Every now and then, I come across a study that makes me hope my first doubtful impression is wrong and that the authors have better evidence to back up their claims. One such case was the hypothesis that the feathered dinosaur Sinornithosaurus had a venomous bite, as was proposed by scientists Enpu Gong, Larry Martin, David Burnhamb and Amanda Falk several months ago. The idea was more interesting than it was well-supported, and now, in the journal Paläontologische Zeitschrift, paleontologists Federico Gianechini, Federico Agnolin, and Martin Ezcurra have confirmed my suspicions about the "venomous dinosaur" idea.
The hypothesis of a venomous Sinornithosaurus was based upon three lines of evidence—apparently long teeth in the upper jaw, grooves in those teeth which could conduct venom, and a pocket in the skull said to be the perfect spot for a venom gland. As Gianechini and colleagues argue, however, all of these features have other explanations that have nothing to do with venom. First, the "elongated" teeth. Rather than being exceptionally long, it appears that the teeth of the Sinornithosaurus Gong and colleagues used in the study had slightly slipped out of their sockets. Sinornithosaurus did not have extraordinarily lengthy fangs.
The supposed "venom grooves" in the teeth of Sinornithosaurus do not stand up to scrutiny, either. These relatively wide furrows in the teeth are not consistent with what is seen in the teeth of creatures known to have venom-delivery systems in their teeth, and actually look little different in this regard from the teeth of many other theropod dinosaurs (none of which have been considered venomous).
Finally, Gianechini, Agnolin, and Ezcurra do not see any evidence of a special pocket in the skull for a venom gland. The proposed structure pointed out by the other team of scientists—what they called the "subfenestral fossa"—does not seem to differ from the surrounding part of the skull, and this part of the Sinornithosaurus skull is similar to that of other theropod dinosaurs that show no evidence of being venomous. All three lines of evidence originally proposed to support the idea of a venomous Sinornithosaurus fail under close examination, and the authors conclude that "further analyses, such as X-ray and histological studies, are necessary in order to propose remarkable interpretations," such as venomous dinosaurs.
Interestingly, however, Paläontologische Zeitschrift also gave the authors of the original study a chance to reply to the critique. In their response, Gong and his peers try to make their case by arguing that since venom glands evolved among lizards and snakes, it might be possible that venom could have evolved among archosaurs (the larger group to which dinosaurs belong, as well as crocodiles and pterosaurs), too. In fact, the authors propose that venom might have been present in the earliest archosaurs, but there is no evidence to support this speculation. From there Gong, Martin, Burnham and Falk attempt to rescue their hypothesis by taking down the new critique, but they fail to provide any substantial new evidence to support their claims. Sinornithosaurus exhibits some traits which might be construed as similar to those in some reptiles with venomous bites, but there is no clear evidence to suggest that it (or any other dinosaur) was venomous. As Gianechini, Agnolin and Ezcurra stated, an array of detailed evidence would be required to support the idea of venomous dinosaurs, and (at present) that evidence does not exist.
Gianechini, F., Agnolín, F., & Ezcurra, M. (2010). A reassessment of the purported venom delivery system of the bird-like raptor Sinornithosaurus Paläontologische Zeitschrift DOI: 10.1007/s12542-010-0074-9
Gong, E., Martin, L., Burnham, D., & Falk, A. (2010). Evidence for a venomous Sinornithosaurus Paläontologische Zeitschrift DOI: 10.1007/s12542-010-0076-7