Ventastega—not a leg to stand on
Published: 4 July 2008 (GMT+10)
Once more, fish-to-tetrapod evolution is getting its shot in the spotlight. Paleontologists have recently unearthed more bones of an ‘early tetrapod’ dubbed Ventastega curonica in the Upper Devonian (Upper Famennian) in Latvia, ‘dated’ to about 365 million years ago.1
Figure 1. Comparison of skull roofs of Tiktaalik to Acanthostega, Ichthyostega and Ventastega. From Ahlberg et al.,1 p. 1202.
Ventastega has been hailed as the latest transitional fossil, one that bridges the gap between Tiktaalik and Acanthostega. But is it all it’s cracked up to be?
A mean feat with no feet
Fins need to turn into weight-bearing limbs for fish-to-tetrapod evolution to work,2 and evolutionists have realised this, making extravagant claims about the supposed smooth transition of fins to limbs, particularly in Tiktaalik.3,4 So, for such publicity about a supposed transitional form between Tiktaalik and Acanthostega, where are the fins/feet of Ventastega? Nowhere to be found!
What was found? The researchers found parts of the shoulder and pelvis. However, Ventastega bears close relation to Acanthostega in these key areas, and from this they inferred that Ventastega’s limbs were similar to Acanthostega’s as well. So in perhaps the key point of transition between fish and tetrapods, Ventastega is completely tetrapod, as far as the evidence goes. So why do they claim Ventastega as a transitional fossil?
How not to get ahead
One does not look to the legs, but the head. They claim that the structure of the skull is intermediate between Tiktaalik and Acanthostega. In an analysis of the skull shape, the overall features, as interpreted by Ahlberg et al., place Ventastega slightly closer to Tiktaalik than Acanthostega in overall morphology (figure 1).
In many of the features of the skull deemed important for fish-to-tetrapod evolution, Ventastega clearly resembles, or is inferred to resemble, Acanthostega. For example, Ventastega is inferred to have a stapes (as in tetrapods), not a hyomandibula (as in fish, including Tiktaalik),5 and the brain case, lower jaw structure and spiracular architecture all resemble those of ‘early’ tetrapods and not Tiktaalik and lobe-finned fish.6 This does not deny that in some features, Ventastega resembles Tiktaalik the most. However, in most features Ventastega resembles either Acanthostega or Tiktaalik; it does not present any intermediate morphologies of its own. In most features deemed important for fish-to-tetrapod evolution, Ventastega has an early tetrapod morphology. Therefore, it is more likely that Ventastega is has an independent mosaic morphology, with most distinct relation to ‘early’ tetrapods.
Fossil fragment fog
The fragments dubbed Ventastega are not the remains of a single skeleton either; they were a compilation of several skeletons, as more than one set of a number of different bones were found.7 They were found in the same horizon, but they had to be inferred to be from the same taxon, rather than demonstrably from the same animal, as with Gogonasus. Therefore, the reconstruction is selective and interpretive, rather than straightforward.
It is easy to get lost in morphological analyses of fossil fragments if not careful. There is a far bigger issue lying behind these analyses though. The fundamental assumption of fish-to-tetrapod evolution is that it happened in mosaic and parallel fashion:
‘Major elements of the tetrapod body plan originated as a succession of intermediate morphologies that evolved mosaically and in parallel among sarcopterygians closely related to tetrapods, allowing them to exploit diverse habitats in the Devonian [emphases added].’8
The way Ventastega is described, it sounds like it had the head of Tiktaalik, and the body of Acanthostega (that is not necessarily true—see above). This describes a mosaic form, which merely has structures that can be found in more than one animal. This is not demonstrative of an evolutionary lineage, but is merely an attempt to fit unresponsive data into an evolutionary strait jacket, and claiming it as evidence for evolution.9,10
Also, there is limited information from fossils—soft parts are usually not preserved, and may not be transitional. This was shown in the recent discovery of Materpiscis attenboroughi (‘Mother fish of Attenborough’), which was fossilized while pregnant. So while this might have been called ‘transitional’ between fish and amphibians, its mode of reproduction was very different from that of the creatures it supposedly bridges—see The oldest pregnant mum not!
What’s a transitional fossil?
