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Re: Dingavis, new ornithuromorph bird from Lower Cretaceous of China



Could Dingavis be the same as Juehuaornis? I have not done all the
legwork necessary to evaluate this question, but considering that the
description of Dingavis does not mention Juehuaornis despite both
being long-snouted Early Cretaceous euornithines, it seems worthy of
exploration.

Confounding matters further, the description of Juehuaornis is brief,
provides no exact measurements of skeletal elements, and is
illustrated with only a single low-res photo of the holotype slab and
counterslab. Regardless, there are some suspicious similarities based
on the information available. All of this is based on a comparatively
quick gleaning of the two description papers and is by no means
intended to be a complete overview.

First of all, the diagnoses of each taxon compared to the
characteristics seen the other.

The diagnosis of Dingavis, compared to Juehuaornis:
-Rostrum forms 63 -65% of total skull length: Rostrum is ~70% of total
skull length in Juehuaornis
-Jugal process of lacrimal caudolaterally excavated: Not described in
Juehuaornis
-Both upper and lower jaws edentulous: Maxillary and dentary teeth
present in Juehuaornis
-Length of carpometacarpus + major digit exceeds humeral length by
25%: From quick-and-dirty measurements taken from the photo in ImageJ,
this ratio is around ~24% in Juehuaornis
-Short alular metacarpal (13.7% of major metacarpal): Alular
metacarpal said to be less than 20% the length of the major metacarpal
in Juehuaornis
-Tarsometatarsus with small but sharp medial and lateral plantar
crests, plantar surface not excavated: Not described in Juehuaornis
-Metatarsal II much shorter than metatarsal IV: Metatarsal II is
shorter than metatarsals III and IV in Juehuaornis, by how much
unreported
-Metatarsal II and IV trochlea plantarly displaced: Not described in Juehuaornis
-Metatarsal II trochlea strongly angled craniomedially: Not described
in Juehuaornis

The diagnosis of Juehuaornis, compared to Dingavis:
-Forelimb and hindlimb almost equal in length: Preserved humerus +
ulna + carpometacarpus length in Dingavis is 124.2 and 132.9 mm and
preserved femur + tibiotarsus + tarsometatarsus length is132.9 and
132.1 mm
-Rostrum forms ~70% of total skull length: 63-65% in Dingavis
-Premaxilla hooked and extends beyond mandible: Not seen in Dingavis
-Anterior of dentary straight: Present in Dingavis
-Teeth only present in maxilla and dentary: Edentulous in Dingavis

The main differences appear to be the presence of teeth and a hooked
bill in Juehuaornis. We'll get to that.

Other similarities shared between the two:
-Femur ~65% the length of the tibiotarsus
-Ulna and humerus almost equal in length
-Pedal claws short and barely curved
-Phalanx 2 on manual digit II dramatically thinner than phalanx 1,
longer than phalanx 1 but shorter than phalanx 1 on manual digit I
-Moderate extensor tubercle on manual digit I
-“Small pubic boot” reported in Juehuaornis; distal pubes said to be
expanded in Dingavis despite lacking a "distinct" pubic boot

Differences:
-Juehuaornis is from the Jiufotang Formation while Dingavis is from
the Yixian. The two formations are already known to have shared some
fauna, so this is not particularly damning.
-Two phalanges are present on manual digit III in Juehuaornis, whereas
Dingavis has only one (suggested to be a fusion of the first and
second phalanges). However, the second phalanx on Juehuaornis is said
to be highly reduced and would be potentially easy to lose postmortem,
or perhaps be present in differing degrees of fusion between
individuals.
-The "hooked bill" in Juehuaornis is barely visible from the photos
provided. Given the disarticulated nature of the Dingavis skull, it
would not surprise me if this feature was distorted or lost through
taphonomy.
-And the biggie: the teeth. The maxillary teeth of Juehuaornis are
reportedly not visible in lateral view and were only identified
through breakage in the specimen. In fact, due to the poor
preservation of the skull, the describers of Dingavis do not discount
the possibility of maxillary teeth. The dentary teeth of Juehuaornis
are not described as being similarly challenging to find (though
small) and are said to be numerous. If truly absent in Dingavis, these
would appear to be the primary point of differentiation between them,
but, if the two are synonymous, this would not be the first time a
Mesozoic euornithine was mistaken to be wholly or partially toothless
in the absence of better-preserved skull material (cf. Hongshanornis).

On Tue, Jan 12, 2016 at 1:52 PM, Ben Creisler <bcreisler@gmail.com> wrote:
> Ben Creisler
> bcreisler@gmail.com
>
>
> A new paper:
>
>
>
> Jingmai K. O'Connor, Min Wang & Han Hu (2016)
> A new ornithuromorph (Aves) with an elongate rostrum from the Jehol
> Biota, and the early evolution of rostralization in birds.
> Journal of Systematic Palaeontology (advance online publication)
> DOI:10.1080/14772019.2015.1129518
> http://www.tandfonline.com/doi/full/10.1080/14772019.2015.1129518
>
>
> A new species of Early Cretaceous ornithuromorph with an elongate
> rostrum is described from the Sihedang locality of the Lower
> Cretaceous Yixian Formation in north-eastern China. Like the
> longipterygid enantiornithines, rostral elongation in Dingavis
> longimaxilla gen. et sp. nov. is achieved primarily through the
> maxilla, whereas neornithines elongate the premaxilla and
> rostralization is far more extreme than observed in early birds.
> Notably, in the rostrum of Xinghaiornis, the most ‘longirostrine’
> Early Cretaceous ornithuromorph, the premaxilla and maxilla contribute
> to the rostrum equally. These lineages together highlight the
> diversity of configurations in which early birds experimented with
> rostralization of the skull. The 65% upper limit in rostral
> proportions of Early Cretaceous taxa with elongate maxillae and the
> fact that this morphology was abandoned in more derived taxa suggests
> that in Aves this skull configuration provided less structural
> stability.
>
> http://zoobank.org/urn:lsid:zoobank.org:pub:9D8A429F-BBA7-47EF-BFD0-ADFB7118833A