Gerald Mayr & Stephan F.K. Schaal (2016)
Gastric pellets with bird remains from the Early Eocene of Messel.
PALIOS (advance online publication)
Gastric pellets (i.e., regurgitated indigestible food remains) are rare in the fossil record. Here, we describe three gastric pellets with bird remains from the early Eocene Messel fossil site in Germany. A small, ball-shaped specimen that contains various broken bird bones resembles the pellets of owls and may have been produced by the Messel owl Palaeoglaux artophoron, which would make it the oldest owl pellet identified so far. The two other gastric pellets with bird remains have more elongated shapes and probably stem from snakes or other squamates. Both contain partially articulated bird skeletons, one of which belongs to an undescribed species that is otherwise unknown from the abundant avian fossil record from Messel. The fossil pellets described here therefore not only contribute to a better understanding of the avifauna of Messel, but are also important for reconstructing trophic webs and add to an understanding of the early Eocene Messel ecosystem.
William Ruger Porter, Jayc C. Sedlmayr and Lawrence M. Witmer (2016)
Vascular patterns in the heads of crocodilians: blood vessels and sites of thermal exchange.
Journal of Anatomy (advance online publication)
Extant crocodilians are a highly apomorphic archosaur clade that is endothermic, yet often achieve large body sizes that can be subject to higher heat loads. Therefore, the anatomical and physiological roles that blood vessels play in crocodilian thermoregulation need further investigation to better understand how crocodilians establish and maintain cephalic temperatures and regulate neurosensory tissue temperatures during basking and normal activities. The cephalic vascular anatomy of extant crocodilians, particularly American alligator (Alligator mississippiensis) was investigated using a differential-contrast, dual-vascular injection technique and high resolution X-ray micro-computed tomography (μCT). Blood vessels were digitally isolated to create representations of vascular pathways. The specimens were then dissected to confirm CT results. Sites of thermal exchange, consisting of the oral, nasal, and orbital regions, were given special attention due to their role in evaporative cooling and cephalic thermoregulation in other diapsids. Blood vessels to and from sites of thermal exchange were studied to detect conserved vascular patterns and to assess their ability to deliver cooled blood to neurosensory tissues. Within the orbital region, both the arteries and veins demonstrated consistent branching patterns, with the supraorbital, infraorbital, and ophthalmotemporal vessels supplying and draining the orbit. The venous drainage of the orbital region showed connections to the dural sinuses via the orbital veins and cavernous sinus. The palatal region demonstrated a vast plexus that comprised both arteries and veins. The most direct route of venous drainage of the palatal plexus was through the palatomaxillary veins, essentially bypassing neurosensory tissues. Anastomotic connections with the nasal region, however, may provide an alternative route for palatal venous blood to reach neurosensory tissues. The nasal region in crocodilians is probably the most prominent site of thermal exchange, as it offers a substantial surface area and is completely surrounded by blood vessels. The venous drainage routes from the nasal region offer routes directly to the dural venous sinuses and the orbit, offering evidence of the potential to directly affect neurosensory tissue temperatures. The evolutionary history of crocodilians is complex, with large-bodied, terrestrial, and possibly endothermic taxa that may have had to deal with thermal loads that likely provided the anatomical building-blocks for such an extensive vascularization of sites of thermal exchange. A clear understanding of the physiological abilities and the role of blood vessels in the thermoregulation of crocodilians neurosensory tissues is not available but vascular anatomical patterns of crocodilian sites of thermal exchange indicate possible physiological abilities that may be more sophisticated than in other extant diapsids.
Martín O. Pereyra, Molly C. Womack, J. Sebastián Barrionuevo, Boris L. Blotto, Diego Baldo, Mariane Targino, Jhon Jairo Ospina-Sarria, Juan M. Guayasamin, Luis A. Coloma, Kim L. Hoke, Taran Grant & Julián Faivovich (2016)
The complex evolutionary history of the tympanic middle ear in frogs and toads (Anura).
Scientific Reports 6, Article number: 34130 (2016)
Most anurans possess a tympanic middle ear (TME) that transmits sound waves to the inner ear; however, numerous species lack some or all TME components. To understand the evolution of these structures, we undertook a comprehensive assessment of their occurrence across anurans and performed ancestral character state reconstructions. Our analysis indicates that the TME was completely lost at least 38 independent times in Anura. The inferred evolutionary history of the TME is exceptionally complex in true toads (Bufonidae), where it was lost in the most recent common ancestor, preceding a radiation of >150 earless species. Following that initial loss, independent regains of some or all TME structures were inferred within two minor clades and in a radiation of >400 species. The reappearance of the TME in the latter clade was followed by at least 10 losses of the entire TME. The many losses and gains of the TME in anurans is unparalleled among tetrapods. Our results show that anurans, and especially bufonid toads, are an excellent model to study the behavioural correlates of earlessness, extratympanic sound pathways, and the genetic and developmental mechanisms that underlie the morphogenesis of TME structures.
Matthew J. Vavrek (2016)
The fragmentation of Pangaea and Mesozoic terrestrial vertebrate biodiversity.
Biology Letters2016 12 20160528
During the Mesozoic (242–66 million years ago), terrestrial regions underwent a massive shift in their size, position and connectivity. At the beginning of the era, the land masses were joined into a single supercontinent called Pangaea. However, by the end of the Mesozoic, terrestrial regions had become highly fragmented, both owing to the drifting apart of the continental plates and the extremely high sea levels that flooded and divided many regions. How terrestrial biodiversity was affected by this fragmentation and large-scale flooding of the Earth's landmasses is uncertain. Based on a model using the species–area relationship (SAR), terrestrial vertebrate biodiversity would be expected to nearly double through the Mesozoic owing to continental fragmentation, despite a decrease of 24% in total terrestrial area. Previous studies of Mesozoic vertebrates have generally found increases in terrestrial diversity towards the end of the era, although these increases are often attributed to intrinsic or climatic factors. Instead, continental fragmentation over this time may largely explain any observed increase in terrestrial biodiversity. This study demonstrates the importance that non-intrinsic effects can have on the taxonomic success of a group, and the importance of geography to understanding past biodiversity.