Dorudon atrox picture courtesy of Mark Uhen

WHY CREATIONISM IS WRONG: TRANSITIONS

Moderate Creationists,or anti-Darwinists claim that there are no 'transitional' fossils.

What do they mean? What are 'transitional forms' that Darwin's theory requires to be found in the fossil record and what else do Creationists mean? In some cases it is simply the change of one group of animals from one higher-level taxonomic group to another, like between the classes Reptilia and Aves, reptiles to birds.

Whales used to be the favourite example of all anti-Darwinists, because a clear fossil sequence from land-going to marine whales was unknown. However since 1979 a clear sequence of fossil whales that bridge the gap has been unearthed, covering the period between 53 million years ago [53 mya] to 40 mya, when the first fully marine whales are found.

The illustration above is one such species in the sequence. Dorudon atrox is a fully aquatic animal,but it retains a small set of hindlegs indicating its terrestrial origins, like other whales from its day, some 40 mya. A species like it became the ancestor of modern whales - toothed whales [Odontocetes] and baleen whales,[ Mysticetes], about 35mya.

Now that the fossil gap for whales is filled the Creationists have few high-profile animal groups to be sceptical about their fossils. Often their literature is still full of claims that 'major transitions' still have no clear fossil record. Let's look at those 'major transitions' in some detail...

  • INVERTEBRATE TO VERTEBRATE

    Currently very few fossils mark this transition, but they exist. Vertebrates are technically creatures with bone, belonging to the Phylum CHORDATA. Boneless chordates [eg Pikaia] precede the first vertebrates [eg Conodonts] in the fossil record, so that's not an issue. A related transition is from non-Chordate to Chordate, and these too follow correct temporal order [eg the appearance of Yunanzoon, a Hemi-Chordate.] The real problem is that such fossils tell us very little about how it happened. Most of the 'action' happens while the animals are developing. On this basis 'chordates' are grouped with Echinoderms, because the embryos of the two follow a similar developmental path in their earliest stages. Recently fossil embryos have been recovered from rocks from the transitional period [570 mya - 520 mya] which shows that all our questions could yet be answered by the fossils.

  • FISH TO AMPHIBIAN

    When people think of fish they think of fish like marlin, tuna and salmon, all of which belong to the Teleostean fishes. Land-going vertebrates [collectively called Tetrapods] did not come from Teleost fishes, but from the Sarcopterygian or lobe-fin fishes, which include the coelocanths and the lungfishes and our ancestors. Amongst fossil lobe-fins are fishes that blur the borderline between 'fish' and 'tetrapod' - the Pandericthyids - and tetrapods that are very fishy.

    Pandericthys is a fish with paired fins with leg-bones just like a tetrapod's legs, but missing toes. It's skull is so close to being a tetrapod's skull that that's what it was first thought to be.

    Acanthostega is a tetrapod with legs, shoulders and hips not strong enough for life on land, but it has a full set of toes - eight of them. This fishy tetrapod also has a fully finned tail and a set of fish's gills.

  • AMPHIBIAN TO REPTILE

    Reptiles is something of an imprecise term. AMNIOTE is more correct and applies to all land-going vertebrates that wrap their eggs in an amnion. Some put a soft shell around it - reptiles, and primitve mammals - while others put a hard shell around it - birds - or keep the unshelled amnion within their bodies to let the embryo develop - like advanced mammals do. The Amniotes probably diverged very early on from the ancestors of modern amphibians. Since eggs very rarely fossilise for small animals and not at all for amphibians it is very hard to distinguish between ancient amniotes and their amphibian kin.

    Some modern amphibians do give us hints as to how it happened - the change from water-laid eggs to eggs laid-on-land. Species of frog are known that carry their tadpoles with them in large yolky eggs and some frogs have eliminated the tadpole stage entirely from their development. Such 'intermediate' means of reproduction hint at what went on perhaps 340 mya.

    Here's a very good news article on Casineria kiddi a possible early amniote from 340 mya...CASINERIA

    Here's some more technical discussions of amniotes at the Tree of Life Project...AMNIOTES

    Talk.Origins, of course, has a section on Amniote origins...TRANSITIONS FAQ

  • REPTILE TO MAMMAL

    The Reptile to Mammal transition is one of the best known. Hundreds of species bridge the gap between the two vertebrate classes.

    What is a reptile and what is a mammal anyway? Modern and fossil reptiles usually have complex lower jaws that have several bones. A mammal has just one jaw-bone, the dentary, and several small bones involved in hearing that form from the same embryonic material during development as the jaw.

