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1
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Osteological correlates for quadrupedality in ornithischian dinosaurs

100%
Maidment S. C. R., Barrett P. M.
Acta Palaeontologica Polonica
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2014
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tom 59
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nr 1
The evolution of quadrupedality from bipedal ancestors is an exceptionally rare transition in tetrapod evolution, but it has occurred several times within the herbivorous dinosaur clade Ornithischia. Stegosauria, Ankylosauria, and Ceratopsidae are all uncontroversially quadrupedal, while basal ornithischians and basal ornithopods are uncontroversially bipedal. However, stance in iguanodontian ornithopods, including the hadrosaurs, and in non-ceratopsid ceratopsians is debated because robust osteological correlates of quadrupedality have not been identified. We examine a suite of characteristics that have been previously proposed as osteological correlates for bipedality or quadrupedality in dinosaurs. These include both discrete anatomical features, which we assess as correlates for quadrupedality using character optimization onto a composite cladogram, and proportional ratios, which we assess as correlates by reconstructing nodal ancestral states using squared-change parsimony, followed by optimization. We also examine the correlation of these features with body size. An anterolateral process on the proximal ulna, hoof-shaped manual unguals, a transversely broadened ilium, a reduced fourth trochanter and a femur longer than the tibia are found to be robust correlates of quadrupedality in ornithischian dinosaurs. Along the ceratopsid “stem” lineage, quadrupedal characters were acquired in a stepwise fashion, with forelimb characters developing prior to changes in the hind limb. In contrast, iguanodontid ornithopods display a mosaic of character states, indicating varying degrees of facultative quadrupedality that probably arose for a variety of different reasons. Hadrosaurs are found to possess all character states associated with quadrupedality and were probably predominantly quadrupedal. In general, quadrupedal ornithischians do not appear to have been constrained by their bipedal ancestry to a particular order of character acquisition.
2
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Cranial anatomy of the iguanodontoid ornithopod Jinzhousaurus yangi from the Lower Cretaceous Yixian Formation of China

81%
Barrett P. M., Butler R. J., Xiao-Lin W., Xing X.
Acta Palaeontologica Polonica
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2009
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tom 54
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nr 1
35-48
The Yixian Formation (Lower Cretaceous) of Liaoning Province, China, is justifiably famous for its exceptionally preserved fauna, which includes a remarkable diversity of non−avian dinosaurs. Here, we provide the first detailed description of the cranial skeleton of the iguanodontian ornithopod Jinzhousaurus yangi. Many previously unrecorded features have been recognised, permitting a new and more robust diagnosis for this taxon, which is based on a suite of autapomorphic features. Jinzhousaurus and an unnamed sauropod represent the largest, but some of the least abundant, animals in the Jehol Biota, a situation that contrasts with many other Lower Cretaceous faunas in which large dinosaurs are common faunal components. This rarity may be due to either palaeoenvironmental constraints or taphonomic bias, although it is not possible to choose between these alternatives on the basis of current data.
3
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A reassessment of the purported ankylosaurian dinosaur Bienosaurus lufengensis from the Lower Lufeng Formation of Yunnan, China

81%
Raven T. J., Barrett P. M., Xu X., Maidment S. C. R.
Acta Palaeontologica Polonica
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2019
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tom 64
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nr 2
The earliest definitive ornithischian dinosaurs are from the Early Jurassic and are rare components of early dinosaur faunas. The Lower Lufeng Formation (Hettangian–Sinemurian) of Yunnan Province, China, has yielded a diverse Early Jurassic terrestrial vertebrate fauna. This includes several incomplete specimens have been referred to Ornithischia, including the type specimen of the thyreophoran “Tatisaurus” and other generically indeterminate material. The highly fragmentary Lufeng ornithischian Bienosaurus lufengensis was described briefly in 2001 and identified as an ankylosaurian dinosaur. Recent studies have cast doubt on this hypothesis, however, and given that the referral of Bienosaurus to Ankylosauria would result in an extensive ghost-lineage extending between it and the first definitive eurypodans (ankylosaurs + stegosaurs) in the Middle Jurassic, the holotype specimen is re-examined and re-described. We identify Bienosaurus as a probable thyreophoran dinosaur, although the fragmentary nature of the material and the absence of autapomorphies means that the specimen should be regarded as a nomen dubium.
4
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Sauropod dinosaur remains from a new Early Jurassic locality in the Central High Atlas of Morocco

