Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
Zemes un vides zinātnes Earth and Environment Sciences - Latvijas ...
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O.A. Lebedev. A new tetrapod from Russia<br />
85<br />
Proterogyrinus (Holmes 1984), Crassigyrinus (Panchen 1985; Clack 1998) <strong>and</strong><br />
Anthracosaurus (Panchen 1977) the posteromesial part of the postfrontal widens, deeply<br />
wedging into the parietal. However, in contrast to the condition in Acanthostega <strong>and</strong> in<br />
accordance with that in Ventastega (Lukševics, pers. comm.) the lateral sides of the<br />
prefrontals must have adjoined the lateral sides of the frontal <strong>and</strong> postfrontal together,<br />
<strong>and</strong> the lateral process of the postorbital must have abutted the posterolateral part of<br />
the postfrontal, rather than wedged between it <strong>and</strong> the parietal. The contact surface for<br />
the postorbital is preserved at the posteriormost tip of the postfrontal on the left side of<br />
the specimen. The infraorbital canal leaves the bone shortly anteriorly to this contact<br />
area. A prono<strong>un</strong>ced swollen ridge forms the orbital margin.<br />
Only the anterior parts of the parietals are preserved. Posteromedially the parietals<br />
become thinner at its centre <strong>and</strong> form a depression on the dorsal side, probably r<strong>un</strong>ning<br />
forwards from the pineal foramen. On the ventral side the most impressive features are<br />
deep grooves r<strong>un</strong>ning alongside the parietal-postfrontal contact. These grooves bear<br />
blood vessel impressions, which lead to moderately large foramina opening into the<br />
canals inside the bone. The mesial part of the parietals is occupied with a narrow<br />
impression of the sphenethmoid.<br />
The only lower jaw element preserved is an incomplete left angular (PIN 2657/<br />
347) (Fig. 4). In most respects it agrees with the corresponding bones in Ichthyostega<br />
(Jarvik 1952), Acanthostega (Clack <strong>and</strong> Coates 1993), Ventastega (Ahlberg et al. 1994),<br />
Fig. 4. Jakubsonia livnensis gen. <strong>and</strong> sp. nov., incomplete angular, PIN 2657/347. A, lateral<br />
view; B, mesial view.