Paleozoic Era – Cambrian Period (542 – 488 million years ago). The basic body plans of all modern animals were set during the Cambrian Period. Not every Cambrian body plan was successful. But those that did succeed set the pattern for every animal that followed. The oceans became more oxygenated and this was the fuel for further evolution. Cambrian was a time of great evolutionary innovation, with many major groups of organisms appearing within a span of only forty million years. It wasn’t until the Cambrian that there was a sufficient reduction in the number of oxygen-depleting bacteria to permit higher oxygen levels in the waters. Most of the major groups of animals, especially those with hard shells, first appeared in the fossil record. There were new behaviours and strategies — such as active hunting by new specialised predators. As hunters were more efficient they forced their prey to adapt or die out. Other animals developed specialisations for burrowing deeply into sediment, and making complex branching burrows. The Cambrian saw marine plants diversify with the appearance of mineralized algae, such as the coralline red algae and green algae. Important new animals that weren’t destined to keep going were the archaeocyathans. These are strange cup-shaped animals that are possibly related to sponges. They made the ocean bottom a lot more structured by managing to build quite significant reefs, well before corals had evolved. Time machine travellers might find it good for a holiday. World climates were mild there were no glaciers. Landmasses were scattered with extensive shallow-water reefs. None of the continents were located at the poles so land temperatures were balmy. In fact, global climate was probably warmer and more uniform than it is today. This does not mean that life in the Cambrian seas would have been familiar to a modern-day SCUBA reef diver. Although almost all of the living marine phyla were present, most were represented by classes that have since gone extinct or faded in importance. Cambrian echinoderms were strange-looking things. Early in the Cambrian Period the first bivalves (seashells) and arthropods appeared followed by other shelled animals like the first molluscs, and brachiopods. The more familiar starfish, brittle stars, and sea urchins had not yet evolved. Crinoids (featherstars) were rare. The sea level rose significantly making new habitats for odd invertebrates, such as trilobites. And while jawless vertebrates were present in the Cambrian, it was not until the Ordovician that fish became common. Also on the down side there were no dive resorts, in fact, plants had not yet evolved. The terrestrial world was devoid of vegetation and inhospitable to life as we know it. The ocean was the place where all the action was happening. There were some pretty big climatic changes at the end of the period, as with all periods. The surviving Cambrian species and body forms we can find today are pretty small, and very weird. Forams Some very tiny planktonic and bottom dwelling animals called forams may have survived. Modern forams are primarily marine, although some can survive in brackish conditions. Foraminifera are found in the deepest trenches of the ocean. Dying planktonic Foraminifera continuously rain down on the sea 15 floor in vast numbers, their mineralized bodies are then preserved as fossils. Beginning in the 1960s, scientific and oil exploration deep-sea drilling have been bringing up sediment cores bearing Foraminifera fossils by the millions. These have been used to date the seabed geology and find oil pockets. Graptolite Plankton Graptolites were colonial planktonlike animals with multiple cups on a long central rod, each cup housing a tiny filter-feeding animal. Graptolites started in the Late Cambrian and became abundant later. Graptolites were thought to have become extinct during the late Paleozoic. Recently, however, living creatures resembling graptolites were found in sediment dredged from the deep sea off New Caledonia. In 1992 Noel Dilly, sorting through a pile of smelly sludge retrieved by French oceanographers from the seafloor off New Caledonia, found himself looking at a graptolite last seen alive around 300 million years ago. Some graptolites attached to the seafloor, and those looked either like a bushy seaweed or like a flattened bagpipe. Because graptolites were floating organisms, they were widely distributed by ocean currents and settled in between layers of ancient rocks. Why are these tiny things worth knowing about? For one thing you can used graptolite fossils to date rocks and find gold deposits. Prospectors in colonial Australia used this