MORPHO-FUNCTIONAL FEATURES OF THE JAW APPARATUS OF FAMILY EURYLAIMIDAE (suboscine passerines) E.N. Zubkova, L.P. Korzun
Introduction Eurylaimidae are one of the relict families of the Old World. Broadbills are largely brightly coloured confined to the wetter parts of Africa (2 genera - 4 species) and to SouthEast Asia (6 genera - 11 species). Members of the Eurylaimidae exhibit a wide spectrum of feeding habits and diets, and display a variety of adaptations to specialised diets. A minore of species are specialised frugivores (Calyptomena and Pseudocalyptomena), with the remainder being insectivorous. However, the lack of a sharp cutting edge to the bill means that Calyptomena broadbills are unable to manipulate large fruts easely and therefore tend mostly to eat soft frutis, such as figs. The insectivorous broadbills have bills that are long as well as broad with a hook at the tip, making them formidable predators of large insects such as orthopterans as well as enabling some species to tackle small vertebrates (Lambert, Woodcock, 1996). Most species of insectivorous broadbills also very occasionally eat fruit, as indicated by the presence of seeds in specimens of a number of species.
Methods
Eurylaimus javanicus
Calyptomena viridis
Cymbirinchus macrorinchos
Smithornis capensis
Fig. 1. Side view of scull.
Obtained morphological data were analyzed together with ecological data on food adaptation the broadbills, taken of the literature. The designation and the description of muscles and aponeurosises of the jaw aparatus are resulted according to Dzerzhinsky & Potapova (1974). The description of the hypoglossal apparatus was done according to Korzun (1978).
Results
Let's more in detail consider distinctions found in these birds. Inside of the Asian group the frugivorous broadbill in many respects differs from the insectivorous birds. Short, but wide, the beak of Calyptomena viridis the easiest and openwork owing to the big bone nostril (Fig. 1). In it species are found out a prefrontal bone and all 3 condyles in the maxillary joint (at the others broadbills this group the prefrontal bone and the caudal condyle are absent). Other structure have the ligaments of maxillary apparatus - the postorbital ligament wide, terminates on zygomatic arch, instead of on the bottom jaw; the external articulate ligament oriented almost vertically (at others studied broadbills it oriented gentle). The external adductor at Calyptomena noticeably is weaker. The terminal aponeurosis of the superficial portion of the external adductor it is smallest.
Fig. 2. The hypoglossal apparatus of Eurylaimus yavanicus.
Fig. 3. The jaw muscles of Smithornis capensis.
Tabl. The comparison of structure of the jaw muscles among Asian ggoup of insectivorous broadbills.
Subgroup I (Psarisomus)
Subgroup II (Eurylaimus, Cymbirinchus, Serilophus)
Structure of the terminal superficial aponeurosis Small narrow strip (as at Smithornis and
Large wide dilobar
Calyptomena)
At comparison the exterior of the broadbills with others passerines to draw attention its disproportionate large head in relation to its small body. The large eyes necessary for these birds by search of prey in dense crones have pressed maxillary muscles. Deficiency of a place on the side of the skull is compensated by a deep temporal hole that is possible only at the wide skull. The large solid beak and wide pharynx in aggregate with the big massive muscles with long fibers the containing small quantity aponeurosis, allow these birds not only to catch and keep prey, but also to crush it in the basis of the beak. On it show its specifically strengthened basis of a beak (to the greatest degree it is expressed at the Asian insectivorous broadbills) and the structure of a prokinetic zone which is adapted to maintain similar loadings owing to a mobile joint and specific bone stop. The role in manipulations with object in a voluminous beak plays its tongue by means of which the bird can place prey in the most convenient for crush position. Opportunities of work with object in the beak considerably are expanded with the mechanism “levation” tongue (Korzun, 1978). Ability to manipulations is useful also at braiding a complex nest from blades and thin twigs that are inherent for broadbills. Freedom of movements the jaw is promoted by absence at the Asian insectivorous broadbills the caudal condyle in the maxillary joint. It can be useful for them during hunting these birds usually long sit without movement, looking out for suitable prey which then catch in a prompt throw. At the smallest (but having improbably large beak) from broadbills Smithornis it is possible to explain presence of the this condyle to that this bird as a whole conducts more active way of life. In comparison with other birds close with it in the sizes of a body, african broadbill is capable to consume rather large prey which completely compensates to it expenses of energy. Presence caudal condyle at Calyptomena viridis, possibly, is connected with necessity to tear off the attached fruits, using the so-called “mechanism of lock-out of the maxillary joint”. Realization of this function is connected with longitudinal sliding movements in a maxillary joint. At forward position of the bottom jaw concerning a square bone and at the tense external articulate ligament, caudal condyle rests against a arthrodial surfaces, interfering with rotary movements in a joint (Dzerzhinsky, 1972). At compressing object in such conditions the top jaw receives power advantages, in comparison with bottom, that allows to resist effectively to the superfluous force created on maxilla at tear attached fruit. Features of a structure of the maxillary muscles, found at Psarisomus, yet have not received interpretation which, possibly, will appear after expansion of the list studied suboscine passerines.
Structure of the rostral part of the deep portion Absence the mediorostral aponeurosis
Presence the mediorostral aponeurosis
The different device of the pterygoid muscle
The different device of the aponeurosis structure of the superficial pseudotemporal muscle
The distinctions of the muscles of jaw apparatus found in Asian insectivorous broadbills divide them in two subgroups. The first subgroup consists of the one genus Psarisomus, the genera Eurylaimus, Cymbirinchus and Serilophus concerning to another subgroup. Examples of such distinction in the table. The African broadbill (Smithornis capensis) is of mosaic nature in having a combination of all three sets of features. The details close with frugivorous broadbill: • the device of a maxillary joint (3 condyles); • presence of a prefrontal bone; • structure of the terminal superficial aponeurosis.
