The birdlike raptor Sinornithosaurus was venomous

Abstract

We suggest that some of the most avian dromaeosaurs, such as Sinornithosaurus, were venomous, and propose an ecological model for that taxon based on its unusual dentition and other cranial features including grooved teeth, a possible pocket for venom glands, and a groove leading from that pocket to the exposed bases of the teeth. These features are all analogous to the venomous morphology of lizards. Sinornithosaurus and related dromaeosaurs probably fed on the abundant birds of the Jehol forests during the Early Cretaceous in northeastern China.dromaeosaur | Jehol | grooved fangs | venomous delivery system O ne of the more bizarre innovations in organismic evolution is the ability to manufacture toxic substances. Venomous taxa occur in a variety of ecologic settings and include insects, lizards, snakes, and mammals (1-5). Clearly, venom has evolved numerous times in many different lineages employing various delivery apparatus. A combination of morphological and molecular research has recently shown that venomous taxa are far more widespread and primitive within tetrapod lineages than had previously been suspected (6).Sinornithosaurus is a dromaeosaurid closely related to the 4-winged glider Microraptor gui and therefore within the early avian radiation (7). It has unusually long maxillary teeth that are morphologically similar to those of "rear-fanged" snakes specialized to carry poison (Fig. 1). This type of fang discharges venom along a groove on the outer surface of the tooth that enters the wound of the bitten animal by capillary action (8, 9). Supporting this interpretation in Sinornithosaurus is an additional space on the lateral surface of the maxillary bone that we interpret on the basis of analogy with venomous squamates as having housed a venom gland. This previously undescribed fossa, herein termed the subfenestral fossa, could have housed an elongate, ascinar venom gland similar to that found in rear-fanged (i.e., opisthoglyphous) snakes (10, 11). We suggest that the venom traveled in ducts to the bases of the teeth and mixed with the saliva in a manner also similar to extant venomous squamates (6). The position of the venom collecting duct was probably along the oblique ventral surface of the maxilla, where there is a supradental groove (i.e., longitudinal depression running along the base of the tooth row). This groove bears small pits that seem to be related to tooth sites and may represent the location of small venom reservoirs. These depressions were illustrated and mentioned in the original description of Sinornithosaurus, but their purpose was not addressed. As in modern venomous taxa that employ grooved fangs, the ducts feed the venom to the base of the teeth. The mechanism for dispensing the venom may be similar to the system used by open-fanged snakes and lizards that discharge it under low pressure provided largely by force of the bite-a strategy for prey control rather than quick death (12). We believe Sinornithosaurus was a venomous predator that fed on birds by using its long fangs to...

Theropod teeth from the Middle-Upper Jurassic Shishugou Formation of northwest Xinjiang, China

“…Moreover, the lateral teeth tend to have a wide apicobasally elongated concavity on the basolabial surface of the crown (Gianechini et al 2011; CH personal observations), a depression which is also usually well-developed on the lingual surface of the crown. These lingual and labial concavities are particularly clear in some dromaeosaurids such as Sinornithosaurus (Xu and Wu 2001) and were interpreted as a venom delivery duct (Gong et al 2010(Gong et al , 2011. Finally, the mesial teeth of dromaeosaurids are different from those of Megalosauridae; they either lack a mesial carina, as in Tsaagan (IGM 100-1015) and Velociraptor (AMNH 6515), or the mesial carina curves strongly lingually, as in Deinonychus (Ostrom 1969), Dromaeosaurus (Currie et al 1990;Currie 1995) and Saurornitholestes (Currie et al 1990).…”

The Osteology of Alioramus, A Gracile and Long-Snouted Tyrannosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Mongolia

“…Where the tooth roots are exposed, the labial and lingual surfaces are depressed, giving the impression of a groove. Such grooves were recently mistaken as adaptations for a venomous delivery system in a dromaeosaurid (Gong et al, 2010), but are widespread among theropods and almost uniformly present whenever a tooth root is exposed (Gianechini et al, 2011).…”

An investigation of the evolution of the anguimorph lizard venom system

“…The teeth of helodermatid lizards are deeply grooved in a manner convergent with those of some advanced snakes, in which grooved, venom-delivering teeth have independently evolved on multiple occasions and display extensive variation (Russel and Bogert, 1981;, This is also convergent with various other extant and extinct venomous lineages including archosauriforms (Mitchell et al, 2010), conodonts (Szaniawski, 2009), sphenodons (Reyonso, 2005, insectivorous mammals such as shrews and solenodons (Cuenca-Bescos and Rofes, 2007;Dufton, 1992;Ligabue-Braun et al, 2012;Rofes and Cuenca-Bescos, 2009) and bird-like dinosaurs hypothesised to specialise in preying upon early birds (Gong et al, 2010).…”