On Unusual Peculiarities of Head Morphology in Therocephalian Hexacynodon purlinensis

Leonid P. Tatarinov


A rudimentary chordal canal and pits for basicranial muscles with three pairs of openings for segmental ventral nerves were indicated on basioccipital of H. purlinensis. Up to now these nerves in land vertebrates were reported only for larvae of some amphibians. The groove on the occipital edge of squamosum, in which the external acoustic meatus is traditionally reconstructed, is connected with vascular openings on the distal part of mastoid process and with broad vascular canal trending between squamosum and quadratum. External to the medial sutural junction of basioccipital and basisphenoid the two bones are separated by fissure. Basisphenoid forms a short process here passing into the groove on the edge of basisphenoid. This articulation corresponds to the rudimentary intracranial joint in crossopterygians. In the bottom of basioccipital just anterior to the occipital condyle are deep cavities, connected by diminutive foramina in condyle with the vertebral canal. This cavity probably contained the posterior endolymphatic sac, and foramina conveyed endolymphatic ducts. The anterior endolymphatic sac was located possibly in the cavity anterior to fenestra ovalis, delimited by basioccipital, basisphenoid, and prootic. Due to the development of oblique crest on the quadrate condyle the opening of mouth was attended by lateral displacement of lower jaw. Such a displacement was possible only in condition if intramandibular mobility between dental (and splenial) and postdental block of mandibular bones.


morphology; skull; therocephalians; Hexacynodon

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Allin E. F. (1986), «The auditory apparatus of advanced mammal-like reptiles and early mammals,» in: N. Hotton, P. D. MacLean, J. J. Roth, and C. E. Roth (eds.), The Ecology and Biology of Mammal-Like Reptiles, Smithsonian Inst. Press, Washington–London, pp. 283 – 294.

Belogolovii Yu. A. (1911), «Segmental position of bound in Sauropsid skull,» Uch. Zap. Mosk. Univ. Old. Estes. Istor., 28, 3 – 239.

de Beer Gavin R. (1937), The Development of the Vertebrate Skull, The Clarendon Press, Oxford.

Bjerring H. C. (1953), «Relationships of coelanthiforms,» in: P. H. Greenwood, R. S. Miles, and C. Patterson (eds.), Interrelationships of the Fishes. Zool. J. Linn. Soc., No. 53, Suppl. 1, Acad. Press, London, pp. 179 – 205.

Bjerring H. C. (1977), «A contribution to structural analysis of the head of craniate animals,» Zool. Scr., 6(2), 127 – 183.

Bjerring H. C. (1978), «The ‘intracranial joint’ versus the ‘ventral otic fissure’,» Acta Zool. (Stockh.), 59(3), 203 – 214.

Boonstra L. D. (1953), «The lower jaw articulatory region in some pristerognathis therocephalians,» Ann. South Afr. Mus., 42(1), 54 – 63.

Crompton A. W. (1984), «On the skull of OligokyphusBull. Br. Mus. (Nat. Hist.) Geol., 9(3), 67 – 82.

Dempster W. T. (1930), «The morphology of the amphibian endolymphatic organ,» J. Morphol. Physiol., 50(2), 71 – 126.

Gregory W. K. (1910), «The orders of mammals,» Bull. Am. Mus. Nat. Hist., 27, 1 – 524.

Hopson J. A. (1956), «The origin of the mammalian middle ear,» Am. Zoologist, 6(7), 437 – 450.

Ivakhnenko M. F. (in press), «Revision of Permian tetrapods of the USSR,» Trudy Paleontol. Inst. RAN [in Russian].

Jarvik E. (1960), Théories de lýevolution des vertébrés reconsidérées a la lumière des récentes découvertes sur les vertébrés inférieurs, Masson et Cie, Paris.

Jarvik E. (1975), «On the saccus endolymphaticus and adjacent structures in osteolepiformes, anurans, and urodeles,» in: Colloq. Int. Center Nat. Rech. Sci., Vol. 218, Paris, pp. 191 – 211.

