Excursion Chapter 4: The Fossil Record
Outline of the Pandas Chapter
This chapter tries to convince us that there is no fossil evidence for evolution; that there are gaps and no transition forms; that all forms appear "fully developed and functional"; that evolution is untestable because it is a theory about unique past events.
The text quoted from Dobzhansky (1957) on p. 91 (Footnote 1) continues in the original as follows:
"The applicability of the experimental method to the study of such unique historical processes is severely restricted before all else by the time intervals involved, which far exceed the lifetime of any human experimenter. And yet, it is just such impossibility that is demanded by antievolutionists when they ask for "proofs" of evolution which they would magnanimously accept as satisfactory. This is about as reasonable a demand as it would be to ask an astronomer to recreate the planetary system, or to ask an historian to reenact the history of the world from Caesar to Eisenhower."
Pandas concludes that theories of origins can't be tested empirically, yet on the very next page admits that they can be tested by looking for convincing similarity between present and past causes and by considering circumstantial evidence. Now all scientific theories are explanations postulating mechanisms involving entities that cannot be directly observed (ex: atoms, electrons, subatomic particles, electromagnetic waves, curved space, etc.). They are all tested against circumstantial evidence. One deduces what observable consequences a theory would have, then looks for them under appropriate circumstances. The procedure is the same whether one is investigating ephemeral, short-term repeatable phenomena or long-term unique phenomena. The philosopher of science, Karl Popper, considers evolution a fact and Darwinism (i.e. the mechanism of natural selection) a scientific theory and the methods of the historical sciences perfectly compatible with those of science in general (Sonleitner, 1986). For an example of testing an evolutionary hypothesis, see the supplement on Science.
Major Features Of The Fossil Record
The fossil record is a highly biased record of past life. The vast majority of organisms die and are eaten or decay and leave no trace of their former existence, the material of their bodies being recycled in the ecosystem. Organisms that produce hard mineral skeletons and live in shallow marine environments are the most likely to leave traces in the fossil record. Terrestrial organisms living on flood plains near water are most likely to be buried in river or lake deposits. Yet such continental deposits, being of limited extent and in locations at higher altitudes on the earth's surface are much more likely to be eroded away in subsequent eras. Deep sea sediments are destroyed by subduction of ocean plates and rarely, if ever, incorporated into land surfaces to appear as sedimentary outcrops.
Only about 8 to 10 of the animal phyla (normally producing large populations of individuals with hard skeletons or shells in the shallow water marine habitat) have extensive fossil records and are actually found in the Cambrian period. Highly unusual deposits, such as the Burgess Shale, only emphasize, through their preservation of unique soft-bodied forms, how strongly biased is the "normal" fossil record. Because soft parts can be preserved only under very special circumstances, there are only about a dozen or so extensive deposits of soft-bodied creatures (Gould, 1983). Many phyla of soft-bodied forms have no fossil record at all; some are found only in such special deposits as the Burgess Shale.
Although fossil species appear to persist unchanged through many strata, sequences of species clearly showing evolutionary trends abound, and records of one species transforming into another also exist (see below) although such are rare. And, of course fossil species are fully formed and functional! A partially formed and nonfunctional organism would die before or shortly after birth. Such species couldn't possibly exist to form fossils. Actually the phrase "fully formed" is used by Gould (1977) to describe the first appearance of a species in the fossil record. Gould simply meant that usually such species have all the features that characterize them throughout their subsequent period of stasis. He did not mean that higher categories (genera, families, orders, etc) appear fully formed in this sense (they don't) nor did he mean that transitional forms are not fully formed in the sense that they are incomplete and nonfunctional.
It's important to note that design proponents are divided on the issue of the earth's age. In truth, virtually all of them claim that the earth is young, identifying them as the well-known creationists. But the fact that intelligent design can embrace two such radically different interpretations of the earth's geology is proof that "intelligent design" is empty of any specific explanatory content. The intelligent designer/God is supernatural working by supernatural means! Pandas admits this on p. 100.
Early Expectations Of The Fossil Record
Contrary to the assertions of Pandas, we do find transitional forms between many major groups; these are documented in any volume on vertebrate or invertebrate paleontology. Pandas claim that many phyla should emerge high in the branches of a phylogenetic tree has no basis in evolutionary theory and is just creationist wishful thinking. This idea is found in Augros and Stanciu (1987, p. 169) and Taylor (1983, p. 69). It should seem obvious that the main branches (phyla) of the evolutionary tree should occur at its base, just as is the case with actual trees. On the other hand, smaller categories such as Classes and Orders (ex: the Mammals) have arisen comparatively recently. Today many of the gaps between major groups have been filled; intermediate forms between species are rare, but do exist as will be seen below in the section on Gaps In The Fossil Record. The quote from Darwin (footnote 2) is from Darwin, 1968, p. 292.
