In paleontology, organisms could leave petrified remains known as trace fossils, which record their biological activity without preserving the organism's remains. Also known as ichnofossils, these remnants include animal tracks, burrows, and resting traces, which could be found in the exact location as body fossils.
New Fossil Resting Trace
A group of experts in the Riley Formation of central Texas discovered a new type of trace fossil from the middle Cambrian period (500 million years ago). It is slightly younger than the famous Burgess Shale Fauna in Canada and reveals the life conditions in tidal settings of this time.
The prehistoric animal that produced the fossil was around 6 cm (2.36 in) long and belonged to a group of crustaceans known as phyllocarids. They are the distant ancestors of crabs and lobsters and were probably like their earliest kind, called Arenosicaris, found in Wisconsin around that time.
The fossil resting trace consists of small isolated traces on the underside of a sandstone slab, composed of imprints of the arthropod's tail spines, abdomen, gill plates, walking legs, and antennae. It was named Minterichnus shieldi after Dr. Nicholas Minter, who researched trace fossils, and Mr. Elgean Shield, who discovered the fossil in 1937.
The fossil shows ancient behavior where animals get trapped in a tidal pool before establishing themselves on land. This transition is considered an important stepping stone in the evolution of life.
Tidal pools used to be occupied by languid brachiopods, worms, and stranded dying phyllocarids, while dendroid graptolites and trilobites inhabited the deeper tidal channels.
The ancestors made the oldest tracks on dry land of millipedes, known as euthycarcinoids, on ancient coastal dunes and tidal flats around the same time. Meanwhile, mollusks, euthycarcinoids, and phyllocarids all left traces on ancient tidal flats half a billion years ago. They represent the precursors of mollusks, millipedes, and terrestrial crustaceans.
From Aquatic to Terrestrial Life
One of the crucial evolutionary changes in vertebrate history is the water-to-land transition, which occurred during the Palaeozoic Era about 419-359 million years ago. It enabled key morphological and physiological modifications in most animal species.
Scientists widely accept that all life on Earth started underwater. However, around 400 million years ago, some vertebrates, like fish, began to develop limbs and other characteristics that allowed them to explore life on land. One of the most vital features that evolved was the lungs, which gave vertebrates the ability to breathe above water.
The reason why marine animals went onto land remains a mystery to this day. Some scientists suggest that this could be a way to escape predators or at least lay eggs in a safer place. Another possibility is the presence of new food sources that the animals were trying to access.
For marine vertebrates to survive terrestrial life, they need to overcome some challenges. They should not only be able to breathe, but they must also be able to withstand the effects of gravity. Additionally, they should minimize water loss and adjust their senses to suit them for air instead of water. These adjustments helped shape the morphology of ancient vertebrates, which can be observed in the evolution of their body parts.
RELATED ARTICLE: Ancient Trilobites Grew and Aged Like Modern Crustaceans
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