Thursday, 3 March 2016

New Large Kem Kem Abelisaurid

The Cenomanian sediments of the Moroccan-Algerian formation Kem Kem Beds has previously been known to yield indeterminate abelisaurid abelisauroid remains (Richter et al., 2013), but these have only been attributed to rather medium-sized teeth. Recently, however, Cau & Chiarenza 2016 have described a 'partial right femur' (OLPH 025) that measures 170mm in length - extrapolating from this measurement, the animal's total length  would have been ~9m, on par with Carnotaurus and Ekrixinatosaurus, meaning that abelisaurids reached their 'size peak' during the middle Cretaceous period - however, this paper seemingly doesn't account for the giant Kenyan abelisaurid remains (?11-12m TL).
Chiarenza AA, Cau A. (2016A large abelisaurid (Dinosauria, Theropoda) from Morocco and comments on the Cenomanian theropods from North AfricaPeerJ 4:e1754
Abstract:

We describe the partially preserved femur of a large-bodied theropod dinosaur from the Cenomanian “Kem Kem Compound Assemblage” (KKCA) of Morocco. The fossil is housed in the Museo Geologico e Paleontologico “Gaetano Giorgio Gemmellaro” in Palermo (Italy). The specimen is compared with the theropod fossil record from the KKCA and coeval assemblages from North Africa. The combination of a distally reclined head, a not prominent trochanteric shelf, distally placed lesser trochanter of stout, alariform shape, a stocky shaft with the fourth trochanter placed proximally, and rugose muscular insertion areas in the specimen distinguishes it from CarcharodontosaurusDeltadromeus and Spinosaurus and supports referral to an abelisaurid. The estimated body size for the individual from which this femur was derived is comparable to Carnotaurus and Ekrixinatosaurus (up to 9 meters in length and 2 tons in body mass). This find confirms that abelisaurids had reached their largest body size in the “middle Cretaceous,” and that large abelisaurids coexisted with other giant theropods in Africa. We review the taxonomic status of the theropods from the Cenomanian of North Africa, and provisionally restrict the Linnean binomina Carcharodontosaurus iguidensis and Spinosaurus aegyptiacus to the type specimens. Based on comparisons among the theropod records from the Aptian-Cenomanian of South America and Africa, a partial explanation for the so-called “Stromer’s riddle” (namely, the coexistence of many large predatory dinosaurs in the “middle Cretaceous” record from North Africa) is offered in term of taphonomic artifacts among lineage records that were ecologically and environmentally non-overlapping. Although morphofunctional and stratigraphic evidence supports an ecological segregation between spinosaurids and the other lineages, the co-occurrence of abelisaurids and carcharodontosaurids, two groups showing several craniodental convergences that suggest direct resource competition, remains to be explained.


Fukuivenator paradoxus: Weird New Maniraptoran

From the infamous lower Cretaceous period Kitadani Dinosaur Quarry, where the most iconic Japanese dinosaurs have been found, is Fukuivenator paradoxus. A maniraptoran, it's the first from Kitadani (and possibly Japan, unless there is some literature I'm not aware of), and the type sp├ęcimen (FPDM-V8461) exhibits an unusual mixture of basal maniraptoriform and derived dromaeosaurid characters, meaning that this theropod is an entirely new lineage of basally-branching maniraptoran. Plus, being part of this new lineage and simultaneously looking so similar to dromaeosaurids means that this is an instance of homoplasy ('convergent evolution') within Coelurosauria.

Yoichi Azuma, Xing Xu, Masateru Shibata, Soichiro Kawabe, Kazunori Miyata and Takuya Imai. 2016.  A Bizarre Theropod from the Early Cretaceous of Japan Highlighting Mosaic Evolution among Coelurosaurians. Scientific Reports. 6(20478); DOI: 10.1038/srep20478

Abstract:

Our understanding of coelurosaurian evolution, particularly of bird origins, has been greatly improved, mainly due to numerous recently discovered fossils worldwide. Nearly all these discoveries are referable to the previously known coelurosaurian subgroups. Here, we report a new theropod, Fukuivenator paradoxus, gen. et sp. nov., based on a nearly complete specimen from the Lower Cretaceous Kitadani Formation of the Tetori Group, Fukui, Japan. While Fukuivenator possesses a large number of morphological features unknown in any other theropod, it has a combination of primitive and derived features seen in different theropod subgroups, notably dromaeosaurid dinosaurs. Computed-tomography data indicate that Fukuivenator possesses inner ears whose morphology is intermediate between those of birds and non-avian dinosaurs. Our phylogenetic analysis recovers Fukuivenator as a basally branching maniraptoran theropod, yet is unable to refer it to any known coelurosaurian subgroups. The discovery of Fukuivenator considerably increases the morphological disparity of coelurosaurian dinosaurs and highlights the high levels of homoplasy in coelurosaurian evolution.