Thursday, October 10, 2013

PREHISTORIC INSECTS

PREHISTORIC SPIDERS              

Evolution of spiders

From Wikipedia, the free encyclopedia
Jump to: navigation, search
A spider in Baltic amber
The evolution of spiders has been going on for at least 400 million years, since the first true spiders (thin-waisted arachnids) evolved from crab-like chelicerate ancestors. Today, there are 42,473 described spider species within the diverse phylum of arthropods.
Major developments in spider evolution include the development of spinnerets and silk secretion.

Early spider-like arachnids

Among the oldest known land arthropods are Trigonotarbids, members of an extinct order of spider-like arachnids.
Sharing many superficial characteristics with spiders, Trigonotarbida were terrestrial, respired through book lungs, and walked on eight legs with two additional legs adapted to use around their mouth. Arguments still remain open as to whether they possessed the ability to create silk. This had been popular thought for quite some time, until an unpublished fossil was described with distinct microtubercles on its hind legs, akin to those used by spiders to direct and manipulate their silk.
Regardless, Trigonotarbida are not considered true-spiders. They are generally accepted as an independent early offshoot within the Arachnida clade, and not directly ancestral to modern spiders.

Emergence of true spiders[edit]

At one stage the oldest fossil spider was believed to be Attercopus which lived 380 million years ago during the Devonian. Attercopus was placed as the sister-taxon to all living spiders, but has now been reinterpreted as a member of a separate, extinct order Uraraneida which could produce silk, but did not have true spinnerets.
The oldest true spiders are thus Carboniferous in age, or about 300 million years. Most of these early segmented fossil spiders from the Coal Measures of Europe and North America probably belonged to the Mesothelae, or something very similar, a group of primitive spiders with the spinnerets placed underneath the middle of the abdomen, rather than at the end as in modern spiders. They were probably ground dwelling predators, living in the giant clubmoss and fern forests of the mid-late Palaeozoic, where they were presumably predators of other primitive arthropods. Silk may have been used simply as a protective covering for the eggs, a lining for a retreat hole, and later perhaps for simple ground sheet web and trapdoor construction.
As plant and insect life diversified so also did the spider's use of silk.Mygalomorphae and Araneomorphae) appeared more than 250 million years ago, presumably promoting the development of more elaborate sheet and maze webs for prey capture both on ground and foliage, as well as the development of the safety dragline. The oldest mygalomorph, Rosamygale, was described from the Triassic of France and belongs to the modern family Hexathelidae. Megarachne servinei from the Permo-Carboniferous was once thought to be a giant mygalomorph spider and, with its body length of 1 foot (34 cm) and leg span of above 20 inches (50 cm), the largest known spider ever to have lived on Earth, but subsequent examination by an expert revealed that it was actually a middling-sized sea scorpion.

 








Spiders with spinnerets at the end of the abdomen (
By the Jurassic, the sophisticated aerial webs of the orb-weaver spiders had already developed to take advantage of the rapidly diversifying groups of insects. A spider web preserved in amber, thought to be 110 million years old, shows evidence of a perfect "orb" web, the most famous, circular kind one thinks of when imagining spider webs. An examination of the drift of those genes thought to be used to produce the web-spinning behavior suggests that orb spinning was in an advanced state as many as 136 million years ago. One of these, the araneid Nephila jurassica, from about 165 million years ago, recorded from Daohuogo, Inner Mongolia in China, is the largest known fossil spider.[1]
The 110-million-year-old amber-preserved web is also the oldest to show trapped insects, containing a beetle, a mite, a wasp's leg, and a fly.[2] The ability to weave orb webs is thought to have been "lost", and sometimes even re-evolved or evolved separately, in different breeds of spiders since its first appearance.
A list of fossil spiders, down to species level, can be found at the American Museum of Natural History's website.[1]

Meganeura

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Meganeura
Temporal range: 305–299Ma Late Carboniferous
Reconstruction
Cast of an original fossil of a Meganeuridae
Scientific classification
Kingdom:Animalia
Phylum:Arthropoda
Class:Insecta
Superorder:Odonatoptera
Order:Meganisoptera
Family:Meganeuridae
Genus:Meganeura
Species
  • Meganeura brongniarti
  • Meganeura monyi
  • Meganeura vischerae
Meganeura is a genus of extinct insects from the Carboniferous period approximately 300 million years ago, which resembled and are related to the present-day dragonflies. With wingspans of up to 65 cm (25.6 in), M. monyi is one of the largest known flying insect species; the Permian Meganeuropsis permiana is another. Meganeura were predatory, and fed on other insects.
Fossils were discovered in the French Stephanian Coal Measures of Commentry in 1880. In 1885, French paleontologist Charles Brongniart described and named the fossil "Meganeura" (large-nerved), which refers to the network of veins on the insect's wings. Another fine fossil specimen was found in 1979 at Bolsover in Derbyshire. The holotype is housed in the Muséum national d'histoire naturelle, Paris.

