In an ecosystem, the strongest links between species are often dietary. A food chain is a sequence of living beings in which each individual consumes its predecessor. The first link in the chain is usually a chlorphyllous (photosynthesizing) plant. In seas and oceans, phytoplankton plays this role.

Many clues allow paleontologists to reconstruct the links in the Miguasha estuary food chain, all the way from plant material and aquatic microorganisms to large predators.

Animal types, fish anatomy, stomach contents and fossilized excrement all provide insight into predators and their prey, and the mode of life for each of these species.

At the top of the food chain are bacteria that decompose organisms after they die. Numerous concretions in the Escuminac Formation contain organic remains, sometimes whole fish, and are thought to have formed as the result of bacterial metabolism.
In an ecosystem, the strongest links between species are often dietary. A food chain is a sequence of living beings in which each individual consumes its predecessor. The first link in the chain is usually a chlorphyllous (photosynthesizing) plant. In seas and oceans, phytoplankton plays this role.

Many clues allow paleontologists to reconstruct the links in the Miguasha estuary food chain, all the way from plant material and aquatic microorganisms to large predators.

Animal types, fish anatomy, stomach contents and fossilized excrement all provide insight into predators and their prey, and the mode of life for each of these species.

At the top of the food chain are bacteria that decompose organisms after they die. Numerous concretions in the Escuminac Formation contain organic remains, sometimes whole fish, and are thought to have formed as the result of bacterial metabolism.

© Miguasha National Park 2007

<i>A conchostracan</i>

Conchostracans are small crustaceans protected by thin valves of chitin. These tiny creatures were a dietary staple for many fish in the ancient Miguasha estuary.

Miguasha National Park

© Miguasha National Park 2007


The waters of the ancient Miguasha estuary were overflowing with fish, some of them predators, some prey, some both. By studying the anatomy of fish fossils, it is possible to establish which role each type of fish played in this past environment.

The best evidence for determining predation is dentition: the number, kind and arrangement of teeth or tooth-like structures in vertebrates. For example, the actinopterygian Cheirolepis had many sharp teeth, the characteristic mark of a predator, as did sarcopterygians Miguashaia, Eusthenopteron, Quebecius and Holoptychius, and the elpistostegalian Elpistostege. Eusthenopteron in particular must have been one of the most fearsome of these predatory fish, with its hydrodynamic body and strong fins. The sword-like “razor blades” in the jaw of the placoderm Plourdosteus also indicate a carnivorous nature despite the absence of sharp teeth.

Direct evidence of predator–prey relationships may be obtaine Read More
The waters of the ancient Miguasha estuary were overflowing with fish, some of them predators, some prey, some both. By studying the anatomy of fish fossils, it is possible to establish which role each type of fish played in this past environment.

The best evidence for determining predation is dentition: the number, kind and arrangement of teeth or tooth-like structures in vertebrates. For example, the actinopterygian Cheirolepis had many sharp teeth, the characteristic mark of a predator, as did sarcopterygians Miguashaia, Eusthenopteron, Quebecius and Holoptychius, and the elpistostegalian Elpistostege. Eusthenopteron in particular must have been one of the most fearsome of these predatory fish, with its hydrodynamic body and strong fins. The sword-like “razor blades” in the jaw of the placoderm Plourdosteus also indicate a carnivorous nature despite the absence of sharp teeth.

Direct evidence of predator–prey relationships may be obtained by examining stomach contents. We know, for example, that acanthodians like Homalacanthus were the prey of large predators, such as Eusthenopteron, and that the latter would sometimes take part in cannibalistic practices, as did another actinopterygian, Cheirolepis.

Prey may also be identified by examining the contents of fossilized excrement known as coprolites. For example, the abundance of acanthodian scales and spine fragments in coprolites reveal that these little fish, the most abundant in the waters of the Miguasha paleoestuary, were the preferred food of other fish.

The growing list of known species in fossilized excrement suggests that most Miguasha fish species were, at one time or another, the prey of a larger predator. Together with the evidence from stomach contents, which indicates that the most ravenous of these fish went as far as to eat fellow creatures of the same species, one can’t help but imagine the Miguasha paleoestuary as an aquatic “Jurassic Park”!

© Miguasha National Park 2007

<i>Eusthenopteron foordi</i>

It was during the Devonian Period that sarcopterygian fish gave rise to the first terrestrial vertebrates. Eusthenopteron foordi (shown here) was long thought to be the transitional animal between fish and tetrapods, sharing features with both, but recent discoveries have shown that the elpistostegalians are even more closely related to four-legged vertebrates.

Jean-Pierre Sylvestre
2003
© Miguasha National Park


The predator Eusthenopteron foordi

The small acanthodians of the ancient Miguasha estuary were the prey of choice for the powerful sarcopterygian Eusthenopteron foordi.

Illustration by François Miville-Deschênes
2003
© Miguasha National Park


It happened from time to time that fish died with a full stomach at Miguasha and their last meal became fossilized with the rest of their remains. These uncommon discoveries not only tell us about a predator’s preferred prey, they also provide valuable information about the anatomy of its digestive system.

Some predatory fish have been found with whole prey in their abdominal cavity, the most astounding example being a 19-cm long Homalacanthus in the belly of a 46-cm long Eusthenopteron. Swallowed head first, the Homalacanthus accounts for 40% of the predator’s body length, indicating the great extent to which its digestive tract could expand. Although impossible to know for certain, the death of this predator may have been due to the enormous size of its meal!

