Our paper "Ontogenetic similarities between giraffe and sauropod neck osteological mobility"compares the range of motion and neutral pose of the necks of juveniles and adults of extant #giraffes and Spinophorosaurus (Middle #Jurassic #Niger).
THREAD 1/15
journals.plos.org/plosone/articl…
THREAD 1/15
journals.plos.org/plosone/articl…
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED 2/15 The goal was to test whether there exist ontogenetic-related differences in the range of motion (ROM) and posture of #sauropods. Given there have been many doubts casted on virtual ROM analyses, extant giraffes were used as comparison.
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED 3/15 Assembling the virtual skeleton of a newborn giraffe allowed us to reject the hypothesis that articulating bare bones in osteologically neutral pose (ONP) could not predict the amount of intervertebral tissue separating adjacent vertebrae. (Image from @MikeTaylor & Wedel 13)
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 4/15 The neck articulated in ONP (maximum overlap of the zygapophyses) rendered 27.03% of the complete neck length as intervertebral space, almost the same present in the necropsied newborn individual from which the CT-scanned skeleton came from (27.27%)
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 5/15 However, the neck of the adult giraffe barely rendered 4.8% of the complete neck length as intervertebral space, suggesting the amount of intervertebral space diminishes with growth (which had already been suggested by @MikeTaylor & Wedel 2013, among others) in giraffes.
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 6/15 Regarding Spinophorosaurus, both studied necks (juvenile and holotype) were found in articulation, though strongly dorsiflexed. The juvenile was found with the condyles barely inside the cotyles, while the adult had its condyles deeply nested inside the cotyles.
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 7/15 Both specimens were digitized using digital photogrammetry. Articulating the 3D bones in ONP revealed intervertebral spaces ranging from 12.4% to 15.86% on the juvenile specimen, while the adult barely had 4.5% of intervertebral space.
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 8/15 On the other hand, the osteological range of motion (ROM) analyses showed that all extreme postures adopted by living giraffes, which had been claimed to required disarticulation of cervical vertebrae, could be replicated without disarticulating vertebrae!
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 9/15 Regarding Spinophorosaurus, both specimens could replicate similar postures which are attained by live giraffes without disarticulating their cervical vertebrae. This implies the same feeding capabilities, but remember: capabilities do not imply behavior!
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 10/15 Also, as in giraffes, the amount of osteological ROM was greater in the grown holotype Spinophorosaurus specimen than on the juvenile. This is despite similarly shaped pre-postzygapophyseal facets, so it is due centrum - zygapophyses distance (Fig. from Stevens 2013)
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 11/15 Overall, our conclusions are 1) that ONP can be more than just a "standard" pose in which to compare different skeletal mounts, but can also reveal some paleobiological infor 2) living giraffes do not disarticulate their necks to attain even the most extreme neck poses.
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 12/15 3) Intervertebral spaces between cervical centra in early ontogenetical stages are very large in extant giraffes and Spinophorosaurus, decreasing as ontogeny advances; and 4) grown specimens have a greater osteological range of motion in both taxa.
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 13/15 A educated hypothesis ahead: these conclusions could imply that the early evolution of the cervical mobility in sauropods is a product of changes in developmental timing of cervical vertebrae (aka heterochronies), although more sampling is required to test the hypothesis.
@frco_ortega @PD_Mocho @PLOSONE @mupe_elche @SrParamo @biouned @UNED @MikeTaylor 14/15 So, Spinophorosaurus increased its overall neck range of motion while reducing the intervertebral space while growing. Given niche partitioning was granted just from differences in size, the reason behind this could be a remnant of evolutionary processes (Art by Diego Cobo)
