A new species of bird that lived about 105 million years ago has been identified from two fossil bones found near Richmond, in the Australian state of Queensland. Tenuicruris piscanexum is only the second bird species from the Cretaceous period formally described from fossils found in Australia.
The fossils were discovered at separate sites in the Toolebuc Formation, a geological formation about 105 million years old known for its wealth of marine animal fossils. Among the remains found in the region are fossils of plesiosaurs, pliosaurs, ichthyosaurs, turtles, sharks, chimaeras, bony fish, and pterosaurs.
One of the bones was found by Kevin Petersen, former curator of the Kronosaurus Korner, while searching for fossils in one of the public collecting areas near Richmond. The specimen appeared in a layer particularly rich in fish remains and dispersed teeth of large marine predators.
About a week later, after a rainfall event, Petersen found a second bone that also seemed unusual to him. He photographed the two specimens and sent the images to Matt White, a researcher at the University of New England.
“I recognized them immediately as bones of birds,” explains the researcher. “These specimens are particularly important because very few have been found in Australia, and until now there had been none directly comparable.”
The analysis allowed identifying one of the fossils as a tarsometatarsus, a set of foot bones that is fused in birds, and the other as a tibiotarsus, a leg bone. Both were relatively well preserved, though partially embedded in rock concretions.
To avoid damaging the fossils, the researchers used non-destructive imaging techniques. The specimens were scanned at the Australian Nuclear Science and Technology Organisation (ANSTO), enabling later creation of three-dimensional models of the bones and analysis without the need to remove them completely from the rock.
The comparison between the new tibiotarsus and the remains of Nanantius eos, so far the only Cretaceous bird species formally identified in Australia, revealed anatomical differences sufficient to establish a new taxon.
The name Tenuicruris piscanexum refers to the slender characteristics of the bird’s limbs and to the fish-rich layer where the remains were found. Phylogenetic analysis places the new species among the Enantiornithes, a diverse group of birds that lived during the Mesozoic Era and that constitutes an important part of the fossil record of birds from that period.
The discovery is particularly significant due to the scarcity of Cretaceous bird fossils in Australia. Although there are more than 11,000 bird species currently, the skeletal fossil record of Cretaceous birds in the country is very limited, with fewer than a dozen isolated bones known.
The oldest traces of birds found in Australia date back to the Early Cretaceous, about 128 to 120 million years ago, in deposits in Victoria. Feathers as isolated remains and tracks have also been found, as well as some opalized remains of birds in the Lightning Ridge region.
Until now, Nanantius eos, described in 1986 from an isolated tibiotarsus of the Toolebuc Formation, was the only Cretaceous bird formally identified in Australia. The discovery of Tenuicruris piscanexum thus doubles the number of formally named Australian Cretaceous bird species from skeletal remains.
“Although the newly discovered remains consist of isolated bones, they are extremely rare — this is the second Cretaceous bird named in Australia,” says Dean Lomax of the University of Bristol, after examining the specimens. According to the researcher, the discovery provides new data about the environment and the diversity of animals that existed in the Richmond region.
The researchers consider that, although isolated, these bones may provide relevant information about the diversity and ecology of birds at a time when much of present-day Australia was covered by an inland sea.
The study was published in the Journal of Vertebrate Paleontology. The fossils will be deposited at the Kronosaurus Korner Museum.
