Ancient web spins evolution story BBC - June 22, 2006
Ancient web spins evolution story BBC - June 22, 2006
The oldest-known spider web with prey still entrapped has been
found preserved in a chunk of amber in Spain. The mesh of silk
strands snaring the remains of a fly, beetle, mite and wasp,
dates back 110 million years to the time of the dinosaurs.
The fossil web appears to have been designed along the same
lines as the round nets woven by modern spiders.
Early web-spinner found in amber BBC - June 14, 2006
True orb weaving spiders found trapped in amber from 121-115 million years ago are the oldest of their type yet found. The spiral webs have proven an extremely successful strategy for catching prey - evidenced by the great diversity of orb weavers present today.
Two specimens are described in the UK Royal Society journal Biology Letters.The fossil spiders were found embedded in amber from Alava in northern Spain. They date to the Lower Cretaceous.
Amber is a form of protective resin extruded from trees that has hardened over millions of years. It is very useful to scientists studying the history of past life because ancient animals and plants are often preserved in the gem-like material.
David Penney of the University of Manchester, UK, and Vicente Ortuno of the University of Alcala, Spain, assign the arachnids to a new species: Mesozygiella dunlopi.
Typical orb webs consist of outer frame lines to which radial (spoke-like) lines are attached, providing support for the characteristic spiral sticky line that occupies most of the web's surface .By using two different types of silk - one strong and rigid, the other weaker but stretchy - the orb weaver creates a web with the required strength and flexibility to cope with the impact of fast-flying insects - and the struggling which occurs once the prey is captured in the sticky trap.
Web of intrigue
The evolutionary success of this design can be seen in the high diversity of true orb weavers, which currently number 2,847 living species.
This astonishing diversity also owes much to the way in which the basic design can be easily modified. "One modification to the web is quite fantastic," Dr Penney told the BBC News website. "Picture a normal, spiral orb web and picture running down from it a ladder-type structure which is also made from sticky silk. This has evolved to trap moths, which have scales that rub off." When a moth flies into a normal orb web, it's the scales that stick and the moth tumbles out of it. But with the ladder structure, the moth tumbles down until all the scales come off and eventually it gets caught."
In Biology Letters, Penney and Ortuno write that spiders may have expanded in number and diversity during the Cretaceous.An explosion in the abundance of flowering plants begot an expansion of the insects which pollinated them. These in turn provided prey for the spiders, the authors suggest, which prospered as a result.
There are fossil spiders that date from the Devonian (350-420 million years ago) - long before even the dinosaurs. In some of these mineral fossils, it is possible to see evidence of spinnerets, the organs spiders use to spin their web silk.But it is often unclear how fossil spiders used them; some species spin web silk to line their burrows and to protect egg sacs.
Spider blood found in 20 million year old fossil PhysOrg - September 30, 2005
Two droplets of blood, technically known as haemolymph, have been preserved in the amber which also contains the spider - Filistatidae - a family commonly found in South America and the Caribbean. The droplets are the first identified examples of spider blood ever found in an amber fossil. It is possible the blood could be used to extract DNA. The fossil, which is 4cm long and 2cm wide, was discovered in the Dominican Republic and dates back to the Miocene period.
Palaeontologist Dr David Penney, of the School of Earth, Atmospheric and Environmental Sciences, has now used the blood droplets to trace how, when, and where the spider died all those years ago. "It's amazing to think that a single piece of amber with a single spider in it can open up window into what was going on 20 million years ago. By analysing the position of the spideršs body in relation to the droplets of blood in the amber we are able to determine how it died, which direction it was travelling in and even how fast it was moving.
In the latest issue of the journal Palaeontology (2005, vol. 48, part 5) David describes how the spider died. He believes the spider was climbing up a tree when it was struck head-on by a sudden strong flow of resin. The spider then became engulfed in the resin and died. He argues that the shape and position of the blood droplets reveals which direction the spider was travelling in. It also reveals which of the spideršs legs broke first.
David discovered the fossil in 2003 during a visit to the Museo del Ambar Dominicano in Puerto Plata, Dominican Republic. His research initially focused on the spider which he identified as an entirely new species of spider. On his return to the UK, further research revealed the droplets of blood and the information the fossil contained.
Ancient arthropod caught moulting BBC - May 6, 2004
The Cambrian arthropod was found in the famous Burgess Shale, Canada. Exoskeletons are the most common body arrangement among Earth's animals. Insects, spiders and crustaceans have them, while mammals, birds and fish have endoskeletons. An exoskeleton provides a hard casing that offers some protection from predators. But there is a downside: it does not allow the body to expand. If an animal sporting an exoskeleton wants to grow, it must dump it temporarily before forming another, in a larger size. Scientists have suspected that the strategy of moulting (ecdysis) has been around since the first arthropod - about 545 million years ago - or even longer. They have been supported in this belief by circumstantial evidence. For example, a few fossil trilobite specimens were found in what looked like a post-moult state.
Oldest spider silk preserved in amber BBC - August 7, 2003
A dinosaur-era spider web is found preserved in amber.
The specimen is described in the journal Nature by Swiss researcher Dr Samuel Zschokke, from the University of Basel. Small globules of glue that would have stuck down any insect unlucky to get caught up in the silk are still clearly visible on the thread.
Primitive organisms
Amber is a form of protective resin extruded from trees that has hardened over millions of years. It is very useful to scientists studying the history of past life because ancient animals and plants are often preserved in the gem-like material. This is particularly true of arthropods like insects and spiders.
The oldest known spider found in a piece of amber was unearthed on the Isle of Wight in the UK recently. But the 125-million-year-old creature, Cremygale chasei, is by no means the earliest in the fossil record. There are specimens that date from the Devonian (350-420 million years ago) - long before even the dinosaurs. And in some of these mineral fossils, it is possible to see evidence of spinnerets, the organs spiders use to spin their web silk.
The newly reported specimen was actually recovered in 1969 from amber beds located near Jezzine in Lebanon - but its importance has only recently been recognised.
Time limit
The preserved strand is just four millimetres in length and bears tiny glue droplets, which in modern-day spiders are produced by a spider's silk-producing glands to form an adhesive coating around the fibre.
Dr Zschokke says the diameter of the ancient thread, and the size, density and arrangement of the droplets closely match those in webs made by recent araneoids - the superfamily that today includes common garden spiders that spin ornate, spiral orbs. But he adds, "As the specimen contains only a single thread, we cannot identify with certainty the type of web of which this thread was a part. It may have been part of an orb-web or of a gum-footed web. However, the fossil thread could have been part of a web type that no longer exists today. In any case, the present specimen is direct evidence for the antiquity of viscid spider silk."
It is certainly the oldest example of spider silk on record - and it may be hard to beat. Experts say the time period is pushing at the limit for amber preservation and mineral fossils would not retain the details of a spider's web.
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