technique often during the “Rush”. Horsehoe Crabs The ancient relatives of horseshoe crabs were present 520 million years. Only the horseshoe crab form is actually a survivor. The surviving species are a remake and have only been around for about 20 million years. Horseshoe crabs are one of the few animals that has no predators. Horseshoe crabs are omnivorous scavengers, feeding upon small bivalves, molluscs, worms, dead fish and algae. Sexual maturity is not reached for nine to 12 years. The larger female horseshoe crab can weigh up to 5 kg. Mating season for the horseshoe crab takes place during the spring and summer full moons. The female comes ashore to deposit between 2,000 and 30,000 eggs in each nest in the sand. When the moon is full again, the 1 cm long larvae hatch and return to the water. In about 1 year juvenile horseshoe crabs will reach about 4 cm in width. The spike-shaped tail, functions as a tool for digging in sand and a lever if the animal finds itself upside down. The horseshoe crab is equipped with 4 pairs of jointed walking legs each ending in a claw. The fifth pair is larger and allows the animal to lurch forward. The middle segment of each leg is covered with spines used to chew food before it is passed forward and into the mouth located at the base of the legs. The animal can chew only when it moves. Horseshoe crabs have 10 eyes located all over their bodies, most located on the back or sides of the animal. In spite of the number of eyes, horseshoe crabs still have poor eyesight. 16 Horseshoe crabs have weird blood that contains hemocyanin, which contains copper. This causes the blood to turn blue when exposed to air. A protein found in the blood of horseshoe crabs is used to detect impurities in intravenous medications. Horseshoe crab blood has also been used in cancer therapy research, leukemia diagnosis and to detect vitamin B12 deficiency. Because of the time it takes for horseshoe crabs to reach sexual maturity, it is important that population densities remain high. Horseshoe crab harvests for bait and biomedical purposes have been restricted. In Asia it is caught for food. There are 4 species of horseshoe crabs found in the world today. Limulus polyphemus is the only species found in the Atlantic Ocean. The remaining three are found in SE Asia. They are only found in Australia as fossils. Ostracods Ostracods are microscopic, shrimplike crustaeans sometimes known as seed shrimp. They live inside bean-shaped shells. Ostracods feed within the surface plankton, or on the bottom of marine and fresh waters. They have a wide range of diets, and the group includes carnivores, herbivores, scavengers and filter feeders. Ostracods first appeared in the Cambrian and evolved during the Ordovician, some reaching almost a centimetre in length. Modern ostracods, however, are microscopic in size. Some 70,000 species once existed but today there are only 13,000 species that have been identified. A large portion of diversity is still undescribed and Australia is one of the world’s ostracod biodiversity hotspots. Sea Spiders Sea spiders are soft-bodied arthropods, found widely in modern oceans. Sea spiders look much like the common “daddy long leg” spiders. For two-centuries there has been a controversy about the relationship of sea spiders to land spiders. They have long been a mystery. The earliest possible fossils are of larvae are from the Cambrian era. The fossil record of their relationship is sparse because of their delicate nature. One later adult specimen has been found from volcanic ash that trapped ancient sea life, rapidly encasing the creatures in a concretelike cast. Trapped in stone with all the animals it lived with, this species appears to have lived in a similar way to modern ones, on the seabed, or perhaps on sponges. They were everywhere. French scientists have found Jurassic fossils from an area that was 200M deep. The modern examples can also be found from the shore region down to the deep sea. University of Oxford paleobiologists have so far found the oldest and most complete sea spider fossil to date in Herefordshire. The fossils are often too delicate to excavate, so U.K. researchers took digital images of the fossil at 20-micrometer intervals as they ground through the surrounding rock. The team reconstructed the slices in a computer. Modern Sea spiders tend to be slow-moving creatures, which crawl among seaweed or across the sea floor. Pycnogonids typically prey on sessile (non-moving) organisms such as sponges, sea anemones or bryozoans. The proboscis is simply stuck into the victim and the fluid contents are sucked up — a feeding strategy resembling that of a parasite.