The Devonian period was one of the five subdivisions of the Paleozoic Era. This period saw a great number of geological and biodiversity changes across the planet. It lasted approximately 56 million years and witnessed the development of diverse animal groups, especially those in marine habitats. There were also changes in the habitats of terrestrial animals, with the appearance of large plants and the first land animals. Devonian fauna was known for being the most diverse in the world. However, this period is also infamous for an extinction event in which more than 80% of species disappeared.
Therefore, we are going to dedicate this article to tell you everything you need to know about the Devonian fauna.
Devonian fauna development
This period was perfect to develop life. And it is that the temperatures were more pleasant during this time and allowed a good development of the fauna and flora. All the seas existing in this period had a high standard of living. And it is that in the oceans those most primitive species such as sponges could develop. Siliceous sponge species began to appear and by flourishing on coral reefs they were able to develop different adaptations. Siliceous sponges have a greater resistance to environmental conditions and the presence of predators.
Coral reefs and benthic algae also played a fundamental role in the development of ocean morphology . A large reef at that time stretched for thousands of kilometers, enclosing an entire continent. The Devonian fauna underwent one of the greatest changes in aquatic ecosystems with the appearance of nektonic animals. Many of these new animal species were predators.
When there is a new development of a species or adaptation to the environment, pressure is exerted on the trophic chain. That is, if there are new predators that hunt their prey, it promotes a new behavior in the species that need to flee and escape these situations alive. This translates into a period of evolution and adaptation to new conditions that generates a diversification of the genes of animals and plants.
In aquatic ecosystems, we have also seen the diversification of mollusks, leading to the appearance of the first ammonoids. These ammonoids evolved from nautiloids during the Early Devonian period. Nautiloids persisted, although with less diversity and abundance.
Aquatic Devonian fauna
In freshwater habitats, bivalves began to proliferate and invade. At that time, trilobites began to decline gradually, although new life forms continued to appear. Some trilobites were quite large. Meanwhile, eurypterid arthropods continued to be a significant group of predators.
During this expansion, the aquatic fauna of the Devonian underwent significant changes in fish growth. Placoderms and sharks, both bony fish and sarcopterygians, were particularly prominent, and it was from these that terrestrial vertebrates, such as ray-finned fish, were derived. This latter group is now predominant in the seas. Some scientists refer to the Devonian fauna as the Age of Fishes. This is due to the abundance of diverse and well-preserved fossils of these fish, many of them found in freshwater lake deposits.
Coelacanths already existed during this time. In the middle of the Devonian period, placoderms began to outcompete ostracoderms. This led to the emergence of Ichthyostega and Acanthostega from the sarcopterygian lineage. These two genera are linked to the transition from fish to tetrapods. This historical transition occurred during the transition between the Devonian and Carboniferous periods.
One of the major questions surrounding these fish is whether they were freshwater or marine. This uncertainty arises because many freshwater fish have been found in deposits of ancient red sandstone. This terrestrial area was formed by the closure of the Iapetus Ocean. This is the main reason for the doubt about whether these fish were freshwater or marine. The earliest records of these fish come from marine environments, although most are Silurian freshwater fish. From there, different groups of fish emerged.
Colonization of the land
Another key feature that makes Devonian fauna stand out is the colonization of land. During the Silurian period , arthropods likely invaded the land. However, the earliest evidence comes from the Lower Devonian Rhynie Chert formation in Scotland. This deposit preserves a whole community of plants and arthropods that provided valuable information about the early ecology of the first terrestrial environments.
Numerous plant species helped arthropods, including scorpions, mites, and winged insects, to thrive in a suitable ecosystem. Marine and freshwater arthropods had to evolve to terrestrial environments thanks to the development of air respiration . However, it is difficult to establish a more accurate sequence of arrival of mites, scorpions, and centipedes to the terrestrial ecosystem based solely on the fossil record. All of these arthropods have remarkably diverse descendants today, which have adapted to a wide range of environmental conditions, thanks in part to the development of vascular plants.
Before the appearance of vertebrates, the entire primitive world was populated by arthropods. There is a certain amount of controversy that continues to rage in the scientific world regarding the moment when vertebrates ventured out of the water and the reasons that led them to do so. It must be admitted that it is difficult to imagine that an animal that lives in a marine ecosystem would end up developing adaptations to an environment in which it has not lived and does not need to live.
I hope that with this information you can learn more about the Devonian fauna.