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



A correction to my previous message: The ulna of Juehuaornis is said
to be longer than the humerus, not almost equal in length.

On Wed, Jan 13, 2016 at 12:04 AM, Alberta Claw <albertonykus@gmail.com> wrote:
> 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