[dinosaur] Origin of avian predentary bone and unique cranial kinesis in Cretaceous ornithuromorphs.

Ben Creisler
[email protected]

A new paper:

Alida M. Bailleul, Zhiheng Li, Jingmai O’Connor, and Zhonghe Zhou (2019)
Origin of the avian predentary and evidence of a unique form of cranial
kinesis in Cretaceous ornithuromorphs.
Proceedings of the National Academy of Sciences (advance online publication)
doiL https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1073_pnas.1911820116&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=d5mlLyBZ_fh9WeVMh2HA6O96ScaVOhtqkIY8ILixuyw&s=N1LJ22rcK5uRmZs_Hf5rTVy0A8ssUCSIZ-ts91Dzuw8&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__www.pnas.org_content_early_2019_11_12_1911820116&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=d5mlLyBZ_fh9WeVMh2HA6O96ScaVOhtqkIY8ILixuyw&s=RfsT_u9rYTbTFEVH9b2T6SCI3N1JfTNcqWCWauWLdeo&e= 


Significance

The avian predentary is a small, rarely preserved skeletal structure found
only in toothed Mesozoic ornithuromorph birds. The origin and function of
this enigmatic bone is poorly understood. Based on skeletal tissue
identification in a specimen of the Early Cretaceous Yanornis martini, we
propose developmental, structural, and functional hypotheses for this
element. It consists of trabecular bone with a caudal articular surface for
the dentary covered by cartilage. Tissue mechanobiology suggests this
contact was kinetic, representing a previously unknown type of avian
cranial kinesis. We hypothesize that the avian predentary was a
biomechanically induced sesamoid that coevolved with an edentulous portion
of the premaxilla, together representing a successful morphotype that
combined a small beak with a proprioceptive system.

Abstract

The avian predentary is a small skeletal structure located rostral to the
paired dentaries found only in Mesozoic ornithuromorphs. The evolution and
function of this enigmatic element is unknown. Skeletal tissues forming the
predentary and the lower jaws in the basal ornithuromorph Yanornis martini
are identified using computed-tomography, scanning electron microscopy, and
histology. On the basis of these data, we propose hypotheses for the
development, structure, and function of this element. The predentary is
composed of trabecular bone. The convex caudal surface articulates with
rostromedial concavities on the dentaries. These articular surfaces are
covered by cartilage, which on the dentaries is divided into 3 discrete
patches: 1 rostral articular cartilage and 2 symphyseal cartilages. The
mechanobiology of avian cartilage suggests both compression and kinesis
were present at the predentary–dentary joint, therefore suggesting a yet
unknown form of avian cranial kinesis. Ontogenetic processes of skeletal
formation occurring within extant taxa do not suggest the predentary
originates within the dentaries, nor Meckel's cartilage. We hypothesize
that the predentary is a biomechanically induced sesamoid that arose within
the soft connective tissues located rostral to the dentaries. The
mandibular canal hosting the alveolar nerve suggests that the dentary teeth
and predentary of Yanornis were proprioceptive. This whole system may have
increased foraging efficiency. The Mesozoic avian predentary apparently
coevolved with an edentulous portion of the premaxilla, representing a
unique kinetic morphotype that combined teeth with a small functional beak
and persisted successfully for ~60 million years.
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News:

New finding on origin of avian predentary in Mesozoic birds

https://urldefense.proofpoint.com/v2/url?u=https-3A__www.eurekalert.org_pub-5Freleases_2019-2D11_caos-2Dnfo111819.php&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=d5mlLyBZ_fh9WeVMh2HA6O96ScaVOhtqkIY8ILixuyw&s=Wm4ILDeyPwYHw00MmxDWhI3arlsTG1mks_f5-qRPbYk&e=