Ian Randall describes new research that brings birds and dinosaurs closer together, just as T H Huxley first envisaged.
Geoscientist Online 29 October 2009
The re-evaluation of a dinosaur specimen has provided stronger evidence for a link between birds and dinosaurs. A team from the Shenyang Normal University’s Palaeontological Institute in China have reclassified
Anchiornis huxleyi as a troodontid, a bird-like dinosaur, rather than a bird, based on newly discovered specimens.
Anchiornis, a genus whose name literally means ‘nearly bird’, was first analysed from a specimen found in lake-bed deposits of Middle Jurassic age from Yaolugou, in Western Liaoning. The species name was given in honour of Thomas Henry Huxley, an early convert to Darwinian evolution, who first suggested the possibility of a close connection between birds and dinosaurs.
The 34cm-long creature displays impressions of feathers on both its limbs and head.
Anchiornis was originally believed to be a true basal bird. However, studies of a more complete specimen, which has a preserved skull, causes
Anchiornis to be now considered a non-avian dinosaur; one that is close to birds.
On his blog, palaeontologist David Hone of the
DinoBase public forum explains that up to half of the characteristics used to analyse dinosaur specimens are located in the skull; the overall similarity of troodontid and birds caused problems in firmly diagnosing the initial specimen. Further samples helped to remove this issue and give a more precise diagnosis.
“While we already knew that troodontids had feathers, including on their legs, this is a particularly good example and does extend our knowledge of how these evolved.” Hone said.
This is significant because of its effect on the so-called ‘temporal paradox’, which concerns the fact that the most bird-like dinosaurs known to science, the maniraptorans, are found in the Cretaceous, after the time at which birds evolved in the Late Jurassic; supporters of the BAND hypothesis (Birds Are Not Dinosaurs) argue that if these were the predecessors to birds, then we should expect to see them earlier. It has been argued, however, that the paradox is non-existent, as maniraptoran remains have been uncovered from the Jurassic. The reclassified
Anchiornis, now known to be a feathered dinosaur appearing before birds, helps to fill this gap, weakening the argument.
Hone told
Geoscientist Online: “We do have a clear progression of the bony anatomy and the evolution of feathers running from pretty basal theropods right up to modern birds so that whole area …is very solid.”
Reference
- Nature 461, 640-643 (1 October 2009) Published online 24 September 2009 A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus Dongyu Hu, Lianhai Hou, Lijun Zhang & Xing Xu