The above picture is a cladogram of the chelicerata species. As you can see from the image, the chelicerta have evolved tremendously since the beginning of their existence.
EXPLAINING THE CLADOGRAM:
aglaspidid: small horseshoe crab-like arthopods
lemoneites: marine chelicerata, with many extinct ancestors
xiphosurida: live in shallow waters, with soft/sandy bottoms. They sometimes come onshore to mate.
chasmataspida: rare, extinct group of arthopods, related to sea scorpions and horseshoe crabs
eurypterida: extinct aquatic arthopods
scorpiones: arachnids, most closely related to the scorpion
SCORPIONS
When they first appeared on earth, they were marine animals, only living in the water. Some sea scorpions used to be able to grow over 2 meters in length, making them some of the biggest arthropods known to man. The change from large to small happened to give these scorpions an ability to hide from predators. It also helped them with hunting, because they didn't need as much food when they were smaller. Overtime, more scorpions started living in freshwater areas, and then when they started to develop amphibian-like qualities, they moved to the land. They started using "book lungs", similar to those of today's scorpions, and being able to move efficiently across land. They also started moulting and shedding, and mating the same way modern-day scorpions do (through transfer of sperm).
SPIDERS
Spiders have evolved from ancestors similar to that of the crab. The ability to make their own web has developed over time, along with the capability to produce venom. We know this because of the early fossils found showing the spiders without spinnerets, telling us spiders once lived without this ability. Spiders have evolved to be smaller, and hide from predators. Fossils also show prehistoric spiders had a significantly larger abdomen than those of today, and some also with shorter legs. Spiders used to be so large, they were equal to the size of a human head.
EXPLAINING THE CLADOGRAM:
aglaspidid: small horseshoe crab-like arthopods
lemoneites: marine chelicerata, with many extinct ancestors
xiphosurida: live in shallow waters, with soft/sandy bottoms. They sometimes come onshore to mate.
chasmataspida: rare, extinct group of arthopods, related to sea scorpions and horseshoe crabs
eurypterida: extinct aquatic arthopods
scorpiones: arachnids, most closely related to the scorpion
SCORPIONS
When they first appeared on earth, they were marine animals, only living in the water. Some sea scorpions used to be able to grow over 2 meters in length, making them some of the biggest arthropods known to man. The change from large to small happened to give these scorpions an ability to hide from predators. It also helped them with hunting, because they didn't need as much food when they were smaller. Overtime, more scorpions started living in freshwater areas, and then when they started to develop amphibian-like qualities, they moved to the land. They started using "book lungs", similar to those of today's scorpions, and being able to move efficiently across land. They also started moulting and shedding, and mating the same way modern-day scorpions do (through transfer of sperm).
SPIDERS
Spiders have evolved from ancestors similar to that of the crab. The ability to make their own web has developed over time, along with the capability to produce venom. We know this because of the early fossils found showing the spiders without spinnerets, telling us spiders once lived without this ability. Spiders have evolved to be smaller, and hide from predators. Fossils also show prehistoric spiders had a significantly larger abdomen than those of today, and some also with shorter legs. Spiders used to be so large, they were equal to the size of a human head.