Author: zooks777

Everyone has heard of the demise of the dinosaurs around 65 million years ago, and has probably seen a trilobite.  Moths are not so common in the geological record.  Jes Rust of the University of Göttingen is one lucky palaeontologist.  In the lowermost sediments of the Tertiary Period in Denmark, about 55 million years old, he found a huge swarm of lepidopterans with representatives of at least seven species.  (Rust, J., 2000.  Fossil record of mass moth migration.  Nature, 405, p. 530-531.

Rust reckons that the 1700 specimens bedded in marine sediments represent mass migrations over the precursor of the modern North Sea.  They are not just in a single layer, but several horizons.  The find probably records annual, summer migrations much like those occurring today when winds are calm and land temperatures high.  Rust’s analysis suggests no major climatic or environmental shifts took place during deposition the 30 metres of sediment of the evocatively named Fur Formation.  To add to the oddity of the local geology, he has also found that slightly older sediments in the area contain giant ants, damsel flies and crickets, that by any stretch of the imagination could not have flown far.  They represent near-shore sedimentation, whereas the moth beds, devoid of such feeble fliers, formed in deeper water.  Stratigraphers should note that this is the first case where insects have traced a marine transgression.

Our feathered friends

Notwithstanding Sir Fred Hoyle’s contention that the famous Archaeopterix fossils from the 145 million-year old Solenhofen Limestone are forgeries, feathers are found as fossils.  But a recent find throws a lizard among the pigeons (precisely a small, squat reptile from the Triassic of central Asia) as regards the not unpleasant view that birds are the surviving descendants of the last dinosaurs.  (Jones, T.D. et al., 2000.  Nonavian feathers in a late-Triassic archosaur.  Science, 288, p. 2202-2205; Stokstad, E., 2000.  Feathers, or flight of fancy. Science, 288, p.2124-2125).

Fossils of Longisquama insignis have appendages that are remarkably like feathers, though less well-preserved examples were first regarded as long scales, hence the beast’s name.  If they are feathers, Longisquama is far too old to be a dinosaur, but may have begun a line of feathered reptilians from which the birds eventually evolved.  The authors of the new interpretation argue that feathers are unlikely to have evolved more than once.  Most vertebrate palaeontologists cite the very close skeletal similarities between theropod dinosaurs and birds as evidence for a close evolutionary relationship, sometime in the Cretaceous Period.  Feather specialists are dubious, suggesting the similarity is superficial and that Longisquama‘s ‘plumage’ are more like ribbed membranes.

Under no circumstances should readers tease or otherwise annoy ducks.  Australian palaeontologists have unearthed fossil evidence that a family of enormous, flightless birds – the dromorthinids or ‘thunder birds’ – which roamed Australian rain forests from 24 Ma to as recently as 50 ka, were not related to emus as previously thought, but were ducks.  “Fine”, you might think.  “Pretty big ducks”.  “Quack, quack”.  This is an unwise attitude.

Newly discovered in Queensland, 15 Ma old fossils of the giant and fondly named Bullockornis – estimated at 3 m tall and weighing a third of a ton – include its beak.  This is not akin to the beak of Daffy Duck – it was other anatomical details that placed dromorthinids among the anseriforms – but a serious pair of biting shears with immense musculature, fronting a head about the size of a horse’s.  The even taller, though lighter moas of New Zealand had small heads in proportion to body size, and, like ostriches and emus, were undoubtedly herbivores.  Bullockornis was either a fearsome predator or a pretty awesome scavenger.  The only Australian mammalian predator that might conceivable have been a competitor was the 15 Ma old marsupial lion, Wakaleo vanderleueri; about Rottweiler size, but better equipped in terms of fangs.

Full proof of its predatory habits awaits discovery of remains that preserve the stomach contents of this dangerous duck.  Should that materialize, and the excellence of preservation in the Miocene limestones of Queensland suggests that it is possible, Bullockornis would have been the largest land predator since the demise of the dinosaurs.