    The fossils show a gradual takeover of jaw function by the dentary and a reduction in the size of the other jaw-bones which become intimately involved with hearing. Starting with the very reptilian Sphenacodonts mammal ancestors then became the more mammalian Therapsids and finally the very mammalian Cynodonts that differ from mammals in still having composite jaw bones.

    The Cynodonts were probably warm-blooded, furry animals that laid eggs, similar in reproduction to modern Monotremes like the platypus and echidna [themselves on the ancestral line to Marsupials.] Even 'advanced' mammals, the Placentals show a range of reproductive systems that have reptilian analogies. The pathway from reptile to mammal is blurred across hundreds of species.

    Here's some links that cover the Reptile-Mammal Transition in more detail...

    Ken Harding's Evolution Education Resource Centre discusses the transition in terms of reproduction...MARSUPIALS

    Talk.Origins covers the various stages that the THERAPSIDS went through to become MAMMALS...TRANSITION FAQ

    And Lenny Flank covers the Transition and shows where Creationists have distorted and lied about the facts...THERAPSIDS

  • REPTILE TO BIRD

    Edward Hitchcock described the first Dinosaur footprints in the 1830s believing them to belong to fifteen foot birds. Since then a multitude of bird-like dinosaurs have been found, some even sporting feathers. The oldest bird of which we have good skeletal remains is Archaeopteryx which shares many features in common with the 'Raptors' of Jurassic Park fame. After Archaeopteryx follow more advanced birds which lose bit by bit their dinosaur-like features, as they correspondingly gain more advanced bird-like features. But features once thought unique to birds, like feathers, are now known to be present in flightless dinosaurs.

    In recent years bird-like dinosaurs, like Protarchaeopteryx, Caudipteryx, Sinosauropteryx and very recently Microraptor have been found sporting feathers or feather-like coatings. These challenge our artificial definitions of what a 'bird' is and what a 'dinosaur' is. Some ornithologists [bird scientists] have refused to accept the evidence, instead claiming that the more bird-like dinos are 'birds' while the feathery coatings aren't feathers.

    Their main reasoning against the dino-bird link is based on biomechanics, the study of how living things move. The dinosaurs first suggested as bird relatives are a LOT larger than birds and their limb proportions make them unlikely candidates to become flyers. However as smaller bird-like dinosaurs are found, such as Microraptor, this argument begins to lose its force. Dinosaur scientists have never claimed that birds came from dinosaurs as large as Velociraptor anyway. They have generally held that the bird ancestors were once bird-sized, and the eventually flightless lineages steadily grew larger, as flightless birds have done through out time.

    An interesting possibility then emerges, that once flying 'birds' became the various advanced predatory dinosaurs, as first suggested by Gregory S. Paul. Since the discovery of an Oviraptor sitting on a nest like a brooding hen, this theory is not so strange.

  • LAND-GOING TO AQUATIC REPTILES

    Through-out the history of reptiles various lineages have gone back to the Ocean. The most spectacular are the PLESIOSAURS [which included the gigantic PLIOSAURS, such as Liopleurodon from the 'Walking with Dinosaurs' series] and the ICHTHYOSAURS, both of which have detailed fossil records and very few gaps in their fossil records. Crocodiles similarly have an extensive fossil-record and so not too many puzzles surround their history. Other spectacular marine reptiles are the MOSASAURS which were giant marine lizards [up to 17 metres long] akin to present day MONITOR lizards.

    The Turtles, technically known as CHELONIANS, present a real puzzle - maybe. Part of the puzzle is just what kind of reptile group turtles belong in. Very primitive reptiles lack openings in their skulls [known as FENESTRAE] and are known as ANAPSIDS. Turtles at first analysis seem to be ANAPSIDS since they lack such openings - but this may not be an ancestral feature of the turtle group. Recent molecular analysis of their genes allies them with ARCHOSAURS, such as the modern crocodilians.

    Several reptilian lineages actually produced forms akin to turtles - the anapsid PAREIASAURS show a step-by-step evolution from unshelled to shelled forms, and the euryapsid PLACODONTS also show a similar evolution, with some forms that are very turtle-like, such as HENODUS and PLACOCHELYS. Recent genetic evidence allies chelonians with crocodiles, which in turn belong to a group of diapsid reptiles called THECODONTS, one lineage of which were the AETOSAURS, several of which had shell-like armour akin to turtle shells. Unpublished fossils of AETOSAURS are very turtle-like, but detailed study awaits their published scientific description. Puzzle solved? More evidence will tell.

  • LAND-GOING TO AQUATIC MAMMALS

    As mentioned above a range of species now cover the gap between land-going and marine whales. What about other marine mammals like sea-lions, seals and walruses - collectively known as PINNIPEDS? These have a fairly patchy fossil record but they are clearly related to bears and dogs. Genetic studies have clarified a lot of the ambiguities surrounding their evolution.

