In a paper on Early Cretaceous fossilized feather molting,
O’Connor et al. 2020 presented several specimens, among them an unnamed juvenile STM-34-1 (Figs. 1–3). The specimen originally appeared in part in Zheng et al. 2012 in their study on sternum ontogeny. O’Connor was a co-author then, too.
Note the shorter forelimb
and longer hind limb in the juvenile, which has no tail feathers preserved as well as those elsewhere on the body and limbs. Birds, like other archosaurs, develop allometrically, changing in shape as they mature. By contrast, pterosaurs, like other lepidosaurs, develop isometrically, not changing in shape as they mature, contra traditional thinking.
STM 34-1 is from
Liutiaogou, Ningcheng, Chifeng, Inner Mongolia, Lower Cretaceous.
Chiappeavis is from
Jianchang, Liaoning Province, northeastern China. Jiufotang Formation, Lower Cretaceous
A phylogenetic analysis that tested STM 34-1
was not presented by O’Connor et al. 2020, nor by Zheng et al. 2012.
O’Connor JK, Falk A, Wang M and Zheng X-T 2020. First report of immature feathers in juvenile enantiornithines from the Early Cretaceous Jehol avifauna. Vertebrata PalAsiatica 58(1):24–44. DOI: 10.19615/j.cnki.1000-3118.190823
Zheng XT, Wang XL, O’Connor JK et al., 2012. Insight into the early evolution of the avian sternum from juvenile enantiornithines. Nat Commun, 3: 1–8.