Re: [dinosaur] 2016 in paleontology + Dippy's last days in London + burrows around Omeisaurus + more

[Tim Williams <tijawi@gmail.com>]

Ben Creisler <bcreisler@gmail.com> wrote:

> 2016 was a successful year for paleontology
>
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.wildprehistory.com_news_2016-2Dwas-2Da-2Dsuccessful-2Dyear-2Dfor-2Dpaleontology_&d=DwIBaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=Z3eGHNM7M5T7CsuZ4ZAXqsgLt62lItVtDy_bznJ9lqs&s=YOgbTi2tMMBMuImM5mLNmmzvWtqiqx3OQOH75YPrUHg&e=
>  


These two 2016 publications weren't included in the list, despite
having a major impact on how we view the origin(s) of flight in
theropod dinosaurs:

Dececchi et al. (2016) The wings before the bird: an evaluation of
flapping-based locomotory hypotheses in bird antecedents. PeerJ
4:e2159; DOI 10.7717/peerj.2159

Domyan et al. (2016) Molecular shifts in limb identity underlie
development of feathered feet in two domestic avian species. eLife
2016;5:e12115. DOI: 10.7554/eLife.12115

Using biomechanical models based on aerodynamic principals and in vivo
experiments, Dececchi &c found that a bunch of non-avian paravians and
basal avians could have been true fliers that took off from the
ground: _Microraptor_, _Archaeopteryx_, _Jeholornis_, _Sapeornis_,
confuciusornithids.  (Other work by the same authors also puts
_Rahonavis_ in this category.)  The size of the wings (forewings),
combined with the leaping abilities of the hindlimbs, was found to be
the most important determinant for achieving a ground-based stationary
take-off.  Ground-level take-off and powered flight therefore
originated prior to the development of a specialized musculoskeletal
flight apparatus (hugely expanded pectoral muscles; sternal keel;
triosseal canal; dorsolateral glenoid; etc).  Additionally, certain
non-avian paravians were found to have benefited from
flapping-assisted locomotion, without being capable of true flight,
including _Anchiornis_, _Changyuraptor_, _Aurornis_, and maybe
_Eosinopteryx_.

Dececchi &c also found no evidence that Wing Assisted Incline Running
(WAIR) was involved at all in incipient flight evolution in theropods.
Instead, WAIR is more likely to be a highly derived behavior unique to
certain juvenile birds, and was exapted from advanced flight ability.

Overall, the results are consistent with non-avian paravians
(including _Anchiornis_ and _Microraptor_) and the most basal avians
all being terrestrial bipeds.  So there's no need to restore any
paravian as an arboreal quadruped; nor any need to regard a
four-winged "tetrapteryx" gliding stage as ancestral to avian flight.

In general, we may be putting too much stock in 'hindwings' when
inferring the volant (gliding or flight) potential of certain
non-avian theropods - especially so-called "tetrapteryx" taxa like
_Microraptor_ and _Anchiornis_.  This is reinforced by molecular
studies by Domyan &c, who identified genes involved in the transition
from scaled to feathered feet in pigeons and chickens.  Their work has
important implications for "four-winged" (tetrapteryx) paravians, as
they themselves state:

"Building on classical breeding experiments in both pigeons and
chickens, we find that a relatively
small number of genetic changes account for a large proportion of the
variation in epidermal
appendage morphology and distribution. Thus, major determinants of
dramatic phenotypic variation
can be mechanistically simple and therefore potentially evolve
rapidly. In pigeons, these mechanisms
can generate wing-like feathers on a hindlimb that is not used for
powered flight or gliding. This, in
turn, suggests that wing-like foot and leg feathers in other species,
such as non-avian dinosaurs,
might result from developmental constraints on the morphology of large
limb feathers, rather than
from functional adaptations for flight"