Size[edit]

Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen is diffused through the insect's body via its tracheal breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed (Harlé & Harlé, 1911) that Meganeura was only able to fly because the atmosphere at that time contained more oxygen than the present 20%. This hypothesis was dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability.[1] If this hypothesis is correct, these insects would have been susceptible to falling oxygen levels and certainly could not survive in our modern atmosphere. Other research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion".[2] Recent analysis of the flight energetics of modern insects and birds suggests that both the oxygen levels and air density provide a bound on size.[3]
A general problem with all oxygen-related explanations of the giant dragonflies is the circumstance that very large Meganeuridae with a wing span of 45 cm (1.5 ft) also occurred in the Upper Permian of Lodève in France, when the oxygen content of the atmosphere was already much lower than in the Carboniferous and Lower Permian.[4]
Bechly (2004) suggested that the lack of aerial vertebrate predators allowed pterygote insects to evolve to maximum sizes during the Carboniferous and Permian periods, maybe accelerated by an evolutionary "arms race" for increase in body size between plant-feeding Palaeodictyoptera and Meganisoptera as their predators.[5]

Ancient 'Frankenstein' Insect Discovered

0
 
0
 
0
Share
0
 

Tuesday, October 1, 2013

PREHISTORIC   PLANTS                              
The cladoxylopsids are a group of plants known only as fossils that are thought to be ancestors of ferns and horsetails.
They had a central trunk, from the top of which several lateral branches were attached. Fossils of these plants originate in the Middle Devonian to Early Carboniferous periods (around 390 to 320 million years ago), mostly just as stems.
Cladoxylopsida contains two orders. The order Hyeniales is now included in Pseudosporochnales.
Intact fossils of the Middle Devonian cladoxylopsid Wattieza show it to have been a tree, the earliest identified in the fossil record as of 2007.                                                                                                                                                                                                                   
Gangamopteris is a genus of Carboniferous-Permian, very similar to Glossopteris. Previously, it was classified as fern with reproduction by seed. The genus is usually only applied to leaves, making it an form taxon.[verification needed] Gangamopteris dominates some coal deposits, such as those of the Beacon Supergroup.
In Paleorrota geopark in Rio Grande do Sul, Brazil, were found Gangamopteris obovata. Were located on the Mina Morro do Papaléo in Mariana Pimentel and Quitéria in Pantano Grande. Dating from the Permian and were in the Rio Bonito Formation. In the town of Cachoeira do Sul, met Gangamopteris sulriograndensis were discovered.                                    
Protosalvinia is a prehistoric plant found commonly in shale from shoreline habitats of the Upper Devonian period. The name Protosalvinia is a misnomer. The name literally means early Salvinia, and was given in the erroneous belief that the fossils were an earlier form of the living aquatic fern Salvinia. It is no longer believed that the fossils come from a fern, but deciding exactly what the fossils represent is still a matter of debate. This is surprising when one considers how much is known about the fossils.
The most likely interpretation of Protosalvinia is that it represents either a fossil liverwort or brown alga, although no definitive brown algae have been identified from before the Tertiary period, and examination of the spore structure shows no features in common with living groups of brown algae. The living plant was a thallus with short dichotomous branching. The branches in the largest species were as much as one centimeter across. In some fossils, the branching lobes lie flat, but in others the tips of the branches are curled up over the fossil, giving it a round outline. Embedded in the tissues of the thallus are chambers in which spores (200 micrometre diameter) were produced by meiosis.
Microscope slide mount of Protosalvinia sp. showing bifurcating thallus.
Because Protosalvinia is usually preserved as a compression fossil, it can be difficult to determine whether its anatomy is more like a plant or an algae. Some biochemical evidence favors interpretation as an algae. Lignin and Cutin have been found in the thalli, and sporopollenin in the spore walls. The grouping of the spores found in the thallus favors interpretation as a plant. The absence of any stomata on the surface is inconclusive, as all bryophytes lack stomata on the main body of the plant.
However, the tips of Protosalvinia branches show evidence of conceptacle-like dips.
Protosalvinia is found in association with conodont elements.
For the present, the relationships of Protosalvinia remain uncertain.              SOURCE:WIKIPEDIA

Wednesday, August 7, 2013


  HELICOPRION:SHARK OR AMMONITE?                                                    Is Helicoprion a shark or an Ammonite? As humans we will ever know, all we can do is imagine. The reason I believe that the Helicoprion tooth spiral isn't a tooth spiral at al  is because. All prehistoric shark teeth have cracks in them from being used to kill their prey. But the fossilized teeth have no cracks in it what so ever. And if you were to take a Helicoprion tooth spiral and turn it on its side(see figure 1.1) it would be in the same shape as an Ammonite's shell. The shell would have sharp barbs all over the shell(see figure 1.2) if it really was a Ammonite shell. The barbs would make a great defense against Hybodus the reason(see figure 1.3) I believe Hybodus would be a predator on Ammonites is because it has teeth that look very similar to that of the Bull shark(see figure 1.4) and that is because the Bull shark's teeth are perfect for crushing shells. And to remind you this is only a theory.                         
Figure 1.1

Figure 1.2
Figure 1.4

Figure 1.3










                                       
MEGALODON                                                              
Megalodon  meaning "big tooth", from Greek μέγας (megas, "big") and ὀδον (Odon, from ὀδούς, odous, "tooth")) is an extinct species of shark that lived approximately 28 to 1.5 million years ago, during the Cenozoic Era (late Oligocene to early Pleistocene).
The taxonomic assignment of C. Megalodon has been debated for nearly a century, and is still under dispute. The two major interpretations are Carcharodon Megalodon (under family Lamnidae) or Carcharocles Megalodon (under family Otodontidae).Consequently, the scientific name of this species is commonly abbreviated C. Megalodon in the literature.
C. Megalodon is regarded as one of the largest and most powerful predators in vertebrate history, and likely had a profound impact on the structure of marine communities. Fossil remains suggest that this giant shark reached a maximum length of 14–18 meters (46–59 ft.),and also affirm that it had a cosmopolitan distribution.[1] Scientists suggest that C. Megalodon looked like a stockier version of the great white shark, Carcharodon carcharias.                                                                                                Source:wikipedia