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[dinosaur] Kem Kem titanosaur + Judith River tyrannosaurids + rhabdodontid bone histology




Ben Creisler
bcreisler@gmail.com

A new paper and two older papers not yet mentioned:

Many thanks to Nizar Ibrahim for notice of this paper:

Nizar Ibrahim, Cristiano Dal Sasso, Simone Maganuco, Matteo Fabbri, David M. Martill, Eric Gorscak and Matthew C. Lamanna (2016)

Evidence of a derived titanosaurian (Dinosauria, Sauropoda) in the 'Kem Kem beds' of Morocco, with comments on sauropod paleoecology in the Cretaceous of Africa.

Cretaceous Period: Biotic Diversity and Biogeography.   Bulletin of the New Mexico Museum of Natural History and Science 71: 149-159

(no current online link)


A well preserved middle caudal vertebra from middle Cretaceous (?Albian–lower Cenomanian) deposits informally known as the “Kem Kem beds” exposed in the Gara Sbaa region of Morocco is attributed to a large-bodied titanosaurian sauropod dinosaur. It represents one of the best-preserved and most complete skeletal elements reported for this sauropod group from the Kem Kem sequence. The vertebra is generally similar to middle caudals of the lithostrotian titanosaur Baurutitan britoi from the Upper Cretaceous Bauru Group of Brazil, but differs in several respects, such as: (1) a transversely compressed (as opposed to more square in posterior view) centrum; (2) a taller, anteroposteriorly longer, and more anteriorly positioned neural spine; and (3) prezygapophyses that are subtriangular in lateral view. It represents an animal that likely attained a very large body size (possibly over 25 m in total length), considerably larger than the diplodocoid Rebbachisaurus garasbae, the only named sauropod from the Kem Kem assemblage. Additional, selected specimens from the Kem Kem beds are described, with some probably referable to Titanosauria. In the Kem Kem sequence, sauropod fossils are far less common than those of predatory dinosaurs, which include several coeval, multi-ton taxa. This was likely due to an abundance of potential aquatic prey as well as complex niche partitioning among sympatric theropods, pterosaurs, and crocodyliforms. Nevertheless, some predators, such as the giant theropod Carcharodontosaurus saharicus, likely preyed on sauropods. The taxon represented by the new vertebra (and possibly other isolated remains from the Kem Kem region) and the giant Egyptian titanosaurian Paralititan stromeri rank among the largest known sauropods. Most other North African Cretaceous sauropods appear to have reached only modest adult body sizes; this could, however, be an artifact of the limited number of fossils and uncertainty in the ontogenetic stages represented by most specimens. The morphology of the Kem Kem vertebra suggests that the taxon it represents may have been more closely related to South American and/or European titanosaurians than to other members of this clade from sub-Saharan Africa. 

 


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From last year:



Sebastian G.  Dalman  & Spencer G. Lucas (2015) 

New data on the tyrannosaurid theropods from the middle Campanian Lower Judith River Formation of north-central Montana. 

Bulletin of the New Mexico Museum of Natural History and Science 68: 77-89.

(no current online link)



We document previously undescribed isolated cranial, axial, dental, and appendicular skeletal elements of tyrannosaurid theropods, which were collected in the middle Campanian deposits of the Lower Judith River Formation in north-central Montana. Examination of these bones and some of the teeth indicates that they belong to members of the Albertosaurinae clade. The cranial material described here is a cast of a well-preserved and nearly complete isolated right dentary that is referred to Gorgosaurus sp. The referral of the dentary to this genus is based on the proportions of the minimum dorsoventral depth of the main body of the dentary and the anteroposterior length of the tooth row, which is similar to that of subadult examples of Gorgosaurus libratus from the Dinosaur Park Formation of Alberta, Canada. Additionally, the paleogeographic and paleostratigraphic position of the specimen further supports the generic identification. The dentary of Gorgosaurus sp. exhibits a combination of morphological characters that differ from G. libratus and from other North American tyrannosaurid taxa, supporting the previous assumptions that the genus Gorgosaurus was morphologically diverse. The morphological characters include a sinuous “chin” that lacks the characteristic strong projection at its anteroventral margin, large and deep vascular foramina located at the alveolar margin on the anterolateral surface of the bone, and a strongly convex anteroventral articular facet for the splenial. The axial and appendicular skeletal elements described here are also referred to Gorgosaurus sp. and several isolated teeth to cf. Gorgosaurus sp., respectively. The referral of these skeletal fossil elements to Gorgosaurus is based on the paleogeographic and paleostratigraphic position and the overall morphology similar to that of G. libratus. Additionally, several small unserrated premaxillary teeth are identified here as cf. Daspletosaurus sp. Given our current knowledge, the unserrated D-shape in cross-section premaxillary teeth referred to tyrannosaurids represent an ontogenetic dimorphism that is known, thus far, only for Daspletosaurus and Tyrannosaurus. The paleogeographic and paleostratigraphic position of the teeth further supports their referral to cf. Daspletosaurus sp. and not to another North American tyrannosaurid.  


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A dinosaur paper from 2014 not previously mentioned on the DML (pdf is free)



Edina Prondvai (2014)

Comparative bone histology of rhabdodontid dinosaurs. 

Palaeovertebrata 38 (2)-e1. 

doi: 10.18563/pv.38.2.e1

http://www.palaeovertebrata.com/Articles/view/47


A comparative bone histological study of the three known genera of the endemic European ornithopod dinosaur family, Rhabdodontidae, is presented here in an ontogenetic context. Investigated specimens were assigned to different ontogenetic stages based exclusively on the histological indicators of osteologic maturation during diametrical bone growth; an entirely size-independent method as opposed to most previous studies. Qualitative comparison of bone histology of corresponding ontogenetic stages and elements among the three valid rhabdodontid genera, Mochlodon, Zalmoxes, and Rhabdodon, revealed some consistent patterns. Genus specific histological differences within Rhabdodontidae are most expressed between Rhabdodon and the Mochlodon-Zalmoxes clade. These indicate a prolonged phase of fast growth and a less constrained cyclicity in the growth dynamics of Rhabdodon, as opposed to the slower and more regulated growth strategy reflected in the bones of Mochlodon and Zalmoxes. These genus specific differences are consistent with the phylogenetic interrelation of the genera and are most probably related to the pronounced differences in body size. However, when compared to other ornithopods, most detected histological features in rhabdodontids do not seem to reliably reflect either phylogenetic relations or body size. A notable common feature of all rhabdodontid genera irrespective of body size is the ontogenetically early onset of cyclical growth and secondary remodelling; a pattern that more resembles the condition found in derived ornithopods than that described in more basal taxa which are closer relatives of rhabdodontids. The recognition of taxon-specific histological patterns as well as patterns indicative of ecological and thereby functional traits clearly requires more accurate, preferably quantitative evaluations.   


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