The Early Origin Of The Phyla
Pandas' varying claims that 95% of the phyla (overview chapter 4) or all phyla but Platyhelminthes and some Burgess Shale forms (excursion chapter 4) appear at the beginning of the Cambrian Period is incorrect. In particular Pandas' Figure 4-2, purporting to show the fossil record of the known phyla, is false. (Why are not the lines in the figure labeled?) According to Valentine (1987), who provides a fully labeled figure of his own for the animal phyla—reproduced here as Figure 4.3, only 7 (possibly 8) of the phyla are found at the beginning of the Cambrian, 3 more appear in the mid-Cambrian, 2 in the Ordovician, 4 more in the Devonian, 3 more in the Carboniferous, 1 in the mid-Tertiary, and 6 (including Platyhelminthes) have no fossil record at all. Depending on whose classification is followed the number of phyla without a fossil record would vary from 6 to 19. (The bizarre forms from the Burgess shale are not included in Valentine's figure and the 3 Carboniferous appearances are of soft-bodied forms from Illinois. Three of the Cambrian phyla (Cnidaria, Arthropoda and Annelida) possibly occur in the Precambrian. Of all the phyla only the Cnidaria, Porifera, Mollusca, Brachiopoda, Arthropoda, Echinodermata, and Bryozoa are abundant in the fossil record. The others are found only sporadically. Thus the lines in Pandas Figure 4-2, continuous from the Cambrian to the present, indicating appearance in all fossil strata are incorrect and misleading.
Of the non-animal phyla, the prokaryote Cyanophyta and bacteria are found in the Precambrian. The Rhodophyta or red algae (mid-Cambrian), Chlorophyta or green algae (late Cambrian) and Eumycota or fungi (Devonian) may have appeared in the Precambrian. The Pyrrophyta or dinoflagellates appeared in the late Ordovician; the Phaeophyta or brown algae possibly appear in the Devonian; the Chrysophyta or diatoms and golden-brown algae appear in the late Jurassic; the Bryophyta in lower Carboniferous and the Tracheophyta in the Silurian but mainly in the Devonian and Carboniferous. Three algal phyla, The Xanthophyta or yellow-green algae, the Euglenophyta and the Myxomycota or slime molds have no fossil record at all (Stewart, 1983).
All of the phyla may have appeared early in the earth's history, but the fossil record documents possibly 5 in the Precambrian (not counting many of the strange soft-bodied forms in the Ediacara fauna) and 13 at some time in the Cambrian (not counting the strange forms in the Burgess shale.)
The Cambrian "explosion" was preceded by the soft-bodied fauna of the Precambrian Ediacara fauna and many trace fossils: burrows and tracks of soft-bodied forms for several hundred millions of years back into the Precambrian (Stanley, 1976). Fossils of eukaryote cells go back 1 billion years and Prokaryote bacterial and blue-green algal communities go back 3.5 billion years (Kaveski and Margulis, 1983). The Cambrian "Explosion" itself coincided with an extensive marine transgression flooding the continental shelves following a late Precambrian glaciation that enormously increased living space in the shallow marine life zone (Clarkson, 1986, p. 48). This may have triggered a great adaptive radiation of animal forms, which, along with the acquisition of hard skeletons and shells, produced the rich fossil faunas of the Cambrian. Hard skeletons may have arisen under the pressure of predator-prey interactions. Traces of incipient skeletonization are found with some Ediacara forms (Kaveski and Margulis, 1983). Once all the major niches were filled by this first radiation of phyla, there was possibly no ecological "room" for the subsequent evolution of any new phyla, only the further development and specialization of classes, etc., among the already existing phyla. Thus the Cambrian adaptive radiation was similar to that of the mammalian orders after the extinction of the dinosaurs and other reptilian forms at the end of the Mesozoic left open many ecological niches. Stanley (1976) reviews the Precambrian and Cambrian fossil record in detail and concludes (p. 72):
"If the foregoing assessment is generally correct, we can abandon the traditional view that the origins of major fossil taxa near the start of the Cambrian were so sudden and simultaneous as to represent a major enigma."
The Valentine quote (Pandas footnote 3) is from Valentine and Erwin, 1987, p. 84.
Fossil Stasis And Gaps Within The Phyla
Lack of transitional forms between the phyla is probably due to the soft-bodied nature of those forms in the 50 to 100 million years preceding the Cambrian which precluded fossilization. Again, contrary to the assertions of Pandas, we do have unambiguous transitional series linking Hyracotherium to the modern horse, the reptiles to the mammals, remarkable transitional forms between fishes and amphibians, and between reptiles and birds, and other miscellaneous transitional series in a hundred or more forms (Simpson, 1953, p. 224). Paleontologists such as Raup, Gould and Stanley do not deny these statements, their quotes on Pandas, p. 96. are taken out of context; their correct meaning will be explained below.
The Meaning Of Gaps In The Fossil Record
Imperfect Record, Incomplete Search, Jerky Process
Depositional and erosional gaps are very common and well-documented in the geological record (Carroll, 1988, pp. 570 fol.; Smith, 1988, Eldredge, 1987, p. 12 fol.). Many of our gaps in the fossil record result from the absence of sedimentary deposits of certain ages. Thus, for example, Romer (1968, p. 230 fol.) mentions the lack of Ordovician continental sediments, the dearth of freshwater sediments in the Silurian, the paucity of continental deposits of Mississippian, early Jurassic and early Cretaceous ages. It also must be remembered that although a sedimentary formation may have a large areal extent, the only parts accessible to palaeontologists are the places where surface outcrops occur. This is especially true for vertebrates. (Invertebrate fossils can be recovered from well cores and are used to identify the sedimentary layers below the surface.)
That real gaps occur in the record of fossils is shown by the gaps existing in the temporal ranges of higher taxa as determined by first and last occurrence. Examples are given by Smith (1988, p. 144) and Simpson (1953, p. 371). Paul (1982) concludes that the fossil records of echinoderms and vertebrates are at least 25% and 40% incomplete at familial and generic levels, respectively. The fact the latest fossil coelacanths come from the Cretaceous, yet there is a living coelacanth, Latimeria, shows how great such gaps can be.
