The Miguasha fossil bed⤒🔗

Setting:←↰⤒🔗

Hills, covered with lush vegetation, slope steeply to the sea. Their forest cover looks unfamiliar since the most conspic­uous plants are strange trees with large complicated fern-like foliage. There is no beach, nor even a shallow shelf at the edge of the sea. Rather the cliffs plunge steeply downward so that even close to the land, the water is very deep. Through­out the water column (profile of the depths from the deepest to shallowest) a rich community of fishes pursues their daily activities. Some fish eat, others are eaten. However something is not nor­mal. Rain is falling over the entire area. Gushing streams have begun to cascade from the cliffs into the sea. Soil and even bare rock are starting to erode away from the hillsides.

Scene 1: The action begins←↰⤒🔗

As the day dawns, deep in the wa­ter, most fish pursue their finny lives. It is impossible, even at these murky depths, to miss the heavily armored Bothriolepis fish, about five inches long or smaller, zipping hither and yon with vacant but strangely fierce expressions fixed by bony plates on their heads and thorax. Most other fish of the community can also be found lurking at these extreme depths. The crustacean Asmusia is down here too, but its distribution is patchy, at some levels extremely dense and scarce at oth­ers. Some fishes seem particularly to fa­vor the spots where the crustaceans con­gregate. See, there is the lungfish Scaumenacia dining on Asmusia.¹   The ray fin Cheirolepis also seems to prefer levels rich in the crustaceans, but one speci­men at least, elects to eat a smaller indi­vidual of its own kind, head first!²  Also there is the fleshy finned predator, Eu­sthenopteron with a small acanthodian fish Homalacanthus, inside its gut.³  Some of these acanthodian fishes, like Triazeuga­canthus, evidently have adopted the strat­egy of safety in numbers. They are congregated into very dense patches at some levels in these murky depths, while at other levels they are completely absent.

As one moves upward in the water column there are gaps between the bot­tom populations and other levels with much evidence of life. There are also fewer species in the next cluster, mostly the dominant species: lungfish Scaume­nacia, the armored Bothriolepis, and the graceful predator Eusthenopteron with fleshy fins, but also there are a few small acanthodians and the crustacean Asmusia. Moving ever upward past spo­radic distributions of fish, we finally en­counter dense numbers of young lungfish Scaumenacia and young ar­mored Bothriolepis ⁴ as well as the jaw-less but not flattened fish Endeiolepis , and the large fleshy finned predator Holoptychius. Then, almost at the sur­face, we encounter yet again large num­bers of the dominant fishes. At this level we note particularly dense schools of young Bethiolepis.

There are signs however that this natural scene is about to be disturbed. As rain continues to fall and the storm in­tensifies, dense slurries of sediment and plant parts from the slopes above, begin to sweep downward through the water column and outward across the distant sea bottom. Surprised fish turn their heads upstream in an effort to prevent being washed away. These underwater avalanches of sediment descend at in­credible speeds upon the hapless fish, firstly at the lowest levels. Rivers of sand and clay, in pulse after pulse, sweep down upon the fishy community in the depths. The sediments separate as they settle so that characteristic patterns of coarser and finer layers mark the accumulating de­posit. The biota (entire living commu­nity) has no chance. One and all are suddenly interred even as they struggle to escape. These avalanches of sediment are called turbidity currents and special­ists easily identify them. Such patterns are considered to be an indication of the rapid deposition of these sediments. In­deed, all the sediments that are laid down in this body of water are turbidites.⁵

Progressively higher levels of the fishy community are overcome. Some­times plant debris from the land is trapped along with the fish. Near the bottom, a school of Eusthenopteron are trapped. Most of the individuals are small, but a large specimen nearly 1m long is also buried. This variation in size is a good sign of sudden catastrophe. Just above these fish, a layer of tree fern leaves is trapped and then more Eusthenopteron. ⁶ Much higher up, near the surface of the sea, Eusthenopteron are buried gently enough that their three dimensional shape is preserved. Sandstone and plant debris washed from the land, fill the body cavity of one speci­men.⁷  Some leafy material may have floated long enough to be buried near the surface of the water as well as in the depths. Perhaps the fish, in distress, sucked the debris into its gut.

The curtain on this scene comes down on the eerie aftermath of these events. Nothing moves. A slurry of sedi­ment has entombed all creatures. The process of decay of organisms and con­solidating of the sediments begins. The sediments become rock and eventually the rock column becomes dry land. Ero­sion begins to reveal some fossil fishes.

Scene 2: The same setting, many years later.←↰⤒🔗

Years pass. Scientists appear, anx­ious to decipher what happened here so long ago.

