{"id":144,"date":"2008-07-16T15:00:08","date_gmt":"2008-07-16T03:00:08","guid":{"rendered":"https:\/\/blog.waikato.ac.nz\/bioblog\/2008\/07\/a_very_early_tetrapod_indeed_1\/"},"modified":"2008-07-16T15:00:08","modified_gmt":"2008-07-16T03:00:08","slug":"a-very-early-tetrapod-indeed-1","status":"publish","type":"post","link":"https:\/\/blog.waikato.ac.nz\/bioblog\/2008\/07\/a-very-early-tetrapod-indeed-1\/","title":{"rendered":"a very early tetrapod indeed"},"content":{"rendered":"

\"Blogging<\/a>I’ve been fascinated by the story of early tetrapod evolution (where ‘tetrapod’ = an animal with 4 legs) for years, since reading Carl Zimmer’s wonderful book At the water’s edge <\/i>(1998). Our understanding of when & where tetrapods evolved has been steadily extended by a series of fossil finds, most recently the ‘fishapod’ Tiktaalik<\/a><\/i>. This was definitely a fish, but one where the fleshy base of its fin contained not only the familiar 1-2-many pattern of bones that we see in our own arms & legs but also a flexible wrist.<\/p>\n

And now… there’s Ventastega<\/a>. <\/i><\/p>\n

<\/p>\n

Ventastega<\/i>‘s a valuable find because it sits somewhere in the gap between the fish Tiktaalik<\/i> and the definitely tetrapodal Acanthostega <\/i> & Ichthyostega<\/i>. I say ‘somewhere’ because it’s obviously transitional, in the sense that it shows a mosaic of features (some more fish-like, some more like Acanthostega<\/i> & other early tetrapods, but Ahlberg & his colleagues note that Ventastega<\/i> doesn’t stand exactly between the two. It lived at roughly the same time as Acanthostega<\/i> (about 350 million years ago) & may represent a lineage that became extinct. This is in itself an exciting idea as it suggests that early tetrapods were actually a pretty diverse bunch of organisms, with several different lineages in existence at the same time.<\/p>\n

So what did this animal look like? The following images are from PZ Myer’s Pharyngula <\/a>article on Ventastega<\/i> (in turn, from the original Nature paper by Ahlbert et al<\/i>. cited below).<\/p>\n

\"\"A<\/p>\n

Ahlberg & his colleagues think that in life the animal was probably about 1m long. The top image shows the bones they’ve found, superimposed on an outline of Acanthostega<\/i>. They’ve done this because the skeletal similarities suggest that the two animals were fairly similar in form. (Look at that tail – it’s shape tells you that this is an animal that still spends a fair bit of time in the water.) The next row of images shows its skull, together with a reconstruction (the final row of pictures). This has a lot of bones in common with the earlier Tiktaalik <\/em>(likewise the fang-like teeth), but its overall shape is more similar to that of Acanthostega<\/em>.<\/p>\n

In addition to the well-preserved skull, there are also bones from the pectoral (shoulder) girdle and part of the pelvic girdle, and a bone which the team feels is likely to be from the animal’s tail. The pectoral girdle is similar to that of other early tetrapods & quite different from that of Tiktaalik.<\/i> On this basis, the research team conclude that the animal had limbs with digits. (I remember being quite excited, years & years ago now, when I first read – in Stephen Jay Gould’s book Eight Little Piggies<\/i> – that early tetrapods had more than the 5 fingers typical of modern tetrapods: nine, in the case of Acanthostega<\/i>.)<\/p>\n

So there you are: a lovely fossil that enhances our knowledge of a very early period in the evolution of terrestrial vertebrates (including ourselves) \ud83d\ude42<\/p>\n

P.E. Ahlberg, J.A. Clack, E. Luksevics, H. Blom & I. Zupins (2008) Ventastega curonica<\/u> and the origin of tetrapod morphology. Nature<\/u> 453<\/strong>: 1199-1204 <\/span> <\/span><\/cite> <\/p>\n

S.J. Gould (1993) Eight little piggies<\/u>. Norton.<\/cite><\/p>\n

C. Zimmer (1998) At the water’s edge: fish with fingers, whales with legs.<\/u> Touchstone.<\/cite><\/p>\n","protected":false},"excerpt":{"rendered":"

I’ve been fascinated by the story of early tetrapod evolution (where ‘tetrapod’ = an animal with 4 legs) for years, since reading Carl Zimmer’s wonderful book At the water’s edge (1998). Our understanding of when & where tetrapods evolved has been steadily extended by a series of fossil finds, most recently the ‘fishapod’ Tiktaalik. 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