One must be careful in interpreting quotations about gaps and transitional forms. When a transitional forms is found, it doesn't eliminate a gap but divides a large one into two smaller ones. Thus, as the fossil record becomes more complete the number of gaps actually increases although their average size decreases. Also, there is more than one level of transitional form. Figure 4.1 presents a hypothetical phylogenetic tree. A descendent species (B) may be linked to an ancestor (A) through a chain of species and speciations. Fossils of each of the species are transitional forms illustrating the evolutionary trend from ancestor to descendent (dark dots in fig. 4.1). In addition there are the transitional forms between each of the species (open dots in fig. 4.1). It is the transition forms between species that are rare. These are the ones being referred to by Raup (1979, footnote 4), Gould (1977, footnotes 5, 6) and Stanley (1979, footnote 7) in the quotations given on p. 96 of Pandas. Although they may be rare, they are not completely nonexistent! Eldredge (1985, pp. 78 fol., 88) found two instances of transitional sequences between species of phacopid trilobites that he was studying. Williamson (1981) reported several cases of transitional forms between species in Cenozoic African fossil molluscan faunas. These instances corroborate the punctuated equilibrium model. Pandas' assertion (on p. 98) that punctuated equilibrium rests entirely on the absence of data is incorrect. The explanation for the "punctuated" changes is simply allopatric speciation by natural selection in small peripheral populations (Eldredge, 1985, pp. 85, 118). This is not a fanciful alternative to neo-Darwinism, but a mechanism discussed in detail by Mayr (1963) who considered it a part of modern neo-Darwinism (Mayr, 1967; Sonleitner, 1987). Dawkins (1986, pp. 250-251) considers punctuated equilibrium a minor modification of neo-Darwinism. The most common misconception of "punctuated equilibria", one that is always cited by creationists, is that it is a saltationist model of overnight change based on sudden large-scale mutations (Eldredge, 1985, p. 141, Sonleitner, 1987).
Gingerich (1983) documents several cases of intermediate transitional forms linking species of mammals which follow a more gradualistic pattern. Carroll (1988) discusses three more examples of well-documented progressive changes within species and genera and lists references to seven others. Chaline (1987) gives several examples of gradual change in the rodent fossil record. Both Carroll (1988) and Smith (1988) conclude, on the basis of many studies of evolutionary rates, that evolution is neither exclusively gradual nor punctuational but irregular or opportunistic, sometimes exhibiting gradual and sometimes punctuational patterns. Thus the fossil record does provide instances of direct fossil evidence for evolutionary change between species. For a comprehensive review of transitional forms in the fossil record, see Cuffy (1984).
Transitional species are much more common and acknowledged by all palaeontologists. Eldredge (1982) mentions two between the cheirurid and phacopid trilobites. On the right-hand side of fig. 4.1, the fossils produced by the hypothetical phylogenetic tree are used to document a phylogenetic sequence between the ancestral form (A) and the descendent form (B). Note that only one of them (the circled one) is on the direct line of descent. In practice it is almost impossible to demonstrate that a particular fossil was on the direct line of descent between two forms or on a side branch, even though it represents a transitional stage. This is the problem that Patterson is referring to in the quotes given on p. 106 (footnote 10 from Patterson in Sunderland, 1981, p. 21 or 1988, p. 89.) and on p. 113 of Pandas (footnote 16 from Patterson, 1978, p. 133). Thus, if this diagram were to represent the evolution of birds from theropod dinosaurs, Archaeopteryx might be the circled dot or one of the others.
Sudden Appearance Or Face Value Interpretation
It is interesting that Eldredge and Gould consider that punctuated equilibrium is the face value interpretation of the fossil record! Considering the bias of the fossil record to organisms with robust skeletons and shells, and the lack of sedimentary deposits of any number of ages, especially terrestrial, continental ones, one cannot assume, as Pandas does (p. 98) that the known fossil record is reasonably complete. Actually Pandas is assuming that it is complete without qualification. The claim that the pattern of phylogenetic origins is illustrated by Pandas' Figure 4-4 may be true only if the bars represent species. Yet groups of species present undeniable evolutionary trends (see Figure 4.1; Eldredge, 1985, pp. 129, 222; Stanley, 1979, pp. 190, 194, 247; Stanley, 1986, p. 163). Pandas' further claim that new knowledge is only extending species ranges into older and older strata is false. New finds may be of older species that represent transition forms closer to the ancestral form of the group. One only has to compare the vertebrate paleontology works of Romer (1945), Romer (1966) and Carroll (1988) to see all the new forms—genera, families, orders—that have been discovered in the past 50 years! Examples are Petrolacosaurus, the earliest and most primitive diapsid reptile (Reisz, 1977), the whales with regressed hind legs (see below), and the conodont animal (Aldridge and Briggs, 1989).
It should be noted that Pandas' table of "living fossils" exaggerates the situation. The animals mentioned represent genera (aardvarks, alligators, sturgeons, horseshoe crabs, galatheid crabs, echinoneid sea urchins), families (New World Porcupines, Snapping turtles, Sirens, Bowfin fishes) and orders (Notostracan crustaceans). There is a Precambrian fossil that superficially looks like Kakabekia (Galston, 1978).