Also the details inherent in each the Asian subgroups are found out in it. So, the device of a superficial portion of the external adductor is similar to those at Psarisomus from the subgroup I. And presence the mediorostral aponeurosis pulls together it with the subgroup II. Have been found out as well the details inherent only in this species (Fig. 1, 2): special structure medial aponeurosis and pterygoid muscle, large initial aponeurosis depressor, merged with a occipitomaxillary cord, details in the disposition of muscles hypoglossal apparatus.
Functional interpretation of morphological data
The present morfological investigation has been lead on the broadbills (Eurylaimidae) form clade of the Old World suboscinene passerines. From representatives of the Asian group have been studied Eurylaimus javanicus, Cymbirinchus macrorinchus, Serilophus lunatus, Psarisomus dalhousiae and Calyptomena viridis, from the African group has been taken Smithornis capensis. The anatomic researches carried out consist in dissection of specimen head and detail sketches pf the scull and the muscles of the jaw apparatus (with registration shape and interrelations of aponeurosises); and the functional analysis of the apparatus as a whole.
Has been shown, that Eurylaimidae as a whole form a natural group with a common plan of the structure of jaw apparatus. All of them have a wide bill and a wild pharynx, and also differ by rather simple pinnate structure of the jaw muscles, consisting of relatively long muscle fibres (with respectively long amplitude of contraction) and a small number of aponeurosises (Tabl.). Also broadbills have thin and long ligamentum postorbitale (the given cord at frugivorous broadbill has other structure). Such features of a structure provide ability to wide gape of jaw, that allows these birds to consume large enough food objects. All broadbills have specifically strengthened basis of a beak, especially strongly evident at the Asian insectivorous birds (at Cymbirinchus it is shown to the greatest degree - it maxilla and mandibule is strong expanded, that does its beak especially strong). The large almost vertical maxillary processes of nasal bones rest against the wings of mesethmoideum, transferring loading from a beak on a skull (Fig. 1). To it promotes the procinethic zone of the beak which at broadbills looks like mobile connection. Such features indicates that the broadbills possess ability to specific processing a food in the basal part of the bill. A number of morphological features of the structure of the tongue of broadbills are connected with this specialization, their tongues being wide, fleshy and possessing sufficiently high degree of mobility (Fig. 2). It is possible to judge the last on degree of development of muscles of the hypoglossal appatarus which at the given birds are well expressed.
Dept. of Vertebrate Zoology Biological Faculty Moscow State University Vorobievy gory, Moscow 119992, Russia e-mail:
[email protected]
Summary Broadbills are deeply adapted for consume of large food items. The jaw apparatus of this birds is adapted to griping large prey and its effective processing in the basis of the beak. Owing to features of the hypoglossal apparatus and tongue these birds can cope not only with large prey, but also have kept ability to manipulations with small objects that plays an important role in gathering fine insects and at weaving complex nest. The Smithornis bears in itself features of all studied broadbills. Its place in system of the suboscine passerines Old World yet clearly, possibly, will help comprehension of it studying other African representatives of this group.
Acknowledgement The author expresses M.V. Kaljakin sincere gratitude for granting of the fixed material, and also valuable data on biology of this birds; F.J. Dzerzhinsky and K.B. Gerasimov for the help in carrying out of the given research; to colleagues from the Museum of Natural History of Paris for granting of the specimen Calyptomena viridis. Literature cited
Notation conventions Cranium: Jg – jugale, Md – mandibula, Mst – mesethmoideum, mxns – proc. maxillaris nasalis, Pf – praefrontale, Pl – palatinum, Po – proc. orbitalis quadrati, Ppo – proc. postorbitalis, Pt – pterygoideum, Pz – proc. zygomaticus, Q – quadratum. Muscles: Aec – m. adductor mandibulae externus profundus caudalis, Aem – m. add. md. ext. medialis, Aer – m. add. md. ext. profundus rostralis, Aes – m. add. md. ext. superficialis, Bmc, Bmr – m. branchiomandibularis caudalis & rostralis, Cga, Cgp – m. ceratoglossus anterior & posterior, Ch – m. ceratohyoideus, Dm – m. depressor mandibulae, Gg – m. genioglossus, Hg – m. hypoglossus, Mh – m. mylohyoideus, Pc – m. pterygoideus caudalis, Pdl – m. pt. dorsalis lateralis, Pdm – m. pt. dorsalis medialis, Pvl – m. pt. ventralis lateralis, Pvm – m. pt. ventralis medialis; Ppt, Pq – m. protractor pterygoidei & quadrati, Psp и Pss – m. pseudotemporalis profundus & superficialis, Sh – m. serpihyoideus, Sth – m. stylohyoideus. Aponeurosises: ace – ap. caudalis externa, acg – ap. centralis glossae, adi, ado – ap. dorsalis insertionis & originalis, ai – ap. interna, ali, alp – ap. lateralis insertionis & originalis, akg – ap. kerato-glossi, am – ap. medialis, amq – ap. medioquadrata, amr – ap. mediorostralis, ams – ap. mediosuperficialis, apc – ap. pterygoidea caudalis, app, aps – ap. pseudotemporalis profunda & superficialis, asa, asp – ap. superficialis anterior & posterior, avi – ap. ventralis insertionis. Ligaments: Lje, Lji – lig. jugomandibulare externum & internum, Lp – lig. postorbitale.
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