Thursday, October 8, 2009

Some far, far distant human relatives

Relatives mind. At this remove in time it is simply impossible to identify what was directly ancestral to us.

This goes for just a few million years ago, let alone tens of millions.

Henry Gee, a former editor of Nature, discussed this problem in his book Deep Time. That is, the impossibility of recovering any sensible narrative from the past.

Imagine a corridor stretching on into the far distance in front of you. On either side of it are doors. Millions of doors.

Each door leads to a room representing an extinct animal or plant, each representing a piece of the jigsaw puzzle of the history of life on Earth.

But as you go down the corridor and try one door after another you discover that, with very few and rare exceptions, they are all locked.

The fact is that the vast majority of what has ever lived on Earth is unknown to us and will never be known to us. Either they left no fossils to find or the fossils will never be found.

This is why you can't create narratives about this species evolving into that species and so on and so on.

All that we can confidently assert is that a lineage, however defined, had its antecedents in this or that group. But it is literally impossible to identify THE ancestor.

Thus we mammals can trace our ancestry back to the so-called mammal-like reptiles (yes I know, puritan systematists have rejected the term, but I think it is still useful).

So here are some of our far distant relatives, even if we don't know exactly where they lie in the family tree relative to us.

Synapsid skulls in lateral view. A, Cotylorhynchus, a Lower Permian caseid. B, Varanosaurus, a Lower Permian ophiacodontid. C, Dimetrodon, a Lower Permian sphenacodontid. D, Titanophoneus, an Upper Permian therapsid. Redrawn from B, Berman et al. (1995); C, Romer and Price (1940), and D, Orlov (1958). Abbreviations: An, angular; Ar, articular; Bc, braincase; D, dentary; E, epipterygoid; F, frontal; J, jugal; L, lacrimal; M, maxilla; N, nasal; P, parietal; Pm, premaxilla; Po, postorbital; Pof, postfrontal; Prf, prefrontal; Pt, pterygoid; Q, quadrate; Qj, quadratojugal; Sa, surangular; Sp, splenial; Sq, squamosal; St, supratemporal; T, tabular. Scale bars equal 1 cm.

Posted via email from Garth's posterous

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