Evolutionists object to the view of intelligent design (creationism) because it doesn't provide an explanation, only a supernatural mystery. Pandas devotes two chapters (i.e. 2 and 3) to evolutionary mechanisms. Where are the chapters devoted to intelligent design mechanisms? There are none. How does(do) the intelligent designer(s) create organisms? What are their methods and limitations? None are given because the proponents of intelligent design (creationists) have none. They all assert that the designer (creator) is supernatural and uses supernatural means. It one doesn't know how the designer(s) work and what their goals are, one cannot deduce the nature of what they would produce. Why are creations periodically wiped out? Why are they reintroduced? (as in the case of Latimeria after the Cretaceous extinction of the coelacanths). Without specific answers to these questions, we cannot know whether the intelligent design hypothesis fits the fossil data or not. Certainly the fossil record is not as Pandas describes it. The first fishes are agnaths without jaws, bony internal skeletons and some without paired fins; the earliest bird, Archaeopteryx didn't have a beak but toothed jaws and its wing was more of a feathered arm, etc.
Examples Of Major Gaps In The Fossil Record
Pandas' claim that the fossil record does not show a progressive development of mammalian characters is utterly false. The quoted "authority" (Lewin, 1981, footnote 9 on p. 100) is Roger Lewin, reporter for Science, apparently creating a snappy sentence to close his one-page report in 1981. This is the same year that the second of two papers by Kermack, Mussett and Rigney on Morganucodon, the animal exactly straddling the fence between reptiles and mammals, was published. In contrast, J. A. Hopson, professor of anatomy and evolutionary biology at the University of Chicago says that the reptile to mammal transition is "considered by palaeontologists to be the best-documented example in the fossil record of an evolutionary sequence connecting two major structural grades." (Hopson, 1987). Carroll (1988, p. 360) states "The sequence from the early amniotes to the early mammals is the most fully documented of the major transitions in vertebrate evolution." Eldredge (1987, p. 151) says " it's one of the very finest examples of anatomical evolution yet found in the fossil record."
The reptilian subclass Synapsida includes two orders, The Pelycosauria, known from the Pennsylvanian to the Upper Permian and the Therapsida, from the middle Permian into the Mid-Jurassic. The Pelycosaurs retain many of the features of early reptiles. Most of the skeletal features common to mammals appeared over time in the therapsids, whose latest members can hardly be distinguished from the Mesozoic mammals.
"Late mammal-like reptiles and earliest mammals now known intergrade so perfectly that anatomical definition depends arbitrarily on a single point: the nature of the articulation of mandible and skull. Even that is not clear-cut, because opinion differs as to whether "reptiles" became "mammals" when they acquired a dentary squamosal articulation (Kermack and Mussett, 1958) or when the articular-quadrate articulation (not known ever to have been lost) ceased to function as suspensorium (Crompton, 1958)"—Simpson (1960, p. 169).
For more details about this well-documented transition, see the supplement: The Reptile-Mammal Transition.
Throughout the Mesozoic, the mammals remained small shrew-like animals, represented in the fossil record mainly by fragments of teeth, jaws and skulls and few post-cranial bones (Stahl, 1974, p. 400). It was not until the demise of the dinosaurs, that the numerous orders of Tertiary mammals appeared. Pandas' oversimplified diagram (Figure 4-7) conceals a number of important points about the origin of these orders.
The Earliest Members Of The Modern Orders Of Mammals Are Very Similar
The origin of these orders occurred in the late Cretaceous and Palaeocene. This was an age of extensive uplift and erosion and terrestrial deposits are rare, being found only in Montana, Wyoming and Alberta. Although a large quantity of fossils have been found, most of these are fragments and many of the animals are known only from isolated teeth. Identifying incipient branches from the mammalian stem is rendered even more difficult because these forms had not diverged far enough to clearly show the traits characteristic of the later Cenozoic orders. Although some of these mammals are referred to as primitive primates, ungulates and carnivores, they were "all small clawed animals that scampered after insects and perhaps supplemented their diet with soft-boded invertebrates and some plant food." (Stahl, 1974, p. 421-423). The mammalian orders are not strikingly isolated in the fossil record. Some ancestral forms from the late Cretaceous and Paleocene are known (see Carroll, 1988, chapters 19, 20).
Horizontal And Vertical Classifications
The system of hierarchic taxonomic groups, which works well with living organisms, is ill-suited for the inclusion of fossil forms which document a branching phylogenetic tree. There are two ways to divide a phylogenetic tree into discrete groups, the horizontal and vertical classifications. In a horizontal classification, the ancestral forms near the stem of the tree are put into a separate group from their descendants, while a vertical classification extends the descendent groups as far down the tree as they can be traced by fossils (see Figure 4.2). Vertical classifications tend to be preferred by evolutionists, although they separate into different categories primitive forms that actually may be very similar. (Stahl, 1974, p. 423; Simpson, 1945, p. 18). The early and mid-Paleocene mammals were quite similar; if we knew no placentals after the middle Paleocene and thus had no reason for separating and classifying them vertically with their descendants, they would all be placed within one order (Simpson, 1953, p. 342). Carroll (1988, p. 505, 578) and Stanley (1979, p. 65) also discusses these classification practices and their application to the origin of the mammalian orders.
