Cambrian trilobite
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In that vast amount of time before creationism's god allegedly created a small flat planet with a dome over it, containing nothing and nowhere that wasn't known to the Bronze Age Canaanite pastoralists who first wrote about it, when 99.9975% of Earth’s history happened, there were swarms of trilobites living in the seas and regularly molting to leave hard body parts to fossilise in the marine sediment.
They did this so frequently that trilobites are now amongst the commonest of fossils, but nevertheless fossils preserving the soft body parts are rare, like the soft body parts of the rest of the Cambrian biota.
However, just such a fossil has turned up in upstate New York that shows something surprising - it has an additional pair of legs to the usual trilobite complement. This discovery is the subject of a paper in the journal Palaeontology (the journal of the Palaeontological Association) by Jin-Bo Hou from Nanjing University and Professor Melanie Hopkins, curator and chair of the American Museum of Natural History’s Division of Paleontology. The discovery is described in an American Natural History Museum news article:
Tell me all about trilobites and their place in the history of life on Earth. Trilobites were an incredibly diverse group of marine arthropods that lived during the Paleozoic Era, playing a significant role in the history of life on Earth. They are some of the earliest known complex life forms, with fossils dating back over 500 million years. Here's a breakdown of their significance and characteristics:
- Origins and Evolution
- First Appearance: Trilobites first appeared during the Cambrian Period, about 521 million years ago, during a time known as the Cambrian Explosion which saw a rapid diversification of life.
- Diverse Lineage: They represent one of the earliest branches of arthropods, a group that today includes insects, arachnids, and crustaceans.
- Adaptability: Over 20,000 species of trilobites are known, making them one of the most successful and adaptable groups of early animals. Their body structure and lifestyles allowed them to occupy a wide range of marine environments.
- Physical Characteristics
- Body Structure: Trilobites are characterized by their three-lobed, three-part bodies: a head (cephalon), a segmented thorax, and a tail (pygidium). The name "trilobite" refers to the three longitudinal lobes—one central and two lateral—that run the length of their bodies.
- Exoskeleton: They had a hard, calcified exoskeleton, which helped preserve their fossils well. This exoskeleton was molted periodically as they grew, like modern arthropods.
- Eyes: Trilobites were among the first animals to develop complex eyes, with many having compound eyes made of calcite, similar to modern insects.
- Ecology and Behavior
- Habitat: Trilobites were exclusively marine and thrived in a variety of environments, from shallow coastal waters to deep-sea floors.
- Feeding Habits: They had diverse feeding strategies. Some were scavengers, others were predators, and some likely filtered food from the sediment. Their ability to adapt to different ecological niches helped their proliferation.
- Swimming and Burrowing: Trilobites were efficient swimmers, but many species also burrowed into sediment. Some species had spines or flattened bodies, likely as adaptations for life on the seafloor.
- Fossil Record
- Widespread Fossils: Trilobites left a rich fossil record, and their fossils are found worldwide. This makes them important index fossils, helping geologists date rocks and understand ancient environments.
- Diversity Over Time: The number of trilobite species peaked during the Ordovician Period (about 485 to 444 million years ago), but their diversity started to decline after this.
- Extinction
- Permian Extinction: Trilobites persisted for about 270 million years before finally going extinct during the Permian-Triassic Extinction Event about 252 million years ago. This mass extinction wiped out over 90% of marine species, including the trilobites.
- Causes: The exact causes of their extinction, like many marine organisms, are linked to significant environmental changes, including ocean anoxia (lack of oxygen), volcanic activity, and possibly asteroid impacts.
- Place in the History of Life
- Early Arthropod Dominance: Trilobites are an example of early arthropod dominance in marine ecosystems. Their wide variety of forms and ecological strategies show how quickly complex life diversified in Earth’s oceans after the Cambrian Explosion.
- Evolutionary Legacy: Although they left no direct descendants, trilobites are related to modern arthropods, which today represent the most diverse animal group on Earth.
- Scientific Importance: Trilobites provide valuable insight into the evolutionary history of life. Their well-preserved fossils help scientists understand early ecosystems, the development of eyes, and the anatomy of early arthropods.
Conclusion
Trilobites were among the most successful early life forms on Earth, adapting to various marine environments and evolving a wide range of forms and sizes. Their long reign over the Paleozoic seas and eventual extinction mark key moments in Earth's biological history, leaving behind a vast fossil record that continues to provide insights into life hundreds of millions of years ago.
