page_title: Euchambersia
section_title: Venom
hierarchical_section_title: Euchambersia / Paleobiology / Venom
caption_attribution_description: English: Fig 10. Cross sections through the teeth of various mammals redrawn from literature and compared to Euchambersia. Mesial is on the top, labial is on the right. * indicates venomous species.
context_page_description: Euchambersia is a genus of therocephalian therapsid that lived during the Late Permian, approximately 255 million years ago, in what is now South Africa. The genus contains a single species, Euchambersia mirabilis, named by paleontologist Robert Broom in 1931 from a skull missing the lower jaws; a second skull, belonging to an immature individual, was later described. It is a member of the family Akidnognathidae, which historically has also been referred by as the synonymous Euchambersiidae.
  Euchambersia was a small and short-snouted therocephalian, possessing large canines as is typical of the group. However, it is notable among therocephalians for possessing ridges on its canines and a large indentation in the side of the skull. Under the erroneous assumption that the canines are grooved instead of ridged, it has been proposed that these structures supported a venom delivery mechanism. More recently, the internal structure of the skull of Euchambersia has been used as stronger evidence in favour of the hypothesis that it was venomous; other possibilities, such as the indentation supporting some sort of sensory organ, still remain plausible.
context_section_description: The large maxillary fossae of Euchambersia have been continual subjects of debate regarding their function. However, most researchers agree that they held some sort of secretory gland. While Broom initially argued that the fossae may have contained the parotid salivary glands, this proposal was rejected by Boonstra and J.P. Lehman, who noted that the parotid glands tend to be placed behind the eye; they respectively suggested that the fossae held modified lacrimal glands and Harderian glands. However, the latter is also unlikely because Harderian glands are usually placed inside the eye socket. Franz Nopcsa suggested that the maxillary fossae housed venom glands (which may have been derived from lacrimal glands), with the ridged canines and the notches behind the canines allowing the venom to flow passively into the victim's bloodstream. This hypothesis was widely accepted throughout the 20th century and the characteristic morphology of Euchambersia was used to support possible venom-bearing adaptations among various other prehistoric animals, including the therocephalian Ichibengops. 
  Much of this acceptance has been based on the erroneous assumption that the canines are grooved instead of ridged; grooved canines in Euchambersia would parallel the fangs of various venomous snakes as well as the venom-delivering incisors of the living solenodons. This interpretation, which has consistently appeared in literature published after 1986, was determined by Julien Benoit to be the result of the propagation of Broom's overly reconstructed diagram of the skull, without the context of the actual specimens. This line of evidence has been raised to support the necessity of a re-evaluation the hypothesis of a venomous bite in Euchambersia. Additionally, Benoit argued that grooved and ridged canines are not necessarily associated with venomous animals either, as shown by their presence in hippopotami, muntjacs, and baboons, in which they play a role in grooming or sharpening the teeth; in the latter two, ridged canines are also accompanied by a distinct fossa in front of the eye, which is entirely unconnected with venom. Furthermore, grooved and ridged teeth in non-venomous snakes are used to reduce suctional drag when capturing slippery prey like fish or invertebrates.
  CT scanning of the known specimens of Euchambersia by Benoit and colleagues was subsequently used to provide more concrete support in favour of the venom hypothesis. The canals leading into and from the maxillary fossae, as revealed by the scans, would primarily have supported the trigeminal nerve as well as blood vessels. However, the fact that the canals also directly lead to the root of the canines would suggest that they had a secondary role in venom delivery. In all, Euchambersia seems to have had a venom gland (housed in the maxillary fossae), a delivery mechanism of the venom (the maxillary canals), and an instrument by which a wound for venom delivery can be inflicted (the ridged canines), which satisfy the criteria of a venomous animal as defined by Wolfgang Bücherl. Benoit et al. noted that this does not conclusively demonstrate that Euchambersia was actually venomous, especially given the previously stated objections. Additionally, there are no living animals with a delivery system analogous to the proposed system for Euchambersia (most deliver venom through the lower jaw, while snakes have specialized ducts.
  An alternate hypothesis suggested by Benoit et al. involves some kind of sensory organ occupying the maxillary fossa. Uniquely among therapsids, the canal within the maxilla is exposed on the back side of the maxillary fossa, which implies that the canal, carrying the trigeminal nerve, would probably have extended across the fossa, outside of the outline of the skull. Benoit et al. hypothesized that the fossa may have supported a specialized sensory organ analogous to the pit organ of pit vipers and some other snakes, or alternatively a ganglion of nerve cells. It is also possible that this organ functioned as a replacement for the parietal eye in Euch
caption: Cross-section of the canine of Euchambersia as originally illustrated by Broom (top left), with the subsequent "grooved" reconstruction (top centre) and new reconstruction based on CT scans (top right), compared to those of other mammals (bottom)
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