Most jawless fish that thrived in the Silurian Period sported large bony shields on their head and trunk to protect them from predators. For this reason, the Greek root aspis, which means “shield”, is found in the names of some agnathan groups, such as the cephalaspids, arandaspis and galeaspids. The anaspids were an exception, however, and their name means “without a shield”.

Anaspids were a common group of jawless fish in Silurian time. Specimens measure 10 to 15 cm long and have only been discovered in regions that were once part of Euramerica. Unlike other agnathans, whose bodies were often flat, anaspids had a narrower and more slender body, closer to that of a “typical” fish. Their caudal fin (their tail) was strongly hypocercal, meaning that the lower lobe pointed downward and was larger than the upper lobe. This feature represents the extension of the fish’s notochord (the main axial support of the body) into the tail’s lower lobe.

Anaspids had 6 to 15 gill openings on either side of their body behind their mouths, a tri-radiate spine behind this series of openings, and median scales running along their Read More
Most jawless fish that thrived in the Silurian Period sported large bony shields on their head and trunk to protect them from predators. For this reason, the Greek root aspis, which means “shield”, is found in the names of some agnathan groups, such as the cephalaspids, arandaspis and galeaspids. The anaspids were an exception, however, and their name means “without a shield”.

Anaspids were a common group of jawless fish in Silurian time. Specimens measure 10 to 15 cm long and have only been discovered in regions that were once part of Euramerica. Unlike other agnathans, whose bodies were often flat, anaspids had a narrower and more slender body, closer to that of a “typical” fish. Their caudal fin (their tail) was strongly hypocercal, meaning that the lower lobe pointed downward and was larger than the upper lobe. This feature represents the extension of the fish’s notochord (the main axial support of the body) into the tail’s lower lobe.

Anaspids had 6 to 15 gill openings on either side of their body behind their mouths, a tri-radiate spine behind this series of openings, and median scales running along their backs. Current phylogenetic reconstructions closely link anaspids and ostracoderms to the first jawed vertebrates – the gnathostomes.

Two Miguasha fish species, Endeiolepis and Euphanerops, were traditionally classified as anaspids based on their general appearance (long body and hypocercal tail). This would make them the only known anaspids to appear in the Devonian Period. They had up to 30 gill openings and did not posses bony scales or spines. These differences compared to other anaspids make their evolutionary position debatable. Are they really anaspids or do they form a distinct group? Certain features of Miguasha’s “anaspids” are very comparable to those of modern lampreys. Euphanerops, Endeiolepis and lampreys, for example, all share the same gill type, and the histological structure of the internal cartilaginous elements is surprisingly similar.

Recently discovered Euphanerops specimens with finely preserved details have revealed new anatomical differences, many of which remain enigmatic. For the time being, the question of the true affiliation of Miguasha’s “anaspids” is unresolved. This is a story whose ending must read “To be continued...”

© Miguasha National Park 2007

<i>Euphanerops longaevus</i>

A specimen of Euphanerops with the impression of the long branchial basket visible on the ventral side of the animal. Also evident is the strongly downward-pointing axis of the tail (caudal fin).

Illustration from François Miville-Deschênes
1999
© Miguasha National Park


About sixty specimens of Endeiolepis have been found in the Escuminac Formation, all extracted from a few sandstone layers within the same small area of the cliffs.

Until very recently, Endeiolepis was described as being quite similar to Euphanerops, the main difference being a long series of elongated scales forming a ventrolateral protuberance on each side of Endeiolepis’ body. These structures were previously interpreted as the marks of ventral fins, similar to those found in some Silurian anaspid species.

But a recently discovered Endeiolepis specimen revealed an abdomen that split open as the fish decayed, making it possible to study the well-preserved details of these “scaly” ventral structures from the inside. It turns out that this feature was not related to fins after all; instead, it represents a series of small internal gill pouches, like those of today’s lamprey. But unlike the lamprey, which has seven pairs of gill pouche Read More
About sixty specimens of Endeiolepis have been found in the Escuminac Formation, all extracted from a few sandstone layers within the same small area of the cliffs.

Until very recently, Endeiolepis was described as being quite similar to Euphanerops, the main difference being a long series of elongated scales forming a ventrolateral protuberance on each side of Endeiolepis’ body. These structures were previously interpreted as the marks of ventral fins, similar to those found in some Silurian anaspid species.

But a recently discovered Endeiolepis specimen revealed an abdomen that split open as the fish decayed, making it possible to study the well-preserved details of these “scaly” ventral structures from the inside. It turns out that this feature was not related to fins after all; instead, it represents a series of small internal gill pouches, like those of today’s lamprey. But unlike the lamprey, which has seven pairs of gill pouches, Endeiolepis had about 30, as is also the case for Euphanerops. The finely preserved details in the recent Endeiolepis specimen also showed the outline of small gill lamellae.

