, which had previously been synonymized with Dacentrurus and Stegosaurus respectively. The recently described genus Alcovasaurus is resolved as a basal thyreophoran, but this is most likely a consequence of a very high degree of missing data and the questionable ontogenetic stage of the specimen. Examination of the effects of continuous data on the analysis suggest that while it contains a phylogenetic signal congruent with that of discrete data and provides better resolution than discrete data alone, it can affect topologies in unpredictable ways, particularly in areas of the tree where there are large amounts of missing data. The phylogeny presented here will form the basis for future work on the palaeobiology of the plated dinosaurs.

Illustration: Davide Bonadonna 

Thomas J. Raven and Susannah C. R. Maidment. 2017. A New Phylogeny of Stegosauria (Dinosauria, Ornithischia).  Palaeontology. 60(3); 401–408. DOI: 10.1111/pala.12291 

 twitter.com/ThePalAss/status/854257910276292608

[Paleontology • 2015] Evidence for Sexual Dimorphism in the Plated Dinosaur Stegosaurus mjosi (Ornithischia, Stegosauria) from the Morrison Formation (Upper Jurassic) of Western USA

Fig 4. Hypothetical silhouettes of male and female Stegosaurus mjosi.
  The wide morph exhibits more overlap between adjacent plates than does the tall morph, leading to a more continuous display surface. Sexual dimorphism in the size and shape and plates might have also occurred with other sexual differences such as sexual dichromatism.

doi: 10.1371/journal.pone.0123503.g004

Abstract

Conclusive evidence for sexual dimorphism in non-avian dinosaurs has been elusive. Here it is shown that dimorphism in the shape of the dermal plates of Stegosaurus mjosi (Upper Jurassic, western USA) does not result from non-sex-related individual, interspecific, or ontogenetic variation and is most likely a sexually dimorphic feature. One morph possessed wide, oval plates 45% larger in surface area than the tall, narrow plates of the other morph. Intermediate morphologies are lacking as principal component analysis supports marked size- and shape-based dimorphism. In contrast, many non-sex-related individual variations are expected to show intermediate morphologies. Taphonomy of a new quarry in Montana (JRDI 5ES Quarry) shows that at least five individuals were buried in a single horizon and were not brought together by water or scavenger transportation. This new site demonstrates co-existence, and possibly suggests sociality, between two morphs that only show dimorphism in their plates. Without evidence for niche partitioning, it is unlikely that the two morphs represent different species. Histology of the new specimens in combination with studies on previous specimens indicates that both morphs occur in fully-grown individuals. Therefore, the dimorphism is not a result of ontogenetic change. Furthermore, the two morphs of plates do not simply come from different positions on the back of a single individual. Plates from all positions on the body can be classified as one of the two morphs, and previously discovered, isolated specimens possess only one morph of plates. Based on the seemingly display-oriented morphology of plates, female mate choice was likely the driving evolutionary mechanism rather than male-male competition. Dinosaur ornamentation possibly served similar functions to the ornamentation of modern species. Comparisons to ornamentation involved in sexual selection of extant species, such as the horns of bovids, may be appropriate in predicting the function of some dinosaur ornamentation.

Evan Thomas Saitt. 2015. Evidence for Sexual Dimorphism in the Plated Dinosaur Stegosaurus mjosi (Ornithischia, Stegosauria) from the Morrison Formation (Upper Jurassic) of Western USA.

PLoS ONE.  DOI: 10.1371/journal.pone.0123503

[Paleontology • 2014] Osteoderm Distribution has Low Impact on the Centre of Mass of stegosaurs

Abstract

It has been hypothesized that the pronounced differences of stegosaur humeral shapes, with large forms having more slender and small forms having more robust humeri, may be explained by a difference in relative centre of mass (COM) placement caused by differing distributions of osteoderms. To test this hypothesis, digital 3-D models of the bones and osteoderms of the Tanzanian stegosaur Kentrosaurus aethiopicus and of the North American stegosaur Stegosaurus armatus were used to create a 3-D computer-aided design life reconstruction. On these models osteoderm placement was varied drastically, recreating both existing and hypothetical forms. These models show that COM position varies somewhat with realistic osteoderm distributions, but insufficiently to explain major differences in humeral shape. The uniform weight distribution between forelimbs and hindlimbs found between the two taxa also casts doubt on the hypothesis that differences in relative COM position caused by other factors than osteoderm distribution can explain differences in humeral robustness.

