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84 ADVANCES IN PALAEOICHTHYOLOGY
trace of medial suture. The frontals are short; they are only 2.4 times longer than wide.
The posterior half of their lateral contact area is occupied by the postfrontal contact,
the anterior part served for the prefrontal attachment (Fig. 3). This condition is not
observed in the Devonian tetrapods Ichthyostega (Jarvik 1952), Acanthostega (Clack
and Coates 1993) or Ventastega curonica (Lukševics, pers. comm.); however, it may
be found in the long-snouted anthracosauromorphs, for example Proterogyrinus scheelei
Romer, 1970 (Holmes 1984), Eoherpeton watsoni Panchen, 1975 (Smithson 1985)
and Anthracosaurus russelli Huxley, 1863 (Panchen 1977). However, in these species
the frontal is very long, because of the general elongation of the preorbital part of the
skull. In Jakubsonia, on the contrary, a short frontal in combination with a long contact
to the prefrontal might suggest large orbits, rather than a long snout. The anterior edge
of the frontals shows no sutural contact; on the contrary, the bone becomes thinner here
suggesting participation in the posterior margin of an internasal fontanelle as in
Tulerpeton (Lebedev and Clack 1993) or in Ventastega (Lukševics et al. 2003). The
lateral side of the left frontal, however, shows a rather deep notch, which houses the
infraorbital canal opening. This notch might be interpreted as a contact for the left
nasal. The lateral parts of the fronto-parietal suture are visible at the ventral side of the
skull roof. Mesially a sheath of spongy matter of the connecting ethmosphenoid obscures
the suture (Fig. 2B).
Fig. 3. Jakubsonia livnensis gen. and sp. nov., reconstructed interorbital fragment of the skull
roof. Abbreviations: Fr, frontal; Pa, parietal; Poc, contact margin for the postorbital; Pof,
postfrontal; Prf, position of prefrontal; or, orbit; soc, supraorbital canal; son, notch housing the
anterior opening of the supraorbital canal in the frontal.
From the frontals the supraorbital canal turns laterally and enters the narrow,
semilunate postfrontals. The shape of this bone is characteristic of the Devonian tetrapods
Ichthyostega (Jarvik 1952), Acanthostega (Clack and Coates 1993) and Tulerpeton
(Lebedev and Clack 1993). In the later Carboniferous tetrapods, for example