Nestled on the southern shore of the Gaspe Peninsula on the northern shore of the Bay of Chaleur, sits a world class museum about which most Cana­dians are entirely ignorant. The museum is in a small provincial park consisting of land overlooking the bay, fossil bearing cliffs and the beach below. Purchased by the Quebec government in the 1970s to protect a spectacular assemblage of fossil fishes, the land was designated a provin­cial park (Parc national de Miguasha) in 1985. A few years later this park was also designated a UNESCO World Her­itage Site. Visitors to the museum do not take long to discover that fossils from these cliffs tell a fascinating tale of hor­ror and destruction.

This fossil bonanza has not been en­tirely unknown. Indeed paleontologists in the nineteenth century discovered the site, and interested experts since then have made pilgrimages there, and have also arranged for exquisite specimens to be shipped to them in their home coun­tries. Indeed, one Swedish scientist dedi­cated almost his entire career (about 55 years) to the study of one taxon found at Miguasha, particularly to one spectacular specimen sent in 1922 to Sweden. This incredibly preserved whole fish, sent by local farmers in the area, cost a colleague a mere $50. The original owner however never got around to in-depth studying of the specimen. Thus in 1935 the project was conferred upon a young scientist Eric Jarvic (1907-1998). The objective of these men was to trace the transition of fishes into four footed land animals (tetrapods). Jarvic devoted his career to Eusthenopteron because this organism was believed to be dose to the direct line of descent to land creatures. Unfortunately, as with most evolutionary theories, opinions change with time, and Eusthenopteron has been reduced to footnote status, as different fishes are now considered more closely related to the tetrapods.

American scientists also have shown considerable interest in the Miguasha fossils. It was to protect the site from American ownership, that the Quebec provincial government finally took an interest in the area in the 1970s. Even today teams of scientists conduct careful digging inside a portion of cliff reinforced with scaffolding. They also comb the beach several times a day for new fossils which have eroded from the adjacent cliffs. These fossils, as well as the earlier specimens shipped to foreign destinations, reveal fascinating infor­mation about this ancient community. Fishes, however, seem remote from the interests of most other people. Who would be interested in the story of these creatures? The answer is everyone! This is not a boring tale, but a cataclysm of amazing proportions.

Dramatic evidence of the sudden fate of the Miguasha fishes is evident throughout the rock column (formerly the water column). It is impossible to miss the message. One sign that the en­tire rock column of 118 m represents one community, is the fact that the same species are found throughout these lay­ers.⁸ TTT The present day cliff at the museum is nowhere near 118 m tall however, since the layers have slipped somewhat side­ways (like a stack of papers). Another indication that the event was rapid and catastrophic, is that specimens at many depths are preserved in the postures of life. Fossil specimens, which are eating or have recently eaten a meal (as judged by stomach contents) really have been found as fossils. A three dimensional Bothriolepis has been found in the posture of swimming. Indeed, the experts report that many specimens of this fish died in postures of life, "oriented by some com­mon external agent."⁹  This external agent was actually brisk water currents ad­vancing from the northwest, presumably from the direction of the land. Through­out the water column, beleaguered and distressed fishes headed into this strange current and were entombed in that posi­tion.¹⁰ Moderately high in the rock col­umn, for example, seven specimens of the lungfish Scaumenacia (all about 18 cm long) have been discovered, all ori­ented to the northwest.¹¹ Similarly, close to the top, young armored Bothriolepis, all about 8 cm long, have been found densely concentrated, with most of them oriented in the same direction.¹²The fact that young and mature alike died, indi­cates the sudden nature of the disaster.¹³

Another indication of the sudden nature of this event is the exquisite na­ture of the preservation of some speci­mens. Many fish are preserved in three dimensions, some with bony tissue de­tailed enough to find out the arrange­ment of soft tissue (for example Eusthenopteron) and a Bothriolepis speci­men, currently on display in the Miguasha museum, contains some pre­served blood vessels and nerves near the head. More fascinating phenomenon are the Scaumenacia (lungfish) with exploded guts ¹⁴ FF as well as Eusthenopteron and Fleu­rantia. The abdominal cavities are open at the front and a few scales lie nearby in the sediments. It seems that gas gener­ated in these decaying bodies could not escape because of the enclosing sedi­ments. Finally the abdominal wall gave way and the gas eventually dispersed into the sediments.

Faced with these astonishing arti­facts, the geologists in this scene come to the obvious conclusion that the burial of these fishes was very rapid.¹⁵ Most ex­perts would, however, conclude that the process stretched over an extended pe­riod of time, perhaps thousands or mil­lions of years (rapid pulses with long periods of normalcy in between).

That is not a reasonable conclu­sion. The fact that the whole rock col­umn is so similar in manner of deposition and species represented, and that the evidence uniformly speaks of rapid processes, suggests that this was a one-time event, a flood of astound­ing proportions — no doubt a worldwide phenomenon. Indeed there are few museum exhibits that testify so obvi­ously and dramatically to sudden cata­strophe as does the small museum at Miguasha, Quebec.

