The Psittaciformes (parrots and cockatoos) are characterised by their large beaks, and are renowned for their ability to produce high bite forces. These birds also possess a suite of modifications to their cranial architecture interpreted to be adaptations for feeding on mechanically resistant foods, yet the relationship between cranial morphology and diet has never been explicitly tested. Here, we provide a three-dimensional geometric morphometric analysis of the developmental and biomechanical factors that may be influencing the evolution of psittaciformesâ distinctive cranial morphologies.
Contrary to our own predictions, we find that dietary preferences for more- or less- mechanically resistant foods have very little influence on beak and skull shape, and that diet predicts only 2.4% of the shape variation in psittaciform beaks and skulls. Conversely, evolutionary allometry and integration together predict almost half the observed shape variation, with phylogeny remaining an important factor in shape identity throughout our analyses, particularly in separating cockatoos (Cacatuoidea) from the true parrots (Psittacoidea).
Our results are similar to recent findings about the evolutionary trajectories of skull and beak shape in other avian families. We therefore propose that allometry and integration are important factors causing canalization of the avian head, and while diet clearly has an influence on beak shape between families, this may not be as important at driving evolvability within families as is commonly assumed.
In mammals, the infraorbital canal provides a passage for the infraorbital ramus of the maxillary branch of the trigeminal nerve. The infraorbital nerve ensures tactile sensitivity of the upper teeth and face between the eye and upper lip and, more significantly, the innervation of mystacial vibrissae (whiskers). In contrast, most non-mammalian synapsids display a more "reptilian-like" ancestral condition in which a long and ramified maxillary canal completely enclosed the infraorbital nerve along with other branches of the trigeminal nerve. The phylogenetic transition from the ancestral "reptilian-like" to the derived "mammal-like" condition has been hypothesized to occur at the base of the Probainognathia clade. Using ÎCT and synchrotron scanning, this study aims to document this transition in detail by focusing on a sample of non-mammalian probainognathian cynodonts and early mammaliaforms. We find that the mammalian condition is the result of a gradual shortening of the maxillary canal, which enabled the infraorbital nerve to ramify within the soft tissues of the face. Mobile whiskers became possible only after the mammalian infraorbital nerve had evolved, which suggest that these structures appeared in Probainognathus and more derived cynodonts. Finally a foramen located on the ventral margin of the lacrimal bone, which has been often homologized with the infraorbital foramen of derived Probainognathia and early Mammaliaformes, is most probably homologous to the mammalian zygomaticofacial foramen.
A conceptual model is established for nitrogen cycle during oceanic anoxic events.
N shows a decrease in nitrate availability after the end-Permian mass extinction.
The loss of NO was compensated, in anoxic conditions, in the form of NH.
Loss of dissolved nutrient-N in anoxia waters culminated in low ocean productivity.
Ammonium intoxication is a previously unexplored killing mechanism for extinctions.
The aftermath of end-Permian mass extinction was marked by a â5 million year interval of poorly-understood, extreme environments that likely hindered biotic recovery. Contemporary nitrogen isotope variations are considered, using a new conceptual model, to support a scenario that shows intensive nitrate-removal processes gradually depleted the global oceanic nitrate inventory during long-lasting oceanic anoxia. Enhanced nitrogen fixation shifted the oceanic nitrogenous nutrient (nutrient-N) inventory to an ammonium-dominated state. Ammonium is toxic to animals and higher plants but fertilizes algae and bacteria. This change in ocean chemistry could account for the intense and unexplained losses of nektonic taxa and the proliferation of microbial blooms in the Early Triassic. The transition from a nitrate ocean to an ammonium ocean was accompanied by a decrease in respiration efficiency of organisms and a shrinking oceanic nutrient-N inventory, ultimately leading to generally low productivity in the Early Triassic oceans. These unappreciated nutrient changes during episodes of prolonged ocean anoxia may be the key life-limiting factor at such times.
Earliest marine connection of the Araripe Basin, northeastern Brazil, during the Aptian.
Well preserved palynomorphs from the Santana Formation.
Microforaminiferal linings underlying the evaporitic "Ipubi Layers", Santana Formation.
Marine influence and arid conditions led to evaporite precipitation in the Araripe Basin.
Integrated sedimentologic and palynological analysis of four outcrops in the Aptian succession of the Araripe Basin provides information on the earliest marine connection of this basin. Palynological samples revealed well-preserved palynomorphs with diverse assemblages composed of pteridophyte spores and gymnospermic pollen grains, especially Classopollis, besides phytoclasts and abundant amorphous organic matter. Microforaminiferal linings were retrieved from two samples, both from the Santana Formation, immediately underlying the "Ipubi Layers". The few specimens recognized are well preserved, very similar to each other in size and shape (trochospiral morphology), and usually embedded within amorphous organic matter. These records indicate that the lower Crato Member was deposited in a marine environment. The increasing marine influence in the Araripe Basin, coupled with increasing aridity, allowed the accumulation of evaporites ("Ipubi Layers") in restrict portions of the basin. The small size of the inferred marine connection is probably why it has been so difficult to identify its precise geographic location.