Source:  Stephanie Pain, The Demon Duck of Doom.  New Scientist, 27 May 2000

Life sneaked through ‘Snowball Earth’

The awesome magnitude of glacial epochs in the late-Precambrian from about 850 to 590 Ma was first brought to popular attention by the late Preston Cloud in his book Oasis in Space.  More recent work than his centred on the position of the continental masses that underwent repeated glaciation at that time.  One puzzle was the close association in time and place of glacigenic sediments with thick sequences of biogenic carbonates, as well as the fact that every continent preserves evidence for glaciations during this lengthy episode.  Carbonates today are manufactured at tropical latitudes, but that cannot be certain for all geological time.  So the key technique in checking for low-latitude ice sheets was using magnetic field evidence, in particular the inclination of remanent magnetism preserved in rocks of that age.  This gives a good approximation for their latitude at the time.

Repeatedly, investigators found evidence that large Neoproterozoic ice sheets able to extend to sea level did indeed occur on continents straddling the equator at that time.  That presents a major climatic problem.  Ice reflects incoming solar energy extremely well – and at that time solar power was probably somewhat less than its present value.  Ice at the equator implies ice everywhere and runaway cooling, so that the oceans would freeze over too.  This would seem to be a  situation from which there could be no thermodynamic escape, except by slow build up of volcanic carbon dioxide to give global warming by the ‘greenhouse’ effect.  Clearly, the Earth did emerge from a ‘snowball’  state, but even a short period of complete ice cover would annihilate marine life forms dependent on photosynthesis.  The whole of the Eucarya would quickly disappear, though bacterial forms depending on chemical and thermal  energy sources could have survived in the depths, kept liquid by geothermal energy.  Eucarya did survive, at least some did, for following the so-called ‘Cryogenian’ period the fossil record properly begin with a vengeance in the Cambrian Explosion.  Quite possibly the enormous stress placed on primitive, small Eucarya by repeated long periods of global glaciation helped accelerate the pace of evolutionary change.  But that demanded at least some ice-free parts of the oceans.

William Hyde, Thomas Crowley, Steven Baum and Richard Peltier (25 May 2000,Nature  vol. 405, p 425) have modelled the climate when Earth had its continents clustered mainly in the southern hemisphere in the late Precambrian.  For the first time they build into a late-Precambrian climate model the effects of ice sheets themselves, as well as the mathematics of energy balance and general air and ocean circulation.  Even with reduced solar input and no build-up of CO2 they found that air temperatures could have been high enough to sustain a permanent belt of open water at tropical latitudes, while clustered continents were ice bound.  A spin-off from this result is that isolated, ice-free continental fragments in the tropics of the time may preserve fossils of those few metazoa that did make it through the big freezes- the long sought missing ancestors for the Cambrian Explosion of life as we know it.

Does the fossil record present a true picture of the history of life, or should it be viewed with caution?  The further back in time, the less well preserved are the fossils found in rocks, and they are harder to find.  Estimates of the diversification of life through time would therefore seem to be plagued by an unavoidable bias. The problem is partially resolved by the observation that different fossil groups show similar patterns of diversity rising with time. Palaeontologists at the University of Bristol in England recently showed how new assessment methods, in which the order of fossils in the rocks (stratigraphy) is compared with the order inherent in evolutionary trees (phylogeny), provide a more convincing analytical tool (M.J. Benton, M.A. Wills, R. Hitchin, 2000. Quality of the fossil record through time. Nature,  vol.403, pp.534-537).  The two parameters, stratigraphy and phylogeny, are independent but relate to the same history. Their assessment of relationships between stratigraphy and phylogeny, for a sample of 1,000 published phylogenies, show no evidence for diminution in the quality of the fossil record going backwards in time. Although ancient rocks clearly preserve less information than more recent ones, if fossil information is scaled to the finest, global stratigraphic division, the stage, and the taxonomic level of the family, the fossil record of the past 540 million years provides uniformly good documentation of the course of evolutionary change..

