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Re: [dinosaur] Dinosauria reclassification joins Ornithischia and Theropoda in Ornithoscelida

The clade Dinosauria has been re-defined in the article, so that a
sauropod (_Diplodocus_) is now added as a specifier, in addition to a
theropod (_Passer_) and an ornithischian (_Triceratops_).  Otherwise,
all sauropodomorphs (as well as herrerasaurids) would have been tipped
out of the Dinosauria, which would have been limited to the
Theropoda+Ornithischia clade (= Ornithoscelida of Baron et al.).  So
this revised definition of Dinosauria is a sensible move, to ensure
that theropods and sauropods and ornithischians are always dinosaurs.

But I'm uneasy about the revised definition of Saurischia, which has
only one internal specifier (a theropod).  Given the topology given by
Baron et al., a better idea might have been to drop Saurischia
altogether, rather than salvage it as the name for the new
Herrerasauridae+Sauropodomorpha clade.  Firstly, this rump Saurischia
overturns an established tradition that Saurischia as a group should
include theropods; I'd say that no Saurischia at all is better than a
Saurischia sans Theropoda.  Secondly, the sister clade to
Ornithoscelida could simply be called Sauropodomorpha, with
herrerasaurids simply considered basal sauropodomorphs; the prevailing
stem-based definition of Sauropodomorpha allows for this.  Instead
Baron et al. re-define Sauropodomorpha to exclude herrerasaurids, such
that the two are sister taxa within a 'new' Saurischia.

Baron et al.'s phylogeny implies that a supinated, grasping hand is
primitive for dinosaurs, and they further suggest that "the ability to
grasp with the manus played an important role in early dinosaur
evolution".  It's an entirely reasonable hypothesis; but I'm
skeptical.  I lean toward the view that theropod forelimbs weren't
really all that useful for grasping (especially prey capture).  Like
Persons & Currie (2017; dx.doi.org/10.1016/j.jtbi.2017.02.032), I
suspect that the tendency to ascribe great adaptive significance to
the freed hands of dinosaurs at least partly reflects our own human
bias.  Most Triassic theropods and herrerasaurids had short forelimbs;
as Persons & Currie (2017) put it, it's "difficult to envision them
grappling with any prey that could not have already been seized by the
jaws".  So I doubt the 'grasping' manus conferred on early dinosaurs
some evolutionary edge over other archosaurs (including other bipeds).

_Eoraptor_ (which Baron et al. put back in the Theropoda, as the most
basal theropod) and basal sauropodomorphs ('prosauropods') share a
specialized medially ‘twisted’ phalanx 1 of manual digit I
(pollex/thumb) .  This 'twisted' pollex is a convergent feature
acquired by _Eoraptor_ and sauropodomorphs independently, or it is
primitive for dinosaurs.  Either way, the function of the twisted
pollex is unclear; it might have been used for defense or
intraspecific combat.  Once freed from a function in locomotion and
weight-bearing, dinosaur hands might have been employed for defensive
purposes, more so than grasping.