The mammalian fossil record refutes the Pandas' statement that fossil types are fully formed when they first appear. The therapsids acquired mammalian osteological characters gradually over millions of years. The early Tertiary mammals fossils are very much alike. Hyracotherium, the ancestor of the horse and linked to modern horses by a complete transitional sequence, and Homogalax, the ancestor of the tapirs, (representing two suborders of the Order Perissodactyla) are almost identical in structure and require a skilled palaeontologist to distinguish them (Simpson, 1960, pp. 122-123). Similarly the earliest chalicotheroid Paleomoropus (representing another perissodactyl suborder) differs from the above two forms only by slight differences in the teeth (Radinsky, 1969). The difference between Hyracotherium and its ancestors in the earlier heterogeneous ungulate order Condylarthra, involves slight specializations in the teeth and jaws for chewing plant material and in the ankle for running (Radinsky, 1966). The first artiodactyl was, except for its tarsal joint, a typical member of the Condylarthra (Mayr, 1963, p. 596). The earliest carnivores (the creodonts) also have many characters in common with the condylarths. One genus of the Condylarthra, Protogonodon contains, on balance of resemblance in small details, some species that could be classified as carnivores and others as ungulates. All the early Paleocene carnivores and ungulates together are less varied than species occurring in some single living family among the recent carnivores (Simpson, 1953, p. 345). Higher taxa (in this case mammalian orders) start out as ordinary speciations and only after much diversification of the descendants of those species are they recognized as such (Carroll, 1988, p. 578; Simpson, 1953, p. 342).
Changes In The Mammalian Fauna During The Tertiary
Of the 32 orders of mammals, 14 are entirely extinct, and the extant orders contain many extinct forms. Of the 257 families, 139 or 54% are extinct; of the 2864 genera, 1932 or 67% are extinct. Table 4.1 shows the percentage of families extinct in each epoch and the geological age of the 932 extant genera documents a progressive changes in the mammalian fauna to those of the present day. Thus Pandas' Figure 4-7 is incomplete and in error; there were no advanced carnivores and ungulates in the Eocene. Also the solid vertical bars hide the changes that occurred within each group and the great similarity of the early forms of all the orders. See Figures 4.5 and 4.6 for more accurate diagrams of the mammalian fossil record. Figure 4.6 in particular, shows some of the more recently found ancestral forms of the mammalian orders.
Although the origin of whales is represented by a fossil gap, there are evolutionary trends in the known fossils. The earliest genera, known only from cranial material, have skulls closely resembling terrestrial mammals of the early Cenozoic, especially the mesonychids. They also retained a primitive tooth count with distinct incisors, canines, premolars, and multirooted teeth, which are modified or lost in later whales. The skull of the oldest known whale, Pakicetus, (Gingerich, 1983; Carroll, 1988) from the early Eocene of Pakistan is intermediate between those of the late Eocene whales and mesonychids; the auditory bullae are only partially modified for hearing in water. The remains (which do not include any post-cranial elements) were found in sediments deposited at a river mouth together with remnants of terrestrial mammals. Pakicetus may have been amphibious, spending time both on land and in the water.
The earliest whales also retain a vestigial pelvic girdle joined to the vertebral column which is lost in later whales (Stahl, 1974, p. 488; Carroll, 1988, p. 523, Landau, 1983). Quite recently, new specimens of a middle Eocene whale Basilosaurus have been found that possess tiny but functional three-toed hind limbs (Gingerich et al, 1990). The loss of the hind limbs in later whales has been accomplished apparently by suppressing the action of a hind limb developmental system still retained by modern whales. Hind limb rudiments are present in the embryo and there are a number of observations at whaling stations of whales exhibiting hind limbs with various degrees of development (Conrad, 1983). Why should an intelligently designed whale have a developmental system to produce functional hind limbs which is normally not activated?
The ancient whales from the Eocene (Archaeoceti) were toothed predators. From the features of their skulls, it is inferred that they lacked the echolocation mechanisms of modern toothed whales (Odontoceti) and the filter feeding structures of the modern baleen whales (Mysticeti). The late Oligocene Mammalodon from Australia is a toothed mysticete structurally intermediate between the mysticetes and the archaeocetes. The extinct cetotheres are intermediate between Mammalodon and the living mysticetes (Fordyce, 1984). The extinct family Agorophiidae is temporally and morphologically intermediate between archaeocetes and more advanced odontocetes (Carroll, 1988, p. 525).
The later Eocene whales still have paired nostrils near the front of the skull. Subsequent fossils form a sequence with the nostrils migrating farther and farther back onto the top of the head. This was accomplished without changing their position relative to the skull bones—the maxillary and premaxillary bones being "dragged" backwards over the more posterior elements (Romer, 1945, p. 486 fol.; Colbert, 1980, p. 328-329).
Although bats are the second largest mammalian order (after the rodents) they have by far the poorest fossil record. Having delicate skeletons and living mainly in the tropics is not conductive to fossil preservation. Also, the early insectivores are known only from teeth and skull fragments Without post-cranial skeletal material, such fossils cannot be identified as being bat ancestors (Romer, 1968, p. 181; Simpson, 1945, p. 180). For example, the Paleocene Zanycteris and Picrodus may have been ancestral bats instead of insectivores (Simpson, 1945, p. 180); Adapisoriculus (a tree shrew?) and Leptacon may also have been bats or semi-bats (Hall, 1984). The earliest identifiable bat, Icaronycteris from an Early Eocene lake bed deposit has a fully developed wing that is primitive in some aspects (Hall, 1984; Jepsen, 1970).
