Tiktaalik was a tetrapod with legs that was still mostly lobe-finned fish. Ventastega is a tetrapod with legs that is closer to earlier lobe-finned fish like Acathostega. Here’s a bit from the Nature News:
Initially described in 1994, early specimens of Ventastega curonica were fragmented, and hard to interpret. New examples from Latvia have now allowed researchers to reconstruct the head, shoulders and part of the pelvis of the ugly looking beast (press release, research paper in Nature).
The editor’s summary in Nature notes that the new work shows Ventastega has the skull shape of an early tetrapod but the proportions of a fish. It provides new insights in the evolution of early land-dwelling vertebrates (called tetrapods) some 370 million years ago in the Late Devonian period.
“From a distance, it would have looked like an alligator,” says study author Per Ahlberg, of Uppsala University in Sweden (BBC). “But closer up, you would have noticed a real tail fin at the back end, a gill flap at the side of the head; also lines of pores snaking across head and body. In terms of construction, it had already undergone most of the changes from fish towards land animal, but in terms of lifestyle you are still looking at an animal that is habitually aquatic.”
Ahlberg speculates that it was crawling around on sandy banks and eating stranded fish in tidal creeks (AP).
Ted Daeschler, paleontologist at the Academy of Natural Sciences in Philadelphia, explains to National Geographic that although we have a general outline of the transition between fish and tetrapods there’s a lot we don’t know. It’s like building a house, he says: “We’ve got the frame built. We know what the rooms are shaped like. But we haven’t put in the electricity, installed the lamps, or put Sheetrock on the walls.”
Picture upper: Philip Renne and Per Ahlberg
Picture lower: Ventastega in side view / Per Ahlberg
Here’s the abstract from Thursday’s Nature:
Nature 453, 1199-1204 (26 June 2008) | doi:10.1038/nature06991; Received 22 November 2007; Accepted 9 April 2008
Ventastega curonica and the origin of tetrapod morphology
- Subdepartment of Evolutionary Organismal Biology, Department of Physiology and Developmental Biology, Uppsala University, Norbyvägen 18A, 752 36 Uppsala, Sweden
- University Museum of Zoology, Cambridge, Downing Street, Cambridge CB2 3EJ, UK
- Department of Geology, University of Latvia, Rainis Blvd 19, Riga LV-1586, Latvia
- Natural History Museum of Latvia, K. Barona Str. 4, Riga LV-1712, Latvia
The gap in our understanding of the evolutionary transition from fish to tetrapod is beginning to close thanks to the discovery of new intermediate forms such as Tiktaalik roseae. Here we narrow it further by presenting the skull, exceptionally preserved braincase, shoulder girdle and partial pelvis of Ventastega curonica from the Late Devonian of Latvia, a transitional intermediate form between the ‘elpistostegids’ Panderichthys and Tiktaalik and the Devonian tetrapods (limbed vertebrates) Acanthostega and Ichthyostega. Ventastega is the most primitive Devonian tetrapod represented by extensive remains, and casts light on a part of the phylogeny otherwise only represented by fragmentary taxa: it illuminates the origin of principal tetrapod structures and the extent of morphological diversity among the transitional forms.