When: Cretaceous (~100 million years ago)
What: Melittosphex is a fossil bee. It is the oldest bee fossil ever found, and this tiny tiny (only 3 millimeters long!) specimen, beautifully preserved in amber, can tell us much about the evolution of this amazing group of social insects. The closest relatives to living bees are the wasps, and some wasps are more closely related to bees than they are to other groups of wasps. The crabronid wasps (the digger-wasps) are the wasps most closely related to bees. These wasps are solitary and while the adults feed on nectar, the young larva feed on a spider or insect that mom-wasp procures for them.
Melittosphex is assuredly more closely related to bees than any wasp, with a great deal of anatomical features found only in bees today, such as the morphology of its hindlimbs and the presence of intricately branching hairs on body. Melittosphex also has features reminiscent of its wasp ancestry that are not seen in any living bee species today; specific spurs on its middle pair of legs and a very slender rear most ‘foot’. This combination of features shows that Melittosphex is an excellent example of a transitional fossil, falling between the crabronid wasps and all living species of bees.
Knowledge of Melittosphex and its kin is critically important for determining how the solitary carnivorous (as larva) wasps gave rise to the eusocial herbivorous bees. But that is not all! These ancient bees also help inform us to how the modern plant biota was established. Today’s flora is dominated by angiosperms - the flowering plants, but this is a relatively recent state of things. The earliest known fossils of angiosperms date to only the Jurassic period, and it is not until the early Cretaceous that body fossils are known. It is at about 100 million years ago that the great angiosperm radiation can be seen, and shortly after this the flowering plants begin to dominate. The one specimen of Melittosphex known preserves minute pollen grains between the branching hairs on its body, showing that even 100 million years ago bees were involved in pollination of these flowing plants. It has long been thought that bees and angiosperms evolved in tandem, that each group depends on the other for its success, and little Melittosphex offers more support for this view.
Reconstruction by Marianne Collins
When: Cambrian (~505 million years ago)
Where: Specimens first known from the Burgess Shale of Canada, now possibly found in other sites in North America of similar ages.
What: Perspicaris is another enigmatic stem arthropod from the Burgess Shale fossil lagerstatten deposit. It is a bivalve arthropod, like our last Burgess Shale fossil Tuzoia, but has more bits than just its eyes sticking out, so more conclusions as to its life style can be drawn. Sticking out from the front of its carapace are eyes and relatively thick antennae and emerging posteriorly is a powerful tail. Perspicaris swam though the water column under its own power, but swam to the bottom of the paleo-ocean to feed. Sediment preserved in the gut of a few specimens shows this animal was a deposit feeder; consuming loose mud on the ocean floor and processing all minute food particles from these sediment grains.
The evolutionary relationships of Perspicaris are not well known, like Tuzoia it is proposed to either be related to a subgroup of crustaceans or to be a stem taxon to all living arthropods. As you probably have concluded, the relationships between all of these taxa is an area of paleontology that really needs more people working on it!
Reconstruction by Marianne Collins
When: Cambrian (~520 - 500 million years ago)
Where: First described from Burgess Shale formation in BC, Canada, now found fairly worldwide in beds of simular ages.
What: Tuzoia is a bivalve arthropod first known from the Burgess Shale formation. It may seem odd that an animal that looks like an upside down taco with sunglasses on is an arthropod, but this is not as crazy as it first appears! In the crustacean subgroup of Arthropoda many taxa have a bivalve (2 parts that cover a great deal of the animal with a hinge in the middle) shell, if not as adults then in their larva forms. One example of a living group that has this type of shell as adults is the ostracods, and more well known taxa such as lobsters have shells such as this in their juvenile stages. To complicate matters even more, there are a number of fossil taxa, some also known from this locality, that have simular shells.
In life Tuzoia swam freely though the water column. Without knowledge of its mouth parts its difficult to know if it was a filter feeder or a small predator. Tuzoia reached a maximum size of about 7 inches (~180 mm).
For more information and images see: http://www.burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=125&m=5&&ref=i
And check out the Burgess Shale tag on Daily Fossil to see other odd odd animals from this formation!
When: Carboniferous (~315 to 300 million years ago)
Where: at least North America and Europe, possibly worldwide
What: Archimylacris is a 3 inch (~8cm) long ‘roachoid’. This over 300 million year old fossil insect and its kin have been commonly referred to as ‘ancient cockroaches’, but studies have revealed they are ancestral to all of the Dictyoptera (roaches, termites, and mantises). Fossils of Archimylacris are fairly common in the Carboniferous, but most of the specimens are fragmentary with isolated wings being the most numerous component recovered by far. Specimens such as the one shown above are found in nodules (a solid blob with mineral composition different from the surrounded rocks). These specimens revealed much more of the animal’s morphology, as the whole specimen is present, but what is available for study is greatly limited to the fracture plane that is broken open. A fairly recent study microCAT scanned the specimen, revealing the complete morphology in intricate detail, and generating a cgi model as a reconstruction. This study revealed that Archimylacris lived much like modern roaches do, in dense forests eating detritus and capable of fast scurrying, possibly rearing up on their hind legs as they ran. It is easy to see how Archimylacris and other fossils that we now identify as stem Dictyoptera were first thought to be ancestral to only roaches; the roach body plan is one that has been conserved for hundreds of millions of years. Modern roaches retain many primitive features, whereas termites and especially mantises have greatly transformed over millions of generations.
