Sunday, November 4, 2007

Living Trilobites?


Photo by C. Gronau

Is is possible that any trilobites survived beyond the Permian extinction, 250 million years ago? Is there evidence of trilobites surviving in modern times? I think we can safely say no to both of those questions, but there are some modern creatures with compelling similarities to the vanished and ancient arthropod group known as trilobites.



The serolid isopod above is an amazing example of how contemporary creatures with lifestyles similar to the presumed lifestyles of trilobites can adapt a similar appearance. Though outwardly appearing to resemble a trilobite, this animal is actually a relative of crabs and lobsters. Isopods are extremely numerous and adaptable, living in virtually every marine environment, including the Antarctic and deep ocean. They also live under rocks and decaying plants on land.



The young of the Madagascar hissing cockroach is better able to forage through jungle leaf litter and hide from potential predators because of its flattened, trilobite-like form, but this creature is an insect. Another insect known as the trilobite beetle got its name for obvious reasons...

Trilobite Beetle


It's also easy to see the superficial resemblance of horseshoe crabs to trilobite fossils, and one would assume these creatures had close kinship, but the horseshoe crabs' lack of calcite lenses in their eyes, as well as other structural differences clearly places them in a group outside of trilobite orders.

horseshoe crab


Triops, or tadpole shrimp are crustaceans that share legs with similarly structured gills and gantobases (structures used for maceration and transportation of food) with those of trilobites.

Triop (1)


Another group of polyplachophoran mollusks known as chitons have fooled beach combing observers into thinking they had stumbled upon fossilized or living trilobites.

Trilobite Fossil Look-alike

It seems that many living creatures find the same benefits of protection and flexibility that served the ancient trilobites by exploiting variations of flattened, segmented armor.


European Sowbug - Oniscus asellus

Paralejurus hamlagdadicus


7 comments:

Nick said...

I am curious why people reject the isopod or horseshoe crab as evolutionary descendants of the trilobite, yet have got no trouble at all with birds from dinosaurs?

Andrew said...

One of the main differences between the extinct trilobites and existing crustaceans is that crustaceans lack several of trilobites' defining characteristics, a specific example being calcite lenses in their eyes. The only living creatures with calcite lenses are a certain fly species and some types of brittle star.

http://www.sciencenews.org/articles/20010825/fob2.asp

The unique combination of highly specialized features identifies trilobites as a separate arthropod group from crustaceans(isopods) or horseshoe crabs. Crustaceans have long existed along side trilobites as discreetly genetically differentiated arthropod group, as incapable of interbreeding as scorpions and centipedes.

Nick said...

That makes sense. Still, I wish it were possible to extract some DNA from trilobites to establish definitively how they sit in the evolutionary tree versus DNA still extant today! Of course I understand morphology and other indicators allow us to do the analysis with some degree of confidence, but some part of me wants to think some of those ancient chromosomes are still crawling around somewhere!

Andrew said...

I wish some were still around as well, in some deep ocean trench, like in the Godzilla movies. I really wish they'd made the move from salt to fresh water or from inter tidal to terrestrial environments, then there'd have been a better chance of their survival into modern ages- maybe... They might've been picked off by the early small mammals.

Sushroom said...

Babies!!!

obama numbscull said...

You go through so many mental hoops so that you can find proof of evolution. Even when similar designs are found all over, but in no straight line. You continue to search for evolution and reject God.

Mike Welton said...

I love trilobites. They have facinated me since I was a child. The fossil record shows they existed for 300 million years. Humans will be lucky to exist for another 100. I hate it when religious circles treat our evolution as a joke. Denying it is like denying your parents existed. The truth is out there. Wake up!