Re: [dinosaur] Theropod and bird lifestyles from ungual bone curvatures (free pdf)

[Tim Williams <tijawi@gmail.com>]

This is one of those cases where the Abstract presents an
oversimplified (and somewhat misleading) summary of the actual study.
For example:

"Our model predicts arboreal lifestyles for _Archaeopteryx_ and
_Microraptor_ and a predatory ecology for _Confuciusornis_."

The data in the study do not actually support an arboreal lifestyle
for _Archaeopteryx_ and _Microraptor_, or a predatory ecology
_Confuciusornis_.  This is made clear in the body of the paper, which
is quite candid in this respect:

"Claws belonging to _Archaeopteryx_, _Confuciusornis_, and
_Microraptor_ had a wide spread.
_Archaeopteryx_ specimens plotted within all morphospaces, and right
and left PD-III claws of
the same specimen plotted quite far apart from each other. This was
also the case for _Microraptor_,
for which two claws belonging to a single specimen plotted in
different morphospaces
(predatory and perching) and received different classifications
accordingly (Table 5). Though
all were classed as predatory (Table 5), the four _Confuciusornis_
claws were recovered in the
overlaps between predatory, perching, and scansorial morphospaces and,
in some instances,
plotted outside of extant morphospaces altogether (Fig 4)."

The fact that individual unguals from the same species or even the
same specimen could produce "conflicting predictions" tells us how
fraught using ungual curvature is for determing ecologies.  These
"conflicting predictions" were also the fate of_Jeholornis_ and
_Sapeornis_, in additon to _Archaeopteryx_, _Confuciusornis_, and
_Microraptor_.  There's nothing wrong with this.  It just tells us
that the ecologies of these maniraptorans were complex, and don't fit
neatly into discrete categories (arboreal, predatory, scansorial,
terrestrial).

However, claiming elongate forelimbs is an adaptation for arboreal
locomotion in maniraptorans (as the study does on several occasions)
is extremely ill-advised.  _Velociraptor_ had long forelimbs, as did
many other large (or large-ish) maniraptorans.  Even worse is the
claim that "swivel wrist joints" (= semilunate carpal) are likewise an
adaptation for arboreal locomotion; this is just ridiculous.  I blame
Chatterjee's 'The Rise of Birds' for that one.

On Thu, Feb 6, 2020 at 5:49 AM Ben Creisler <bcreisler@gmail.com> wrote:
>
> Ben Creisler
> bcreisler@gmail.com
>
> A new paper with free pdf:
>
> Savannah Elizabeth Cobb & William I. Sellers (2020)
> Inferring lifestyle for Aves and Theropoda: A model based on curvatures of 
> extant avian ungual bones.
> PLoS ONE 15(2): e0211173.
> doi: 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.1371_journal.pone.0211173&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=Mukc7ickrgBD78eZzMiE20P84DwkbC_Xk8sF5g-3zEE&s=m7n6pcstdz-uyAbl_CkExIrS6EKBzxnoP8i3yYXP5eE&e=
>  
> https://urldefense.proofpoint.com/v2/url?u=https-3A__journals.plos.org_plosone_article-3Fid-3D10.1371_journal.pone.0211173&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=Mukc7ickrgBD78eZzMiE20P84DwkbC_Xk8sF5g-3zEE&s=YvFItzb-PnpwPcQ8gXqIeU_YzFGtR2yRYaIl0leVzf0&e=
>  
>
> Free pdf:
> https://urldefense.proofpoint.com/v2/url?u=https-3A__journals.plos.org_plosone_article_file-3Fid-3D10.1371_journal.pone.0211173-26type-3Dprintable&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=Mukc7ickrgBD78eZzMiE20P84DwkbC_Xk8sF5g-3zEE&s=o2H4ZzwL9wdmeD5uB3qabbVRmvxHNv2Zz874UQDIbkk&e=
>  
>
>
> Claws are involved in a number of behaviours including locomotion and prey 
> capture, and as a result animals evolve claw morphologies that enable these 
> functions. Past authors have found geometry of the keratinous sheath of the 
> claw to correlate with mode of life for extant birds and squamates; this 
> relationship has frequently been cited to infer lifestyles for Mesozoic 
> theropods including Archaeopteryx. However, many fossil claws lack keratinous 
> sheaths and thus cannot be analysed using current methods. As the ungual 
> phalanx within the claw is more commonly preserved in the fossil record, 
> geometry of this bone may provide a more useful metric for paleontological 
> analysis. In this study, ungual bones of 108 birds and 5 squamates were 
> imaged using X-ray techniques and a relationship was found between curvatures 
> of the ungual bone within the claw of pedal digit III and four modes of life; 
> ground-dwelling, perching, predatory, and scansorial; using linear 
> discriminant analysis with weighted accuracy equal to 0.79. Our model 
> predicts arboreal lifestyles for Archaeopteryx and Microraptor and a 
> predatory ecology for Confuciusornis. These findings demonstrate the utility 
> of our model in answering questions of palaeoecology, the theropod-bird 
> transition, and the evolution of avian flight. Though the metric exhibits a 
> strong correlation with lifestyle, morphospaces for PD-III curvatures overlap 
> and so this metric should be considered alongside additional evidence.
>
> ====