MASS EXTINCTIONS

TIMING THE END-TRIASSIC MASS EXTINCTION

The close of the Triassic Period marks one of the five biggest mass extinctions in Earth’s history. Until recently its age was not known sufficiently well to match the extinction with possible causes.  A recent paper (J. Palfy, J.K. Mortensen, E.S. Carter, P.L. Smith, R.M. Friedman, H.W. Tipper 2000. Timing the end-Triassic mass extinction: First on land, then in the sea? Geology, vol.28, pp.39-42) reports a U-Pb zircon age of 199.6 +/- 0.3 Ma from a tuff layer in marine sedimentary rocks that span the Triassic-Jurassic transition. The dated level lies immediately below the last occurrence of conodonts and a prominent change in radiolarian faunas.  Other recently obtained U-Pb ages connected with fossil time divisions based on ammonites confirm that the Triassic Period ended ca. 200 Ma.  This is several million years later than suggested by previous time scales (208 Ma). Published dating of continental sections suggests that the extinction peak of terrestrial plants and vertebrates occurred before 200.6 Ma. The end-Triassic biotic crisis on land therefore appears to have preceded that in the sea by at least several hundred thousand years.

DELAYED BIOLOGICAL RECOVERY FROM MASS EXTINCTIONS

One of the most significant features of mass extinctions is the recovery and diversification of surviving life forms that follow them.  Post-extinction recovery is seen by many as a major factor in biological evolution.  However, palaeobiologists have worked mainly on recoveries following the “Big Five” mass extinctions.  Palaeontologists from the Department of Geology and Geophysics at Berkeley, California have examined how fast life rebounds after extinctions throughout the geological record of the last 540 Ma.  This general study (J.W. Kirchner & A. Well 2000. Delayed biological recovery from extinctions throughout the fossil record. Nature, vol.404, pp.177-180) shows that the rate of appearance of new species (origination) lags roughly 10 Ma behind extinctions, rather than replenishing diversity immediately after them.  This applies to the “Big Five” as well as to minor, background extinctions

The Berekely scientists’ results suggest that there are intrinsic limits to how quickly global biodiversity can recover after extinction events, regardless of their magnitude.

They also imply that today’s anthropogenic extinctions will diminish biodiversity for millions of years to come.

WERE THE DINOSAURS FRIED BY ULTRAVIOLET LIGHT?

From Astronomy Now, 3 May 2000

http://spaceflightnow.com/news/n0005/03dinosaurs/

BY NEIL ENGLISH

Over the past few decades, the rise and fall of the dinosaurs has captured the imagination of the public and the scientific community alike. While it is clear that the impact of a large asteroid straddling the coastline of what is the Yukatan peninsula in Mexico some 65 million years ago, may have wiped out these magnificent reptiles, the debate still rages as to precisely how they met their demise.

Many scenarios have been suggested, including a kind of nuclear winter in which enormous quantities of dust were ejected into the stratosphere, circling the globe and blotting out sunlight for weeks or months. But not everyone agrees that such a successful biological lineage as the dinosaurs could have been obliterated in this way.

Now, two American scientists – Charles Cockell of NASA’s Ames Research Centre In California, and Andrew Blaustein of Oregon State University, have worked out the events that occasioned themselves immediately after the KT impact.

In a recent paper communicated in Ecology Letters, they explain that the levels of nitrogen and sulphur oxides produced during the impact event would have all but destroyed the ozone layer, hereby doubling the levels of lethal UV radiation incident on the earth’s surface. This deluge of ionising radiation would have put additional stresses on the biosphere already stretched to the extreme by the impact.

What is even more remarkable though, is that significant sulphate deposits are only found over 1 percent of the earth’s surface, rendering the KT extinction event particularly lethal for the dinosaurs, but not for our kind – the small, furry, milk-suckling mammals.

Copyright 2000, Astronomy Now