For a cool movie of the reconstruction, and a bit more details as to how it was accomplished, visit: http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_14-4-2010-15-39-48
When: Cambrian (~500 million years ago)
What: Skara is one of the many tiny species of arthropods collected from an amazing swedish fossil locality. These fossils are notable for the intricate morphology still present, with many examples preserving individual cila, pours, and every tiny plate that makes up these animals’ shells. These fossils are made of phosphate, and what is preserved is actually a secondary coating of this compound which was deposited shortly after the animal died and was buried, thus these specimens are hollow and exceedingly fragile. Fossils with this type of preservation are called ‘orsten fossils’. This mechanism of fossilization has been found in several places around the world, the swedish locality is in Västergötland and was discovered in 1975 by Klaus J. Müller, a professor of micropaleontology at the University of Bonn. During the time of deposition, this part of Sweden, like most of the region, was covered by a shallow and warm sea.
All of these fossils are exceedingly tiny, the largest that has been found is only about 2 millimeters along its longest axis. Large animals evidently cannot be preserved by a phosphate coating. Skara is actually one of the larger specimens, coming in at a whopping 1.2 millimeters long! This form has a long flexible tail and trunk, with 5 pairs of anterior appendages. It has no eyes, and has been reconstructed as a benthic filter feeder. Skara has been placed in its own group, the Skaracarida. It is a crustacean arthropod, there are over 60,000 species of living crustaceans - including lobsters, crabs, shrimp, and barnacles, to name just a few. Within Crustacea Skara is closely related to the copepods. These tiny tiny fossils are extremely important, as they tell us a lot about the Cambrian world that was unknown to science before their discovery, such as how diverse non-trilobite arthropods already were at this early time. Additionally, as such small forms are preserved, juveniles of many fossil species are known and in some cases complete growth series.
For more information about these amazing fossils, visit the CORE website: http://www.core-orsten-research.de/index.html (Skara is in their logo!)
Meganeura - The Giant Dragonfly
When: Carboniferous (~305-299 million years ago)
What: Meganeura is the largest dragonfly, with a wingspan of 2.5 feet (~75 cm) in some specimens. The largest living dragonfly is a comparatively weensy 7.5 inches (~19 cm) across at the wings. A scientific debate had centred upon why Meganeura was able to become so large. It has been suggested that it was only able to reach such a great size due to the relatively higher levels of oxygen in the Carboniferous air. This is based partly upon the way most modern insects respire, they do not truly breathe, but instead simply diffusion oxygen throughout their small bodies. However, more recent studies show that larger insects do breathe via compression and expansion of their trachea. Additionally insects much larger than those today have been found in later rocks which do not show evidence of elevated oxygen levels. More research needs to be done to determine the impact of oxygen levels upon the maximum size of insects.
Only a few fossils have been found of Meganeura, but despite this, almost every scene ever of a Carboniferous forest has one of these animals perched upon a giant club moss tree. I do not blame them, I could not resist either. Other animals in these dense forests with Meganeura were a gaggle of other gigantic insects and arthropods, a great variety of amphibians, and the first reptiles. This was the start of the true colonization of land by vertebrates; it has also been suggested it was the arrival of these predators which limited the size of insects such as Meganeura in later time periods.
Early Cambrian Trilobites - The first trilobites
When: Appear in the early Cambrian ~ 526 million years ago
What: Trilobites are arthropods. Trilobites appear suddenly in the early Cambrian, and are almost immediately found worldwide. They are one of the major players in the Cambrian Explosion. Their apperance is so consistant that the presence of these animals defines the start of a subperiod within the Cambrian. The first records of trilobites include members of all nine orders (major subclades within Trilobita), meaning that they had to be present for some time before their first appearance in the fossil record. It is important to note that it is only shells that are preserved at first, so the lack of a record previously could be due to the previous lack of a mineralized external skeleton for trilobites. however, this interpretation has its own problems - as it implies the nine orders independently developed hard shells. Another possible explanation is that previous to 526 million years ago the water chemistry was such that preservation of the shells was impossible. The photo and reconstruction above are probably of the early genus Paradoxides. This early trilobite, like most of the first ones to appear, was capable of swimming but mostly crawled along the bottom, searching for minute food particles in the surface sediments.
As stated before trilobites are arthropods. This massive group includes animals with a hard external skeleton, such as lobsters, insects, spiders, etc. The placement of trilobites in this group is not debated. What is much more contentious is their placement within the clade. At first they were placed as the sister-group to the crustaceans (lobsters and crabs, for example) but now it is thought that the horseshoe crab is their closest living relative, far removed from the rest of Arthropoda.
- Sea Scorpion
When: Late Silurian ~ 430-420 million years ago
Where: In ancient relatively shallow seas, swimming over what is today North America and Europe. They are very common in the eastern US, and are the state fossil of New York.
What: Eurypterus is the most well known member of the Eurypterida. Okay that probably didn’t help much! These animals are arthropods (insects, spiders, crustaceans, etc) and in the group that incudes the horseshoe crabs, spiders, and scorpions. They are not actually scorpions, though they are closely related to them. Like a lot of living arthropods, they grow by successive molting and can become very large, in fact the largest arthropods known were eurypterids! Most fossil are small, just a few centimeters, but the largest one is over 4 feet (120cm) long from head to tail tip! They moved both by swimming though the water with their large paddles arms and walking on the substrate with their smaller legs. They were carnivorous and most likely at the top of the food chain in their day - jawed fishes were just starting to appear. Its possible the evolution and migration of these fishes is what lead to the extinction of the sea scorpions.