/* */ Rosa Rubicondior: Evolution News - How Lizard's Teeth Fatally Bite Creationism

Monday, 18 October 2021

Evolution News - How Lizard's Teeth Fatally Bite Creationism

3D reconstruction of the skull of an Amazon racerunner (Ameiva ameiva) captured through an X-ray micro-CT scan. Complex teeth with multiple tips ("cusps") are visible on the jaws. This feature—also seen in the dentition of early mammals—evolved many times in independent lizard groups.
Image: Fabien Lafuma
Plant-eating lizards on the cusp of tooth evolution | University of Helsinki

A couple of Creationist articles of faith have taken a beating with another biology paper that refutes them without even trying, as usual. This time it is the evidence of transition from simple to complex teeth in multiple lineages of lizard in response to the advantages that a vegetarian diet had over an insectivorous diet, and then the evidence that this evolution towards increasing complexity sometimes went into reverse.

This reversal is contrary to creationist dogma that says evolution always involve increasing complexity and new information and that any loss of information (and so loss of complexity) is invariably detrimental.

The paper is by a team of researchers from the Universities of Helsinki and Lyon and the Geological Survey of Finland, led by associate professor, Nicolas Di-Poï of the Institute of Biotechnology, University of Helsinki, and is published open access in Nature Communications. The Helsinki University news release explains:
Tooth shape is closely linked with diet

The teeth of squamates have received limited attention, even though they twice outnumber mammals in species numbers, and span many habitats and geographic ranges.

Professor Nicolas Di-Poï, co-author
Associate Professor
Institute of Biotechnology,
University of Helsinki, Finland
Scientists have richly documented the connection of tooth shape and diet in mammals, showing very diverse teeth fuelled their evolutionary success. But what about other toothed animals? The authors chose to study squamates, the group including lizards and snakes. “The teeth of squamates have received limited attention, even though they twice outnumber mammals in species numbers, and span many habitats and geographic ranges”, remarks Nicolas Di-Poï, Associate Professor at the Institute of Biotechnology, University of Helsinki.

The researchers performed comparative analyses on tooth shape and diet data for more than 500 living and fossil species. They found the ancestor to all snakes and lizards had simple peg-like teeth and fed on insects. Later, complex teeth bearing multiple cusps—similar to those of early mammals—evolved multiple times independently in different lizard lineages. The appearance of multiple-cusped teeth allowed some lizard groups to evolve more plant-rich diets, sometimes leading to even more complex teeth.

Lizards’ teeth evolution took two directions

This [loss of tooth complexity] came as a complete surprise, as complex teeth appear as a critical innovation for both squamates and mammals.

This work gives us a more nuanced understanding of how the same critical adaptation evolved in different vertebrate groups.

Fabien Lafuma, co-author
PhD candidate
University of Helsinki, Finland
The team also found that complex teeth and plant consumption provided an evolutionary advantage, as both traits favoured the appearance of new species. However, many lizard lineages also lost complex teeth to re-evolve the ancestral simple tooth morphology. “This came as a complete surprise,” says PhD candidate Fabien Lafuma from the University of Helsinki, “as complex teeth appear as a critical innovation for both squamates and mammals.”

The study suggests that all land-living vertebrates experience the same selective pressures for more cusps to increase plant consumption. Nevertheless, fundamental differences make squamates stand out. Contrary to mammals, tooth evolution was not unidirectional, and numerous lineages reduced complexity over time. This difference could stem from variations in tooth development, showing that minor molecular changes may produce widely different outcomes over evolutionary time scales. Lafuma concludes, “this work gives us a more nuanced understanding of how the same critical adaptation evolved in different vertebrate groups.”
In the abstract to their published findings, the team say:

Teeth act as tools for acquiring and processing food, thus holding a prominent role in vertebrate evolution. In mammals, dental-dietary adaptations rely on tooth complexity variations controlled by cusp number and pattern. Complexity increase through cusp addition has dominated the diversification of mammals. However, studies of Mammalia alone cannot reveal patterns of tooth complexity conserved throughout vertebrate evolution. Here, we use morphometric and phylogenetic comparative methods across fossil and extant squamates to show they also repeatedly evolved increasingly complex teeth, but with more flexibility than mammals. Since the Late Jurassic, multiple-cusped teeth evolved over 20 times independently from a single-cusped common ancestor. Squamates frequently lost cusps and evolved varied multiple-cusped morphologies at heterogeneous rates. Tooth complexity evolved in correlation with changes in plant consumption, resulting in several major increases in speciation. Complex teeth played a critical role in vertebrate evolution outside Mammalia, with squamates exemplifying a more labile system of dental-dietary evolution.

So, there we have clear evidence in the fossil record of the evolution of simple to complex teeth and sometimes complex to simple teeth in multiple lineages of lizard, in response to environmental change and opportunity, examples of convergent evolution in different lineages in response to the same environmental factors, and examples of evolution by loss of complexity when that was advantageous in the prevailing environment.

And of course the biologist involved, like all other biologists and in contrast to claims by the Deception Institute that the TOE is a theory in crisis, are in no doubt that the underlying mechanism of this change is evolution by natural selection, just as Darwin and Wallace described it.

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