PART 2 of the Burgess Shale Fossils:

One of the most unusual-looking Burgess Shale fossils is Hallucigenia sparsa (Walcott, 1911). Hallucigenia is found in the Burgess Shale in British Columbia, and it is found in slightly earlier rocks in China. It is also found as isolated spines elsewhere in the world. Its geologic age is approximately a half a billion years old.

Hallucigenia sparsa (length between 1 and 5 cm long) does not have jointed legs, nor a segmented body, nor a hard exoskeleton. This fossil has been interpreted as being a predecessor to arthropods. It branched off in an evolutionary sense prior to the arrival of arthropods in the fossil record. In other words, Hallucigenia is “an almost arthropod.” It has many sharp, long spines, which Conway-Morris (1977) believed were used as walking legs. 

Hallucigenia sparsa was originally described as a species of a polychaete worm belonging to genus Canadia Walcott, 1911. Walcott did not figure this fossil until 1931. Conway-Morris (1977) redescribed this fossil and assigned to his new genus Hallucigenia, which was commonly referred to as “the worm with the missing head” because its “head” turned out to be just a stain of decomposed organic matter. The name Hallucigenia is Latin, meaning “wandering of the mind.

Ramsköld and Xianguang (1991) reinterpreted Hallucigenia as belonging to a stem group of onychophorans (or velvet worms), which are rare, caterpillar-like animals alive today in rain forests. There are about 100 living species). Ramsköld and Xianguang (1991) discovered also that Hallucigenia actually has legs, thus they inverted the life-orientation of this fossil and reported that the spines were used for protection, not for walking.

Cited References:

Conway-Morris, S. 1977. A new metazoan from the Cambrian Burgess Shale of British Columbia. Paleontology 20:623-640. [requires a subscription or pay-per-view fee].

Ramsköld, L. and H. Xianguang. 1991. New Early Cambrian animal and onychophoran affinities of enigmatic metazoans. Nature 351 (6323):225-228. [requires a subscription or pay-per-view fee].

Walcott, C.D. 1911. Cambrian geology and paleontology. II. Middle Cambrian annelids. Smithsonian Miscellaneous Collections 57(5):109-144.

THE MIDDLE CAMBRIAN Burgess Shale

In the early 1900’s, a sharp-eyed paleontologist named Walcott was doing field work in British Columbia, and he found a Lagerstätte from the Middle Cambrian Burgess Shale Member of the Stephen Formation. 

The Cambrian Period began 541 million years ago. The Burgess Shale is of Middle Cambrian age in the earliest part of the Paleozoic.

A “Lagerstätte” is a German word used to designate any exceptionally well preserved fossil fauna or flora. Walcott and subsequent researchers collected and described more fossils. They stored them in established museums so that other paleontologists could access them for detailed study. Eventually, researchers began to realize that the Burgess Shale Lagerstätte represented soft-bodied animals that existed near the beginning of complex animal life on Earth. The research process took many years, and the findings were, in some cases, quite controversial about the exact type of organism that each different fossil represented. Research continues to the present day. The Burgess Shale fossil area is now a World Heritage Site. The localities are protected and require authorization to visit. Unauthorized collecting is prohibited.

The modes of preservation of the Burgess Shale Lagerstätte are either impressions (as shown above in the example of a an early “velvet worm” type of animal) in brown mudstone, or, more spectacularly, as  paper-thin carbonized (whitish to gray) imprints in very fine-grained black to gray siliceous mudstone. 

One popular interpretation about their burial environment is that the animals lived in shallow-marine waters at the edge of an underwater cliff. They were transported a short distance by currents over the cliff and down into deep-quiet waters, where they were rapidly buried by muds. Like most interpretations, this one was recently challenged, and some workers maintain that the animals actually lived at the bottom of the cliff and were not transported there. 

The next five posts highlight examples of fossils found in the Burgess Shale strata. These examples show some rather strange-looking animals, including (the last of the examples) of possibly the first back-boned animal.

Lambis, the "Scorpion" Conch

The shallow-marine gastropod genus Lambis Röding, 1758 belongs to family Strombidae, which makes up the “true conchs” of the world. 

Three of the 10 living species (not including 14 hyrbrid “species”) of Lambis are illustrated in this post. They all live in very shallow waters in the Indo-Pacific, and, in much less common cases, the Red Sea. Their shells are large and thick, with many long, hollow digitations along the side of the shell, and knobs or protuberances can be present on the dorsum (top) of the shells. In addition, they all have a “peep-hole” notch (called the strombid notch) for the right eye. Their anterior end has a short or long anterior canal.

 

Lambis scorpius (Linnaeus, 1758), height 11.3 cm, width 5.5 cm, thickness 3 cm; three views: ventral, dorsal, and right side, in that order. This moderately common species lives in coral-reef areas in the Indian Ocean and Western Pacific regions. Its knobby digitations help this gastropod “blend in” with the rubble it lives in.

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Lambis lambis (Linnaeus, 1758), height 15 cm, width 8.5 cm, thickness 5.5 cm. Three views: ventral, dorsal, and right side, in that order. This Indo-Pacific species lives in mangroves or on reef flats from low tide to 5 m depths.

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Lambis millepeda (Linnaeus, 1758), height 14.5 cm, width 5.5 cm, thickness 3 cm. Three views of one specimen: dorsal, ventral, and right side, in that order. An internal view (cut section) of another specimen. This Indo-Pacific species lives on sand and rubble in shallow waters. This specimen is from Marshall Islands, Jaluit Atoll.

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Lambis is known with certainty only from the Recent record. This geologic range of this genus has been reported in some online databases as being Paleocene to Recent, but these reports are taxonomically out-of-date and incorrect. The current consensus among most experts is that these Paleocene and Eocene reports pertain to the gastropod Sulcogladius goniophora (Bellardi, 1852) of Eocene age from Western Europe and Pakistan. That species belongs to family Rostellariidae. A few experts have put forth the concept that Sulcogladius belongs in the Rostellariidae genus Rimellopsis Lambiotte, 1974.