New specimen of Protopteryx (1 Viewer)

[albertonykus]

O'Connor, J.K., X. Zheng, Y. Pan, X. Wang, Y. Wang, X. Zhang, and Z. Zhou (2020)
New information on the plumage of Protopteryx (Aves: Enantiornithes) from a new specimen
Cretaceous Research (advance online publication)
doi: 10.1016/j.cretres.2020.104577
https://www.sciencedirect.com/science/article/pii/S0195667120302639

Protopteryx fengningensis is from the 130.7 Ma Huajiying Formation making it one of the oldest known enantiornithines. Contributing to its significance, this taxon is also commonly resolved as the basal-most enantiornithine in phylogenetic analyses. Protopteryx preserves several unusual morphologies that are otherwise absent in the Enantiornithes but common in the Ornithuromorpha such as the procoracoid and lateral processes on the coracoid and proximally convex humeral head. Thus, the morphology of this taxon hints at the morphology of the ornithothoracine common ancestor. Here we supplement existing data with information from a new specimen as well as new morphological data from the holotype and paratype. The new specimen preserves gaps in the right wing suggestive of a sequential molt. The presence of two gaps suggests that, unlike neornithines, primaries and secondaries molted simultaneously. This represents an intermediate condition between Microraptor, in which several feathers are growing simultaneously and sequentially, and modern birds with sequential molts, in which a single feather is replaced at a time. A single patch of feathers was sampled revealing preserved eumelanosomes, indicating that at least part of the remiges was darkly colored.

 

[Fred Ruhe]

Systematic Paleontology

Aves Linnaeus 1758
Ornithothoraces Chiappe 1995
Enantiornithes Walker 1981
Protopteryx fengningensis Zhang and Zhou 2000
Holotype: IVPP V11665
Paratype: IVPP V11844 (Zhang and Zhou, 2000).
Referred specimens: BMNHC-PH1060A/B and BMNHC-PH1158A/B (Chiappe et al., 2019a); STM7-143 (
described herein).
Locality and horizon: Luozigou locality, Youfang and Jiecaigou sections 130–129 Ma Protopteryx-horizon of the Huajiying Formation in the Sichakou Basin, Fengning County, Hebei, China (He et al., 2006; Jin et al., 2008; Yang et al., 2020)(Fig. 2).
Emended diagnosis: medium sized enantiornithine with the following unique combination of characters: first phalanx of the alular digit elongate (alular digit/major metacarpal length ratio is 0.84, greater than other enantiornithines); distal end of the minor metacarpal slightly passing the distal end of the major metacarpal; first phalanx of the major digit shorter than the second phalanx; coracoid with small procoracoid process; lateral process of coracoid prominent; interclavicular angle 50°; hypocleidium approximately half of the length of the clavicular ramus; sternum with a single pair of caudal trabeculae; V-shaped caudal margin of sternum; humeral head globe-shaped; caudoventrally projected cranioventral corner of the ilium; metatarsal I that measures 25% the total length of metatarsal II (Table 1)(revised from Chiappe et al., 2019 and Zhang and Zhou, 2000).
Remarks: Chiappe et al. (2019) added the presence of a bowed first phalanx of the alular to the diagnosis. Although clearly present in BMNHC-Ph1060 and Ph1158, this feature is not present in the new specimen nor is it clearly visible in the holotype or paratype – in these specimens the distal portion of the phalanx projects somewhat cranially but the proximal majority is straight. This feature appears to be variable and thus should not be used in the diagnosis at this time. Contra Chiappe et al., 2019, the lateral (sternolateral of Chiappe et al., 2019) process of the coracoid is not hooked. In Protoperyx the concave lateral margin is continuous with the lateral extension but a hook formed by a distinct omal projection like that present in Gansus is absent (You et al., 2006).
There are numerous subtle differences between the specimens assigned to P. fengningensis. The lateral trabeculae are expanded in BMNHC-Ph1158 but not in STM7-143 and IVPP V11844. In addition, the proportions differ between the two BMNHC specimens: one has a longer femur while the other has a longer humerus and the proportions between the pygostyle and metatarsal III differ by 20% (Table 1). Potential differences are obscured by ontogenetic differences; BMNHC-Ph1060 and Ph1158 are the largest specimens and show at least some features indicative of advanced maturity (fused carpometacarpus). However, fan-shaped expansions of the lateral trabeculae are demonstrated in juvenile enantiornithines (Zheng et al., 2012) making it uncertain whether this variation between Protopteryx specimens can be attributed to differences in relative ontogenetic stage. Due to this uncertainty we suggest that for now all referred specimens be regarded as Protopteryx sp. until further data becomes available.

Fred