Roland B. Sookias (2016)
The relationships of the Euparkeriidae and the rise of Archosauria.
Royal Society Open Science 3: 150674.
For the first time, a phylogenetic analysis including all putative euparkeriid taxa is conducted, using a large data matrix analysed with maximum parsimony and Bayesian analysis. Using parsimony, the putative euparkeriid Dorosuchus neoetus from Russia is the sister taxon to Archosauria + Phytosauria. Euparkeria capensis is placed one node further from the crown, and forms a euparkeriid clade with the Chinese taxa Halazhaisuchus qiaoensis and ‘Turfanosuchus shageduensis’ and the Polish taxon Osmolskina czatkowicensis. Using Bayesian methods, Osmolskina and Halazhaisuchus are sister taxa within Euparkeriidae, in turn sister to ‘Turfanosuchus shageduensis’ and then Euparkeria capensis. Dorosuchus is placed in a polytomy with Euparkeriidae and Archosauria + Phytosauria. Although conclusions remain tentative owing to low node support and incompleteness, a broad phylogenetic position close to the base of Archosauria is confirmed for all putative euparkeriids, and the ancestor of Archosauria +Phytosauria is optimized as similar to euparkeriids in its morphology. Ecomorphological characters and traits are optimized onto the maximum parsimony strict consensus phylogeny presented using squared change parsimony. This optimization indicates that the ancestral archosaur was probably similar in many respects to euparkeriids, being relatively small, terrestrial, carnivorous and showing relatively cursorial limb morphology; this Bauplan may have underlain the exceptional radiation and success of crown Archosauria.
Proterosuchids are a clade of quadrupedal, carnivorous Permo-Triassic diapsids crucial to understand the successful evolutionary radiation of archosaurs during the Mesozoic. The importance and good fossil record of proterosuchids nourished a renewed interest in recent years, but no function has been proposed for their bizarre snouts. An oversized and downturned premaxilla with up to nine teeth with continuous replacement is present in all proterosuchid species and seems to have represented a physiologically costly phenotype that increased towards adulthood. A non-functional or a species recognition hypothesis are not supported as evolutionary mechanisms that drove this phenotype because features expected for these explanations tend to have a very low or zero physiological cost. There is no evidence favouring – but neither rejecting − that this morphology can be explained by non-sexual and non-social natural selection alone. Mutual social and/or sexual selection is favoured here as the most unambiguously supported explanation for the function and origin of the bizarre snout of proterosuchids based on several lines of evidence, including costliness, positive allometry, positive changes in growth rates and modern analogues. Social and/or sexual selection may have been important evolutionary mechanism in the dawn of the lineage that gave rise to crocodiles and dinosaurs.