[dinosaur] Archosauria hyposphene-hypantrum articulation evolution (free pdf)

Ben Creisler
[email protected]


A new paper in open access:


Candice M. Stefanic and Sterling J. Nesbitt (2019)
The evolution and role of the hyposphene-hypantrum articulation in
Archosauria: phylogeny, size and/or mechanics?
Royal Society Open Science 6(1): 190258
doi: https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1098_rsos.190258&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=TFUDsy7QcJ9YeicsUOUjQSofZNH2NSPDGPiMipIdtTA&s=PNEhs4bJZxZnRM4qL9KUdG0PJjCWO4u25LIEMxyPbP8&e= 
https://urldefense.proofpoint.com/v2/url?u=https-3A__royalsocietypublishing.org_doi_10.1098_rsos.190258&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=TFUDsy7QcJ9YeicsUOUjQSofZNH2NSPDGPiMipIdtTA&s=Qho3s6r_hURY0LUrmUwXBO7DfZjzxDrnVa7lUqV7RiU&e= 

Free pdf:
https://urldefense.proofpoint.com/v2/url?u=https-3A__royalsocietypublishing.org_doi_pdf_10.1098_rsos.190258&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=TFUDsy7QcJ9YeicsUOUjQSofZNH2NSPDGPiMipIdtTA&s=2phsWIXeN976wCcdIodQ5SHFCONofh7cgRSNk3ezN2s&e= 


Living members of Archosauria, the reptile clade containing Crocodylia and
Aves, have a wide range of skeletal morphologies, ecologies and body size.
The range of body size greatly increases when extinct archosaurs are
included, because extinct Archosauria includes the largest members of any
terrestrial vertebrate group (e.g. 70-tonne titanosaurs, 20-tonne
theropods). Archosaurs evolved various skeletal adaptations for large body
size, but these adaptations varied among clades and did not always appear
consistently with body size or ecology. Modification of intervertebral
articulations, specifically the presence of a hyposphene-hypantrum
articulation between trunk vertebrae, occurs in a variety of extinct
archosaurs (e.g. non-avian dinosaurs, pseudosuchians). We surveyed the
phylogenetic distribution of the hyposphene-hypantrum to test its
relationship with body size. We found convergent evolution among
large-bodied clades, except when the clade evolved an alternative mechanism
for vertebral bracing. For example, some extinct lineages that lack the
hyposphene-hypantrum articulation (e.g. ornithischians) have ossified
tendons that braced their vertebral column. Ossified tendons are present
even in small taxa and in small-bodied juveniles, but large-bodied taxa
with ossified tendons reached those body sizes without evolving the
hyposphene-hypantrum articulation. The hyposphene-hypantrum was permanently
lost in extinct crownward members of both major archosaur lineages (i.e.
Crocodylia and Aves) as they underwent phyletic size decrease, changes in
vertebral morphology and shifts in ecology.

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