Paleontologists have found the remains — the well-preserved complete skeleton and feathers — of a short-tailed bird that lived 127 million years ago (Early Cretaceous epoch) in northeastern China.
Jinguofortis perplexus. Image credit: Chung-Tat Cheung.
The ancient bird, dubbed Jinguofortis perplexus, had a body mass of 250 g, a wing span of 27.5 inches (70 cm), and a unique combination of traits.
“This fossil bird had a jaw with small teeth like their theropod dinosaur relatives,” explained Dr. Zhonghe Zhou, a researcher in the Institute of Vertebrate Paleontology and Paleoanthropology, the Chinese Academy of Sciences.
“It also had a short bony tail ending in a compound bone called a pygostyle (that evolved after the earliest known bird, Archaeopteryx); gizzard stones showing that it mostly ate plants; and a third finger with only two bones in it (unlike other early birds).”
Based on its skeleton and feathers, Jinguofortis perplexus probably flew a bit differently than birds do today.
“In flying birds, the shoulder, which experiences high stress during flight, is a tight joint between unfused bones,” the paleontologists said.
“In contrast, Jinguofortis perplexus preserves a shoulder girdle where the major bones of the shoulder, the shoulder blade (scapula) and the coracoid, are fused to one another, forming a scapulocoracoid.”
“The existence of a fused shoulder girdle in this short-tailed fossil suggests evolutionary variety during this stage of evolution, which probably resulted in different styles of flight.”
Jinguofortis perplexus: (A) photograph of main slab; (B) composed line drawing. Red-outline boxes denote the locations of histological samples. Abbreviations: 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. Image credit: Wang et al, doi: 10.1073/pnas.1812176115.
“Generally we think of the modern flight apparatus of living birds as having evolved through the gradual accumulation of refinements to their feathers, muscles, and bones over millions of years,” said Dr. Thomas Stidham, also from the Institute of Vertebrate Paleontology and Paleoanthropology, the Chinese Academy of Sciences.
“However, this new bird fossil shows that the evolution of flight was much more messy.”
Jinguofortis perplexus, together with another, less-known bird fossil called Chongmingia zhengi, form the second earliest diverging group of the short-tailed birds (Pygostylia).
To recognize that status, the researchers have named a new family Jinguofortisidae to include both species.
“The discovery of Jinguofortis perplexus increases the known diversity of pygostylian birds and highlights the importance of developmental plasticity for understanding mosaic evolution in early birds,” they said.
The discovery is reported in the Proceedings of the National Academy of Sciences.
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Min Wang et al. A new clade of basal Early Cretaceous pygostylian birds and developmental plasticity of the avian shoulder girdle. PNAS, published online September 24, 2018; doi: 10.1073/pnas.1812176115