81%
Nicholl C. S. C., Mannion P. D., Barrett P. M.
Acta Palaeontologica Polonica
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2018
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tom 63
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nr 1
Despite being globally widespread and abundant throughout much of the Mesozoic, the early record of sauropod dinosaur evolution is extremely poor. As such, any new remains can provide significant additions to our understanding of this important radiation. Here, we describe two sauropod middle cervical vertebrae from a new Early Jurassic locality in the Haute Moulouya Basin, Central High Atlas of Morocco. The possession of opisthocoelous centra, a well-developed system of centrodiapophyseal laminae, and the higher elevation of the postzygapophyses relative to the prezygapophyses, all provide strong support for a placement within Sauropoda. Absence of pneumaticity indicates non-neosauropod affinities, and several other features, including a tubercle on the dorsal margin of the prezygapophyses and an anteriorly slanting neural spine, suggest close relationships with various basal eusauropods, such as the Middle Jurassic taxa Jobaria tiguidensis and Patagosaurus fariasi. Phylogenetic analyses also support a position close to the base of Eusauropoda. The vertebrae differ from the only other Early Jurassic African sauropod dinosaurs preserving overlapping remains (the Moroccan Tazoudasaurus naimi and South African Pulanesaura eocollum), as well as stratigraphically younger taxa, although we refrain from erecting a new taxon due to the limited nature of the material. These new specimens represent one of the earliest eusauropod taxa and are an important additional data point for elucidating the early evolution of the clade.
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A new centrosaurine from the Late Cretaceous of Alberta, Canada, and the evolution of parietal ornamentation in horned dinosaurs

61%
Farke A. A., Ryan M. J., Barrett P. M., Tanke D. H., Braman D. R., Loewen M. A., Graham M. R.
Acta Palaeontologica Polonica
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2011
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tom 56
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nr 4
In 1916, a centrosaurine dinosaur bonebed was excavated within the Campanian−aged deposits of what is now Dinosaur Provincial Park, Alberta, Canada. Specimens from this now−lost quarry, including two parietals, a squamosal, a skull missing the frill, and an incomplete dentary, were purchased by The Natural History Museum, London. The material was recently reprepared and identified herein as a previously unknown taxon, Spinops sternbergorum gen. et sp. nov. Based upon the available locality data and paleopalynology, the quarry lies in either the upper part of the Oldman Formation or the lower part of the Dinosaur Park Formation. The facial region of the partial skull is similar to putative mature specimens of Centrosaurusspp. and Styracosaurus albertensis, with short, rounded postorbital horncores and a large, erect nasal horncore. Parietal ornamentation is consistent on both known parietals and is unique among ceratopsids. Bilateral, procurved parietal hooks occupy the P1 (medial−most) position on the dorsal surface of the parietal and are very similar to those seen in Centrosaurus apertus. Epiparietals in the P2 or possibly P3 position (lateral to P1) manifest as extremely elongate, caudally directed spikes, unlike the condition in C. apertus, S. albertensis, or any other “derived” centrosaurine. Cladistic analysis suggests that S. sternbergorum is closely related to Centrosaurus and Styracosaurus. Historically, based upon the condition in Styracosaurus and related centrosaurines, it was assumed that the medial−most elongated spikes on centrosaurine parietals correspond to the P3 epiparietal position. The exception illustrated in the new taxon suggests that homologies of epiparietals among basal centrosaurines (e.g., Albertaceratops and Diabloceratops) and derived centrosaurines (e.g., Styracosaurus and “pachyrhinosaurs”) should be reconsidered. The medially−placed, caudally−directed “P3” process of basal centrosaurines may, in fact, be homologous with P2.
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