in a 2001 article referred to the series as not just a documentary but also a "powerful piece of palaeobiological research", showing to the public what the "best minds in palaeobiology have been able to achieve." Numerous scientific journal articles have been written on Walking with Dinosaurs and the phenomenon it created. Scientific errors Although the academic response to Walking with Dinosaurs was largely positive, the series was criticised by some palaeontologists for its speculative storylines and the boldness of some of its claims, noting that some aspects presented as fact were very much speculative and possible to be challenged in the future. In the companion book of the series, Haines admitted that speculating about dinosaur behaviour in of itself is unscientific since the theories cannot be tested, but maintained that it "seems well worth trying to find out more about how [the dinosaurs] may have lived", using both science and reasoned speculation. A handful of decisions and sequences in the series came under particular palaeontological criticism. Several supposed errors identified in the first weeks after the series aired fizzled out after a while, as critics found points about which they disagreed with one another and were unable to definitively prove their views. Most of the errors or otherwise questionable decisions of Walking with Dinosaurs were not the fault of the production team since they worked based on the advice of their consultants. New Blood shows a male Postosuchus urinating to mark a female's territory as his own after she is driven away from it. A number of critics pointed out that birds and crocodiles, the closest living relatives of the dinosaurs, do not urinate; they shed waste chemicals as more solid uric acid. However, Michael J. Benton, a consultant of the series, noted that nobody could prove that this was a real mistake: copious urination is the primitive state for tetrapods (seen in fish, amphibians, turtles, and mammals), and perhaps basal archosaurs did the same. Diplodocus was reconstructed with mostly horizontal necks in Walking with Dinosaurs, an idea consistent with what was thought of their biology at the time, and thus pushed by the palaeontological consultants of the series, but challenged by new research in 2009. The pterosaur identified as Ornithocheirus in Giant of the Skies was actually based on fossils of the pterosaur Tropeognathus, the two having been considered synonyms by David Unwin, one of the consulting palaeontologists.