New York State Fossils Reveal Extra Set of Trilobite Legs
Because of their hard exoskeletons and ability to molt, trilobite fossils are a relatively common find, but rarely do they preserve the soft parts of the animal. Now, newly recovered, exceptionally well-preserved trilobite fossils from upstate New York have led to a new discovery: an extra pair of legs
Examining these fossils, which are described today in the journal Palaeontology, is “just like looking at the appendages of horseshoe crabs on a beach by grabbing them and turning them upside down,” said lead author Jin-Bo Hou from Nanjing University. Hou conducted the study with coauthor Melanie Hopkins, curator and chair of the Museum’s Division of Paleontology.
An extremely well-preserved fossil of Triarthrus eatoni from upstate New York.Daniel Kim /© AMNH
Trilobites are a group of marine arthropods that lived for almost 300 million years until 250 million years ago, when Earth experienced the largest mass extinction in its history. Their closest living relatives today include lobsters and spiders.
Like other arthropods, the bodies of trilobites were made up of many segments. The segments were associated with appendages, which range from antennae used for sensing to legs that moved the animal along the sea floor and assisted with feeding.
Curator and study co-author Melanie Hopkins holding an extremely well-preserved fossil of Triarthrus eatoni from upstate New York.Daniel Kim /© AMNH
The number of these segments and how they are associated with other important traits, like eyes and legs, is important for understanding how arthropods are related to one another, and therefore, how they evolved
Melanie Hopkins, co-author
Division of Paleontology (Invertebrates)
American Museum of Natural History
New York, NY, USA
Counting those segments, especially in the trilobite’s fused head, has been a challenge. To infer the number of segments, researchers look at the grooves on the upper side of the trilobite fossil’s hard exoskeleton and then compare it to the pairs of preserved antennae and legs on the underside of the fossil. But because the soft appendages of trilobites are rarely preserved, there often is a mismatch between these two methods.
In the new study, Hopkins and Hou examined exceptionally well-preserved specimens of T. eatoni from upstate New York, finding an additional, previously undescribed leg underneath the head, no doubt, one of a pair. By making comparisons with another well-preserved trilobite species, Olenoides serratus from British Columbia, the researchers propose a model for how appendages were attached to the head in relation to the grooves in the exoskeleton. This model resolves the apparent mismatch and suggests that the trilobite head included six segments: one associated with the developmental origin of the eyes and five additional segments, associated with one pair of antennae and four pairs of walking legs.
Hou and Hopkins have previously shown that the walking legs of T. eatoni carry micron-sized respiratory structures (gills) and that the function of some of the spines on the walking legs was to keep these gills clean. This study expands upon that work.
AbstractInteresting though this find is from the point of view of the anatomy of these archaic arthropods, the refutation of basic creationist superstitions is two-fold:
Head segments play a critical role in revealing the relationships within major arthropod groups but the accurate determination of their number and relationship is challenging because of the decoupling of dorsal tergites and ventral appendages. In recent decades, trilobites have been considered to have four pairs of cephalic appendages and, commonly, five dorsal segments, which has served as the basis for understanding euarthropod cephalic evolution. Based on multiple analytical techniques applied to well-preserved soft-bodied specimens of the Upper Ordovician olenid Triarthrus eatoni and middle Cambrian corynexochid Olenoides serratus, we argue that an additional pair of cephalic biramous appendages occurred just behind the antennae, indicating that trilobites had five pairs of cephalic appendages and six dorsally expressed segments. We propose that the mismatch between the four dorsal furrows and five ventral appendages in Olenoides may be reconciled by considering the morphology of the hypostome that marks the position of the antenna and the bifurcation of the first glabellar furrow that has two muscle attachment sites fused. The fusion of clustered attachment sites of the cephalic biramous appendages may have aided feeding ability by gathering the limb bases close to the mouth.
- The fact that the scientists interpret the observation in terms of what it tells them about the evolution of these organisms, with no hint that it can't be explained in evolutionary terms, despite the constant claims by creationists that mainstream scientists are abandoning the Theory of Evolution and turning instead to their childish superstition with its magic and unproven entities making chemistry and physics do things they couldn't do on their own.
- The fact that these organisms lived so long before creationists believe there was an Earth for them to live on.
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