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Free pdf:
Tony Harper & Guillermo Rougier (2018)
Petrosal morphology and cochlear function in Mesozoic stem therians.
bioRxiv (advance online publication)
(This article is a preprint and has not been peer-reviewed)
Here we describe the bony anatomy of the inner ear and surrounding structures seen in three of the most plesiomorphic crown mammalian petrosal specimens in the fossil record. Our study sample includes the stem therian taxa Priacodon fruitaensis from the Upper Jurassic of North America, and two isolated petrosal specimens colloquially known as the HÃÃvÃr petrosals, recovered from Aptian-Albian sediments in Mongolia. The second HÃÃvÃr petrosal is here described at length for the first time. All three of these stem therian petrosals and a comparative sample of extant mammalian taxa have been imaged using micro-CT, allowing for detailed anatomical descriptions of osteological correlates of functionally significant neurovascular features, especially along the abneural wall of the cochlear canal. The high resolution imaging provided here clarifies several hypotheses regarding the mosaic evolution of features of the cochlear endocast in early mammals. In particular, these images demonstrate that the membranous cochlear duct adhered to the bony cochlear canal abneurally to a secondary bony lamina before the appearance of an opposing primary bony lamina or tractus foraminosus. Additionally, while corroborating the general trend of reduction of venous sinuses and plexuses within the pars cochlearis seen in crownward mammaliaformes generally, the HÃÃvÃr petrosals show the localized enlargement of a portion of the intrapetrosal venous plexus. This new excavation is for the vein of cochlear aqueduct, a structure that is solely or predominantly responsible for the venous drainage of the cochlear apparatus in extant therians. However, given that these stem therian inner ears appear to have very limited high-frequency capabilities, the development of these modern vascular features the cochlear endocast suggest that neither the initiation or enlargement of the stria vascularis (a unique mammalian organ) is originally associated with the capacity for high-frequency hearing or precise sound-source localization.
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PÃter L. Pap, Orsolya Vincze, Csongor I. VÃgÃsi, Zsuzsa Salamon, Andrea PÃndi, Blanka BÃlint, Andreas Nord, Robert L. Nudds & Gergely OsvÃth (2018)
Vane macrostructure of primary feathers and its adaptations to flight in birds.
Biological Journal of the Linnean Society, bly189 (advance online publication)
The selection pressures that drive flight feather morphology are poorly understood. Using a phylogenetic comparative approach and data from 178 species of birds, we investigated whether both position along the wing length and flight feather length affected vane structure. We found that barb density was lower on distal primaries than on proximal primaries of the leading feather vane. In contrast, on the trailing vane only mid-point barb density differed and, here, it showed denser barbs on the distal primaries. This difference was greater at the feather base than at the tip. Barb angle was higher along the full length of the leading edge vane on the proximal primaries than on the distal primaries. Overall, barb density decreased from base to tip on both trailing and leading vanes on both the proximal and the distal primaries. In general, barb angle was less acute at the feather base than at the tip. Barbs were in general denser in continuous flapping fliers than in soarers and the angle of barbs on both the proximal and the distal primaries was affected by flight type. However, we did not identify consistent differences in the pattern of barb angle change among flight style groups. These findings add new perspectives to our understanding of the functional morphology of the flight feather vane, although we still have limited knowledge on how aerodynamic forces, particularly during take-off and landing, affect the morphology of the feather vane.
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Guillermo NavalÃn, Jen A. Bright, JesÃs MarugÃnâLobÃn & Emily J. Rayfield (2018)
The evolutionary relationship between beak shape, mechanical advantage, and feeding ecology in modern birds.
Evolution (advance online publication)
Extensive research on avian adaptive radiations has led to a presumption that beak morphology predicts feeding ecology in birds. However, this ecomorphological relationship has only been quantified in a handful of avian lineages, where associations are of variable strength, and never at a broad macroevolutionary scale. Here, we used shape analysis and phylogenetic comparative methods to quantify the relationships between beak shape, mechanical advantage, and two measures of feeding ecology (feeding behaviour and semiâquantitative dietary preferences) in a broad sample of modern birds, comprising most living orders. We found a complex relationship, with most variables showing a significant relationship with feeding ecology but little explanatory power, for example, diet accounts for less than 12% of beak shape variation. Similar beak shapes are associated with disparate dietary regimes, even when accounting for dietâfeeding behaviour relationships and phylogeny. Very few lineages optimize for stronger bite forces, with most birds exhibiting relatively fast, weak bites, even in large predatory taxa. The extreme morphological and behavioural flexibility of the beak in birds suggests that, far from being an exemplary feeding adaptation, avian beak diversification may have been largely contingent on tradeâoffs and constraints.
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Tamara A. FranzâOdendaal (2018)
Skeletons of the Eye: An Evolutionary and Developmental Perspective.