Evidence For Evolution In The Mammalian Orders
The fossil record of the horse most convincingly shows that organisms have really evolved. It is a record with possibly only one gap where the record is not complete (Simpson, 1961, p. 224; Simpson, et al, 1957, p. 787; Gould, 1987; Patterson, 1978, p. 131). Other good examples of species lineages are found in the condylarths, other perissodactyls, artiodactyls, taenidonts (Patterson, 1949), titanotheres (Gregory, 1951, vol. 2, p. 825), oreodonts (Stokes, 1973, p. 144), elephants (Aguirre, 1969; Colbert, 1980, p. 430) and carnivores (Dunbar and Waage, 1969, p. 464; Colbert, 1980, p. 341).
Transition forms between Crossopterygian fishes and Labyrinthodont amphibians are represented by the late Devonian fossils Ichthyostega, Elpistostege, and Hesperoherpeton. According to Simpson (1953):
"In these creatures we really do have an essentially continuous transition between two very high categories: classes. The Greenland forms are so completely and amazingly intermediate as to be animals that could not possibly exist if higher categories arose as such and by saltation."
Schmalhausen (1968) says:
"The ichthyostegids were actually transitional forms between the crossopterygian fishes and the Amphibia."
Because of all the fishlike features that they retained, the ichthyostegids were described by the paleontologist Jarvik as four-footed fishes. The bones of the skull, palate and lower jaw are very similar to those of the fish Eusthenopteron except in their proportions—the face is longer in the ichthyostegids. The most distinctive feature of the crossopterygian organization is the division of the skull into two parts, movably articulated with each other. Traces of this division are found in the ichthyostegids, confirming their derivation from the crossopterygians! (Schmalhausen, 1968, pp. 35, 58; Stahl, 1974, chapter 6). In addition, ichthyostegids have other similarities to crossopterygians: labyrinthine type teeth; rudiments of gill covers; a lateral line system of the head is enclosed in bony canals and not in open grooves as in later amphibians; similar vertebral column; a genuine fishlike tail, a laterally compressed body and dermis with fishlike scales. In other respects they are similar to early labyrinthodont amphibians. The lobe fins of the crossopterygian fishes already had all the bony elements of tetrapod limbs, lacking only the distal organization into definite phalanges. Recent discoveries in Greenland reveal that Ichthyostega and the related genus Acanthostega had flipper-like limbs with more than 5 digits (Coates and Clack, 1990; Gould, 1991). Acanthostega apparently had a stapes that controlled palatal and spiracular ventilation movements as is found in lungfishes (Clack, 1990). For more details about this transition, see the supplement: The Fish-Amphibian Transition.
A skeletal pattern appropriate to the ancestors of the amphibians is found in middle Devonian crossopterygians, giving at least 20 million years available for the evolution of the amphibian represented by Ichthyostega (Carroll, 1988, p. 166). The Pandas' statement that the air bladder of the fish had to be transformed into the lungs of the amphibian is incorrect. Lungs evolved first in the earliest freshwater fishes to allow breathing in oxygen-poor ponds by gulping air. Only later when the bony fishes invaded the marine environment did the lung become an air bladder. (Romer, 1949, pp. 331- 333; Gould, 1989)
The differences between amphibians and reptiles lies mainly in their soft parts which are not fossilized. The earliest reptiles from the mid-Carboniferous strata are very similar in their osteology to labyrinthodont amphibians, to the extent that the two groups are hard to distinguish. The order Seymouriamorpha, including the genus Seymouria, which structurally occupies an almost exactly intermediate position between advanced amphibians and primitive reptiles, and once classified as reptiles are now considered to be amphibians. The same is true of the genus Diadectes of the reptile order Diadectomorpha. (Romer, 1968; Stahl, 1974). This prompted Mayr (1963, p. 597) to write, "The amphibians grade so insensibly into the reptiles that the assignment of certain fossils becomes rather arbitrary". Carroll (1988, chapter X) gives an up-to-date and extensive account of the earliest reptiles.
"Modern amniotes are linked to their Paleozoic ancestors by a relatively complete sequence of intermediate forms." (Carroll, 1988, p. 193.)
Although Pandas asserts that "nearly every organism possesses equally and in full measure the defining characteristics of its taxon" (p. 104) this is definitely not true of Archaeopteryx. In fact, Pandas admits that it's some odd-ball kind of "intermediate" form (p. 23, 106). The skeleton of Archaeopteryx is virtually identical to that of a small dinosaur. If has none of the skeletal specializations of birds (even some theropods had fused clavicles (=furculas) (Carroll, 1988, p. 340; Paul, 1988, p. 107; Wellnhofer, 1990, p. 72). The forelimb shows no specialized features and is identical to that in forms such as Compsognathus. Archaeopteryx has no sternum and hence no keel. It did have abdominal ribs like Compsognathus. Thus the teeth and long bony tail are only two of a complete suite of reptilian characters possessed by Archaeopteryx. If it weren't for the preservation of the feather impressions, it would have been identified as a dinosaur (Carroll, 1988, p. 339). In fact that happened to several specimens that had poor or no accompanying feather impressions (Wellnhofer, 1990). Obviously it was not necessary to bridge a large gap in bony structure to transform a dinosaur into a "bird". If birds had become extinct at the end of the Jurassic period, Archaeopteryx would be considered an aberrant and specialized dinosaur and not the ancestor of a new vertebrate class. An extensive discussion of Archaeopteryx, other Mesozoic birds and their relations to the bird-like theropod dinosaurs is given by Paul (1988). See also the supplement: The Reptile-Bird Transition.
