Ben Creisler
Some new non-dino papers:
Significance
To explain how limbs evolved from fins, paleontologists have traditionally studied the endoskeleton. Here, we provide a comparative analysis of the other skeletal system of fins, the dermal skeleton. We describe dermal ray anatomy for 3 species of tetrapodomorph fishes. These data show that, prior to the origin of digits, dermal rays were simplified, the fin web became reduced in size, and the top and bottom of the fin became more asymmetric. These changes reveal how fins became adapted for interacting with the substrate prior to the fin-to-limb transition and that dorsoventral asymmetry is an important, understudied axis of diversification in paired fins.
Abstract
The fin-to-limb transition was marked by the origin of digits and the loss of dermal fin rays. Paleontological research into this transformation has focused on the evolution of the endoskeleton, with little attention paid to fin ray structure and function. To address this knowledge gap, we study the dermal rays of the pectoral fins of 3 key tetrapodomorph taxaâSauripterus taylori (Rhizodontida), Eusthenopteron foordi (Tristichopteridae), and Tiktaalik roseae (Elpistostegalia)âusing computed tomography. These data show several trends in the lineage leading to digited forms, including the consolidation of fin rays (e.g., reduced segmentation and branching), reduction of the fin web, and unexpectedly, the evolution of asymmetry between dorsal and ventral hemitrichia. In Eusthenopteron, dorsal rays cover the preaxial endoskeleton slightly more than ventral rays. In Tiktaalik, dorsal rays fully cover the third and fourth mesomeres, while ventral rays are restricted distal to these elements, suggesting the presence of ventralized musculature at the fin tip analogous to a fleshy âpalm.â Asymmetry is also observed in cross-sectional areas of dorsal and ventral rays. Eusthenopteron dorsal rays are slightly larger than ventral rays; by contrast, Tiktaalik dorsal rays can be several times larger than ventral rays, and degree of asymmetry appears to be greater at larger sizes. Analysis of extant osteichthyans suggests that cross-sectional asymmetry in the dermal rays of paired fins is plesiomorphic to crown group osteichthyans. The evolution of dermal rays in crownward stem tetrapods reflects adaptation for a fin-supported elevated posture and resistance to substrate-based loading prior to the origin of digits.
***
News:
How fish fins evolved just before the transition to land
===
Free pdf:
Highlights
There is some space between the hierarchical structures of barbs and barbules.
The space allows the separated micro-hooklets to recover and interlock.
Shaking wings and preening feathers render deflections on rachis, barbs and barbules.
Deformations of rachis, barbs and barbules provide the energy for vane self-healing.
Abstract
The feather of a bird consists of barbs which again comprise numerous barbules with micro-hooklets. This hierarchically organized feather structure provides a smooth vane to bear the load from the airflow; however, the feather vane is vulnerable to disruption by external pulling forces during collision with the branches of a tree and hitting some small obstacles in flight or strong turbulence. The feather is unable to carry the weight of the bird's body if the vane could not be recovered immediately. Here we discovered that the feather vane can be re-established easily by birds themselves. A bird can always recover its feather vane from ruffled state by shaking its wings and preening its feathers with its beak because of the cascaded geometries of barbs and barbules. This biophysical mechanism of self-healing suggests that the hierarchical vane structure can be used to design artificial feathers for a flapping robot.
===
Paywalled:
Adriana C. Mancuso & Randall B. Irmis (2019)
The large-bodied dicynodont Stahleckeria (Synapsida, Anomodontia) from the Upper Triassic (Carnian) ChaÃares Formation (Argentina); new data for Triassic Gondwanan biogeography.
Ameghiniana (advance online publication)
doi: 10.5710/AMGH.20.12.2019.3302
http://www.ameghiniana.org.ar/index.php/ameghiniana/article/view/1005The non-marine Triassic displays distinct regional differences in tetrapod fossil assemblages even in adjacent regions, and these patterns have been hypothesized to reflect provincialism. For example, in the "Middle Triassic" of Gondwana, the RÃo Seco de la Quebrada Formation (Puesto Viejo Group) in western Argentina shares a number of taxa with the Cynognathus AZ of the Burgersdorp Formation (Karoo Basin) in South Africa. In contrast, the nearly ChaÃares Formation of northwestern Argentina is compositionally distinct and shows more affinities with the Dinodontosaurus AZ of the lower Santa Maria Formation in southern Brazil and the top of the upper Omingonde Formation of Namibia. These problems are exacerbated by recent radioisotopic dates from the ChaÃares Formation and the Puesto Viejo Group suggest these units are actually Carnian in age. We provide new data for the biostratigraphy and biogeography of these units in the form of the first record of a stahleckeriine dicynodont from the ChaÃares Formation, an ulna referable to Stahleckeria von Huene, 1935. This new occurrence strengthens the correlation between ChaÃares, Santa Maria, and the top of Omingonde units but reinforces the differences with the RÃo Seco de la Quebrada and Burgersdorp units. Hypotheses for this provincialism include assemblages of different ages, distinct environments controlled by paleolatitude or paleotopography between basins that formed a barrier to faunal interchange.
====
Also, free pdf:
Free pdf:
https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0226949&type=printableMorphological convergence is an intensely studied macroevolutionary phenomenon. It refers to the morphological resemblance between phylogenetically distant taxa. Currently available methods to explore evolutionary convergence either: rely on the analysis of the phenotypic resemblance between sister clades as compared to their ancestor, fit different evolutionary regimes to different parts of the tree to see whether the same regime explains phenotypic evolution in phylogenetically distant clades, or assess deviations from the congruence between phylogenetic and phenotypic distances. We introduce a new test for morphological convergence working directly with non-ultrametric (i.e. paleontological) as well as ultrametric phylogenies and multivariate data. The method (developed as the function search.conv within the R package RRphylo) tests whether unrelated clades are morphologically more similar to each other than expected by their phylogenetic distance. It additionally permits using known phenotypes as the most recent common ancestors of clades, taking full advantage of fossil information. We assessed the power of search.conv and the incidence of false positives by means of simulations, and then applied it to three well-known and long-discussed cases of (purported) morphological convergence: the evolution of grazing adaptation in the mandible of ungulates with high-crowned molars, the evolution of mandibular shape in sabertooth cats, and the evolution of discrete ecomorphs among anoles of Caribbean islands. The search.conv method was found to be powerful, correctly identifying simulated cases of convergent morphological evolution in 95% of the cases. Type I error rate is as low as 4â6%. We found search.conv is some three orders of magnitude faster than a competing method for testing convergence.