Cratonavis zhui gen. et sp. nov. (1 Viewer)

[Fred Ruhe]

Zhiheng Li, Min Wang, Thomas A. Stidham & Zhonghe Zhou, 2023

Decoupling the skull and skeleton in a Cretaceous bird with unique appendicular morphologies

Nature Ecology and Evolution 1-12
doi:10.1038/s41559-022-01921-w

Abstract: Bird Paleontology

The Cretaceous is a critical time interval that encompasses explosive diversifications of terrestrial vertebrates, particularly the period when the earliest-branching birds, after divergence from their theropod ancestors, evolved the characteristic avian Bauplan that led eventually to their global radiation. This early phylogenetic diversity is overwhelmed by the Ornithothoraces, consisting of the Enantiornithes and Ornithuromorpha, whose members evolved key derived features of crown birds. This disparity consequently circumscribes a large morphological gap between these derived clades and the oldest bird Archaeopteryx. The non-ornithothoracine pygostylians, with an intermediate phylogenetic position, are key to deciphering those evolutionary transformations, but progress in their study has been hampered by the limited diversity of known fossils. Here we report an Early Cetaceous non-ornithothoracine pygostylian, Cratonavis zhui gen. et sp. nov., that exhibits a unique combination of a non-avialan dinosaurian akinetic skull with an avialan post-cranial skeleton, revealing the key role of evolutionary mosaicism in early bird diversification. The unusually elongated scapular and metatarsal one preserved in Cratonavis highlights a breadth of skeletal plasticity, stemming from their distinct developmental modules and selection for possibly raptorial behaviour. Mapped changes in these two elements across theropod phylogeny demonstrate clade-specific evolutionary lability.

Enjoy,

Fred

 

[Fred Ruhe]

Systematic palaeontology

Avialae (Gauthier 1986; ref. 7)
Pygostylia (Chiappe 2002; ref. 8)
Jinguofortisidae (Wang et al. 2018; ref. 9)

Cratonavis zhui gen. et sp. nov.

Etymology

The generic name is derived from craton (referring to the destruction of North China Craton during the Early Cretaceous, an event that underpins the evolutionary setting of the Jehol Biota10) and Latin ‘avis’ (bird).
The specific name is in honour of Dr Rixiang Zhu for his pioneering work of the destruction of North China Craton.

Holotype

IVPP V31106 (housed at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Science), a complete articulated skeleton with associated feathers (Fig. 1 and Supplementary Table 1).

Locality and horizon

Xiaotaizi Village, Lamadong Town, Jianchang Country, Liaoning Province, northeastern China; Early Cretaceous, Jiufotang Formation (~120 Ma (ref. 10)).

Diagnosis

A jinguofortisid that preserves the following synapomorphies of the Jinguofortisidae: fused scapulocoracoid; boomeranged-shaped furcula without a hypocleidium; proximal margin of the humerus centrally concave; and minor metacarpal bowed caudally. Cratonavis is distinguishable from other jinguofortisids on the basis of the following features (*asterisk denotes autapomorphy): ascending process of the maxilla perforated only by a maxillary fenestra; maxillary fenestra
longer rostrocaudally than dorsoventrally; descending ramus of the lacrimal exhibiting a lateral flange*; squamosal process of the quadratojugal substantially longer (3×) than the jugal process; pterygoid with a caudodorsally directed quadrate ramus; prominent retroarticular process on the jaw; thoracic vertebral centra laterally excavated by broad fossae; scapula longer than the humerus; caudal end of the postacetabular process of the ilium dorsally deflected*; metatarsal I approximately 60% of the length of the tarsometatarsus*; and hallux bearing the longest non-ungual and ungual pedal phalanges*.

Fred



Fig. 1 | Holotype of Cratonavis zhui, IVPP V31106. a, Whole skeleton. b,c, Photograph (b) and CT (c) scan of the pectoral girdle. d, Digital reconstruction of the right scapulocoracoid. e,f, Photograph (e) and digital reconstruction (f) of the right forelimb. g, Pelvis and right hindlimb. h,i, Digital reconstruction of the right foot in plantar view (h), and metatarsal I in medioplantar view (i). ac, acromion process; ad-1, alular digit phalanx-1; ad-2, alular digit phalanx-2; am, alular metacarpal; ap, acoracoid process; ce, cervical vertebra; ci, capital incision; dp, dorsal process of ischium; dv, dorsal vertebra; fe, femur; fi, fibula; fu, furcula; gl, glenoid; hu, humerus; il, ilium; is, ischium; m1 to m3, major digit
phalanx-1 to 3; ma, major metacarpal; mi, minor metacarpal; mi-1, minor digit phalanx-1; mt I–V, metatarsals I to V; mu, manus; ra, radius; sc, scapulocoracoid; sp, scapula; ta, tarsometatarsus; ti, tibiotarsus; un, ulna; p-I to p-IV, pedal digits I to IV; po, postacetabular process; pr, pre-acetabular process; pu, pubis; py, pygostyle; sk, skull; sn, synsacrum; st, sternum; sy, symphysis of pubes; uc, uncinate process; l/r, left/right side. Yellow arrowhead in b denotes the cranial
cleft of the sternum, red arrowhead in e indicates the concave proximal margin of humerus and blue arrowheads in g denote the dorsal deflection of the distal ilium. Scale bars, 10 mm (a, b, e and g).