The Anatomical Record (advance online publication)
The ocular skeleton, composed of the scleral cartilage and scleral ossicles, is present in many vertebrates. The morphology of the scleral cartilage and ossicles varies within different extant reptiles (including birds) and also varies dramatically from the morphology in extant teleosts. This incredible range of diverse morphologies is the result of millions of years of evolution. Both the position of these elements within the eye and the timing of development vary amongst different vertebrates. While the development of both the scleral cartilage and scleral ossicles is somewhat understood in reptiles and in teleosts, the functional advantage of these elements is still debated. Most reptiles have a multiâcomponent scleral ossicle ring composed of a series of flat bone plates and a scleral cartilage cup lining the retina, some sharks have calcified cartilage plates, and some teleosts have two bones while most others only have a ring of scleral cartilage. The data presented shows that different vertebrates have adapted to similar selective pressures in different ways. However, the reason why sarcopterygians have a series of overlapping bones in the sclera remains unclear. A better understanding of the ocular skeletal diversity in Reptilia as well as a better understanding of the mechanisms of vision within different environments (i.e. air versus water) and that used by secondarily aquatic organisms is needed. This review discusses the observed variation in morphology and development of the ocular skeleton in the context of evolution and highlights our knowledge gaps in these areas.
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Free pdf:
I. Raselli (2018)Â
Comparative cranial morphology of the Late Cretaceous protostegid sea turtle Desmatochelys lowii.Â
PeerJ 6:e5964
Background
The phylogenetic placement of Cretaceous marine turtles, especially Protostegidae, is still under debate among paleontologists. Whereas protostegids were traditionally thought to be situated within the clade of recent marine turtles (Chelonioidea), some recent morphological and molecular studies suggest placement along the stem of Cryptodira. The main reason why the evolution of marine turtles is still poorly understood, is in part due to a lack of insights into the cranial anatomy of protostegids. However, a general availability of high-quality fossil material, combined with modern analysis techniques, such as X-ray microtomography, provide ample opportunity to improve this situation. The scope of this study is to help resolve its phylogenetic relationships by providing a detailed description of the external and internal cranial morphology of the extinct protostegid sea turtle Desmatochelys lowii Williston, 1894.
Material and Methods
This study is based on the well-preserved holotype of Desmatochelys lowii from the Late Cretaceous (middle Cenomanian to early Turonian) Greenhorn Limestone of Jefferson County, Nebraska. The skulls of two recent marine turtles, Eretmochelys imbricata (Linnaeus, 1766) (Cheloniidae) and Dermochelys coriacea Lydekker, 1889 (Dermochelyidae), as well as the snapping turtle Chelydra serpentina (Linnaeus, 1758) (Chelydridae) provide a comparative basis. All skulls were scanned using regular or micro CT scanners and the scans were then processed with the software program Amira to create 3D isosurface models. In total, 81 bones are virtually isolated, figured, and described, including the nature of their contacts. The novel bone contact data is compiled and utilized in a preliminary phenetic study. In addition, an update phylogenetic analysis is conduced that utilizes newly obtained anatomical insights.
Results
The detailed examination of the morphology of the herein used specimens allowed to explore some features of the skull, to refine the scoring of Desmatochelys lowii in the recent global matrix of turtles, and develop five new characters. The alleged pineal foramen in the type skull of Desmatochelys lowii is shown to be the result of damage. Instead, it appears that the pineal gland only approached the skull surface, as it is in Dermochelys coriacea. Whereas the parasphenoid in confirmed to be absent in hard-shelled sea turtles, ist possible presence in Desmatochelys lowii is unclear. The results of the phenetic study show that Desmatochelys lowii is least similar to the other examined taxa in regards to the nature of its bone contacts, and therefore suggests a placement outside Americhelydia for this protostegid sea turtle. The phylogenetic study results in a placement of Protostegidae along the stem of Chelonioidea, which is a novel position for the group.
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J. Fratani, M. L. Ponssa & V. Abdala (2018)
Evolution of tendon shape in an anuran clade and its relation to size, phylogeny and locomotion.
Journal of Zoology (advance online publication)
Most anatomical specializations related to anuran jumping have been observed in pelvic girdle and hindlimbs, which are characterized by its fused caudal vertebrae and elongated hindlimbs. Still, despite of a greatly specialized body plan, locomotor variation in anurans goes beyond jumping, including specializations for swimming, burrowing, and climbing. Herein, we test for morphological adaptation in three tendinous elements associated with the urostyle and hindlimb joints: the tendon of the longissimus dorsi which inserts on the urostyle and rotates it dorsally; the patellar tendon which goes over the knee joint and connects the larger thigh extensor muscles; and the Achilles tendon which passes over the ankle joint and participates in the catapultâlike mechanism of jumping species. We make an incursion in tendon variation using geometric morphometrics and test if tendon shape is related to size, phylogeny and locomotion in leptodactylid species. Also, we hypothesize that tarsal bone elongation in anura alters the heel into a more âkneeâlikeâ joint affecting tendon shape, and test for patellar and Achilles similarity. We found that a combination of factors drives Leptodactylidae tendon morphological diversity. Allometry, phylogeny and function take part in the longissimus dorsi tendon variation, with significant difference between hopping and all jumping species. The patellar tendon shape scales isometrically with size, with significant shape difference between jumping and jumpingâswimming species. Achilles tendon shape is mainly affected by allometry. Optimization showed a shift for a broader longissimus dorsi tendon shape in the ancestor of Leptodactylus. Finally, and contrary to our prediction, patellar and Achilles tendon shapes are significantly different. Once again, evidence points to a combination of factors explaining shape, rather than a direct and evident functionalâanatomic relation.
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