The curtain descends. The play is over.

Curtain call←↰⤒🔗

This fish community is dated by sec­ular scientists as late Devonian and as such it would be 375 million years old. If this were indeed the case, one might sup­pose that the fish in this community were primitive. Nothing could be farther from the truth. As one famous expert re­marked (Eric Jarvic), these fish all show a high degree of specialization, compara­ble to extant fish.¹⁶ Nevertheless, of the fishes in the Miguasha community, most represent groups which are now entirely extinct. Only the ray finned fish survive (indeed most extant fish are ray fins), and the lungfish (represented by six species), and one coelacanth species. There are also many crustacean species similar to Asmusia surviving today. These fern trees also are extinct. This was a unique community but the story is not about evolution, but about crisis.

REFERENCE

The following page references are all from: H.P. Schultze and R. Cloutier (editors). 1996. Devonian Fishes and Plants of Miguasha, Quebec, Canada. Verlag Dr. Friedrich Pfeil. Munich. 374 pages.Cast of characters

Fern trees (Archaeopteris) — These presumably prefer moist semitropical growth conditions.

Crustacean (Asmusia) — huge numbers of this tiny creature (somewhat like water fleas or shrimp) congregate at certain depths, particularly deep levels in the water column.

Jawless fish — their mouths are permanently open in an 0 shaped expression (like lampreys). Some, covered with thin bony shields, are flattened sea bottom dwellers. The two species represented here, are very rare mem­bers of the community. Some are quite large, possibly up to 80 cm or 32 inches long.

More Jawless fish — Another group, with rounded contours to their bodies, perhaps more lively in their motion through the water, are distinguished by very long gill structures. This group of small fish, up to 10 cm long (4 inches) includes three species, all present throughout the water column, but only in low numbers.

Placoderm fish — with jaws. Prominent bony shields protect head and the front of the body. One group, the an­tiarchs have particularly strong armor. This group is represented by Bothriolepis, the most common fish in the com­munity. These are small fish 17 cm or 7 inches at the longest.

Another placoderm fish — The arthrodires have unusually mobile pectoral fins and a wide mouth gape with prominent teeth set in strong jaws. They are represented by Pleurdosteus, a small fish about the same size as Bothriolepis.

Acanthodian fish — with jaws. These are all very small fish, some present in huge numbers especially at a few lev­els. In silhouette they look like sharks, only they have a bony skeleton and big eyes. Prominent spines decorate the front of each fin, and more spines occur along the abdomen. This group is represented by Diplacanthus, Tri azeugacanthus and Homalacanthus.

Ray finned fish — with jaws. These look much like typical fish in most of our bodies of water. This group is rep­resented by Cheirolepis, a predatory fish growing up to 50 cm (20 inches) long. Its mouth has many sharp teeth and the bones in its fins radiate outward like a fan.

Lungfish — with jaws. A functional lung replaces the air bladder so that these fish can gulp air, but the nostrils do not connect with the mouth cavity. The fins are fleshy lobes, but internal bone support is not strong. This group is represented by Scaumenacia and Fleurantia. The former species is the third most common member of this commu­nity of fishes. Scaumenacia is a good-sized fish with maximum length about 65 cm and an average size of about 18 cm (26 inches and 7 inches respectively). Fleurantia has a deeper body and longer snout, but is otherwise similar to Scaumenacia.

Lobe (fleshy) finned fish — all with jaws. These include the coelacanths, the porolepiform fish and the oste­olepiform fish.

Coelacanths — These have heavy bodies, blunt faces, no lungs, and no connection of nostrils to mouth cav­ity. This group is represented by the rare Miguashia, a feeder of creatures on the sea bottom. Specimens range in size from 8 cm to 45 cm (3 inches to 18 inches).

Porolepiform fish — These differ from coelacanths in their thinner bodies, more pointed snouts, and nos­trils connected to mouth cavity. These are fierce predators up to 1 m long, and they are quite rare in the community. They are represented by Quebecius and Holoptychius.

Osteolepiform fish —These differ from the porolepiforms in the shape of the snout, and more graceful con­tours to the body. Also the fleshy fins have unusually strong bones inside with shoulder girdle support for the bones in the fins. Represented by Eusthenopteron, the second most common fish in the community. Sur­prisingly, this is a predator and some specimens attain considerably more than 1 metre in length. Usually predators do not show such prominent numbers in a community.

Characters conspicuous by their absence — The vast array of marine animals without backbones (inverte­brates), typically seen in such communities, is missing here. Is the sea bottom too dark or too deep for them?

Latecomers to the scene — human palaeontologists (fossil experts) from Europe and North America.