The new digital fossil-mining technique (right) revealed fossilised squid beaks that remain hidden on conventional CT scans. PHOTO: SHIN IKEGAMI
Squid had already established themselves in the marine ecosystem long before their armoured relatives – the ammonites – left the world stage following the meteorite impact.
Not after the meteorite impact, but already 100 million years ago, squid were ecologically dominant in the marine environment. That is the conclusion of Japanese researchers who used new digital techniques to uncover hundreds of squid fossils (Science, 26 June). Until now, it was assumed that this group only flourished after the mass extinction 66 million years ago, when ammonites and belemnites vacated the scene.
The new method – digital fossil-mining – works by grinding rock away layer by layer, scanning each micro-layer before it is destroyed. This allows researchers to create a kind of digital 3D copy of the interior of the rock. In this case, the technique yields images of chitin structures that were previously almost impossible to extract from rock. In total, 263 fossilised squid beaks came to light, distributed across 40 species, 23 genera and 5 families.
TENTACLES
The fossils belong to two main groups of squid: the so-called Oegopsida, species that live primarily in open and deeper waters and often bear hooks or rough suckers on their tentacles, and Myopsida, which occur mainly in shallow coastal waters and generally have smooth suckers. The material shows that these two groups were already undergoing rapid adaptive radiation some 100 million years ago. The morphological variation among early Oegopsida points to rapid evolutionary change, with some forms possessing structural features that later disappeared. The earliest Myopsida, by contrast, already closely resemble modern species, with characteristics that are largely consistent.
Until now, the oldest known occurrences of Oegopsida and Myopsida dated from the Late Cretaceous and the Eocene respectively, but this study pushes those dates back by 15 and 55 million years respectively. At that time, squid were probably already dominant in the marine environment: their fossil remains outnumber those of ammonites and bony fish in the same deposits.
HUNTERS
Whilst the fossil record of ammonites and belemnites is rich, soft-bodied squid leave almost no trace. This is partly why it was long thought that these fast, intelligent hunters only seized their opportunity after the extinction of ammonites and belemnites. This study suggests precisely the opposite: soft-bodied squid had already begun to displace their armoured relatives long before the meteorite impact.
See also:
–Video on the digital detection of fossils in rock. Facebook Science,