365-million-year-old fish with extreme underbite demonstrates vertebrate diversity

Alienacanthus is a member of an extinct group of fish called placoderms

Vertebrates are defined as all animals that possess a backbone, or backbone. Most living vertebrates also possess jaws, teeth, and pairs of fins or limbs.

Fossils from the earliest vertebrates can help us understand not only how these traits originated, but also how they evolved and diversified over time.

our study, Published in Royal Society Open Scienceexamined a 365-million-year-old fossil of a fish with the world’s longest underbite, called Markoski’s heterocanthus. These fossils illustrate the diversity of jawed vertebrates early in their evolution.

Heterocanthus is a member of an extinct group of fish called placoderm, which are some of the earliest jawed vertebrates. They are armored fish that come in all shapes and sizes and are crucial to understanding the evolution of vertebrates and their features, especially jaws and teeth.

Together, placoderm jaws and teeth preserve evidence of feeding strategies and diets, giving us insight into what and how some of our fish ancestors ate.

from spine to chin

In 1957, Polish paleontologist Julian Kulczycki Description of fossil fish From the Holy Cross Mountains in Poland. Among the finds were two long, thin, partially broken bones that he believed were some strange-looking fin spines from a fish. The strange shape of the so-called spines gave the animal its name, Heterocanthus.

In the late 1990s and early 2000s, members of our research team discovered a number of Moroccan specimens containing the same skeletal elements in the collection of the National Museum of Natural History in Paris. The team later discovered more specimens from Poland and Morocco, which we confirmed were placoderms.

Heterocanthus Has a huge round head, pointed nose and big eyes. What Kurtsky thought was the spur turned out to be the lower jaw, which, unlike the upper jaw, extends to the closure of the mouth. The teeth are sharp, slightly curved back to capture live prey, and continue to extend after the mouth is closed.

Unlike other placoderms, the upper jaw of placoderms Heterocanthus Being able to make slight movements independently of the skull helps accommodate the jaw.

most extreme case

elongated lower jaw HeterocanthusIts skull is twice as long as that of placoderms, making it unique among placoderms and extremely rare among other living and fossil groups.In most animals, mandibular protrusion occurs on the upper jaw, as swordfishor both the upper and lower jaws look like Ichthyosaur or gharial.

Among extant species, there is only one tiny fish called half beak Displays an elongated lower jaw.The length of the half beak is only 5 to 10 cm; HeterocanthusThe head and chin alone reach 80 centimeters. The relative length of the lower jaw is also 20% longer than the half beak.

Heterocanthus It also holds the title of the oldest case of mandibular lengthening.The previous record belonged to a shark from 310 million years ago avian prions.

the age of fish

Heterocanthus and while relatives are living there Devonian (358 to 419 million years ago), also known by paleontologists as fish age.During this period, various fish species dominated the oceans, including shark, bony fish, jawless fish and placoderms, which together display a variety of body, head, and jaw shapes.

Heterocanthus Taking diversity to the extreme with such a unique look. Fifteen million years after this animal appeared, the placoderm became extinct.

The evolution of more complex jaws allowed for a wider range of feeding and hunting methods.The oldest placoderm preference quick closing mouth Used to capture prey.But some placoderms start Feeds on hard-bodied animals with hard shells and exoskeletonsothers may have filter feeders.

Heterocanthus Used its sharp teeth to capture and trap live prey, and may have used its elongated jaws to confuse or injure future prey, such as swordfish and some ichthyosaurs.

Learn more

The farther we travel, the more different the Earth’s continents look.In the late Devonian period, when Heterocanthus Poland is located on the northeastern coast, and Morocco is located on the southern shore of the vast ocean. The presence of the same species at both ends suggests that migrations took place in the ocean at that time, despite fluctuations in sea levels.

Heterocanthus This is just one of many recent discoveries from the late Devonian period in Poland and Morocco. These findings suggest that sediments from this age still have high potential to reveal important insights about early vertebrates.

(author: Melina Jobbins, researcher in evolutionary biology at the University of Zurich; Christian Klug (Professor at the University of Zurich and Director of the Museum of Paleontology) Martin Rücklin (Research Group Leader of the Naturalis Biodiversity Center at Leiden University and Senior Researcher at the Leiden Institute of Biology)

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