In short, a group or species that was represented by huge numbers of individuals that lived for a long time, died out only recently, and hung around in deserts or near water, and was quite large and had lots of hard parts, we're likely to know well. A small, soft bodied animal from the deep ocean or middle of a rainforest and was alive only very briefly many hundreds of millions of years ago, we may never know about. In short, we have a great record of fossil deer, we have almost no fossil flatworms.
Understanding these is obviously important for palaeontology. It would be too easy to look at the wealth of dinosaur fossils coming from what were deserts and conclude that these teemed with life when the truth is simply that they preserved many more skeletons than the forests. While the fossil record is really pretty good surrounding the origins of birds, a great many specimens come from very few locations as we are reliant on the fossil-bearing rocks with the quality of preservation to retain the details of the fragile bones of small dinosaurs and early birds.
It should not be a surprise then that there are also gaps in our knowledge precisely because so few areas preserve this kind of material in large numbers.
Still, recognising such issues is that first step in dealing with them and while clearly there is only so much that can be done, there are for example methods available to counter the effects of a limited amount of rocks to dig in on studies of the evolution of fossil groups. Still, such analyses do help ameliorate the problem and of course the ever increasing ranks of fossil finds provide new data to help fill in the gaps in our knowledge and give our studies greater power and scope.
Modern processes may change all that. The fossil record of whales is, and will be for many years, silent about recent changes, such as whaling that started several hundred years ago, and accelerated declines related to ship strikes, pollution and overfishing. But fossils can illustrate the stark difference between pure ecological processes and human-influenced ones. Fossils underpin everything.
If you want to look at how things came to be, you have to look at how it once was. Smithsonian Institution photo. On the border between the Canadian provinces of Alberta and British Columbia, about two hours west of Calgary, Charles Walcott discovered a strange assembly of fossils in Two years into his tenure as the fourth Secretary of the Smithsonian, Walcott had unearthed a cache of some of the best-preserved fossils from the Middle Cambrian, some to million years old.
The weirdness of the Burgess Shale animals is one of their defining features. Their bizarre forms confounded early attempts to categorize their relationships with each other, or with modern animals.
Some of these creatures had been found before, but never in such numbers or fine detail. Soft tissues of these animals—tentacles, legs, antennae and other structures—show up clearly.
This fossil from the Burgess Shale in Canada shows some of the fine detail of Middle Cambrian specimens preserved there in abundance. Sometimes one organism is preserved in flagrante delicto , as it were, feeding upon another—for example, small leaf-eating insects within fossil plant stems [9] , or a fish that died choking on a fish it was trying to swallow [10].
Jeff Wilson and colleagues report another such remarkable specimen in this issue of PLoS Biology , a snake preserved complete and wrapped around a crushed dinosaur egg in a nest of otherwise unbroken eggs, from the Late Cretaceous of India [11]. It seems most likely, as the authors argue, that this 3.
Of course, we cannot be entirely sure unless further specimens come to light showing the bones of juvenile dinosaurs in the stomach region of the snake. In this case, and others, the specimens are key, and the care taken by their collectors and investigators to extract every fine detail.
A 3—5-meter-long madtsoiid snake, Sanajeh indicus , waits to feed on hatchling sauropod dinosaurs as they emerge from their eggs, in a scene from the Upper Cretaceous, some 70 million years ago. The sculpture is based on a fossil dinosaur nest from western India, reported in this issue of PLoS Biology [11].
The scales and patterning of the snake's skin is based on modern macrostomatan snakes, relatives of the fossil form. The hatchling dinosaur is reconstructed from known skeletal materials, but its color is conjectural. The eggs are based directly on the fossils. In making their detailed paleobiological interpretations, Wilson and colleagues [11] used all three methods advocated in this review—empirical observations of a remarkable specimen, coupled with comparison with modern analogs and biomechanical modeling.
In detail, the authors incorporated museum-based research, field research, stratigraphy and sedimentology, histology, embryology, and use of modern analogs into their interpretation of Sanajeh.
The Cuvierian example noted earlier, that a jaw that bears mammalian teeth can tell the paleontologist that it came from, say, a marsupial mole of a particular family, and the needle-like teeth indicate that it fed on insects, is based entirely within the hypothetico-deductive model. It is probable that function and behavior of a fossil bat should be inferred from comparisons with living bats.
But should a dinosaur be compared with living relatives e. Phylogeny might be thought to trump general similarity, but does it? Perhaps it would be pointless to compare a Diplodocus with a sparrow—their body size, morphology, and presumed modes of life are wildly different.
But something informative does come from phylogeny. At one level, parsimony allows paleobiologists to infer the presence of soft-tissue characters and behaviors. A development of the parsimony principle is the extant phylogenetic bracket EPB [12].
According to this principle, osteological correlates of unpreserved features are identified, and these allow inferences about the presence of unpreserved features. At a simple level, we could say that Tyrannosaurus rex presumably had an eyeball with certain properties, because its bracketing living relatives—birds and crocodiles—share many common characters in their eyes.
A further example, perhaps a little more impressive, is the prediction that fossil eggs will some day be found in the Carboniferous. The reasoning is that all living amniotes i. Thus, the first amniote in the Carboniferous, over million years ago, presumably laid a hard-shelled egg, even though the oldest fossil eggs are known only from the Triassic, million years later [13].
When specimens of the small theropod Sinosauropteryx were announced [14] with simple filament-like feathers, paleontologists looked at the phylogenetic trees and realized that this took the origin of feathers back to the base of the Middle Jurassic, some million years ago. This is because Sinosauropteryx is a basal coelurosaur, and the first coelurosaurs are known from the base of the Middle Jurassic; the most parsimonious assumption is that all coelurosaurs possessed some kind of feathers from the start.
Note that the Sinosauropteryx filaments are debated, and some [15] argue they are not feathers but connective tissue, but close study suggests otherwise [16]. In any case, feathers have been reported from nearly every other coelurosaur lineage, and so their origin deep within the phylogeny of theropod dinosaurs appears assured.
Knowing the arrangement of feathers, and perhaps their colors and patterns [16] — [18] , may allow paleobiologists soon to speculate, rationally and calmly, of course, about whether certain dinosaurs used their brightly colored and patterned feathers for camouflage, warning, sexual display, establishing pecking order, or other behaviors and functions. Biomechanical models, combined with considerations of modern analogs, provide powerful insight into certain aspects of the moving parts and skeletons of ancient organisms.
Opportunities have been hugely expanded by the relative ease with which 3-D structures, such as shells, bones, and skeletons, may be scanned and imaged. These images may then be tested using standard engineering software to determine how the structure was shaped by stresses and strains of walking, running, feeding, or head butting.
A useful modeling approach is finite element analysis FEA [19] , [20] , a well-established method used by engineers to assess the strength of bridges and buildings before they are built, and now applied to dinosaur skulls see Figure 2 , among other fossil problems. The skull of T. But the anatomy of the skull reveals a paradox; while T.
Often we can work out how and where they lived, and use this information to find out about ancient environments. Fossils can tell us a lot about the past. Why not find out more about fossils? If you read these pages you should get a pretty good idea of what a fossil is.
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