Historical Geology
Spring 2005

The Largest Trilobite

In the historical life-forms hall of fame, trilobites are the second most favorite life-forms next to the dinosaurs. During the Paleozoic Period, they were among the first arthropods to roam our planet’s sea floors. Spiders, lobsters, and insects have inherited segmented body parts and jointed legs from species such as the trilobite. Some of the trilobites had spines, or had extruding eyes, while others were blind. Not only were their body structures complex, their eyes consisted of thousands of tiny “Crystal Eye” lenses. This was the first naturally complex design of the lens we use today. As abundant as the trilobites were, their existence rapidly decreased before dinosaurs roamed the earth.

During the Cambrian period, the trilobite evolved into many different varieties. There are three main body parts which make up the trilobite. Though the appearance of trilobites may not have been the same, they still consisted of the same body structure. The head portion is called the cephalon. The middle, or body portion, of the trilobite is referred to as the thorax. Then the tail is called the pygidium. Trilobites have the same body structure lengthwise as well. Trilobite’s central portion of their body is called an axial lobe. The lobes to the right and left side of the trilobite are called pleural lobes.

Anatomy of trilobites illustrations courtesy of S. M. Gon III

http://www.trilobites.info/trilobite.htm

Like arthropods today, trilobites had the labor of shedding their calcified exoskeleton to grow physically. This is the reason why so many trilobite fossils are found throughout the world. Without the trilobite’s exoskeleton, it would be very difficult to view or have evidence of what a trilobite looks like. The exoskeleton gave structure and support to the trilobites. Some trilobite exoskeleton’s even evolved into defense mechanisms, such as spines or horns. This made it harder for other predators to prey on the trilobite, but it didn’t make it impossible. Fossils of trilobites were found with intrusions and bites taken out of them. It was later discovered that a unique predator called anomalocaris was hunting the trilobites. Though this predator had a soft body with features to feed on the trilobites, they would disappear after the Cambrian period leaving the trilobites to live hundreds of years later.

1. 2.

Courtesy of The Virtual Fossil Museum (http://www.fossilmuseum.net/)

1. Lichida species trilobite used spines as defense mechanism to prevent from being

eaten.

2. Epithet species “bull horned” trilobite thought to have used horns to plow through the

sea floor in search of food.

Though some trilobites were blind, the species that could see had highly advanced vision. Unlike human eyes, where we can only focus one object either near or far, trilobites had the advantage of seeing both near and far at the same time. In other words everything was in focus. This would help the trilobites in the long run to see food, or see a predator. A trilobite’s eye consists of thousand of double lenses with different refraction to work together. Each lens would have a different cornea separate from its pair lens. The structure of the trilobite’s eye’s would be the making of a lens that scientist would not figure out until millions of years later.

Courtesy of The Virtual Fossil Museum (http://www.fossilmuseum.net/)

Along the Canadian northern Manitoba shores the largest trilobite is discovered. Living at the bottom sea floor 445 million years ago, this trilobite measures out to be 70 centimeters in length. The trilobite tops the number-one spot at being almost 30 centimeters (70%) longer than the previous record. An average trilobite is measured at three to ten centimeters; to find a trilobite this size is truly unique. Arthropods are creatures without backbones. This is the reason for relatively small arthropods. To have an arthropod that is almost two feet long raises question as to the trilobite’s functions. The purpose of an exoskeleton is to give structure and support, without a backbone it seems difficult for large arthropods to have the same support as regular sized arthropods. More questions are followed concerning the blood circulation, oxygen intake, and nervous system functions. These are questions are what keep scientist out searching for more answers, or more questions. One idea of large organisms living in cold weather had to be scratched when finding this arthropod. Though this fossil was found of the shores of Manitoba, during the Paleozoic period this trilobite was living in shallow seas along the equator. Finding this specimen was luck; but to dig it out would take a lot of hard skilled paleontologists and much time.

Courtesy of The Manitoba Museum (http://www.manitobamuseum.mb.ca/mu_trilobite.html)

When digging out the trilobite, for transportation purposes, it had to be removed in four separate pieces. When finding a unique fossil like this trilobite, sometimes the condition which it is kept is not helpful to the paleontologists. After finding the trilobite the advancing of the Hudson Bay prevented the paleontologist to dig up the specimen. Waiting impatiently for the tied to recede, the trilobite appeared only to be too dark into the night to see. The next day the paleontologists arrived at the scene to finally find the trilobite revealed. At this time the scientist were working against the clock of the tide and of the day. In one hour the trilobite was cleaned and removed from the limestone. The trilobite’s species is still yet unknown and is kept at the Manitoba Museum of Man and Nature in Winnipeg. There is also a replica displayed at the University of Manitoba in the department of geological sciences.

Courtesy of The Manitoba Museum (http://www.manitobamuseum.mb.ca/mu_trilobite.html)

Recommended Sites:

http://www.fossilmuseum.net/Evolution/TrilobiteArmsRace.htm

http://www.manitobamuseum.mb.ca/mu_trilobite.html

http://news.bbc.co.uk/1/hi/sci/tech/964027.stm

http://trilobites.info/trilobite.htm

Historical Geology Spring 2005

Historical Geology
Spring 2005