On Thu, Mar 23, 2017 at 5:13 AM, Ben Creisler <bcreisler@gmail.com> wrote:
> Ben Creisler
> bcreisler@gmail.com
> A new paper:
> Matthew G. Baron, David B. Norman & Paul M. Barrett (2017)
> A new hypothesis of dinosaur relationships and early dinosaur evolution.
> Nature 543: 501–506
> doi:10.1038/nature21700
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.nature.com_nature_journal_v543_n7646_full_nature21700.html&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=nxxNbLn-JSUzuh1IomeNVe6wfbM5deC39A9OAgBZ5b4&s=Opm5kBRRAA0ebYARb7s6AY0Oc8YE1j9TcqmneP7hIvY&e=
> Free pdf of supp:
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.nature.com_nature_journal_v543_n7646_extref_nature21700-2Ds1.pdf&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=nxxNbLn-JSUzuh1IomeNVe6wfbM5deC39A9OAgBZ5b4&s=dMqOfY7_gdHoqrBnyNMQEFiRPlN537vhEoU6fUmzkMs&e=
> For 130 years, dinosaurs have been divided into two distinct
> clades—Ornithischia and Saurischia. Here we present a hypothesis for the
> phylogenetic relationships of the major dinosaurian groups that challenges
> the current consensus concerning early dinosaur evolution and highlights
> problematic aspects of current cladistic definitions. Our study has found a
> sister-group relationship between Ornithischia and Theropoda (united in the
> new clade Ornithoscelida), with Sauropodomorpha and Herrerasauridae (as the
> redefined Saurischia) forming its monophyletic outgroup. This new tree
> topology requires redefinition and rediagnosis of Dinosauria and the
> subsidiary dinosaurian clades. In addition, it forces re-evaluations of
> early dinosaur cladogenesis and character evolution, suggests that
> hypercarnivory was acquired independently in herrerasaurids and theropods,
> and offers an explanation for many of the anatomical features previously
> regarded as notable convergences between theropods and early ornithischians.
> ===
> Kevin Padian (2017)
> Dividing the dinosaurs.
> Nature 543: 494–495
> doi:10.1038/543494a
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.nature.com_nature_journal_v543_n7646_full_543494a.html&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=nxxNbLn-JSUzuh1IomeNVe6wfbM5deC39A9OAgBZ5b4&s=88QasmaKfWrAPG3yvWmUQhE25a6pRM7xlOv6kI-A9rg&e=
> The standard dinosaur evolutionary tree has two key branches: the
> 'bird-hipped' Ornithischia and the 'reptile-hipped' Saurischia. A revised
> tree challenges many ideas about the relationships between dinosaur groups.
> See Article p.501
> ======
> News:
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.nature.com_news_dinosaur-2Dfamily-2Dtree-2Dpoised-2Dfor-2Dcolossal-2Dshake-2Dup-2D1.21681&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=nxxNbLn-JSUzuh1IomeNVe6wfbM5deC39A9OAgBZ5b4&s=J9DLDYu6JlwVoNfS-NgMKfvK0nY7obJcJXsLk5OF3sc&e=
> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.theguardian.com_science_2017_mar_22_scottish-2Dfossil-2Dmay-2Dcause-2Dradical-2Dshakeup-2Dof-2Ddinosaur-2Dfamily-2Dtree-2Dsaltopus&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=nxxNbLn-JSUzuh1IomeNVe6wfbM5deC39A9OAgBZ5b4&s=od9EenBKXw1rew8FnzVJg3PMF6YwFG34qJSRoXEknrg&e=
> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.newscientist.com_article_2125580-2Dfirst-2Ddinosaurs-2Dmay-2Dhave-2Dbeen-2Domnivores-2Din-2Dthe-2Dnorth-2Dhemisphere_&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=nxxNbLn-JSUzuh1IomeNVe6wfbM5deC39A9OAgBZ5b4&s=xQlKz9ZMSxrYctHvihh95Pmb4QVj7qSCIcFlG7GXdHI&e=
> https://urldefense.proofpoint.com/v2/url?u=https-3A__phys.org_news_2017-2D03-2Droots-2Ddinosaur-2Dfamily-2Dtree.html&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=nxxNbLn-JSUzuh1IomeNVe6wfbM5deC39A9OAgBZ5b4&s=q6ShQbMtiEUFtUPYj9AJ85ScsobfZ-JLl1sw6t-eQQI&e=
> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.theatlantic.com_science_archive_2017_03_dinosaur-2Dfamily-2Dtree-2Dsaurischia-2Dornithischia-2Dchildhood-2Dshattered-2Dwhat-2Dis-2Dreal-2Danymore_520338_&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=nxxNbLn-JSUzuh1IomeNVe6wfbM5deC39A9OAgBZ5b4&s=x2Q42F4itZNYDCnRE-ezxed8Rok53ahjDpR_Q8e-mf8&e=