John R. Horner
Montana State University
Publications 111
#1Christian Thomas Heck (OSU: Oklahoma State University–Stillwater)H-Index: 1
#2David J. Varricchio (MSU: Montana State University)H-Index: 28
Last.John R. Horner (Chapman University)H-Index: 44
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1 CitationsSource
#1Dana J. Rashid (MSU: Montana State University)H-Index: 2
#2Kevin Surya (MSU: Montana State University)H-Index: 1
Last.John R. Horner (MSU: Montana State University)H-Index: 44
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The avian tail played a critical role in the evolutionary transition from long- to short-tailed birds, yet its ontogeny in extant birds has largely been ignored. This deficit has hampered efforts to effectively identify intermediate species during the Mesozoic transition to short tails. Here we show that fusion of distal vertebrae into the pygostyle structure does not occur in extant birds until near skeletal maturity, and mineralization of vertebral processes also occurs long after hatching. Ev...
1 CitationsSource
#1Alida M. Bailleul (MSU: Montana State University)H-Index: 8
#2John R. Horner (MSU: Montana State University)H-Index: 44
Sutures and synchondroses, the fibrous and cartilaginous articulations found in the skulls of vertebrates, have been studied for many biological applications at the morphological scale. However, little is known about these articulations at the microscopic scale in non-mammalian vertebrates, including extant archosaurs (birds and crocodilians). The major goals of this paper were to: (i) document the microstructure of some sutures and synchondroses through ontogeny in archosaurs; (ii) compare thes...
13 CitationsSource
#1John P. Wilson (MSU: Montana State University)H-Index: 29
#2D. Cary Woodruff (MSU: Montana State University)H-Index: 5
Last.Chris L. Organ (MSU: Montana State University)H-Index: 19
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Rugose projections on the anterior and posterior aspects of vertebral neural spines appear throughout Amniota and result from the mineralization of the supraspinous and interspinous ligaments via metaplasia, the process of permanent tissue-type transformation. In mammals, this metaplasia is generally pathological or stress induced, but is a normal part of development in some clades of birds. Such structures, though phylogenetically sporadic, appear throughout the fossil record of non-avian thero...
5 CitationsSource
#1Alida M. Bailleul (MSU: Montana State University)H-Index: 8
#2John B. Scannella (MSU: Montana State University)H-Index: 6
Last.David C. Evans (U of T: University of Toronto)H-Index: 23
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The sutures of the skulls of vertebrates are generally open early in life and slowly close as maturity is attained. The assumption that all vertebrates follow this pattern of progressive sutural closure has been used to assess maturity in the fossil remains of non-avian dinosaurs. Here, we test this assumption in two members of the Extant Phylogenetic Bracket of the Dinosauria, the emu, Dromaius novaehollandiae and the American alligator, Alligator mississippiensis, by investigating the sequence...
23 CitationsSource
#1Alida M. Bailleul (MSU: Montana State University)H-Index: 8
#2Catherine Nyssen-Behets (UCL: Université catholique de Louvain)H-Index: 8
Last.John R. Horner (MSU: Montana State University)H-Index: 44
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Abstract In histology textbooks, the vertebrate skeleton is represented as almost entirely made of bone and cartilage. This is a false dichotomy and in fact, a continuum of intermediate tissues between bone and cartilage exists. Chondroid bone ([CB] or chondroid tissue), one of the most well-known intermediate tissues, has been reported in mammals, birds and crocodilians. It accommodates (1) rapid growth of the skull and (2) the development of craniofacial sutures. Since CB is present in the ext...
8 CitationsSource
#1John R. Horner (MSU: Montana State University)H-Index: 44
#2Holly N. Woodward (MSU: Montana State University)H-Index: 10
Last.Alida M. Bailleul (MSU: Montana State University)H-Index: 8
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Abstract Evolutionary biologists define “metaplasia” as the permanent transformation of a cell identity, and there are many examples of such transformations in living vertebrates (e.g., chondrocytes transforming directly into osteoblasts). These metaplasias have been observed during the mineralization of “ossified” tendons of living birds. In the present study, we examined “ossified” tendons in Bubo and Meleagris and used the characteristics of these metaplastic tissues to recognize them in seve...
13 CitationsSource
#1Kevin Padian (University of California, Berkeley)H-Index: 16
#2Sarah Werning (SBU: Stony Brook University)H-Index: 8
Last.John R. Horner (MSU: Montana State University)H-Index: 44
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Abstract We propose the hypothesis that in the long bones of large, rapidly growing animals, secondary osteons may form to a greater degree in smaller bones than in larger ones for reasons that may have more to do with the interplay between element-specific growth rates and whole-body metabolic rates than with mechanical or environmental factors. We predict that in many large animals with rapid growth trajectories and some disparity in size in the long bones and other skeletal elements, the larg...
14 CitationsSource
#1Elizabeth A. Freedman Fowler (MSU: Montana State University)H-Index: 2
#2John R. Horner (MSU: Montana State University)H-Index: 44
Background Brachylophosaurini is a clade of hadrosaurine dinosaurs currently known from the Campanian (Late Cretaceous) of North America. Its members include: Acristavus gagslarsoni, which lacks a nasal crest; Brachylophosaurus canadensis, which possesses a flat paddle-shaped nasal crest projecting posteriorly over the dorsal skull roof; and Maiasaura peeblesorum, which possesses a dorsally-projecting nasofrontal crest. Acristavus, from the lower Two Medicine Formation of Montana (~81–80 Ma), is...
19 CitationsSource
#1Holly N. WoodwardH-Index: 10
#2Elizabeth A. Freedman Fowler (MSU: Montana State University)H-Index: 2
Last.John R. Horner (MSU: Montana State University)H-Index: 44
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Abstract Fossil bone microanalyses reveal the ontogenetic histories of extinct tetrapods, but incomplete fossil records often result in small sample sets lacking statistical strength. In contrast, a histological sample of 50 tibiae of the hadrosaurid dinosaur Maiasaura peeblesorum allows predictions of annual growth and ecological interpretations based on more histologic data than any previous large sample study. Tibia length correlates well (R2 > 0.9) with diaphyseal circumference, cortical are...
30 CitationsSource