Lacking a sternum, small pectoral muscles must have been exclusively attached to the furcula. Without a sternum and hence no keel, and also no triosseal canal, the supercoracoideus muscle probably had the same function as in other tetrapods, not being specialized to lift the wings as in modern birds and pterosaurs. The wings were raised by back muscles such as the deltoideus major (Feduccia, 1980, p. 58; Carroll, 1988, p. 342). It also lacked openings in its bones for air sacs. Thus it probably didn't have bird-like lungs (although Paul (1988, p. 104) discusses evidence of the theropod's rib cage that suggests the presence of abdominal air sacs.) The largest wing feathers originate on the ulna, yet the ulna is smooth, in contrast to modern birds where the ulna has small knobs where the feathers are anchored firmly to the bone by ligaments. Thus it would seem that the main feathers of Archaeopteryx were not anchored to the skeleton. All these features suggest that Archaeopteryx was probably a weak flier (Wellnhofer, 1990).
Creationists make much of the fact that the hoatzin of South American has claws. Actually these are found only in the nestlings which use them to climb about the nest and adjacent branches. They are lost in the adult, whose forelimb elements are reduced and fused as in typical modern birds (Feduccia, 1980, p. 45). Actually many modern birds possess one or more wing claws. These are always more fully developed in the embryo and chick and become vestigial or lost in the adults (Fisher, 1940).
Skin, scales and feathers are rarely fossilized so the lack of fossil sequences of transitional feather-forms is understandable. Most birds have reptilian scales on their legs while some, such as the Pheasant and Black Grouse, have feathers on their legs. In the course of development these feathers grow from the leg scales. The early development of the feathers on the other parts of the body is identical to that of scales. Down feathers are just highly branched scales (Heilmann, 1927, p. 129 fol.). Some early Triassic archosaurs, such as Longisquamata had elongate, keeled, overlapping scales which may have aided in thermoregulation as they appear to do in certain modern lizards. Those of Ornithosuchus even had grooves or rays extending from the central rib or keel, suggesting the precursors of feathers (Bakker, 1975; Feduccia, 1980, p. 54; McLoughlin, 1979, p. 32 fol.). Figure 4.4 shows an example of an intermediate scale-feather found in late Jurassic lake deposits of Kazakhstan that has long, thin flat barbs but no barbules (Rautian, 1978).
Other paleontologists suggest that feathers may have evolved directly for flight. If a common squirrel falls or is shaken from a branch, it spreads its limbs, assuming the attitude of a flying squirrel, which allows it, like a human sky diver, to partially control its fall, to swerve at an angle of as much as 60 degrees and land relatively lightly. Thus the slightest fringe of elongated scale or proto-feather along the trailing edge of the forelimb would have an immediate advantage in parachuting or jumping (Feduccia, 1980, p. 57). A similar advantage would accrue from the slightest development of a patagium (i.e. a skin membrane connecting front and hind legs), leading to the flying squirrels, galago, flying phalangers, pterosaurs and bats.
Although all modern birds have horny beaks instead of toothed jaws, tooth buds appear temporarily in the bird embryo. In fact, birds have a complete set of genic instructions for making fully formed reptilian teeth (Kollar and Fisher, 1980; Gould, 1980) which normally are never used!
All the references cited here (Carroll, 1988; Feduccia, 1980; Heilmann, 1927) including all the prominent proponents of punctuated equilibrium (Eldredge, 1987, p. 187; Gould, 1986; Patterson, 1978, p. 133; Stanley, 1981, p. 176; Stanley, 1986, p. 461) consider Archaeopteryx a transition form.
The Origin Of Plants
According to Stanley (1981, p. 174):
"Creationists commonly cite outdated lamentations of botanists and paleobotanists that the fossil record of plants fails to support evolution. The simple truth here is that much of the plant fossil record is terribly incomplete. Also, there has never been more than a handful of people in the world studying fossil leaves, and in the early days serious errors were made in taxonomic assignments. The result was a confused picture of ancient plant life. As I have noted, the biggest problem, the sudden rise of the flowering plants—Darwin's "abominable mystery"—has been resolved by new fossil evidence. We now have fossils documenting a pattern of early adaptive radiation (in the early Cretaceous, see p. 90) Here we have a prime example of how the concept of evolution has been strengthened rather than weakened since the time of Darwin."
The Pandas' quotation from Corner (1961: see Pandas, p. 107, footnote 11) is that author's way of bemoaning the lack of fossil evidence for flowering plants ("...and it is well known that the fossil record tell nothing about the evolution of flowering plants" -Corner, 1961, p. 100). Corner advocates a return to classification and natural history because much plant evolution has been obscured by bad classification—he treats the genus Ficus at length. He also laments the continuing destruction of the tropical rain forest "...with its immense store of plants, saturated with the effects of evolution." Finally, lest the reader still think that Corner is a creationist, the sentence immediately preceding the Pandas' quotation states: "The theory of evolution is not merely the theory of the origin of species, but the only explanation of the fact that organisms can be classified into this hierarchy of natural affinity."
