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[dinosaur] Palaeoneurological clues to mammal evolution + mammal tree + unidirectional pulmonary airflow in vertebrates

Ben Creisler

Some recent (and not so recent) non-dino papers not yet mentioned:

Free pdf:

J. Benoit, P. R. Manger & B. S. Rubidge (2016)
Palaeoneurological clues to the evolution of defining mammalian soft tissue traits.
Scientific Reports 6, Article number: 25604 (2016)

A rich fossil record chronicles the distant origins of mammals, but the evolution of defining soft tissue characters of extant mammals, such as mammary glands and hairs is difficult to interpret because soft tissue does not readily fossilize. As many soft tissue features are derived from dermic structures, their evolution is linked to that of the nervous system, and palaeoneurology offers opportunities to find bony correlates of these soft tissue features. Here, a CT scan study of 29 fossil skulls shows that non-mammaliaform Prozostrodontia display a retracted, fully ossified, and non-ramified infraorbital canal for the infraorbital nerve, unlike more basal therapsids. The presence of a true infraorbital canal in Prozostrodontia suggests that a motile rhinarium and maxillary vibrissae were present. Also the complete ossification of the parietal fontanelle (resulting in the loss of the parietal foramen) and the development of the cerebellum in Probainognathia may be pleiotropically linked to the appearance of mammary glands and having body hair coverage since these traits are all controlled by the same homeogene, Msx2, in mice. These suggest that defining soft tissue characters of mammals were already present in their forerunners some 240 to 246 mya.




Free pdf:

Nicole M. Foley, Mark S. Springer & Emma C. Teeling (2016)
Mammal madness: is the mammal tree of life not yet resolved?
Philosophical Transactions of the Royal Society B: Biological Sciences: 371 (1699)
DOI: 10.1098/rstb.2015.0140
Free pdf:

Most molecular phylogenetic studies place all placental mammals into four superordinal groups, Laurasiatheria (e.g. dogs, bats, whales), Euarchontoglires (e.g. humans, rodents, colugos), Xenarthra (e.g. armadillos, anteaters) and Afrotheria (e.g. elephants, sea cows, tenrecs), and estimate that these clades last shared a common ancestor 90–110 million years ago. This phylogeny has provided a framework for numerous functional and comparative studies. Despite the high level of congruence among most molecular studies, questions still remain regarding the position and divergence time of the root of placental mammals, and certain ‘hard nodes’ such as the Laurasiatheria polytomy and Paenungulata that seem impossible to resolve. Here, we explore recent consensus and conflict among mammalian phylogenetic studies and explore the reasons for the remaining conflicts. The question of whether the mammal tree of life is or can be ever resolved is also addressed.

NOTE: This article is part of a special issue of Transactions of the Royal Society B devoted to "Dating species divergences using rocks and clocks" with some free content:



Robert L. Cieri & C. G. Farmer (2016)
Unidirectional pulmonary airflow in vertebrates: a review of structure, function, and evolution.
Journal of Comparative Physiology B 186(5): 541-552
DOI: 10.1007/s00360-016-0983-3


Mechanisms explaining unidirectional pulmonary airflow in birds, a condition where lung gases flow in a consistent direction during both inspiration and expiration in some parts of the lung, were suggested as early as the first part of the twentieth century and unidirectional pulmonary airflow has been discovered recently in crocodilians and squamates. Our knowledge of the functional anatomy, fluid dynamics, and significance of this trait is reviewed. The preponderance of the data indicates that unidirectional airflow is maintained by means of convective inertia in inspiratory and expiratory aerodynamic valves in birds. The study of flow patterns in non-avian reptiles is just beginning, but inspiratory aerodynamic valving likely also plays an important role in controlling flow direction in these lungs. Although highly efficient counter and cross-current blood–gas exchange arrangements are possible in lungs with unidirectional airflow, very few experiments have investigated blood–gas exchange mechanisms in the bird lung and blood–gas arrangements in the lungs of non-avian reptiles are completely unknown. The presence of unidirectional airflow in non-volant ectotherms voids the traditional hypothesis that this trait evolved to supply the high aerobic demands of flight and endothermy, and there is a need for new scenarios in our understanding of lung evolution. The potential value of unidirectional pulmonary airflow for allowing economic lung gas mixing, facilitating lung gas washout, and providing for adequate gas exchange during hypoxic conditions is discussed.


Jade B. Atkins and Tamara A. Franz-Odendaal (2016)
The evolutionary and morphological history of the parasphenoid bone in vertebrates.
Acta Zoologica 97(2): 255–263
DOI: 10.1111/azo.12131

The parasphenoid is located in the cranium of many vertebrates. When present, it is always an unpaired, dermal bone. While most basal vertebrates have a parasphenoid, most placental mammals lack this element and have an unpaired, dermal vomer in a similar position (i.e. associated with the same bones) and with a similar function. As such, the parasphenoid and the vomer were considered homologous by some early twentieth century researchers. However, others questioned this homology based on comparisons between mammals and reptiles. Here we investigate the parasphenoid bone across the major vertebrate lineages (amphibians, reptiles, mammals and teleosts) including both developmental and evolutionary aspects, which until now have not been considered together. We find that within all the major vertebrate lineages there are organisms that possess a parasphenoid and a vomer, while the parasphenoid is absent within caecilians and most placental mammals. Based on our assessment and Patterson's conjunction tests, we conclude that the non-mammalian parasphenoid and the vomer in mammals cannot be considered homologous. Additionally, the parasphenoid is likely homologous between sarcopterygian and actinopterygian lineages. This research attempts to resolve the issue of the parasphenoid homology and highlights where gaps in our knowledge are still present.