Bony Pits in the Ostrich (Struthio camelus) and Emu (Dromaius novaehollandiae) Bill Tip

Abstract

A specialized region of the bill tip characterized by a complex arrangement of mechanoreceptors and referred to as a bill tip organ, has been identified in numerous avians. A bill tip organ was initially inferred in kiwi species by the presence of numerous, bony pits in the rostrum of the bill, and later confirmed histologically. This study enumerates and compares the number and distribution of pits present in the bill tip in the ostrich and emu. The heads from 10 ostrich and 5 emu were prepared for osteological examination. The pattern and total number of pits was similar between the two species. However, the ostrich had significantly more pits in the regions underlying the Culmen and Gonys, whereas the emu displayed significantly more pits in the dorsal part of the mandibular rostrum. The relatively even distribution of pits in the inner and outer surfaces of both the mandibular and maxillary rostra suggest that the bill tip of the ostrich and emu are equally sensitive externally and intra-orally, as opposed to probing birds, where the major concentration of pits is located on the outer surfaces of the bill tips. The presence of pits in the bill tips of extant paleaognaths may be of relevance in interpreting the pits in the rostra of extinct therapod dinosaurs. The presence of bony pits in a region which is also well supplied with sensory nerves is highly suggestive of a bill tip organ in the ostrich and emu and which needs to be confirmed histologically. Anat Rec, 300:1705-1715, 2017. © 2017 Wiley Periodicals, Inc.

Cretaceous origins of the vibrotactile bill-tip organ in birds

“…The presence of a remote-touch-capable bony bill-tip organ in the basal lithornithids suggests that this bill-tip organ may be the plesiomorphic state among palaeognathous birds. This explains the intriguing presence of a structurally similar billtip organ in modern non-kiwi palaeognaths, as evidenced by bone morphology and/or soft-tissue histology in both extant (emu and ostrich [24,25]; tinamou, rhea and cassowary (this study)) and extinct species (elephant bird and moa (this study)), in the absence of a probe-foraging lifestyle [26,27].…”

“…Only the probe-foraging kiwi are known to use remote touch [6], yet the soft tissue histology and bill-tip microstructure of the extant herbivorous palaeognaths (e.g. emu and ostrich) indicate the presence of a bony bill-tip organ, similar to that possessed by remote-touch probing birds [24,25]. This is at odds with the fact that none of the non-kiwi palaeognaths use probe foraging as a feeding strategy [26,27], nor do they show enlargement of the brain centres associated with the processing of tactile information from the beak, as seen in specialist tactile-foraging birds [10,13].…”

The rostral neurovascular system of Tyrannosaurus rex

“…Studies of early Crocodyliformes, the phytosaur Wannia, and the rauisuchid Vivaron, however, demonstrate that basal archosauriforms had only few supralabial foramina organised in a single line parallel to the tooth row as in early diapsids and squamates, and that the maxillary canal was simple, tubular, and did not send off as many branches as in modern crocodiles (Soares, 2002;Lessner et al, 2016;Lessner and Stocker, 2017). Additionally, highly sensitive rostral integumentary systems are limited to a few distinct clades of modern birds, such as waterfowl, kiwi, ibises, parrots, and shorebirds, which display specialised tactile-foraging behaviours (e.g., probing, dabbling) in conjunction with a highly ramified trigeminal system and richly foraminiferous beak (Gottschaldt and Lausmann 1974;Berkhoudt, 1979;Gottschaldt, 1985;Cunningham et al, 2010Cunningham et al, , 2013Demery et al, 2011;Crole and Soley, 2017;du Toit et al, 2020). Although much work is still required to highlight the numerous specialisations of facial sensitivity in modern archosaurs (Wakimizu and Tsuihiji, 2021), it is safe to state at this stage that the conditions in modern crocodilians and birds is derived for Crocodylomorpha and Theropoda respectively, and were likely absent at the root of the Archosauriformes clade.…”

The True Identity of Putative Tooth Alveoli in a Cenozoic Crown Bird, the Gastornithid Omorhamphus

“…The latter grooves also characterize adult Sylviornis beaks (Mourer-Chauviré and Balouet, 2005) as opposed to juvenile ones (Figure 5B). The remnant pits on the rostral part of adult beaks can be compared with those visible in several extant birds, including those of some ratites which have been interpreted as being related to a sensory bill tip organ (Crole and Soley, 2017;du Toit et al, 2020). The deep grooves in adult Gastornis and Sylviornis are vascular grooves on the surface of the bone that have been interpreted as necessary to maintain and nourish a thick rhamphotheca (Mourer-Chauviré and Balouet, 2005) and their exclusive presence in adults presumably indicates that their formation took place after the cessation of primary bone growth.…”