120-million-year-old fossilized footprints made by a roadrunner-like bird, Shandongornipes muxiai, discovered in Shandong Province, China. (Track four).
In the past few years, China has become famous for the number and quality of bird fossils from the Early Cretaceous that have been discovered there. This week, another such discovery has been reported by an international team of Chinese, American and Japanese scientists. Their discovery of 120-million-year-old fossilized footprints made by a roadrunner-like bird in Shandong Province, China (see map), was published in the European journal, Naturwissenschaften.
The bird that made these tracks was named Shandongornipes muxiai in honor of the teen-aged daughter, Muxia Li, of team member, Rihui Li, a geologist at the Qingdao Institute of Marine Geology.
“It is a huge surprise to find evidence of a roadrunner-like species darting around beneath the feet of Cretaceous dinosaurs,” said Martin Lockley of the Dinosaur Tracks Museum, University of Colorado at Denver, and senior author of the study.
These ancient birds and feathered dinosaurs have changed our understanding of bird origins and evolution. But it is not known whether representatives of contemporary bird groups existed 130 million years ago.
“Whether or not there were any representatives of modern bird groups in the Cretaceous is currently the subject of a lot of debate,” said Jerry Harris of Dixie State College of Utah. Harris was part of the team that recently described the very modern-looking, duck-like bird Gansus yumenensis from similarly aged rocks in China. He was invited to join the Shandongornipes research team because of his expertise on Chinese bird fossils.
“But as research progresses, we are finding more and more evidence that some Cretaceous birds were very similar, though not identical, to modern birds. Shandongornipes is another surprising, but very welcome, example,” Harris added.
“If the tracks had been found in very recent deposits in North America, we would have assumed they were made by the well-known roadrunner,” said Lockley. “But finding them in the Cretaceous of China, long before even the nearest relatives of roadrunners had evolved, makes us call them ‘roadrunner-like’.”
Organisms that live in similar ecosystems and have similar natural histories often evolve matching anatomical structures — a phenomenon known as convergent evolution. For example, dolphins (mammals), sharks (fish), and the now-extinct ichthyosaurs (reptiles) all evolved analogous body shapes because that shape is ideal for rapid swimming.
Similarly, the bird that made the Shandongornipes tracks probably converged on a roadrunner-like body shape and likely exhibited similar behaviors. Our modern roadrunner, Geococcyx, is a species of cuckoo and, like all cuckoos, has two forward-pointing and two backward-pointing toes, a condition known as zygodactyly that is also evident in Shandongornipes tracks.
Roadrunners are the only zygodactyl birds in the world that live primarily on the ground instead of in trees. Zygodactyly evolved in several arboreal bird groups, such as woodpeckers, owls, and parrots, “but none run along the ground with long strides like the roadrunner and the bird that made the Shandongornipes tracks” said Lockley (see figure 1).
Figure 1: Tracks of Shandongornipes muxiai. a Map of holotype trackway (LRH-DH01). b-e Photographs and schematics of individual tracks in trackway (digit numbers labeled), including b photograph of first (left foot, LRH-dz70), c outline drawing of third (left foot, LRH-dz68), d outline drawing of fifth (right foot, LRH-dz66), and e photograph of fourth (left foot, LRH-dz67). f Segment of a trackway made by extant roadrunner G. californianus near St. George, Utah; segment includes same left-right sequence preserved in LRH-DH01 (a) and shown at same scale. g Schematic of fourth Shandongornipes print (LRH-dz67). h Individual G. californianus right footprint [from Elbroch and Marks (2001); used with permission] rotated with hallux in approximately same orientation as Shandongornipes print in(g).
Furthermore, none of these groups have any fossil representatives from the Cretaceous. “In fact, this is the first zygodactyl track ever found anywhere in the fossil record,” Lockley added.
Because of the principle of convergent evolution, the bird that made these fossil tracks is not a roadrunner.
“This means that the Shandongornipes track maker was almost certainly not closely related to modern roadrunners, but lived a roadrunner-like lifestyle,” explained Harris.
Incidentally, Jerry Harris will respond to your questions and comments here.
Original paper; Earliest Zygodactyl bird feet: evidence from Early Cretaceous roadrunner-like tracks. Martin G. Lockley, Rihui Li, Jerald D. Harris, Masaki Matsukawa & Mingwei Liu. Naturwissenschaften [DOI 10.1007/s00114-007-0239-x]
Press release; Tracking a roadrunner from the Age of Dinosaurs