Highlights
Trace fossils on bones are reported from the Upper Cretaceous of the HaÅeg Basin.
Most of the bioerosional traces are indicative of feeding behaviour.
The tracemakers are: termites, beetles, multituberculates, archosaurs and plants.
Association of different traces allows the reconstruction of the taphonomy.
Scavenging and death of the vertebrates occurred on drylands in a fluvial system.
Abstract
Bioerosion on fossil bones offers significant insights into both trophic relationships of ancient ecosystems and vertebrate taphonomy. Here we report six distinct trace fossil categories identified on isolated turtle, crocodyliform and dinosaur remains from the Upper Cretaceous SÃnpetru Formation of the HaÅeg Basin (Romania), for which five different probable tracemakers are identified: (1) termites, (2) dermestid beetles, (3) multituberculate mammals, (4) ziphodont theropod dinosaurs or crocodyliforms, and (5) plants. This extraordinary diversity of bioerosional trace fossils on vertebrate remains reveals insect-vertebrate as well as vertebrate-vertebrate interactions previously undocumented in the continental uppermost Cretaceous of Romania. The association between different traces, especially since many of these are superimposed on top of each other, allows the reconstruction of the detailed taphonomic history of the specimens, indicating four different taphonomic pathways. The vertebrate remains with trace fossils described here were most likely exposed to post-mortem biotic interactions for a prolonged time period before they were transported and/or trampled and finally buried. In the palaeoenvironmental context of a heterogeneous braided river system with low-lying wetlands and more elevated drylands, the death of the vertebrates as well as the scavenging likely occurred on the drylands.
====
Free pdf:
Crocodylomorpha, which includes living crocodylians and their extinct relatives, has a rich fossil record, extending back for more than 200 million years. Unlike modern semi-aquatic crocodylians, extinct crocodylomorphs exhibited more varied lifestyles, ranging from marine to fully terrestrial forms. This ecological diversity was mirrored by a remarkable morphological disparity, particularly in terms of cranial morphology, which seems to be closely associated with ecological roles in the group. Here, I use geometric morphometrics to comprehensively investigate cranial shape variation and disparity in Crocodylomorpha. I quantitatively assess the relationship between cranial shape and ecology (i.e. terrestrial, aquatic, and semi-aquatic lifestyles), as well as possible allometric shape changes. I also characterise patterns of cranial shape evolution and identify regime shifts. I found a strong link between shape and size, and a significant influence of ecology on the observed shape variation. Terrestrial taxa, particularly notosuchians, have significantly higher disparity, and shifts to more longirostrine regimes are associated with large-bodied aquatic or semi-aquatic species. This demonstrates an intricate relationship between cranial shape, body size and lifestyle in crocodylomorph evolutionary history. Additionally, disparity-through-time analyses were highly sensitive to different phylogenetic hypotheses, suggesting the description of overall patterns among distinct trees. For crocodylomorphs, most results agree in an early peak during the Early Jurassic and another in the middle of the Cretaceous, followed by nearly continuous decline until today. Since only crown-group members survived through the Cenozoic, this decrease in disparity was likely the result of habitat loss, which narrowed down the range of crocodylomorph lifestyles.
===
Osmoregulation in birds is complicated, with different organs acting concurrently to regulate this physiological process. Of particular interest is how the urinary excretions of birds can remove excess nitrogen while minimizing the need for dietary water and balancing the physiological demands of oviparity. It has long been concluded from chemical analyses, and more recently from genetic studies, that uric acid is the principal constituent of urine in Aves. However, research has also demonstrated that waste material may be modified in the ceca immediately prior to it being expelled. Here, we quantify the chemical composition of the urine component of excreta of six avian species using X-ray diffraction techniques to test the hypothesis that it is principally composed of uric acid, as commonly reported. None of the analyzed samples were found to contain uric acid. Instead, a variety of compounds including ammonium urate, struvite (magnesium ammonium phosphate), and two unknown compounds, were found. Our results show that the uric acid pathway is indeed the system by which nitrogen is removed in these birds, but that additional modification occurs in the urine prior to excretion. These results raise questions for future research on the urinary excretions of birds, including identification of the unknown compounds found in the present study.
====