[dinosaur] Sapeornis palatal reconstruction and evolution of Paraves cranial kinesis

Ben Creisler
[email protected]

A new paper:

Han Hu, Gabriele Sansalone, Stephen Wroe, Paul G. McDonald, Jingmai K.
O’Connor, Zhiheng Li, Xing Xu, and Zhonghe Zhou (2019)
Evolution of the vomer and its implications for cranial kinesis in Paraves
Proceedings of the National Academy of Sciences (advance online publication)
doi: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1073_pnas.1907754116&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=avauBqKGecrBt1iCqr34_KtVos2IJkYqTvKuev78qME&s=Pxt3-r72wvymFjXhBDpald-KThrMDtkAcoRNovfCDsM&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.pnas.org_content_early_2019_09_04_1907754116&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=avauBqKGecrBt1iCqr34_KtVos2IJkYqTvKuev78qME&s=rmPaND4weFnoLLlhjMKYOk1uk4z9BbpGdBlp-qedSBY&e= 

Significance
Cranial kinesis is an important feature of neornithine birds. However, due
to the rarity of palatal elements in fossils, its origin is poorly
understood. Here we reconstruct the vomer of the troodontid Sinovenator and
the stem bird Sapeornis, and provide the palatal reconstruction of this
Early Cretaceous bird. Using these data we conducted a comprehensive
morphological study of the palate and a 3D shape analysis of the vomer
across Paraves. The results indicate that stem birds, like palaeognaths,
had limited cranial kinesis, a conclusion also supported by the
identification of an ectopterygoid in Sapeornis. This suggests that the
remarkably flexible avian skull is a neognathous innovation, with greater
cranial kinesis ultimately facilitating the radiation of this highly
successful lineage.

Abstract
Most living birds exhibit cranial kinesis—movement between the rostrum and
braincase—in which force is transferred through the palatal and jugal bars.
The palate alone distinguishes the Paleognathae from the Neognathae, with
cranial kinesis more developed in neognaths. Most previous palatal studies
were based on 2D data and rarely incorporated data from stem birds despite
great interest in their kinetic abilities. Here we reconstruct the vomer of
the Early Cretaceous stem bird Sapeornis and the troodontid Sinovenator,
taxa spanning the dinosaur–bird transition. A 3D shape analysis including
these paravians and an extensive sampling of neornithines reveals their
strong similarity to paleognaths and indicates that morphological
differences in the vomer between paleognaths and neognaths are intimately
related to their different kinetic abilities. These results suggest the
skull of Mesozoic paravians lacked the kinetic abilities observed in
neognaths, a conclusion also supported by our identification of an
ectopterygoid in Sapeornis here. We conclude that cranial kinesis evolved
relatively late, likely an innovation of the Neognathae, and is linked to
the transformation of the vomer. This transformation increased palatal
mobility, enabling the evolution of a diversity of kinetic mechanisms and
ultimately contributing to the extraordinary evolutionary success of this
clade.



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