Thalattosuchian braincase sinuses + platypterygiid ichthyosaur from Cenomanian of New Zealand (free pdfs)
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Ben Creisler
Oct 30, 2024, 11:56:48 AMOct 30
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Ben Creisler
New marine reptile papers:
Mark T. Young, Julia A. Schwab, David Dufeau, Rachel A. Racicot, Thomas Cowgill, Charlotte I. W. Bowman, Lawrence M. Witmer, Yanina Herrera, Robert Higgins, Lindsay Zanno, Xu Xing, James Clark and Stephen L. Brusatte (2024)
Skull sinuses precluded extinct crocodile relatives from cetacean-style deep diving as they transitioned from land to sea
Royal Society Open Science 11(10): 241272
doi: https://doi.org/10.1098/rsos.241272
https://royalsocietypublishing.org/doi/10.1098/rsos.241272
Free pdf:
https://royalsocietypublishing.org/doi/epdf/10.1098/rsos.241272
During major evolutionary transitions, groups develop radically new body plans and radiate into new habitats. A classic example is cetaceans which evolved from terrestrial ancestors to become pelagic swimmers. In doing so, they altered their air-filled sinuses, transitioning some of these spaces to allow for fluctuations in air capacity and storage via soft tissue borders. Other tetrapods independently underwent land-to-sea transitions, but it is unclear if they similarly changed their sinuses. We use computed tomography to study sinus changes in thalattosuchian crocodylomorphs that transformed from land-bound ancestors to become the only known aquatic swimming archosaurs. We find that thalattosuchian braincase sinuses reduced over their transition, similar to cetaceans, but their snout sinuses counterintuitively expanded, distinct from cetaceans, and that both trends were underpinned by high evolutionary rates. We hypothesize that aquatic thalattosuchians were ill suited to deep diving by their snout sinuses, which seem to have remained large to help drain their unusual salt glands. Thus, although convergent in general terms, thalattosuchians and cetaceans were subject to different constraints that shaped their transitions to water. Thalattosuchians attained a stage similar to less pelagic transitional forms in the cetacean lineage (late protocetid-basilosaurid) but did not become further specialized for ocean life.
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George R. A. Young, Paul Scofield, Catherine M. Reid, Al Mannering & James S. Crampton (2024)
A platypterygiid ichthyosaur from the Cenomanian of central New Zealand
Journal of Vertebrate Paleontology: e2408391
doi: https://doi.org/10.1080/02724634.2024.2408391
https://www.tandfonline.com/doi/full/10.1080/02724634.2024.2408391
Free pdf:
Mark T. Young, Julia A. Schwab, David Dufeau, Rachel A. Racicot, Thomas Cowgill, Charlotte I. W. Bowman, Lawrence M. Witmer, Yanina Herrera, Robert Higgins, Lindsay Zanno, Xu Xing, James Clark and Stephen L. Brusatte (2024)
Skull sinuses precluded extinct crocodile relatives from cetacean-style deep diving as they transitioned from land to sea
Royal Society Open Science 11(10): 241272
doi: https://doi.org/10.1098/rsos.241272
https://royalsocietypublishing.org/doi/10.1098/rsos.241272
Free pdf:
https://royalsocietypublishing.org/doi/epdf/10.1098/rsos.241272
During major evolutionary transitions, groups develop radically new body plans and radiate into new habitats. A classic example is cetaceans which evolved from terrestrial ancestors to become pelagic swimmers. In doing so, they altered their air-filled sinuses, transitioning some of these spaces to allow for fluctuations in air capacity and storage via soft tissue borders. Other tetrapods independently underwent land-to-sea transitions, but it is unclear if they similarly changed their sinuses. We use computed tomography to study sinus changes in thalattosuchian crocodylomorphs that transformed from land-bound ancestors to become the only known aquatic swimming archosaurs. We find that thalattosuchian braincase sinuses reduced over their transition, similar to cetaceans, but their snout sinuses counterintuitively expanded, distinct from cetaceans, and that both trends were underpinned by high evolutionary rates. We hypothesize that aquatic thalattosuchians were ill suited to deep diving by their snout sinuses, which seem to have remained large to help drain their unusual salt glands. Thus, although convergent in general terms, thalattosuchians and cetaceans were subject to different constraints that shaped their transitions to water. Thalattosuchians attained a stage similar to less pelagic transitional forms in the cetacean lineage (late protocetid-basilosaurid) but did not become further specialized for ocean life.
=====
Free pdf:
George R. A. Young, Paul Scofield, Catherine M. Reid, Al Mannering & James S. Crampton (2024)
A platypterygiid ichthyosaur from the Cenomanian of central New Zealand
Journal of Vertebrate Paleontology: e2408391
doi: https://doi.org/10.1080/02724634.2024.2408391
https://www.tandfonline.com/doi/full/10.1080/02724634.2024.2408391
Free pdf:
https://www.tandfonline.com/doi/epdf/10.1080/02724634.2024.2408391
Understanding of Cretaceous ichthyosaur diversity has substantially increased in recent years; however, Eastern Gondwana’s ichthyosaur fauna is still poorly understood, particularly in New Zealand where only scarce fragmentary material is known. A Cenomanian-aged partial ichthyosaur skeleton has been recovered from the northeastern South Island of New Zealand and is described here. Whilst the specimen is too fragmentary to formally name, this taxon shows an extreme reduction of the basioccipital extracondylar area, a scapula with a prominent acromion process and a strap-like scapula shaft, as well as a complete left pelvic girdle with an elongated depression on the anteroproximal face of the ischiopubis. We suggest that it is a late branching member of the platypterygiid ichthyosaurs, closely related to the Eastern Gondwanan ichthyosaur Platypterygius australis and to many European Cretaceous taxa. However, it appears to be unrelated to the Cretaceous ichthyosaurs of Western Gondwana, suggesting potential regionalism amongst the Gondwanan Cretaceous ichthyosaur populations.
https://www.tandfonline.com/doi/epdf/10.1080/02724634.2024.2408391
Understanding of Cretaceous ichthyosaur diversity has substantially increased in recent years; however, Eastern Gondwana’s ichthyosaur fauna is still poorly understood, particularly in New Zealand where only scarce fragmentary material is known. A Cenomanian-aged partial ichthyosaur skeleton has been recovered from the northeastern South Island of New Zealand and is described here. Whilst the specimen is too fragmentary to formally name, this taxon shows an extreme reduction of the basioccipital extracondylar area, a scapula with a prominent acromion process and a strap-like scapula shaft, as well as a complete left pelvic girdle with an elongated depression on the anteroproximal face of the ischiopubis. We suggest that it is a late branching member of the platypterygiid ichthyosaurs, closely related to the Eastern Gondwanan ichthyosaur Platypterygius australis and to many European Cretaceous taxa. However, it appears to be unrelated to the Cretaceous ichthyosaurs of Western Gondwana, suggesting potential regionalism amongst the Gondwanan Cretaceous ichthyosaur populations.
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