Ekrixinatosaurus (Explosion-Born Reptile) is a genus of dinosaur which lived during the Late Cretaceous. It was a theropod believed to be one of the abelisaurs. Its fossils have been found in Argentina. Only one species is currently recognized, Ekrixinatosaurus novasi, from which the specific name honors of Dr. Fernando Novas for his contributions to the study of abelisaurid theropods.
Discovery and naming[]
The type species, Ekrixinatosaurus novasi, was first described in 2004 by Argentinian paleontologist Jorge Calvo, and Chilean paleontologists David Rubilar-Rogers and Karen Moreno.[1] The fossils were found dispersed over an area of 15m2 in the Candeleros Formation, a geologic formation that outcrops in Río Negro, Neuquén, and Mendoza provinces of Argentina. This formation dates from 100-97 mya.[2], and consists of red beds where other famous vertebrate animals have been discovered, such as Giganotosaurus, Rebbachisaurus, and Andesaurus. The discovery occurred due to excavations for building a gas pipeline conducted by Gasoducto del Pacífico Company in Bajo del Añelo.[1]
Before the discovery of Ekrixinatosaurus, Carnotaurus sastrei and Aucasaurus garridoi were the most complete specimens of the abelisauridae family.[1] The remains of Ekrixinatosaurus helped fill in more information about abelisaur anatomy as it contained portions of the skeleton that were previously unknown, unpublished, or poorly preserved in other specimens.[1] The holotype skeleton (MUCPv-294) was well preserved yet disarticulated. It contained elements including a left and partial right maxillae; basicranium; both dentaries; teeth; cervical, a dorsal, sacral and caudal vertebrae; haemal arches; ribs; ilia, pubis and proximal ischia; left and distal end of right femur; left tibia; left astragalus and calcaneum; proximal end of left fibula and right tibia; metatarsals; phalanges; and a pedal ungual.
Description[]
Ekrixinatosaurus novasi is a large abelisaurid with a relatively large head and robust limbs. The combination of characteristics including a large skull, prominent supraorbital ridge above the dorsal aspect of the orbit, anteroposteriorly compressed cervical vertebrae, and robust, proportionally short hindlimbs with a tibia shorter than femur suggests that this was a massive animal with a great capacity to sustain injuries during intraspecific or interspecific combat.[3] The only known specimen was previously estimated between 7–8 m (23–26 ft) in length,[1] and some suggested that this specimen actually represented the largest abelisaurid yet known at 10–11 m (33–36 ft) in length, surpassing the type of Carnotaurus.[3] However, it was later noted by other researchers that this estimate was based only on the absolute size of the skull, ignoring that limb bone comparisons clearly show Carnotaurus was larger, thus Carnotaurus was larger than Ekrixinatosaurus but with a proportionally smaller head.[4] Most recently, a 2016 study again found it to be smaller (7.4 m) than Carnotaurus (7.8 m).
Skull[]
The skull of Ekrixinatosaurus was boxy and proportionally shorter and deeper than most other large carnivorous dinosaurs. The jaws also curved upwards, a trait shared with some other abelisaurs.[6] The skull is estimated to be approximately 83cm long based on comparisons with Carnotaurus and Majungasaurus, and while Abelisaurus does not have a complete maxilla its preserved size is similar to that of Ekrixinatosaurus.[3] As in other abelisaurids, the facial bones, especially the nasal bones, were sculptured with numerous small holes and spikes. In life, a wrinkled and possibly keratinous skin would have covered these bones.[6] The maxillia was short and contained 16 alveoli, some with short teeth that were flattened laterally with anterior and posterior serrations.[1] The maxilla of Ekrixinatosaurus also exhibits a dorsally projected ascending ramus and a short rostral ramus, suggesting a relatively high skull.
Classification[]
In 2004, Ekrixinatosaurus was placed in the Abelisauridae. The article by Calvo et al. in 2004, also contained a preliminary cladistic analysis of the phylogenetic relationships between Ekrixinatosaurus and those abelisaurids of which at the time relatively complete skeletons were known, finding it to be more closely related to Carnotaurini than to Ceratosaurus.
In 2008, a study recovered it as the sister species of Skorpiovenator.
| Carnotaurinae |
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