Again the simplified diagram in Pandas (Figure 4-12) is designed to hide the evolutionary patterns that actually exist. An analogous diagram (Chart 28.1) from a paleobotany book (Stewart, 1983) summarizing the distribution of the major plant groups in geological time shows groups succeeding each other as would be expected on the basis of evolution. Stewart (1983, chapter 27) also discussed at length the fossil evidence for the origin and evolution of the angiosperms. At various other points in his book, Stewart describes the known transition fossils between other divisions of the plant kingdom. Thus the Pandas' quotations from Bold (1967) on p. 96 (footnote 8) and Corner are out of date.
The quotation from Stanley (1979, p. 39) given on p. 108 of Pandas (footnote 12) is a statement about the gradualistic model and not a statement saying there are no transition forms. Thus consider the following quote from Stanley (1981, p. 174):
"A frequent claim of creationists is that the fossil record contradicts that concept of evolution. One argument here is that there are no transitional forms between distinctive groups of animals or plants. This is not true . . . Archaeopteryx represents a single intermediate form. Elsewhere, despite the punctuational nature of many transitions, we have available series of forms that more fully represent steps in the origins of certain major groups ... in 1966 H. K. Erben announced his discovery that a group of specimens from the Devonian of Germany could be assembled into a graded series showing several stages in the evolution from bactritid nautiloids to ammonoids."
The Origin Of Man
Careful consideration of human anatomy reveals that man was originally "designed" as a four-legged animal and many of the changes related to bipedality are imperfect (Krogman, 1951). Darwin (1871: Pandas, p. 198, footnote 13) did not cite any fossil evidence in his book The Descent of Man because none had yet been found. Pandas claims that still no intermediate fossil forms are found. This is not true. The fossil record "is a steady stream of intermediates." (Eldredge, 1982, p. 128). Also there are many more than just a few dozen specimens as claimed in the quotation from Science 84. This comes from an article written by a science reporter (Rensberger, 1984, Pandas' footnote 14) doing a story on photographs of the "most complete original specimens available" that were later to be exhibited at the American Museum of Natural History later in 1984. As of the late 1970's, it took a three volume 817 page Catalogue of Fossil Hominids (Oakley et al, 1977), to list and describe all the known hominid fossils. M. H. Wolpoff studied the skulls, jaws and teeth of 92 H. erectus specimens alone (Walpoff, 1984). A convenient reference to all this material is Tattersall et al, 1988.
Pandas' Figure 4-13 contains a number of gross inaccuracies that have been pointed out by Scott (1990). Old World monkeys are not older than apes, chimpanzees are pongids, and the fossil forms Pliopithecus, Australopithecus and Oreopithecus have not continued to the present! Gibbons are left out. There are no fossils of chimp, orang and gorilla and none of the fossil records are continuous, as the diagram implies.
Pandas' Figure 4-14 is supposed to show an evolutionary sequence favored by many evolutionists. But it shows 10 hypothetical intermediate forms between A. afarensis and H. habilis, 5 more between habilis and erectus and 5 more between erectus and sapiens. Actual specimens called "archaic sapients" exist; they are not hypothetical. Because of their anatomical closeness and overlapping characteristics, most anthropologists would say that these last three species form a lineage without any further intermediates. For example, the oldest specimens of H. erectus have skull volumes of about 800 cc. Over the next million years the cranial capacity expanded to about 1200 cc. while the jaw and tooth sizes shrunk. The youngest specimens grade into modern man through presapiens (archaic sapiens) forms (Jelinek, 1980, Tattersall et al, 1988, p. 49 fol.).
Again Scott (1990) commented on the illustration of A. africanus in Pandas' Figure 4-15 "as drawn with a chimp thorax, a human pelvis and a cranium from a K-Mart Halloween display. It looks like a tracing from a physical anthropology text, with much lost in translation." Comparison of these figures with similar ones from Johanson and Edey (1981, pp. 182-183) (see Figure 4.7) show that the skull and thorax of A. africanus are portrayed by the Pandas' figure in a grossly inaccurate way and there are minor inaccuracies in the pelvic bones of both A. africanus and H. sapiens. In general, Pandas gives very little information about the hominid specimens. For example, nothing is mentioned about Australopithecine bipedality or the changes in their dentition. All that is mentioned about H. erectus is the brow ridges and sloping forehead. That specimens from all over the world spanning a million years of time should all have been suffering from Vitamin D deficiency is ludicrous.
The sentence on p. 112: "Was Homo habilis really the earliest human being, or was it only a primate like the australopithecines?" is nonsensical. All monkeys, apes and men are primates—as is mentioned on p. 109! Contrary to Pandas, H. habilis had an average brain size of 800 cc.—almost twice as big as a chimp's but with a similar body size (Leakey, 1981, p. 131) and hands similar to the Australopithecines showing very human-like opposable thumb (Johanson and Edey, 1981, p. 321) and finger tips but with still some traces of climbing features (Sussmann and Stern, 1982). The quote from Pilbeam (1984) on p. 113 (footnote 15) simply refers to minor changes in the dating and branching pattern in the phylogenetic tree leading up to hominids and not that Pilbeam has become a creationist! The meaning of the Colin Patterson quote on the same page (footnote 16) has been explained above in the section on GAPS IN THE FOSSIL RECORD. The fossil record really presents irrefutable direct evidence for macroevolution (Halstead, 1984).
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(from Frank Sonleitner's critique of Of Pandas and People)