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[dinosaur] Labidosauriscus species + multituberculate stapes + rhinotheca morphology + more

Ben Creisler

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

Labidosauriscus richardi gen. et sp. nov.Â

Sean P. Modesto, Diane Scott & Robert R. Reisz (2018)
A new small captorhinid reptile from the lower Permian of Oklahoma and resource partitioning among small captorhinids in the Richards Spur fauna.
Papers in Palaeontology (advance online publication)
DOI: 10.1002/spp2.1109ÂÂ

Data archiving statement This published work and the nomenclatural acts it contains have been registered in ZooBank: http://zoobank.org/references/6C169987-227C-4529-9A17-436197288A9F. Data for this study are available in the Dryad Digital Repository: https://doi.org/10.5061/dryad.r58q7.

Two partial reptile skulls and six dentigerous fragments from the lower Permian Richards Spur locality of Oklahoma represent a new genus and species of small captorhinid reptile. Labidosauriscus richardi gen. et sp. nov. is distinguished from other captorhinids in the reduction of the height of the ridges forming the characteristic net-like, ridge-and-pit cranial sculpturing of captorhinids, and the superimposition of a system of finer pits and furrows over the primary ridge-and-pit cranial ornamentation. Labidosauriscus richardi shares with C. laticeps a post-caniniform tooth morphology characterized by convex mesial and distal carinae that form a distinctly asymmetrical apex in labial aspect. The description of L. richardi brings to six the number of captorhinid species known from the productive Richards Spur fissure-fill locality. Each of these species exhibits a distinctive post-caniniform tooth morphology (or multiplication of these teeth), which is consonant with the hypothesis of resource partitioning among the small faunivorous and omnivorous captorhinids at Richards Spur. As an 'exhumed early Permian hill', Richards Spur provides a unique window into early reptile diversification in a distinctive upland environment that is rarely preserved in the tetrapod fossil record.


Julia A. Schultz, Irina Ruf & Thomas Martin (2018)
Oldest known multituberculate stapes suggests an asymmetric bicrural pattern as ancestral for Multituberculata.
Proceedings of the Royal Society B 285 1873 20172779Â
DOI: 10.1098/rspb.2017.2779

Middle ear ossicles (malleus, incus, stapes) are known for few multituberculate taxa, and three different stapedial morphotypes have been suggested: (i) slender, columelliform and microperforate, (ii) robust and rod-like, and (iii) bicrural. Reinvestigation of Upper Jurassic (Kimmeridgian) mammalian petrosals from the Guimarota coal mine in central Portugal (Western Europe) revealed an asymmetric bicrural stapes (ABS) in the paulchoffatiid Pseudobolodon oreas. The middle ear ossicles displaced inside the osseous vestibule were detected by a ÂCT analysis. The Kimmeridgian age of the Guimarota stapes exceeds the stapes from the Early Cretaceous (Barremian) of Asia (about 122â124 Ma) by approximately 30 Myr, and is only slightly younger than the stapes of the recently described Oxfordian euharamiyidan Arboroharamiya allinhopsoni. The Guimarota stapes indicates that the stapes of Lambdopsalis, described as columelliform and microperforate (small stapedial foramen), does not represent a general condition for multituberculates. The stapes of Pseudobolodon is bicrural, the anterior crus sits centrally on the oval footplate, and the stapedial head is simple and smaller than the footplate. We hypothesize that the ABS evolved from the symmetric bicrural stapes (SBS) of non-mammaliaform cynodonts. The ABS appears to be the ancestral morphotype of the mammalian SBS, and the mammalian columelliform imperforate stapes.


Yukine Urano, Kyo Tanoue, Ryoko Matsumoto, Soichiro Kawabe, Tomoyuki Ohashi & Shin-ichi Fujiwara (2018)
How does the curvature of the upper beak bone reflect the overlying rhinotheca morphology?
DOI: 10.1002/jmor.20799Â

The beak has independently been evolved accompanied by the edentulism in many tetrapod linages, including extant Testudinata and Aves, and its form and function have been greatly diversified. The beak is formed by beak bones and the overlying keratinous cover, although their profiles are different from each other. Therefore, it is difficult to reliably reconstruct the entire profile of the beak in extinct taxa, whose keratinous tissues are rarely preserved. For elucidation of the morphological relationship between beak bone and overlying keratinous cover, we compared the curvature distribution of the culminal profiles of the upper beak bone and the overlying keratinous cover (rhinotheca) with each other using CT-scan, in 66 extant testudinatan and avian specimens (Aves: 33 genera, 24 families; Testudinata: 12 genera seven families). In both, rhinotheca and beak bone, the curvature of the profile was nearly constant rostral to a certain point, which was defined as the transition point, and the transition points of the rhinotheca and beak bone were close to each other. The profiles of the rhinotheca and beak bone rostral to their transition point were different in curvature and length. However, the ratio between the curvatures of rhinotheca and the beak bone strongly correlated with the arc angle of the rostral culminal profiles of the beak bone. The upper beak profile in extinct taxa is expected to be reconstructed more reliably using the abovementioned relationship between the beak bone and the rhinotheca.


Martina GregoroviÄovÃ, Alena Kvasilovà & David Sedmera (2018)
Ossification Pattern in Forelimbs of the Siamese Crocodile (Crocodylus siamensis): Similarity in Ontogeny of Carpus Among Crocodylian Species.
The Anatomical Records (advance online publication)
DOI: 10.1002/ar.23792

Crocodylians have highly derived elongated carpus, which is related to their use of forelimbs in many types of gaits as well as in burrowing. The objective of present study was to describe the ossification of the forelimb in five stages of Siamese crocodile (Crocodylus siamensis). The ossification begins approximately at stage 20 in arm and forearm bones moving sequentially to the metacarpal elements. The first carpal elements with ossification centers are radialeâ+âintermedium and ulnare (stage 22â23), and their ossification mode is typical of long bones. Between stages 22 and 24 distal carpals 3, 4, and 5 fuse together to a single formation. In the stage 25, the ossification proceeds to the pisiform, which starts ossifying late during the embryogenesis. The phalangeal formula of the digits is 2,3,4,5,3. Although there are some interspecific differences, it appears that all crocodylians have similarly uniform skeletal pattern, the process of ossification, number of carpal elements and phalangeal formulas probably due to their similar lifestyles.Â


Vivek Philip Cyriac & Ullasa Kodandaramaiah (2018)
Digging their own macroevolutionary grave: Fossoriality as an evolutionary dead-end in snakes.
Journal of Evolutionary Biology (advance online publication)
DOI: 10.1111/jeb.13248Â

The tree of life is highly asymmetrical in its clade wise species richness and this has often been attributed to variation in diversification rates either across time or lineages. Variations across lineages are usually associated with traits that increase lineage diversification. Certain traits can also hinder diversification by increasing extinction and such traits are called evolutionary dead-ends. Ecological specialization has usually been considered as an evolutionary dead-end. However, recent analyses of specializations along single axes have provided mixed support for this model. Here, we test if fossoriality, a trait that forces specialization at multiple axes, acts as an evolutionary dead-end in squamates (lizards and snakes) using recently developed phylogenetic comparative methods. We show that fossoriality is an evolutionary dead-end in snakes but not in lizards. Fossorial snakes exhibit reduced speciation and increased extinction compared to non-fossorial snakes. Our analysis also indicates that transition rates from fossoriality to non-fossoriality in snakes are significantly lower than transition rates from non-fossoriality to fossoriality. Overall our results suggest that broad scale ecological interactions that lead to specialization at multiple axes limit diversification.


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