This Badger Ate Dinosaurs for Breakfast
BBC News claims a new fossil discovery published in Nature,1 a large badger-like carnivorous mammal, ate dinosaurs for lunch. But then again, who knows what time of day the Cretaceous restaurants were open?
The fossil, another in a series of spectacular finds from the Liaoning Province in China, is creating a sensation, because it overturns an assumption that Mesozoic mammals were ecological underdogs – just small, rat-sized vermin, of no account in the arena of the thunder lizards. Now, it appears some mammals were carnivores, big enough to compete with dinosaurs for food and territory. Juvenile psittocosaur bones were found in the stomach contents of the smaller of two specimens of the short-legged mammals. The bigger one was over a meter long, over twice the previous record. Paleontologists speculate they may have resembled badgers or Tasmanian devils, but their lineage does not appear to have any living descendants.
Analyzing the meaning of the find in the same issue of Nature,2 Anne Weil writes, “Discoveries of large, carnivorous mammals from the Cretaceous challenge the long-held view that primitive mammals were small and uninteresting” (emphasis added in all quotes.) One wonders if she has been reading Phillip Johnson lately. She continues, “Have palaeontologists been asking the wrong questions?”
Science Now has a picture of one of the fossils. The BBC News has an artist reconstruction of what the creature might have looked like.
1Hu, Meng, Wang and Li, “Large Mesozoic mammals fed on young dinosaurs,” Nature 433, 149 – 152 (13 January 2005); doi:10.1038/nature03102.
2Anne Weil, “Mammalian palaeobiology: Living large in the Cretaceous,” Nature 433, 116 – 117 (13 January 2005); doi:10.1038/433116b.
Some of the new questions Anne Weil is asking turn the evolutionary story of the Cretaceous upside down:
Hypotheses developed to explain the evolution of mammalian size often focus on dinosaurs. The most frequently repeated speculation is that Mesozoic mammals were forced to remain small by a combination of heavy predation pressure from dinosaurs and the saturation of ecological niches by large reptiles. Are the mammals from the Lujiatun beds large because the dinosaurs are small? This question may be premature, as the fossil deposits are under active excavation and description of the fauna is not complete. Yet the two new specimens of Repenomamus prompt a reversal of the question, if only in speculation: how might mammals have influenced dinosaur evolution? It seems likely that small dinosaurs experienced predation pressure from mammals. Indeed, in describing the diminutive S. changii, which lies evolutionarily at the base of a lineage closely related to that of birds, Xu et al. express surprise that, although the avian lineage continued an evolutionary trend towards small size, closely related dinosaurian lineages became larger again. Maybe these small dinosaurs got larger – or got off the ground – to avoid the rapacious mammals.
So evolutionary theory can explain anything, no matter what the bones. But if early mammals were already large and carnivorous, where is the evolution? No problem; just throw in a few new subplots to the never-ending story. Animals just got larger and smaller according to who was eating whom. The old speculation game is alive and well (read about Doug in the 09/18/2003 commentary).
By the way, Anne added an admission to the public: “Despite the frequently made generalization that Mesozoic mammals were rat-sized, palaeontologists have known for some time that this was not the case” – sizeable mammal fossils are also known from North America and Australia. Time to revise Walking with Dinosaurs – again (see 09/25/2003 entry). The animators don’t mind. The Great Society for Storytellers (see 12/22/2003 entry) provides job security for them, too.