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Smithsonian Herpetological Information Services 1968 /9 CRANIAL KINESIS IN LIZARDS; CONTRIBUTION TO THE PROBLEM OF THE ADAPTIVE SIGNIFICANCE OF SKULL KINESIS by N. N. Iordansky Zoologicheskii Zhurnal (Zoological Journal) volume 45, number 9 pp. 1398-1410 1966 Translated by Dr. Leon Kelso Edited by Carl Gans SMITHSONIAN HERPETOLOGICAL INFORMATION SERVICES 1968 Additional copies available from: Division of Reptiles and Amphibians United States National Museum Washington, D. C. 20560 , , A , 1 The term kinesis, when used as a reference to the skulls of tetrapods, is defined either as the movement of the upper jaw accompanied by specific elements of (or the entire) dermatocran i urn, or as movement of the olfactory region of the neurocranium with respect to the rear part of the axial skull (i.e., of the brain case formed of cartilage-replacement bonesl This phenomenon was first described by Nitzsch in 1822, according to Bradley ( 1 9^3) » w h° discovered that the lizard skull was capable of movement in the f ronto-parietal suture and in the articulation of the parietal bone with the occipital. Bradley studied the chewing musculature and accompanying movements in the skull of lizards. He formulated the first hypothesis of the functional significance of the movement of the upper jaw in relation to the axial skull (see below) and made the first attempt to correlate these movements with the functions of specific muscles. The term "cranial kinesis" was introduced by Versluys (1910) for a construction of the skull in which such movements would be possible, as well as the movements of the lower jaw. Versluys (l910, 1912, 1922, 1927) made a more thorough analysis of tetrapod cranial kinesis. He pointed out the prevalence of kinesis among most of the tetrapod groups, recent and extinct; classified various forms of kinesis, and proposed a theory of cranial kinesis, according to which the tetrapod skull was primitively kinetic; kinesis was inherited by the ancient tetrapods from fish-like ancestors and secondarily lost in several lines . of tetrapod evolu t i on ^ From Versluys comes one of the most widely accepted hypotheses to date on the functional significance of cranial kinesis. Later contributions to the study of kinesis were made by Lakjer (l9 2 7), Marinelli (1928, 1936), de Jong and Brongersma (1927), Hofer (i960) and various other authors. Kinesis in crossopteryg ian fishes was shown by Romer ( 1 937 P er Frazzetta 1962) and in some stegocephal ians ( Pf annenst iel, 193 2 > according to Frazzetta, 1962). An exceptional amount of work on kinesis was devoted to the more specialized and unusual forms of birds and snakes. Comparatively little attention was given to kinesis in the more primitive forms of cranial kinesis (in lizards). A valuable contribution to the study of cranial kinesis in lizards was the work of Frazzetta (1962). Frazzetta by using motion pictures, demonstrated the connection between the movement of the upper jaw and the seizing and consumption of prey, and made the first b iomechan ical analysis of the work of the jaw muscles, - p. 1399 - responsible for movement of the upper jaw. Frazzetta presented a new hypothesis on the functional significance of cranial kinesis (see below). However, Frazzetta, in his analysis of cranial kinesis, focused his attention on one form ( Varanus ), giving less attention to the features of cranial kinesis of other forms studied by him. The type of cranial kinesis exhibited by Varanus , as our work has shown, cannot be considered as either the most primitive or the most widespread among lizards. For a clear presentation of the evolution of skull kinesis and its functional significance, a comparison of kinesis in various skulls beginning with the more primitive forms, i s necessary. MATERIALS AND METHODS We have studied skull structur e i n Sphenodon p_uncta tus and the fol lowing lizards: Cyclur i . I . A_ *. *. macleay qu ana sp ( Iguanidae), ama caucas ica A. lehmann i 1 ^. sa qu i nolenta Phrynoceph *. ret icula tus ( Agamidae), Lacerta med .a*, L_. aq i 1 i s E rem ias arquta . E. gramm ica (Lacertidae), * i i y *. i Eumeces schne der t Ma b u a aurata . Trachysaurus ru qosus (Scincidae), aranus qr i seus V. n * f i *, Varan dae) Tera tosc i ncus sc i ncus , Gecko gecko Platydactylus quttat us . Gymnodactylus casp i * * Gekkon i dae) Oph i ( i i ( i i (Zonu ( saurus apodus nguidae), Tup na mb s sp . T e da e ) Zonurus cordylus from the mate rial of