Although we tend to think of fossils as mere rock casts, shadows of the organisms they once were, the fossil record is revealing that much more is preserved . For example, fossil bones still retain the microscopic structure of bone tissue . Sometimes even at the cellular level. And some sites of exceptional conservation have left us in awe. Or rather, fossilized. Here are a few truly exceptional fossils .
The central nervous system of Chengjiangocaris
Chengjiangocaris was a shrimp-like arthropod that lived during the Cambrian period, a whopping 520 million years ago . One of the specimens that have been found of this primitive arthropod revealed impressions of its central nervous system, formed by a ventral nerve cord that ran through the entire body and a series of ganglia, from which nerves departed, that controlled each pair of legs. It is without a doubt the oldest central nervous system that researchers have been able to observe. In fact, it is very rare for the soft tissues of any organism to fossilize. This occurs in a few sites, those called “ exceptional conservation ” or in German “konservat lagerstatten” . And this is one of them, the Chengjiang deposit in China. The preservation of this cord, ganglia and nerves has been in the form of carbon films, as confirmed by fluorescence microscopy.
El ichthyosaur Stenopterygius giving birth
Ichthyosaurs were the top predators of the ocean for much of the Mesozoic, the age of the dinosaurs. They showed an extreme adaptation to the aquatic environment, with a very hydrodynamic fusiform body that can resemble that of a tuna, a shark or a dolphin. Such was their aquatic adaptation, that they could no longer afford to return to the mainland to lay their eggs, as sea turtles do, for example. And since their young had to breathe air, they couldn’t lay their eggs in the sea, as fish do. Nature’s solution is ovoviviparism : the mother carried her eggs inside her, until they hatched, and gave birth to their young.
We know this thanks to such exceptional fossils as this one, which shows a Stenopterygius -an ichthyosaur that lived in the middle of the Jurassic in Europe- at the moment of giving birth to a young. In addition, this allows us to see that the calves left their mother “tail”, giving birth in a similar way to cetaceans . This makes it easier for the young to reach the surface to breathe as soon as they are born. These ichthyosaurs could reach 4 meters as adults.
The four-winged dinosaur Microraptor
In the late 1990s, the Lower Cretaceous paleontological site of Liaoning in China rose to prominence. It is an exceptional conservation site formed by the accumulation of sediments and volcanic ashes in an ancient lake, which trapped the flora and fauna of that paleoecosystem and preserved it in an exquisite way. The stars of this site are its feathered dinosaurs, discoveries thanks to which the image of dinosaurs has changed in recent years. And one of these wonderful dinosaurs is Microraptor gui . Several fossils have been recovered from this dinosaur and three species have been described. And the amazing thing is not only that it is feathered, but it reveals that it had two pairs of wings . That’s right, not only did they have remige feathers on their arms forming wings, but their hind legs also had them. Hence, it has been proposed that this dinosaur could be able to fly or at least glide with its two pairs of wings.
But the thing does not end there. The Microraptor specimen BMNHC PH881 is so well preserved that its study with a scanning electron microscope allowed us to observe its melanosomes , small organelles that carry pigments. The shape and proportions of these melanosomes, when compared with those of modern birds, have allowed us to reconstruct that this small dinosaur would be black with bluish iridescence . Who said color couldn’t be preserved in the fossil record?
The blade with “zombie” bites
The next exceptional fossil is a leaf of the mallow Byttnertiopsis daphnogenes found at the exceptional Eocene conservation site of Messel , Germany. This 48-million-year-old leaf may not be too conspicuous to the naked eye. In fact, not even the whole leaf is there, since it appears bitten. But seen in detail, it has revealed a whole history of that paleoecosystem.
In detail, it appears not only bitten at its edges. There are also some bites in its secondary nerves that closely resemble bites made by ant jaws. And, in fact, bites of this unusual type have now been described, carried out by ants in the secondary veins of leaves. And the culprit is a parasitoid fungus . The process is as follows: the Ophiocordyceps fungus infects the ant and, due to this infection, the ant ends up abandoning its colony, bites the nerve of the leaf, and never lets go, until it dies. The fungus continues to grow, eventually developing its fruiting body outside the ant’s body, from where it releases its spores. Ants infected by this fungus are called ” zombified ” and their bites are so characteristic that we can reconstruct that this same process already occurred in the Eocene of Messel.
The dividing cells of a Jurassic fern
In 2014, fern fossils from the Osmundaceae family from the Early Jurassic of Sweden were published in the journal Science. The fossil was specifically the stem and rhizomes of the fern, which had been calcified as a result of precipitation in a hydrothermal environment . This precipitation occurred so quickly that it allowed to preserve their tissues at the cellular level , being able to observe the cytoplasm, granules inside the cytosol, the cell nuclei and even the chromosomes in various stages of cell division . There are really few fossils – not of plants anymore, but in general – in which we can get to observe these cellular structures.
For decades we have marveled at the fossils of exceptionally well-preserved sites. But as you can see, these fossils are even more exceptional in light of the most advanced research techniques in paleontology. Thanks to these findings, we have a new picture of the fossil record, which is capable of preserving much more than we thought possible.
References:
Yang, J. et al. 2016. The fuxianhuiid ventral nerve cord and early nervous system evolution in Panarthropoda. PNAS, published online. doi: 10.1073/pnas.1522434113
Li, Q. et al. 2012. Reconstruction of Microraptor and the Evolution of Iridescent Plumage. Science. 335 (6073): 1215–1219.
Hughes, David P et al. 2011. Ancient death-grip leaf scars reveal ant-fungal parasitism. Biology letters, vol. 7,1: 67-70.
Bomfleur, B. et al. 2014. Fossilized nuclei and chromosomes reveal 180 million years of genomic stasis in royal ferns. Science, 343(6177):1376-7.
