Tomial Teeth in shrikes

“I am grateful to Mike Rose, a bird watching colleague based in Thailand, who first pointed out this feature on a twitter post. Although I have occasionally seen tomial teeth in shrikes, I had not questioned its relevance.

“Tomial ‘teeth’ are ‘ventral projections along the rostral tomium of the rhamphotheca‘ [see Sustaita (2014), Cade (1995), Schön (1996)]. These of course are not real ‘teeth’ and are not coated in enamel but keratin. They can be easily missed in the field except at close range.

“The corresponding indentations in the lower mandible are even harder to appreciate. I looked through many of my images of shrikes and found some passable close-ups that show the feature. The above two images are of Brown Shrikes (Lanius cristatus).

“The above image is of a Tiger Shrike (Lanius tigrinus) and below of a Long-tailed Shrike (Lanius schach bentet).

“Lefranc (1997) describes the feature in Lanius shrikes: they have ‘raptor-like bills … The upper mandible shows a subterminal tominal tooth on each side and the lower mandible has corresponding incurvations. This shape bears strong resemblance to that of falcons…’

“‏Karen McDonald (2014) when describing tomial teeth in raptors says ‘the tomial tooth (pl. mandibular tomia) is the outer, or cutting edge of the beak. This ‘tooth’ is the protrusion that extends from the tomial edge of the beak and is thought to be used to deliver the killing blow to prey (severs the spinal cord). The tomial tooth of the upper mandible is often matched by a mandibular notch, or divot, in the lower mandible…. Other birds of prey may show some slight tomial indentations but not to the extent that falcons, kites, and accipiters do.’

“A number of on-line article have described tomial teeth in shrikes as being used to ‘sever the spinal cord’ or ‘deliver the killing stroke‘ with some offering detailed work on issues, see for example Sustaita (2014).”

References:
1. Diego Sustaita, Margaret A. Rubega (2014). The anatomy of a shrike bite: bill shape and bite performance in Loggerhead Shrikes. Biological Journal of the Linnean Society. 112, 485-498. See: LINK
2. Cade TJ (1995). Shrikes as predators. Proceedings of the Western Foundation of Vertebrate Zoology 6: 1-5.
3. Schön M (1996). Raptor-like passerines – some similarities and differences of shrikes (Lanius) and raptors. Oekologie der Voegel 18: 173-216.
4. Norbert Lefranc (1997). Shrikes: A Guide to the Shrikes of the World (Helm Identification Guides), Yale University Press.
5.Tiger Karen McDonald (2014). Featured Feature: Tomial Teeth and Cranial Kinesis. See: http://infinitespider.com/featured-feature-raptor-beaks-adaptations/

Dato’ Dr Amar-Singh HSS
Ipoh, Perak, Malaysia
7th February 2018