Some species apparently did not hesitate to eat smaller members of their own kind. For example, a Cheirolepis was found within the abdomen of another Cheirolepis, and two Read More
It happened from time to time that fish died with a full stomach at Miguasha and their last meal became fossilized with the rest of their remains. These uncommon discoveries not only tell us about a predator’s preferred prey, they also provide valuable information about the anatomy of its digestive system.

Some predatory fish have been found with whole prey in their abdominal cavity, the most astounding example being a 19-cm long Homalacanthus in the belly of a 46-cm long Eusthenopteron. Swallowed head first, the Homalacanthus accounts for 40% of the predator’s body length, indicating the great extent to which its digestive tract could expand. Although impossible to know for certain, the death of this predator may have been due to the enormous size of its meal!

Some species apparently did not hesitate to eat smaller members of their own kind. For example, a Cheirolepis was found within the abdomen of another Cheirolepis, and two Eusthenopteron were observed inside two larger individuals. These are undoubtedly among the oldest cases of vertebrate cannibalism.

Stomach contents in the dipnoan fish Scaumenacia are also quite telling. It fed primarily on small invertebrates, with up to thousands of the small crustacean Asmusia – apparently the only species ever ingested – in its digestive tube.

Even in the absence of stomach contents, the outlines of digestive systems are sometimes visible in the agnathans Euphanerops and Endeiolepis, and the sediment-filled digestive system has been preserved in the form of a cast in several specimens of Bothriolepis. With a ventrally positioned mouth, Bothriolepis fed itself by filtering mud at the bottom of the estuary, and a belly full of sediment helped fossilize its intestinal system. Internal casts, observable in some Bothriolepis specimens once cut into sections, display a concentric spiral like that observed in the intestines of modern day sharks, and is considered to be primitive gnathostome (jawed fish) morphology. Plant fragments in the cololite of a Bothriolepis specimen suggest that plants may have been part of its diet. Cololites are petrified intestinal contents, and the word comes from the Greek kolon for intestine, and lithos for rock.

© Miguasha National Park 2007

The tiny conchostracan Asmusia in the belly of a Scaumenacia specimen

The tiny chitin valves of Asmusia are sometimes found by the thousands in the stomachs of Miguasha fish. In this example, a big Scaumenacia – a dipnoan fish – ingested a gargantuan meal of the little crustaceans. The small valves are visible under the scales and strong bones that cover its abdomen.

Miguasha National Park
2003
© Miguasha National Park


Any biologist will tell you that an easy way to know what an animal ate is to analyze its excrement. Excrement can be fossilized, and there is a lot of it in the Escuminac Formation! Fossilized excrement is called coprolite, from the Greek kopros for excrement, and lithos for stone.

Often in the shape of thin cylinders, the longest coprolites in the Escuminac Formation are more than 7 cm in length, with a diameter of 1.5 cm. The analysis of these remains, even if it is impossible to determine what animal left them, offers valuable information about the relationships between the ancient animals that lived at Miguasha. Most of the coprolites discovered thus far are pieces of acanthodians (scales, spines and bone fragments). By measuring the scales, paleontologists have discovered that there was a certain preference for prey based on size: individuals measuring 10 to 20 cm long had the greatest risk of being consumed, while those shorter than 10 cm, or longer than 20 cm, were generally spared.

Again according to coprolites, the second most commonly preyed upon group was the sarcopt Read More
Any biologist will tell you that an easy way to know what an animal ate is to analyze its excrement. Excrement can be fossilized, and there is a lot of it in the Escuminac Formation! Fossilized excrement is called coprolite, from the Greek kopros for excrement, and lithos for stone.

Often in the shape of thin cylinders, the longest coprolites in the Escuminac Formation are more than 7 cm in length, with a diameter of 1.5 cm. The analysis of these remains, even if it is impossible to determine what animal left them, offers valuable information about the relationships between the ancient animals that lived at Miguasha. Most of the coprolites discovered thus far are pieces of acanthodians (scales, spines and bone fragments). By measuring the scales, paleontologists have discovered that there was a certain preference for prey based on size: individuals measuring 10 to 20 cm long had the greatest risk of being consumed, while those shorter than 10 cm, or longer than 20 cm, were generally spared.

Again according to coprolites, the second most commonly preyed upon group was the sarcopterygians, although the small size of the scales suggests that only young individuals were eaten. Next on the menu came the actinopterygians, followed by Asmusia. The latter was a small crustacean, and although seldom seen in coprolites, it appears to have been consumed by predators of all sizes, as attested by the presence of its little valves in excrement big and small. It seems that everyone enjoyed a little sprinkling of Asmusia now and then!

© Miguasha National Park 2007

Coprolithe

A coprolite from the Escuminac Formation. The top image shows several dark bone fragments (vertical bar is 1 cm). The lower image is an enlarged portion of the same coprolite in which scales of the actinopterygian Cheirolepis canadensis are visible (arrows).

Miguasha National Park
2007
© Miguasha National Park


Learning Objectives

The learner will:
  • identify and classify different types of fossils;
  • explain the stages of fossilization and the best conditions to create and preserve fossils;
  • make assumptions about the evolution of living beings;
  • make assumptions as to the explanation of the disappearance of some species.

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