This discovery is the oldest evidence of respiration through gill pouches. Once believed to be a specialization in existing lampreys and hagfishes, it now seems more probable that gill pouches were an ancestral condition of vertebrates, subsequently lost in the gnathostomes.

By discovering the true nature of the “scaly” ventral structure, however, we have effectively erased the one anatomical trait that distinguished Endeiolepis from Euphanerops! Could this mean that they are one and the same species, or at least very closely related? Palaeontologists now think that this is the case. Their apparent dissimilarity could simply be due to differences in the environments in which they were preserved. Indeed, we only find Endeiolepis in turbidite deposits made of sand, which promote three-dimensional preservation, and Euphanerops in thinly layered clay beds, which tend to flatten specimens.

© Miguasha National Park 2007

<i>Endeiolepis aneri</i>

The jawless fish Endeiolepis, which bears remarkable similarity to Euphanerops.

Philippe Janvier
2006
© Philippe Janvier


In 1900, A. Smith Woodward of the British Museum of Natural History described the first anaspid from Miguasha using a specimen discovered some years earlier. Baptized Euphanerops longaevus, this animal’s unique features fascinated paleontologists.

The absence of paired fins and the somewhat poor preservation of the head made it difficult to distinguish top from the bottom. This is why Woodward’s first illustrations show Euphanerops upside-down, with an epicercal tail and dorsal fin instead of a hypocercal tail and anal fin. This inverted representation suggests that Mr. Woodward’s interpretation was influenced by the paleontological beliefs of his day, which held that any hypothetical ancestor of the gnathostomes must have had an epicercal tail.

More than a century later, the species was better described and presented right side up. We now know that its tail was strangely similar to those of the Silurian anaspids, and that its gill apparatus was exceptionally long, with thirty gill pairs from head to anus. This surprisin Read More
In 1900, A. Smith Woodward of the British Museum of Natural History described the first anaspid from Miguasha using a specimen discovered some years earlier. Baptized Euphanerops longaevus, this animal’s unique features fascinated paleontologists.

The absence of paired fins and the somewhat poor preservation of the head made it difficult to distinguish top from the bottom. This is why Woodward’s first illustrations show Euphanerops upside-down, with an epicercal tail and dorsal fin instead of a hypocercal tail and anal fin. This inverted representation suggests that Mr. Woodward’s interpretation was influenced by the paleontological beliefs of his day, which held that any hypothetical ancestor of the gnathostomes must have had an epicercal tail.

More than a century later, the species was better described and presented right side up. We now know that its tail was strangely similar to those of the Silurian anaspids, and that its gill apparatus was exceptionally long, with thirty gill pairs from head to anus. This surprising discovery means that the branchial basket stretched almost the entire length of its body, requiring a significant rearrangement of its other inner organs. This extreme specialization, which has never been found in any other vertebrate group, was likely an adaptation to life in oxygen-poor waters, like those of the Miguasha estuary.

In 1991, and for several years after, researchers thought that they had unveiled another new anaspid species at Miguasha. Baptized Legendrelepis parenti, this fish differed from Euphanerops longaevus by the greater separation between its anal fin and tail, and the possible presence of a very small dorsal fin. These details turned out to be artifacts of preservation, and both species are now thought to be one and the same.

Like the agnathans, Euphanerops had a cartilaginous internal skeleton. A recent microscope study of various endoskeletal features revealed that the cartilaginous structures had begun to calcify in mature specimens. The manner in which the cartilage was undergoing ossification is quite unusual, and is comparable to the cartilage of today’s lampreys that can be partially calcified by artificial means in the laboratory. Could this represent an evolutionary attempt towards endoskeleton calcification, a trend that was developing concurrently in the gnathostome group?

Ongoing studies of many new specimens of the curious Euphanerops “anaspid” are revealing unique anatomical details, some of which move it closer to lampreys, and others that are more reminiscent of the first vertebrates to have evolved in Early Cambrian time. This animal undoubtedly has more surprises in store for us!

© Miguasha National Park 2007

<i>Euphanerops longaevus</i>

A specimen of Euphanerops with the impression of the long branchial basket visible on the ventral side of the animal. Also evident is the strongly downward-pointing axis of the tail (caudal fin).

Miguasha National Park
2003
© Miguasha National Park


Reconstruction of <i>Euphanerops</i>

Side view of Euphanerops longaevus, a very strange looking fish.

Illustration by Philippe Janvier
2003
© 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.

Teachers' Centre Home Page | Find Learning Resources & Lesson Plans