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Re: [dinosaur] New Archaeopteryx specimen described (free pdf)



This is a great study of an amazing specimen.  The study also directly
contradicts some fairly recent interpretations regarding
_Archaeopteryx_'s anatomy.  Firstly, based on this new specimen,
Rauhut &c infer that _Archaeopteryx_ had a cartilaginous sternum
(contra Zheng et al. 2014 doi/10.1073/pnas.1411070111).  The idea that
a sternum was present but not preserved because it was cartilaginous
(and not ossified) has been proposed before for _Archaeopteryx_ (e.g.
Bock 2013 DOI: 10.1134/S0031030113110038; Foth 2014
doi/10.1073/pnas.1419023111; Mayr 2017 DOI 10.1007/s10336-017-1451-x;
etc).  The existence of a chondrified sternum certainly makes things
easier when reconstructing the musculature of _Archaeopteryx_, because
a sternum is the most logical place for the pectoral muscles to attach
to, especially if they were quite large.  Rauhut et al. mention that
"A triangular crystalline calcite structure found between the right
humerus and the left coracoid, ventral to the glenoid fossa of the
right scapula of the Berlin specimen of _Archaeopteryx_, however, may
provide direct evidence for the presence of cartilaginous sternal
elements".  Note that O'Connor et al. (doi/10.1073/pnas.1419403111)
have pre-emptively pooh-poohed this identification: "We are aware of
the calcitic mass preserved in the Berlin _Archaeopteryx_; however,
the position of the mass (between the scapula and coracoid) is
inconsistent with its interpretation as the sternum."  The presence of
a cartilaginous sternum doesn't hinge on the identification of this
mysterious calcite structure as a sternum, so it likely doesn't matter
either way.

Bock (2013) used the absence of an ossified sternum in _Archaeopteryx_
to argue that it was a passive glider, not an active flapping flier -
but I think this is going too far.  A non-ossified sternum is entirely
consistent with _Archaeopteryx_ being a weak flier, which would fit
with it being an island-dwelling animal that flitted short distances
between islands within the archipelago.  A cartilaginous (rather than
ossified) sternum doesn't preclude it from engaging in some kind of
flapping flight, or from being able to launch itself off the ground in
the first place.  The pygostylian _Sapeornis_, which has a strikingly
similar flight apparatus to _Archaeopteryx_, also lacked an ossified
sternum; this bird has been inferred to be an active flier that used
thermal soaring in addition to flapping (Serrano & Chiappe 2017
doi.org/10.1098/rsif.2017.0182).

Secondly, the first toe (hallux) of _Archaeopteryx_ is interpreted by
Rauhut et al. as being "somewhat opposable".  This is based on the
(putative) posteromedial attachment of metatarsal I on metatarsal II,
plus the mid-shaft curvature of metatarsal I (observed by Rauhut &c in
other _Archaeopteryx_ specimens) that would deflect the distal end
more posteriorly.  Also, phalanx I-1 is twisted, which would help
"bring the ungual of digit I in opposition to the other digits".  [NB
This trait might also be present in _Jeholornis_ - based on a 2008
SAPE abstract by Li & Zhang, where the morphology of phalanx I-1 was
used in support of a partially reversed hallux in this bird.]  Rauhut
&c's interpretation of _Archaeopteryx_'s hallux disagrees with some
previous interpretations that metatarsal I lacked torsion, and
attached to the medial side of metatarsal II (e.g. Mayr et al. 2005
Science 310:1483-1486; Mayr et al. 2007 Zool J Linn Soc 149: 97-116).
However, overall there's not a huge gulf between these two
interpretations of the orientation of the hallux: Mayr &c regard the
hallux of _Archaeopteryx_ as "spread medially" which "indicates that
the foot already had some grasping function", whereas Rauhut &c infer
a more posteromedial orientation for the hallux.  Hallucal orientation
forms a continuum, from anteromedial to medial to posteromedial to
fully retroverted. It's clear that he foot of _Archaeopteryx_ likely
had some grasping function with being fully opposable.

Nonetheless, I can see Feduccia and others pouncing on this new
specimen to bolster their view that _Archaeopteryx_ had a fully
opposable foot, and was therefore a specialized percher - and could
therefore be used as ammunition against a "ground-up" origin of avian
flight.  However, as stated, the aforementioned studies (Rauhut &c and
Mayr &c) all agree that the hallux was not fully reversed/opposable.
Further, metatarsal I is very short, and located quite high on the
metatarsus compared to specialist arboreal perchers.  These features
do not prevent perching - plenty of modern birds can (and do) perch
despite having a relatively short and/or elevated (non-incumbent)
hallux.  But these features (short, elevated hallux) are associated
with birds that spend most of their time on the ground.  Also,
grasping abilities can be linked to predation - as proposed for the
grasping feet of dromaeosaurids and troodontids (Fowler et al. 2011
doi:10.1371/journal.pone.0028964: "Hallucal (D-I) reversal is an
adaptation for grasping, but one of the principal findings of our
analysis is that a grasping foot might have evolved for purposes other
than perching on branches.")  If _Archaeopteryx_ was restricted to
small islands, there might not have been many (if any) large trees for
it to perch on anyway (unlike the Rhenish and Bohemian Massifs to the
north and west, respectively).

