Heart fossilization is possible and informs the evolution of cardiac outflow tract in vertebrates
Thus petrified resin — amber — occasionally contains the perfectly preserved fossils of various organisms, understandably primarily tiny arthropods. Microfossils constitute a special category; these are the fossilized remains of microscopic organisms, mostly algae and blue-green algae, which have even been found in the oldest rocks which, through a combination of happy coincidences, were not exposed to high pressures and temperatures during their geological history and were thus not metamorphosed.
Sensitive microanalytical methods even allow detection of the presence of substances of biological origin in these microfossils and thus confirm that these not always morphologically differentiated structures actually correspond to the fossilized remains of unicellular organisms. The absolute age of fossils and the surrounding rocks can be determined by physical methods, most frequently by determining the ratio of radioactive isotopes and their decomposition products.
Understandably, the results of this dating are accompanied by a statistical error, frequently of orders of a percentage point for modern methods.
In practice, relative dating by the stratigraphic correlation method is employed, based on the two Lyellian principles: on the superposition principle under normal circumstances, older layers are located lower down than younger layers and the leading fossils principles layers containing the same leading fossils are of the same age. This approach utilized the ability to differentiate layers of the same age on the basis of common physical, chemical, lithological or paleontological features.
They are used most frequently for differentiating the same age of layers of paleontological features, specifically the occurrence of the same leading index fossils , i.
The absolute age of individual layers defined on the basis of leading fossils is generally at least approximately known, as it has been possible to quite exactly date a number of boundaries between layers using a number of direct physical methods. Because of the error accompanying absolute dating, relative dating using leading fossils is usually more sensitive, i. The scanning picked up a signal for keratin, the same material that makes up fingernails in humans. Keratin, as it turns out, is a crucial part of what makes the hagfish slime defense so effective.
Hagfish have a series of glands along their bodies that produce tiny packets of tightly-coiled keratin fibers, lubricated by mucus-y goo.
Why are fossilized hairs so rare? -- ScienceDaily
When these packets hit seawater, the fibers explode and trap the water within, turning everything into shark-choking slop. The fibers are so strong that when dried out they resemble silk threads; they're even being studied as possible biosynthetic fibers to make clothes and other materials. Miyashita and his colleagues found more than a hundred concentrations of keratin along the body of the fossil, meaning that the ancient hagfish probably evolved its slime defense when the seas included fearsome predators such as plesiosaurs and ichthyosaurs that we no longer see today.
Features of the new fossil help place hagfish and their relatives on the vertebrate family tree. In the past, scientists have disagreed about where they belonged, depending on how they tackled the question. Those who rely on fossil evidence alone tend to conclude that hagfish are so primitive that they are not even vertebrates. This implies that all fishes and their vertebrate descendants had a common ancestor that -- more or less -- looked like a hagfish.
- The Fossil Record as Evidence for Evolution.
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- Darwin’s “Extreme” Imperfection? | SpringerLink.
- 1. Introduction.
- Fossilized slime of 100-million-year-old hagfish shakes up vertebrate family tree;
But those who work with genetic data argue that hagfish and lampreys are more closely related to each other. This suggests that modern hagfish and lampreys are the odd ones out in the family tree of vertebrates.
Frozen plasticity theory
In that case, the primitive appearance of hagfish and lampreys is deceptive, and the common ancestor of all vertebrates was probably something more conventionally fish-like. Miyashita's work reconciles these two approaches, using physical evidence of the animal's anatomy from the fossil to come to the same conclusion as the geneticists: that the hagfish and lampreys should be grouped separately from the rest of fishes.
Although they're still part of vertebrate biodiversity, we now have to look at hagfish and lampreys more carefully, and recognize their apparent primitiveness as a specialized condition. Paleontologists have increasingly used sophisticated imaging techniques in the past few years, but Miyashita's research is one of a handful so far to use synchrotron scanning to identify chemical elements in a fossil. While it was crucial to detect anatomical structures in the hagfish fossil, he believes it can also be a useful tool to help scientists detect paint or glue used to embellish a fossil or even outright forge a specimen.
Any attempt to spice up a fossil specimen leaves chemical fingerprints that light up like holiday decorations in a synchrotron scan.
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Materials provided by University of Chicago Medical Center. Original written by Matt Wood.
Note: Content may be edited for style and length. Science News. The slimy dead giveaway Modern-day hagfish are known for their bizarre, nightmarish appearance and unique defense mechanism. ScienceDaily, 21 January