H. Mallison. 2014. Osteoderm Distribution has Low Impact on the Centre of Mass of stegosaurs. Foss. Rec. 17, 33-39 doi: dx.doi.org/10.5194/fr-17-33-2014 | www.foss-rec.net/17/33/2014

[Paleontology • 2009] Miragaia longicollum ‘wonderful goddess of the Earth’ • A new long-necked 'sauropod-mimic' stegosaur and the evolution of the plated dinosaurs

Miragaia longicollum

Art: Davide Bonadonna |  http://davidebonadonna.it/?p=204

Stegosaurian dinosaurs have a quadrupedal stance, short forelimbs, short necks, and are generally considered to be low browsers. A new stegosaur, Miragaia longicollum gen. et sp. nov., from the Late Jurassic of Portugal, has a neck comprising at least 17 cervical vertebrae. This is eight additional cervical vertebrae when compared with the ancestral condition seen in basal ornithischians such as Scutellosaurus. Miragaia has a higher cervical count than most of the iconically long-necked sauropod dinosaurs. Long neck length has been achieved by ‘cervicalization’ of anterior dorsal vertebrae and probable lengthening of centra. All these anatomical features are evolutionarily convergent with those exhibited in the necks of sauropod dinosaurs. Miragaia longicollumis based upon a partial articulated skeleton, and includes the only known cranial remains from any European stegosaur. A well-resolved phylogeny supports a new clade that unites Miragaia and Dacentrurus as the sister group to Stegosaurus; this new topology challenges the common view of Dacentrurus as a basal stegosaur.

Keywords: Stegosaurian dinosaurs; Miragaia longicollum; Dacentrurus; neck elongation; niche partitioning; sexual selection

Miragaia skeleton. 

Image courtesy Octavio Mateus

http://archosaurmusings.wordpress.com/2009/03/04/guest-post-miragaia-longicollum-a-new-stegosaur-from-portugal/

Etymology: Miragaia, after the locality and geological unit of the same name; longicollum, after the Latin longus(long) and collum (neck), in reference to its long neck. In addition, the stem Mira- can be read as the feminine form of Latin mirus, meaning wonderful, while Gaia is the Greek goddess of the Earth, so the name also means ‘wonderful goddess of the Earth’.

Locality and horizon: Close to Miragaia at the municipality of Lourinhã (Portugal) in the Late Jurassic (Upper Kimmeridgian–Lower Tithonian) Miragaia Unit of the Sobral Formation (Lourinhã Group).

a family of Miragaia feeding

by ~EoFauna on @deviantART http://eofauna.deviantart.com/

http://jura.0forum.biz/t491-miragaia 

Mateus, Octávio; Maidment, Susannah C.R.; and Christiansen, Nicolai A. 2009. A new long-necked 'sauropod-mimic' stegosaur and the evolution of the plated dinosaurs. Proceedings of the Royal Society B: Biological Sciences. 276 (1663): 1815–1821. doi:10.1098/rspb.2008.1909

http://sobretudoeparcadeverao.blogspot.com/2009/03/dinossauro-miragaia.html

[Paleontology • 2001] Hesperosaurus mjosi • New Primitive Stegosaur from the Morrison Formation, Wyoming, northern America

Hesperosaurus 

(meaning "western lizard", from Classical Greek, ἕσπερο-/hespero- "western" and σαυρος/saurus "lizard") 

a herbivorous dinosaur from the Kimmeridgian to Tithonian epochs of the Jurassic period (approximately 150 million years ago), whose fossils are found in the state of Wyoming in the United States of America. It is from an older part of the Morrison Formation, and so a little older than other Morrison Stegosaurs.

http://en.wikipedia.org/wiki/Hesperosaurus

Carpenter K, Miles CA, Cloward K 2001. New Primitive Stegosaur from the Morrison Formation, Wyoming. In Carpenter, Kenneth(ed). The Armored Dinosaurs. Indiana University Press. pp. 55–75.

http://scienceblogs.com/tetrapodzoology/2010/12/29/stegosaur-wars/

[Paleontology • 1992] Gigantspinosaurus sichanensis • Discovery of Gigantspinosaurus and its scapular spine orientation

Gigantspinosaurus sichuanensis

by ~T-PEKC on @deviantART | http://t-pekc.deviantart.com

Gigantspinosaurus (meaning "giant-spined lizard")

a genus of herbivorous ornithischian dinosaur from the Late Jurassic. It was a stegosaur found in Sichuan, China.

The first fossil was found in 1985 by Ouyang Hui at Pengtang near Jinquan and was reported upon in 1986 by Gao Ruiqi and colleagues, mistaking it for a specimen of Tuojiangosaurus. The type species, Gigantspinosaurus sichuanensis, was described and named by Ouyang in 1992 in an abstract of a lecture. 

The generic name is derived from Latin gigas or giganteus, "enormous", and spina, "spine", in reference to the gigantic shoulder spines. The specific name refers to Sichuan.

http://en.wikipedia.org/wiki/Gigantspinosaurus

Ouyang, H. 1992. Discovery of Gigantspinosaurus sichanensis and its scapular spine orientation. Abstracts and Summaries for Youth Academic Symposium on New Discoveries and Ideas in Stratigraphic Paleontology (in Chinese). 47–49.

http://t-pekc.deviantart.com/art/Gigantspinosaurus-sichuanensis-361078529

http://carnivoraforum.com/topic/9764109/1/

http://en.wikipedia.org/wiki/Gigantspinosaurus

http://blogs.smithsonianmag.com/dinosaur/2012/11/g-is-for-gigantspinosaurus/