Wednesday, May 3, 2017

[Paleontology • 2017] Jianianhualong tengi • Mosaic Evolution in An Asymmetrically Feathered Troodontid Dinosaur with Transitional Features

Jianianhualong tengi  
Xu, Currie, Pittman, Xing, Meng, Lü, Hu & Yu, 2017 

 Life reconstruction by Julius T. Csotonyi | DOI: 10.1038/ncomms14972

Asymmetrical feathers have been associated with flight capability but are also found in species that do not fly, and their appearance was a major event in feather evolution. Among non-avialan theropods, they are only known in microraptorine dromaeosaurids. Here we report a new troodontid, Jianianhualong tengi gen. et sp. nov., from the Lower Cretaceous Jehol Group of China, that has anatomical features that are transitional between long-armed basal troodontids and derived short-armed ones, shedding new light on troodontid character evolution. It indicates that troodontid feathering is similar to Archaeopteryx in having large arm and leg feathers as well as frond-like tail feathering, confirming that these feathering characteristics were widely present among basal paravians. Most significantly, the taxon has the earliest known asymmetrical troodontid feathers, suggesting that feather asymmetry was ancestral to Paraves. This taxon also displays a mosaic distribution of characters like Sinusonasus, another troodontid with transitional anatomical features.

Figure 1: Jianianhualong tengi holotype DLXH 1218.
 (a) Photograph and (b) line drawing of the specimen. Scale bar, 50 cm.

 cav, caudal vertebrae; cv, cervical vertebrae; dv, dorsal vertebrae; fu, furcula; lfe, left femur; lh, left humerus; li, left ilium; lis, left ischium; lm, left manus; lp left pes; lpu, left pubis; lr, left radius; lu, left ulna; md, mandible; rc, right coracoid; rfe, right femur; rfi, right fibula; rh, right humerus; ri, right ilium; rm, right manus; rr, right radius; rs, right scapula; rt, right tibiotarsus; ru, right ulna; sk, skull; ss, synsacrum. 

Figure 7: Life reconstruction of Jianianhualong tengi based on the holotype DLXH 1218.
by Julius T. Csotonyi 

Systematic palaeontology 
Theropoda Marsh, 188121
Coelurosauria Huene, 192022

Maniraptora Gauthier, 198623
Troodontidae Gilmore, 192424

Jianianhualong tengi gen. et sp. nov.

 Etymology.Jianianhua’, the Chinese company that supported this study; ‘long’, the Chinese Pinyin for dragon. The specific name honors Ms Fangfang Teng, who secured the specimen for study.

 Holotype. DLXH 1218, a nearly complete skeleton with associated feathers (Fig. 1) housed at the Dalian Xinghai Museum.

Locality and horizon. Baicai Gou, Yixian County, western Liaoning, China; Lower Cretaceous Yixian Formation.

 Diagnosis. A troodontid distinguishable from other taxa in possessing the following apomorphic features (*indicates autapomorphic feature): maxillary rostral ramus triangular in outline and relatively high dorsoventrally*; maxillary ascending process extending posterodorsally at a high angle (an angle of ∼45° to maxillary ventral margin)*; lacrimal with a long descending process sub-equal in length to anterior process; a prominent ridge along anterior edge of the lateral surface of the lacrimal descending process; a distinct fossa on the dorsal surface of the surangular close to its posterior end; axial neural spine with a convex dorsal margin, transversely thickened anterior margin, and posterodorsal portion expanding strongly posteriorly; long manual phalanx II-1 (slightly shorter than metacarpal III) with prominent proximoventral heel, large groove along the medial surface of more than proximal half of manual phalanx II-1*; highly elongated manual III-2 (slightly longer than metacarpal III)*; robust ungual phalanges (medial ungual proximal depth/ungual length ratio >0.5); ilium with slightly concave dorsal margin in lateral view*; small medial lamina along ischial obturator process dorsal margin; metatarsal IV without prominent ventral flange*.

Figure 2: Cranium of Jianianhualong tengi holotype DLXH 1218.
 (a) Photograph and (b) line drawing of the skull and mandible. Scale bar, 2 cm.
ax, axis; fg, groove with foramina; fo, fossa; imf, internal mandibular fenestra; la, left angular; ld, left dentary; lect, left ectopterygoid; lex, left exoccipital; lf; left frontal; lhy, left hyoid bone; lj, left jugal; lla, left lacrimal; lm, left maxilla; lmf, left maxillary fenestra; ln, left nasal; lp, left parietal; lpt?, left pterygoid?; lpa, left prearticular; lpo, left postorbital; lpsaf, left posterior surangular foramen; lsa, left surangular; lsp?, left splenial?; lso, left supraoccipital; lsq, left squamosal; mc, Meckelian canal; ra, right angular; rart, right articular; rd, right dentary; rf, right frontal; rhy, right hyoid bone; rm?, right maxilla?; rn; right nasal; rp, right parietal; rpa, right prearticular; rq?, right quadrate?; rsa; right surangular; rso, right supraoccipital; rsp; right splenial; rsq, right squamosal. 

Xing Xu, Philip Currie, Michael Pittman, Lida Xing, Qingjin Meng, Junchang Lü, Dongyu Hu and Congyu Yu. 2017. Mosaic Evolution in An Asymmetrically Feathered Troodontid Dinosaur with Transitional Features.
  Nature Communications. 8, Article number: 14972.  DOI: 10.1038/ncomms14972

New Birdlike Dinosaur Had Modern Feathers  @NatGeo


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