    Why did seals and whales turn out so differently though? Whales propel themselves mostly with their tails, while seals use their feet. It seems that seals evolved from ancestors that evolved in cooler waters. A tail provides a means of heat loss for a mammal before it becomes a means of propulsion - and so in cooler climes tail-loss would be strongly selected by evolution. Whales evolved in the warm waters of the ancient TETHYS ocean, pinnipeds in much cooler northern waters.

  • APE TO HUMAN

    According to current taxonomy humans are apes, so no transition as such is needed. However fossils do show that humans evolved from bipedal chimpanzee-like creatures about 5 million years ago. These were the Australopithecines and they diverged into several different species. While Creationists continue to call the Australopithecines just 'apes', they were apes which possessed human teeth and bipedal locomotion. In many ways they are intermediate mixtures [mosaics] of ape and human features.

    One of these mosaic apes evolved into our genus, Homo, about 3 - 2.5 million years ago and by about 2 million years ago this lineage produced the very human-like Homo ergaster/erectus which spread out of Africa into Europe and Asia. From analysis of their growth patterns and morphology Homo erectus was intermediate between the very ape-like Australopiths and ourselves. Homo erectus was the first of our ancestors to make clothes, use fire and probably make boats.

    By about a million years ago human brain size was roughly at modern levels. One lineage moved into Europe and by 130 thousand years ago became Homo neaderthalensis, a sub-species that probably contributed genes to modern Europeans. The rest remained in Africa and by about 300 - 250 thousand years ago began showing signs of modern human, Homo sapiens, morphology. Within the last 200 thousand years various migrations of modern humans produced the various mixes of distinctive features we call 'races' but in reality we are just one species, more closely related than most mammal species.

  • MUCH is yet to be learnt about all these transitions, since we have relatively few fossils for some transitions. BUT few is NOT zero, as the anti-Darwinians claim. And more are found all the time. They are very clear evidence for what Creationists call MACROEVOLUTION - a term that needs explaining because it has been the source of much confusion.

    MACROEVOLUTION: For evolutionary biologists this means evolution of one species into another [or several], or at higher levels of taxonomy. Thus a species of fruit-fly diversifying into dozens in the Hawaiian islands is Macroevolution.

    Creationists frequently claim that evolutionists themselves have claimed that there are no 'transitional forms' and so no 'macroevolution'.

    What they have failed to realise, or perhaps communicate to their target audiences, is the missing transitional forms are forms between two related species - say between the various species of African zebra. And it's true, such transitions are rarely found.

    Why? Because the fossil record is not perfect and neither are our collections from it. To fully document a transition between a parent and descendent species requires hundreds or thousands of fossils to be collected over a continuous time span and a broad area. Most fossil species however are not so well known, and they often require laborious excavation and chancey discovery to be known in detail. Only small animals that leave abundant fossils can be useful in documenting transitions.

    Over the past twenty years palaeontologists have dug up many, many examples of transitions between species. They have done this to study, in detail, the process of evolution and species change. Is species change GRADUAL and affecting the species as a whole, or is it SUDDEN, starting with a small out-lying population that changes and then competes with its parent species? These questions palaeontologists set out to answer 30 years ago.

    BOTH happen is the answer - slow and gradual, and sudden and dramatic... but both findings support Macroevolution's reality.

    Another source of confusion is the concept 'MOSAIC EVOLUTION'. What it simply means is that species intermediate between two higher-taxonomic levels - say between reptiles and mammals - will show a set of features that are a mosaic of the two, ancestral and descended.

    Mammal-like reptiles, the Therapsids, often show reptilian and also mammalian features quite distinctly. A striking example of this mosaic pattern can be seen in several advanced CYNODONT groups that have both reptilian and mammalian jaw-joints. Archaeopteryx is another mosaic, possessing several avian features - chiefly its flight adaptations - and many reptilian features [eg. long-bony tail, claws on its arms, small breast-bone, teeth] that later bird groups lose bit by bit.

    HERE'S a discussion on the LITERAL understanding of Genesis 1 - 11...

    GENESIS

    Other puzzles of Evolution:

    THE CAMBRIAN EXPLOSION: A PUZZLE FOR DARWIN. CAMBRIAN

    HOW CAN A RANDOM PROCESS CREATE COMPLEXITY? RANDOM

    LIFE'S ORIGIN: THE ULTIMATE MYSTERY OF BIOLOGY. ABIOGENESIS

    Fossils show replacement through time. More modern species appear the closer in time we are to the present - hard to explain in a Creation scenario. Here's an exploration of the data that Creationists want to forget... FISH

     

    WHAT IS EVOLUTION?

    Who Is God?

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