Ventastega (Venta referring to the Venta River at the Ketleri Formation where Ventastega was discovered) is an extinct genus of stem tetrapod that lived during the Upper Fammenian of the Late Devonian, approximately 372.2 to 358.9 million years ago. Only one species is known that belongs in the genus, Ventastega curonica, which was described in 1996 after fossils were discovered in 1933 and mistakenly associated with a fish called Polyplocodus wenjukovi. ‘Curonica’ in the species name refers to Curonia, the Latin name for Kurzeme, a region in western Latvia. Ventastega curonica was discovered in two localities in Latvia, and was the first stem tetrapod described in Latvia along with being only the 4th Devonian tetrapodomorph known at the time of description. Based on the morphology of both cranial and post-cranial elements discovered (see below), Ventastega is more primitive than other Devonian tetrapodomorphs including Acanthostega and Ichthyostega, and helps further understanding of the fish-tetrapod transition.
Discovery
Walter Gross was the first person to collect partial Ventastega remains, collecting some teeth in addition to scales from a locality called Ketleri in a Latvian Upper Famennian formation while on a collection trip in 1933. Gross attributed all remains to an osteolepiform fish named Polyplocodus wenjukov, before later in 1944 reattributing some of the fragments to a species called Panderichthys bystrowi when a piece of a lower jaw was collected from the same locality. Additional remains were collected from the locality and from another locality, Pavāri, in the same formation by researchers Per Erik Ahlberg, , and Oleg Lebedev. After this collection they realized the previously collected remains were assigned incorrectly, and were actually part of a newly discovered tetrapod, which they named and described in a paper published in 1996. In the follow years, several more fragments of Ventastega curonica remains have been discovered at both the Ketleri and Pavāri localities, with all specimens residing at the Natural History Museum of Latvia.
Description
Cranial elements
Lower jaw
The Ventastega holotype (LDM 81/521) is a right lower jaw ramus from Pavāri, and was described by Per Erik Ahlberg, Ervīns Lukševičs, and Oleg Lebedev. The lower jaw ramus total length was estimated to be over 200mm. This, combined with other cranial and post-cranial elements of Ventastega, made researchers predict that it was larger than Ichthyostega. The mandible is widest anterior to the first coronoid fang. The dentary is long and shallow, and has a butt joint as the contact with the coronoid series, indicating the dentary is loosely attached to the jaw. Similar to some tetrapods such as Acanthostega and Tulerpeton, the dentary's lateral surface is ornamented on the dorsal side with a smooth section only on the ventral margin. Another lower jaw specimen (LDM 81/552) is the only known complete Ventastega dentary, and shows Ventastega had 89 marginal teeth on each side of the jaw that are all approximately the same size, although they decrease in height as you move distally. Ventastega also has a pair of fangs on each dentary that are situated close to where the two dentaries meet at the most anterior part of the lower jaw, similar to Panderichthyesand Ichthyostega.. On the precoronoid and intercornoid, Ventastega has fangs pairs set within the marginal row of teeth. On the lower jaw, Ventastega had a surangular pit line, which is present in most Sarcopterygians but unknown in any other tetrapods. A primitive characteristic on Ventastega, shared only with fish and Ichthyostega, is the presence of a fully enclosed mandibular sensory canal which opens to the external world through only a single row of pores.