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Blue Beach - Horton Bluff
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Blue Beach - Horton Bluff

Fossils at Blue Beach

The rocks exposed at Blue Beach contain many fossils (Figs. 11-13). In fact, there are so many fossils that it is almost impossible to put your foot down without stepping on a record of ancient, past life. The fossils at Blue Beach-Horton Bluff can be divided into four groups: three groups of body fossils (plants, invertebrates, vertebrates); and trace fossils. Trace fossils are indirect evidence of ancient life and include such things as footprints, body drags, and coprolites.

Figure 11-13
Figure 11 - 13. Fig. 11 shows fish scales, Fig. 12 footprints and Fig. 13 shows burrows. Photographs courtesy of - R.A MacRae (11,13) and H.Wiele (12). Specimen in Fig.12 courtesy of G. Oakey.

Perhaps the most striking plant fossils at Blue Beach are clubmoss trunks and roots. Today, clubmosses (lycopods) are represented by Lycopodium, a small modern fern-like herb. But Carboniferous lycopods grew into stately trees (lycopsids), though with a different structure from modern trees. They were different internally and did not have an outer bark as we know it today. The most common plant fossil at Blue Beach is Lepidodendropsis, an early form of a lycopsid. Lycopsids in the later Carboniferous dominated the .coal swamps', growing to heights of 40 metres. Lycopsids had unusual trunks, the weight being supported by an outer thick rind of bark (periderm). The trunks had very little xylem - the vascular tissue that moves water from the roots and forms the wood of most modern trees - and the interior consisted mostly of spongy, weak tissues. The fossilized roots of lycopsids are called Stigmaria. When in growth position, Stigmaria usually had long rootlets that penetrate radially into the surrounding rock.

Other plant fossils include Asterocalamites (an early Calamites, related to modern-day horsetails), a fern called Adaintites, four different types of seed ferns (plants that looked like ferns, but reproduced by seeds instead of spores), and a seed called Carpolithus (from a gymnosperm). Megaspore beds are also found - megaspores can be seen by the naked eye.

Invertebrates

The invertebrates discovered at Horton Bluff-Blue Beach all stem from the aquatic realm. Some can be observed with the naked eyes, but most are microscopic. Invertebrate fossils include foraminfera, ostracodes ("water fleas"), thecamoebians, polychate worms (Spirorbis), clam shrimp, and a possible trilobite fragment. The invertebrates have been invaluable in determining the different palaeoenvironments preserved in the section. Tibert (1996) used ostracodes and foraminifera to determine that the section had periodic connections with the sea, although the dearth of marine fossils show that open marine conditions were probably not nearby.

Vertebrates

The vertebrate fauna at Blue Beach consists of no less than five different types of fish and a few different types of amphibians. The vertebrate fauna are currently being studied by a number of palaeontologists from around the world. The vertebrate fossils at Blue Beach are of world-wide significance because they are from a very important period of time in the Earth's history. During the Early Carboniferous, vertebrates were still making their transition from water to land. Very few vertebrate fossils have been found from this time period, and this lack or scarcity of fossils has been referred to as "Romer's Gap", after the palaeontologist who first noticed the gap in the fossil record. The fossils at Blue Beach have the potential to fill this critical gap in our knowledge base.

The different types of fish fossils found in the section include acanthodians (bony fish with distinctive spines in front of all fins), chondrichthyians (sharks - cartliaginous fishes), palaeoniscids (ray-finned fishes), crossopterygians (lobe-finned fishes with large, stabbing teeth), and dipnoans (lungfish).

The amphibian record is not as well known - largely because the fossils have not been studied in detail before and also because the fossils tend to be fragmentary in nature.

Trace Fossils

Trace fossils are indirect evidence of ancient life. Trace fossils form in place and as such, give a record of an animal at a very precise time. Trace fossils give us information that body fossils simply cannot - they tell us about the animal's behaviour.

There are many fascinating trace fossils to be found at Horton Bluff-Blue Beach. There are traces of fish swimming and amphibians walking or crawling. There are many invertebrate traces (made by worms and arthropods) that record behaviours such as walking, resting, or feeding.

In 1964, two students conducting a hydrological survey stumbled upon a trail of large fossil footprints 50 m offshore from Horton Bluff, adjacent to Blue Beach (Fig. 14). They were exposed at extreme low tide when a storm had swept away the overlying mud. One of the discoverers, Dr. David Mossman, is now a professor of Geoscience at Mount Allison University in Sackville, New Brunswick.

Dr. Mossman eventually mapped 27 footprints spanning a distance of 20 m. Their preservation in Lower Carboniferous rock made them, at the time, some of the oldest vertebrate tracks in the fossil record. They currently remain the oldest known vertebrate trackways ever found in Canada.

Not only was the trackway old, it was of unprecedented size. Each foot print was 30 cm long and they were spaced 30 cm apart. The tracks are deep with raised edges, suggesting that the

Figure 14
Figure 14. Trackway from Blue Beach. Photograph courtesy G. Van Ryckevorsel.

animal was heavy and the mud very soft when it waddled by approximately 350 million years ago. The absence of claws and the width of the trackway suggest it was made by an amphibian.

It is impossible to identify the animal, as no bones of an amphibian large enough to have made these tracks have ever been found. We can only guess the makers identity and hope for the discovery of its bones. One candidate is the semiaquatic predator Eryops. This bulky amphibian grew to be over 2 m in length. Its size and powerful jaws made it a formidable predator in water. On land, however, it lumbered along on short legs and was itself vulnerable to predation. Another possibility is that the animal that made these large tracks is a type of extinct amphibian more related to crocodiles than to living frogs or salamanders. If so, it probably had fangs and would have been a most feared carnivore in the Carboniferous swamp.

There is a cast of the trackway in the Geology Collections at the Nova Scotia Museum.

   

    Last Modified: 2004-12-10