Finally, there is the proposed "species flock" idea, under which
"populations of the urvogel became isolated on different islands"
after arrival of a common ancestor.  This reminded me of the
intriguing possibility that _Archaeopteryx_ evolved from superior
fliers, but was itself flightless (or on the path to losing flight) as
a result of its insular lifestyle.  This would explain the weak flight
abilities in the skeleton - not primitive or incipient, but a
consequence of secondary flightlessness.  I'm skeptical of this
secondary flightless idea for _Archaeopteryx_, but it has been raised
before 
(www.nature.com/news/theory-suggests-iconic-early-bird-lost-its-flight-1.14142).






On Sat, Jan 27, 2018 at 3:22 AM, Ben Creisler <bcreisler@gmail.com> wrote:
>
>
> Ben Creisler
> bcreisler@gmail.com
>
> A new paper in open access:
>
>
> ====
>
>
> Oliver W.M. Rauhut, Christian Foth & Helmut Tischlinger (2018)
> The oldest Archaeopteryx (Theropoda: Avialiae): a new specimen from the 
> Kimmeridgian/Tithonian boundary of Schamhaupten, Bavaria.
> PeerJ 6:e4191
> doi: 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__doi.org_10.7717_peerj.4191&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=NgS0iwsmBUHhCWGEL-K2ZqsEj2deyoetVYzmcoZgaaA&s=S8pvM3ZdP_KxP71y7o5y5zIlNEP2FVyHK60vKkq0hC4&e=
> https://urldefense.proofpoint.com/v2/url?u=https-3A__peerj.com_articles_4191_&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=NgS0iwsmBUHhCWGEL-K2ZqsEj2deyoetVYzmcoZgaaA&s=vGvJ9BElCfXbvelQ5N2Z9gEY9I7u82XpNf4L0ITaRFA&e=
>
>
>
>
> The iconic primeval bird Archaeopteryx was so far mainly known from the 
> AltmÃhltal Formation (early Tithonian) of Bavaria, southern Germany, with 
> one specimen having been found in the overlying MÃrnsheim Formation. A new 
> specimen (the 12th skeletal specimen) from the earliest Tithonian Painten 
> Formation of Schamhaupten (Bavaria) represents the so far oldest 
> representative of the genus. The new specimen shows several interesting 
> anatomical details, including the presence of a postorbital in contact with 
> the jugal, the presence of a separate prefrontal and coronoid, and 
> opisthocoelous mid-cervical vertebrae. Based on observations on the new 
> specimen, we discuss several problematic issues concerning Archaeopteryx, 
> including the monophyly and diagnosis of the genus, the absence/presence of 
> the sternum, the position of the gastralia, and variation in morphometrics 
> and dental morphology in that genus. Based on a new diagnosis for the genus 
> Archaeopteryx, the Berlin, EichstÃtt, Solnhofen, Munich, Daiting, 
> Thermopolis, 11th, and 12th specimens can be referred to this genus with high 
> certainty. The Maxberg specimen is very probably also an Archaeopteryx, based 
> on overall similarity, although none of the diagnostic characters can be 
> evaluated with certainty. The ninth specimen (âchicken wingâ) might be 
> Archaeopteryx, but cannot be referred to the genus with any certainty. In 
> comparison with other paravians, the presence of distally thickened anterior 
> pectoral ribs indicates that a rather large cartilagenous sternum was present 
> in this taxon. In contrast to non-opisthopubic theropods, opisthopubic taxa, 
> such as Archaeopteryx and many other paravians, have the posterior end of the 
> gastral basket preserved at about half-length of the pubis, which might 
> reflect the post-mortem collapse of enlarged abdominal air sacs in these 
> taxa. Specimens that can be referred to Archaeopteryx show a high amount of 
> variation, both in the morphometrics of the limb bones as well as in the 
> dentition. In respect to the latter aspect, variation is found in tooth 
> number, spacing, orientation, and morphology, with no two specimens showing 
> the exact same pattern. The significance of this variation is unclear, and 
> possible explanations reach from high intraspecific (and possibly ontogenetic 
> and/or sexual dimorphic) variation to the possibility that the known 
> specimens represent a âspecies flockâ of Archaeopteryx, possibly due to 
> island speciation after the initial dispersal of the genus into the Solnhofen 
> Archipelago.
>
>
> ==
>
> News:
>
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.en.uni-2Dmuenchen.de_news_newsarchiv_2018_rauhut-5Farchaeopteryx.html&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=NgS0iwsmBUHhCWGEL-K2ZqsEj2deyoetVYzmcoZgaaA&s=rb_VCrZgwYQg0BQffkfYrw-NEm4f-WPfo-_TPOBIXMk&e=
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__phys.org_news_2018-2D01-2Deleventh-2Darchaeopteryx.html&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=NgS0iwsmBUHhCWGEL-K2ZqsEj2deyoetVYzmcoZgaaA&s=QNS9Mje_DDGfN9_k7t-qZWA2xL7oESN-ByhNOguHQPo&e=
>
> In German
>
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.uni-2Dmuenchen.de_forschung_news_2018_rauhut-5Farchaeopteryx.html&d=DwIFaQ&c=clK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=Ry_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=NgS0iwsmBUHhCWGEL-K2ZqsEj2deyoetVYzmcoZgaaA&s=15gBy7tcKaXLz4Ludy-n5TrASRK9pFN_z-Tbc4z241w&e=
>
>
>
> Virus-free. www.avg.com