[dinosaur] Mesenosaurus efremovi, new synapsid species from Oklahoma + Metoposaurus cranial sutures

Ben Creisler
[email protected]

New papers:

Free pdf:

Sigi Maho, Bryan M. Gee and Robert R. Reisz (2019)
A new varanopid synapsid from the early Permian of Oklahoma and the
evolutionary stasis in this clade.
Royal Society Open Science 6(10): 191297
doi: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1098_rsos.191297&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=2e2pzA00zM253Mwn0sMY83CSyNV4xBI7tkmmInxcH6w&s=U6FZ_wUSV0rRctUXxklHYtnvjyMd7oFNk5Yup15pV1Y&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__royalsocietypublishing.org_doi_abs_10.1098_rsos.191297&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=2e2pzA00zM253Mwn0sMY83CSyNV4xBI7tkmmInxcH6w&s=VwW29eoWPlns0DvIHtEFgtH2CH6eh0cwwc-g5p1aFKE&e= 
Free pdf:
https://urldefense.proofpoint.com/v2/url?u=https-3A__royalsocietypublishing.org_doi_pdf_10.1098_rsos.191297&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=2e2pzA00zM253Mwn0sMY83CSyNV4xBI7tkmmInxcH6w&s=txxaS6bdIkGRJ6Ng7oiNZnzWQxZeJ9cp3RcOgQ4qd-A&e= 


Varanopids are a basal clade of small- to medium-sized non-therapsid
synapsids, whose range extends from the late Pennsylvanian to the late
middle Permian, and are found in North America, Russia, Europe and South
Africa. The greatest varanopid diversity is observed at the fossiliferous
cave deposits near Richards Spur, Oklahoma, well known for the preservation
of a complex early Permian upland community. Two previously described
varanopids, Mycterosaurus and Varanops, are known only from fragmentary
disarticulated material at Richards Spur. A third putative varanopid,
Basicranodon fortsillensis, represented by a partial parasphenoid, has been
synonymized with Mycterosaurus longiceps. This study reports on a new
varanopid taxon, represented by substantially more complete material,
including three nearly complete skulls. Such comprehensive cranial material
allows for a detailed study of the taxon and its relationship to other
varanopids. This new varanopid bears great morphological similarity to
Mesenosaurus romeri from the middle Permian Mezen River Basin of northern
Russia. Phylogenetic analysis recovers a sister relationship between this
taxon and Me. romeri. This relationship, in conjunction with a detailed
morphological comparison, supports the placement of this taxon within
Mesenosaurus, as a new species, Me. efremovi. These results reveal an
unexpected extension of the geographical and temporal range of
Mesenosaurus, contributing to our understanding of varanopid dispersal. The
extended persistence of this basal clade of predatory synapsids,
underscored by the apparent evolutionary stasis of this genus, is unusual
among Palaeozoic tetrapods. This phenomenon implies an exceptionally high
degree of extended ecological resilience across major faunal and
environmental transitions.

Footnotes
Electronic supplementary material is available online at
https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.6084_m9.figshare.c.4693241&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=2e2pzA00zM253Mwn0sMY83CSyNV4xBI7tkmmInxcH6w&s=CWXMshbeVvLBEOvwiIgo4EszdQ42Z23QDaFNfkmlM1Q&e= .

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(pay-walled)

Kamil Gruntmejer,  Dorota Konietzko‐Meier,  Jordi Marcé‐Nogué,  Adam
Bodzioch & Josep Fortuny (2019)
Cranial suture biomechanics in Metoposaurus krasiejowensis (Temnospondyli,
Stereospondyli) from the upper Triassic of Poland.
Journal of Morphology (advance online publication)
doi: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1002_jmor.21070&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=2e2pzA00zM253Mwn0sMY83CSyNV4xBI7tkmmInxcH6w&s=zf4ABX-ty1_y_Id7L3Aw_TW_FJABqzC8DbeBClDnb_M&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__onlinelibrary.wiley.com_doi_10.1002_jmor.21070&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=2e2pzA00zM253Mwn0sMY83CSyNV4xBI7tkmmInxcH6w&s=D-H6OavhQpZytqUkGmm1Zsv21BwUd1khd5Z-bwPspow&e= 


Cranial sutures connect adjacent bones of the skull and play an important
role in the absorption of stresses that may occur during different
activities. The Late Triassic temnospondyl amphibian Metoposaurus
krasiejowensis has been extensively studied over the years in terms of
skull biomechanics, but without a detailed description of the function of
cranial sutures. In the present study, 34 thin sections of cranial sutures
were examined in order to determine their histovariability and interpret
their biomechanical role in the skull. The histological model was compared
with three‐dimensional‐finite element analysis (FEA) simulations of the
skull under bilateral and lateral biting as well as skull‐raising loads for
maximum and minimum principal stress. Histologically, only two sutural
morphologies were recognised in the skull of Metoposaurus: interdigitated
sutures (commonly associated with compressive stresses) are dominant along
the entire length of the skull roof and palate; tongue‐and‐groove sutures
(commonly associated with tensile stresses) are present across the maxilla.
FEA shows a much more complex picture of stress type and distribution than
predicted by sutures. Common to both methods is a predominance of
compressive stresses which act on the skull during biting. The methods
predict different stress regimes during biting in the posterior part of the
skull: where histological analysis suggests compression, FEA predicts
tension. For lateral biting and skull raising, histological and digital
reconstructions show similar general patterns but with some variations.

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