the Zoological Institute of th e Akademiia Nauk USS R, the Zoological Museu of Moscow Uni vers i t y, the Cha ir of Vertebrate Zoolo gy of Moscow Un i vers ity and from our own co lections. We studied the details f cran ial k i nes i s in the alcoholic wet) connective tissue 2 preparat i ons of skulls of 11 specie s of lizards (w i th sk in removed) a d also in the skulls of freshly k i lie d species of Varanidae In add i t i on, the jaw musculature of nine other species of 1 i zards wa s studied. Motion pic tures of the eat ing of prey by Aqama ceucas ica and Lacerta i i aq 1 s were t aken by an aide [assis tant , or proba t i onerj at the Paleont olog ical I nst itute of t ANSSSR, N.N Kalandadze, to whom th e author is very indebted for his he lp in the work. We als wish to expre ss our sincere thanks to B. S. Mateev r,d F. Ya. Dzerzhins kyj (chair of vertebrat zoology, Mosc ow University) for dis cussion of our esults and for crit cal remarks, and for gi the opportuni ty to work with museum materials, the head of the herpetol ogy division of the Zoolog ical In st itute ANSSSR, I . S. Darevsk i i , and ead of the evolution ry morphology division Zoological Mu seum, Moscow Uni vers it y, D. N. Hofmann *An alternate hypothesis of the antiquity of the akinetic skull and independence of development of kinesis in various lines of vertebrate evolution was developed by Edgeworth (1935)- Edgeworth's views do not survive serious criticism and have not received general acceptance. The names of these [llj lizards are designated by an asterisk in the list given above. ) . CRANIAL MOVEMENT OF LIZARDS Following Bradley's work (19O3), on li rd skulls, t hree fund ntal segment s [uni tsj were i si i ngu i shed: the occipital, maxillary, a mand i bular. The occ tal segment was re i nf orced "1 vertebrates and is considered to be immo ble. It is formed of e occipitals and o t i c bones, id also the basi- and paraspheno i ds. The other segm ents are able relativ e to t he occ i p i tal. f to interest us here primarily is the mov i 1 i ty of the ax illar egment, whic hiss i gn i f ied by le term "cranial kinesis". The relationsh s between th maxilla and occ i p i ta 1 sect ions have Lready been described by Bradley, Versluys Hofer, Frazz etta, Oel h (1956) and Webb [1951) and ; have confined ourselves only to their en eration. Th ese relat ships includ e: th e union of ie quadrate, squamosal and the supra-tempo 1 bones with the late ends of the paroc c ip-i tal ( -ocesses "metak i net ic axis" of Frazzetta) the parietal with the pra-occ i p i ta 1, the pterygo i ds ith the bas pterygo i dal of the i i ds th the proof ic bon es. i processes, sometim ep p terygo ;sides this, both segments are joined by t cart i lag i no us and me anous orb i to -tempo ral Lements of the brain case. All these conn tions allow a 1 im i ted gree of move ment f the ixillary segment relative to the occipital first, as a whole, i urns around the me tak i ne t ic i or, ) <is with the anterior end upward and forwa ( protract i ) or dow rd and back ard (r e tract ;sides this, the maxillary segment during 0- and retra ction cha s conf igurat on s i nee it - insists of a series of related divisions pa i red: ( 1 quadrate nes, (2) ep pteryg i ds, -- -- P. 1400 (3) palatal divisions; — and unpaired: (i) parietal division, and (5) the snout [muzzle], which always breaks down further into (5 a ) central and paired (5 D ) lateral parts. The composition of all these divisions with the exception of the quadrate and ep pterygo i d. differs as also differ i the peculiarities of kinesis in the various forms of lizards (see table). -- fi 1 -- opposite movement of all the above-mentioned elements of the maxillary segment of the craniun takes place. However, among the various forms of lizards, there are essential differences in the peculiarities of cranial kinesis and in the composition of the various sections of the maxillary segment (cf. Aqatna table). First, the kin ds ot lizards studied fall primarily into two groups: (l) C yclura . a shaft [corej participating in cranial Lacerta , and Oph i saurus , in which the palatal unit is solid movements as an indivis ible integer [whole unit] — unquestionably a more primitive stage; (2) Eumeces , . in the palatine unit is articulated Varanus . Tera tosc i ncus , Gecko . Gymnodactylus . and Zonurus which along the palato-pteryg oidal juncture to the anterior and posterior parts, movable relative to one another.
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