One of the many news items about this latest fossil find concludes with an interesting note from none other than Dr Neil Shubin, co-discoverer of the Tiktaalik fossil, and arch evopropagandist:
‘The earliest tetrapods probably evolved between 5 million and 7 million years before Tiktaalik, [Shubin] notes, and the new fossils will help researchers predict what those creatures would have looked like.’11
However, Tiktaalik is often listed as a transitional fossil, including by Shubin himself:
‘New discoveries of transitional fossils such as Tiktaalik make the distinction between fish and the earliest tetrapods increasingly difficult to draw [emphasis added].’
The problem here is that what is actually meant by the term ‘transitional fossil’ in these cases is not what popular parlance takes the term to mean. In popular understanding, a ‘transitional fossil’ is a fossil that is involved in a direct evolutionary lineage. In the case of Tiktaalik, people think it is the ancestor of all living tetrapods (i.e. a fish begat Tiktaalik begat a tetrapod).12 But then how did the grandson beget his own grandfather? This is very similar to the case of true birds, even possessing beaks, dated to well before their alleged feathered dinosaur ancestors.
However, as is plain from Shubin’s reasoning, this is not what he means by ‘transitional fossil’. He does not put Tiktaalik in any direct lineage between fish and tetrapods. Rather, he is saying that the morphology of Tiktaalik has some characteristics in common with lobe-finned fish, and others in common with ‘early’ tetrapods. Like all other claimed ‘transitional fossils’, Tiktaalik and Ventastega are mosaic forms, which provide no support for fish-to-tetrapod evolution because they are merely forcing resistant data into an evolutionary mould.
Ventastega, like other claimed ‘transitional fossils’, doesn’t stand up under scrutiny. Much information is lacking, especially the limbs, so the designation of transitional fossil is dubious even from the start. Ventastega is described as having a Tiktaalik-shaped head, and an Acanthostega-shaped body. This alone places it as a mosaic form, a creature with fully formed parts brought together from different animals, which itself creates a fully functional animal independent of others. However, even this is dubious, as Ventastega is by far more likely to be just another ‘early’ tetrapod like Acanthostega.
There has also been much equivocation in the literature on fish-to-tetrapod evolution on the definition of ‘transitional fossil’. What is meant in the scientific literature is not what is meant in popular speech. This serves to further confuse the public, and cause them to think that evolution is proved by this parade of ‘transitional fossils’. However, the parade is only convincing if the ‘transitional fossils’ label has a leg to stand on. Like Ventastega though, it doesn’t.
- Ahlberg, P.E., Clack, J.A., Lukševičs, E., Blom, H. and Zupinš, I., Ventastega curonica and the origin of tetrapod morphology, Nature 453:1199–1204, 26 June 2008. Return to text.
- Doyle, S., ‘Walking’ sharks—evolution in action? Journal of Creation 21(1):10–11, 2007. Return to text.
- Sarfati, J., Tiktaalik—a fishy ‘missing link’ , Journal of Creation 21(1):53–57, 2007. Return to text.
- Jaroncyk, R. and Doyle, S., Gogonasus a fish with human limbs? Journal of Creation 21(1):48–52, 2007. Return to text.
- Evolutionists believe that stapes, a middle ear bone, is a modified hyomandibula bone, and was modified to allow for hearing above water. Return to text.
- Ahlberg et al., ref. 1, p. 1199–1203. Return to text.
- Ahlberg et al., ref. 1, p. 1199. Return to text.
- Daeschler, E.B., Shubin, N.H. and Jenkins, F.A., Jr, A Devonian tetrapod-like fish and the evolution of the tetrapod body plan, Nature 440 (7085):757–763, 6 April 2006; p. 762. Return to text.
- Garner, P. The fossil record of early tetrapods: evidence of a major evolutionary transition? Return to text.
- ReMine, W.R., The Biotic Message, St Paul Science, St Paul, MN, pp. 289–290, 1993; see review by Don Batten, Journal of Creation 11(3):292–298, 1997. Return to text.
- Perkins, S., Fossil helps document shift from sea to land, Science News, 25 June 2008. Return to text.
- This is obviously only a simplistic representation because evolutionists would assume further transitional animals between a fish and Tiktaalik, and Tiktaalik and a hypothetical ‘tetrapod ancestor’. However, it is in principle a correct summary of a direct lineage. See also Woodmorappe, J., Does a transitional form replace one gap with two gaps? Journal of Creation 14(3):5–6, 2000. Return to text.