Jarvik E. (1980), Basic Structure and Evolution of Vertebrates. Vols. 1 – 2, Acad. Press, London–New York.

van Kampen P. N. (1905), «Die Tympanalgegend des Saugetiereschädels,» Morphol. Jahrb., 34(5), 321 – 722.

Kemp T. S. (1972), «The jaw articulation and muskulature of the whaitsiid Therocephalia,» in: K. A. Jousey and T. S. Kemp (eds.), Studies in Vertebrate Evolution, Winchester Press, New York, pp. 213 – 230.

Kemp T. S. (1982), Mammal-Like Reptiles and the Origin of Mammals, Acad. Press, London–New York.

Kühne W. G. (1956), The Liassiic Therapsid Oligokyphus, Brit. Mus. (Nat. Hist.), London.

Mee-Mann Chang (1982), The Braincase of Youngolepis, a Lower Devonian Crossopterygian from Yunnan, South-Western China, Univ. Stockholm, Swedish Mus. Nat. Hist., Stockholm, pp. 1 – 113.

Millot J. and Anthony J. (1958), Anatomie de Latimeria chalumnae. I. Squeletter, muscles et formation de soutien, Centre Nat. Rech. Sci., Paris.

Northcutt Glenn R. (1986), «Lungfish neural characters and their bearing on sarcopterygian phytogeny,» in: W. E. Bemis, W. W. Burggren, and N. E. Kemp (eds.). The Biology and Evolution of Lungfishes, J. Morphol., Centennial Suppl. 1, pp. 277 – 298.

Parrington F. R. (1979), «The evolution of the mammalian middle and outer ears: a personal review,» Biol. Rev., 54(7), 369 – 387.

Regel’ E. D. (1968), «Development of axial chondrocranium and its connections with upper division of jaw arch in Ranodon sibiricus (Hynobiidae, Amphibia),» Trudy Zool. Inst. Akad. Nauk SSSR, 46, 5 – 85 [in Russian].

Regel’ E. D. and Epshtein S. M. (1972), «Segmentation of the interarcual region of skull in AnuraZool. Zh., 11, 1517 – 1528 [in Russian].

Roček Z. (1986), «An ‘intracranial joint’ in frogs,» in: Z. Roček (ed.), Studies in Herpetology. Proc. 3rd Ord. Gen. Meet. Soc. Eur. Herpetol., Prague, 1985, Charles Univ. Press, Prague, pp. 49 – 54.

Tatarinov L. P. (1968), «Morphology and systematics of the northern Dvina cynodonts (Reptilia, Therapsida: Upper Permian),» Postilla Peabody Mus. Yale Univ., 126, 1 – 51.

Tatarinov L. P. (1974), «Theriodonts of the USSR,» Trudy Paleontol. Inst. Akad. Nauk SSSR, 143, 3 – 252 [in Russian].

Tatarinov L. P. (1976), Morphological Evolution of Theriodonts, and General Questions of Phylogenetics, Nauka, Moscow [in Russian].

Tatarinov L. P. (in press), «New late Permian therocephalian Viatkosuchus sominiPaleontol. Zh. [in Russian].

Tatarinov L. P. (in press), «New dates on the structure of the theriodonts,» in: 2nd Int. Curviér Paleontol. Colloq.: «The Fossil Reptiles of the Europe,» Montbelliard, Sept. 1992.

Thomson K. S. (1967), «Mechanism of intracranial kinetics in fossil rhipidistian fishes (Crossopterygii) and their relatives,» Proc. Linn. Soc. (London) Zool., 46(3), 223 – 253.

Vorob’eva E. L. (1977), «Morphology and features of evolution of crossopterygians,» Trudy Paleontol. Inst. Akad. Nauk SSSR, 162, 3 – 239 [in Russian].

Watson D. M. S. (1951), Paleontology and Modern Biology, Yale Univ. Press, New Haven–London.

DOI: https://doi.org/10.30906/1026-2296-1994-1-1-1-12


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