English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

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.

Comparative cranial morphology of the Late Cretaceous protostegid sea turtle Desmatochelys lowii