Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2018 Oct 16;115(42):10708-10713.
doi: 10.1073/pnas.1812176115. Epub 2018 Sep 24.

A New Clade of Basal Early Cretaceous Pygostylian Birds and Developmental Plasticity of the Avian Shoulder Girdle

Affiliations
Free PMC article

A New Clade of Basal Early Cretaceous Pygostylian Birds and Developmental Plasticity of the Avian Shoulder Girdle

Min Wang et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Early members of the clade Pygostylia (birds with a short tail ending in a compound bone termed "pygostyle") are critical for understanding how the modern avian bauplan evolved from long-tailed basal birds like Archaeopteryx However, the currently limited known diversity of early branching pygostylians obscures our understanding of this major transition in avian evolution. Here, we describe a basal pygostylian, Jinguofortis perplexus gen. et sp. nov., from the Early Cretaceous of China that adds important information about early members of the short-tailed bird group. Phylogenetic analysis recovers a clade (Jinguofortisidae fam. nov.) uniting Jinguofortis and the enigmatic basal avian taxon Chongmingia that represents the second earliest diverging group of the Pygostylia. Jinguofortisids preserve a mosaic combination of plesiomorphic nonavian theropod features such as a fused scapulocoracoid (a major component of the flight apparatus) and more derived flight-related morphologies including the earliest evidence of reduction in manual digits among birds. The presence of a fused scapulocoracoid in adult individuals independently evolved in Jinguofortisidae and Confuciusornithiformes may relate to an accelerated osteogenesis during chondrogenesis and likely formed through the heterochronic process of peramorphosis by which these basal taxa retain the scapulocoracoid of the nonavian theropod ancestors with the addition of flight-related modifications. With wings having a low aspect ratio and wing loading, Jinguofortis may have been adapted particularly to dense forest environments. The discovery of Jinguofortis increases the known ecomorphological diversity of basal pygostylians and highlights the importance of developmental plasticity for understanding mosaic evolution in early birds.

Keywords: Mesozoic; bird; development; phylogeny; plasticity.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
J. perplexus gen. et sp. nov., IVPP V24194. (A) Photograph of main slab. (B) Composed line drawing. Red-outline boxes denote the locations of histological samples. c, covert feathers; cv, cervical vertebrae; dr, dorsal ribs; dv, dorsal vertebrae; fu, furcula; gi, gizzard; lf, left femur; lh, left humerus; li, left ischium; lil, left ilium; lm, left manus; lp, left pes; lr, left radius; lsc, left scapulocoracoid; lt, left tibiotarsus; lu, left ulna; pu, pubis; py, pygostyle; re, remiges; rf, right femur; rh, right humerus; rm, right manus; rp, right pes; rr, right radius; rsc, right scapulocoracoid; rt, right tibiotarsus; ru, right ulna; s, synsacrum; sk, skull; st, sternum; t, tail feathers. (Scale bar, 5 cm.)
Fig. 2.
Fig. 2.
Skeleton anatomy and morphometric analysis of Jinguofortis. (A and B) LSF photograph and line drawing of the skull in the main slab (IVPP V24194a). (C) LSF photograph of the pectoral girdle in the main slab. (D) Forelimb showing the preserved primary (numbered I–X) and secondary (numbered 1–4) remiges in the counterslab (IVPP V24194b). (E) Binary plotting of the aspect ratio and wing loading of basal avian clades (Arc, Archaeopteryx; Con, Confuciusornis; Ena, Enantiornithes; Jel, Jeholornis; Jin, Jinguofortis; Orn, stemward ornithuromorphs) under the context of modern avian flight styles. Arrow in C indicates the concave proximal margin of the humerus. am, alular metacarpal; a1-2, proximal and distal phalanges of alular digit; cv, cervical vertebrae; de, deltopectoral crest; dt, dentary teeth; dv, dorsal vertebrae; fu, furcula; i1-2, first and distal phalanges of the minor digit; ju, jugal; lc, left coracoid; ld, left dentary; lh, left humerus; ln, left nasal; lp, left premaxilla; lr, left radius; ls, left scapula; lu, left ulna; lw, left wing; m, major metacarpal; ma, maxilla; mi, minor metacarpal; m1–3, proximal, intermediate, and distal phalanges of the major digit; ns, neural spine; pt, premaxillary teeth; rc, right coracoid; rd, right dentary; rh, right humerus; rn, right nasal; rr, right radius; rs, right scapula; ru, right ulna; rw, right wing; sp, splenial; st, sternum; su, surangular. [Scale bars: 1 cm (AC) and 2 cm (D).]
Fig. 3.
Fig. 3.
Changes to the scapula and coracoid in vertebrates with a focus on basal avian clades. A simplified tree of vertebrates (Left) shows the scapula (colored in blue) and coracoid (in green) fused into a scapulocoraocid (in gray) in most major tetrapod clades (see SI Appendix, SI Text, for details). Simplified cladogram of basal Aves (Right) shows the changes to the shoulder girdle and manus (see SI Appendix, Fig. S8, for complete phylogenetic result). Thick green lines near each clade denote temporal range with the first-appearance datum denoted. Major changes to the shoulder girdle and manus across basal avian phylogeny are summarized: (1) in most nonavian theropods, the scapula and coracoid are fused into a scapulocoracoid at an obtuse angle, and they have a manual phalangeal formula of 2–3-4; (2) scapula and coracoid become separated and form an angle of ∼90°; (3, 4) independent evolution of a fused scapulocoracoid in the Confuciusornithiformes and Jinguofortisidae; (6) minor digit is reduced resulting in a manual phalangeal formula of 2–3-2; (7) scapula and coracoid are decoupled and form an acute angle with further manual digit reduction evolving in derived ornithuromorphs; (8) alternatively, it is equally parsimonious that a fused scapulocoracoid evolved at the base of Pygostylia and was lost in pygostylians crownward of Jinguofortisidae (5).

Similar articles

See all similar articles

Cited by 2 articles

Publication types

LinkOut - more resources

Feedback