SALAMANDERS

The evolutionary and creationism models make different predictions on how salamanders should be represented in the fossil record. Which is supported by the actual fossil evidence? The evolutionary and creationism models make predictions on the type of groups that salamander species can be divided into. The evolutionary, creationism, and intelligent design models make different predictions about the types of variations that can be observed within these groups. Which is supported by the actual evidence?

EVOLUTIONARY MODEL

If evolution has occurred, then the types of salamander alive today are not expected to have been present throughout the early part of life's history. The relationships among modern salamanders should form a nested hierarchy showing degrees of varying relatedness. At each level of classification, populations can acquire new features as they adapt to their niche. The same types of modifications which separate one group from another may be observed within a group.

CREATIONISM MODEL

If the creationism model is correct, then every "kind" of modern salamander has always existed. There should be no period of the fossil record and certainly no period during the fossil record of life on land, which lacks salamander fossils. Every "kind" of salamnder would have been in existence since the first week of life on earth. While evolution may occur within a "kind", one "kind" cannot evolve from another. As a result, each "kind" has no relation by descent to any other "kind" and an examination should prove which organisms are completely unrelated to each other. The variations which occur within a "kind" should be minor compared to those which differ between "kinds".

INTELLIGENT DESIGN

If intelligent design has occurred, then some/substantial evolution could have taken place in salamander lineages. However, each separate "design" should be impossible to develop over time. The variations on a specific "design" should not significantly alter the "design" or create a complex new "design".

 

WHICH OF THESE TWO PREDICTIONS IS SUPPORTED BY FOSSIL EVIDENCE?

Not only does the fossil evidence strongly support the evolutionary model, it contradicts the predictions of the creationism model.

There are more than 350 modern species of salamanders. They can be found on every continent except Australia and Antarctica and range from the tropics to vicinity of the Artic circle. They have adapted to a diversity of habitats including treetops, the forest floor, and aquatic environments. The largest are more five feet in length. In eastern North America, it is estimated that the mass of all of the resident salamanders in a unit area exceeds that of the mammals and birds combined (Mattison, 1998; Pugh, 1998). If they had always existed on earth, it is reasonable to suppose that creationists could find fossils of salamanders from the eras which make up the majority of earth's history. They haven't. Salamanders are first known in the fossil record from the Jurassic (Pough, 1998)

ANATOMICAL AND MOLECULAR COMPARISONS OF FROGS SUPPORT A CLASSIFCATION SCHEME WHICH CREATES A NESTED HIERARCHY OF RELATED ORGANISMS

Based on molecular and anatomical characteristics, salamanders (Order Urodela) can be classified into the family Sirenidae (which some feel should be classified as its own separate order and two suborders: Cryptobranchoidea (2 families) and Salamandroidea (6-7 families, depending on the classification scheme). These two suborders form a clade apart from the sirens. The familes of the suborder Salamandroidea form a branching hiearchy of relatedness, as do the subfamilies, tribes, and genera of the larger families (such as Plethodontidae) (Mattison, 1998; Pugh 1998). One study of mitochondrial DNA suggested that the family Ambystomidae is more closely related to the families of Cryptobranchoidea rather than those of Salamandroidea with which it is usally classified (Samuels, 2005).

cladogram

Salamanders do not support the creationist concept of "kinds". Salamanders do not form a group which is equally unrelated to all other amphibians (let alone all other organisms), the suborders are not equally unrelated, the families are not equally unrelated, the subfamilies are not equally unrelated, and the genera are not equally unrelated.

CREATIONISTS CANNOT AGREE ON HOW TO CLASSIFY FROGS INTO "KINDS"

The Bible does not include a word for salamander (although members of the family Salamndridae do inhabit parts of the Middle East including Israel). What level of salamander classification do creationists identify with the "kind"? Despite the use of the word "kind" for thousands of years, there is absolutely no modern consensus on how it could be used to classify modern organisms such as salamanders. For the most of the past millenium, "kind" was considered to be roughly equivalent to "species". Because biologists have provided strong evidence that species do evolve from other species and some species of salamander can interbreed, very few modern creationists would equate the "kind" with species. Is a "kind" equivalent to the taxonomic category of genus? subfamily? family? order? Modern creationists cannot agree. Certainly, there is no evidence that one of these categories in salamander classification is qualitatively different from the others (i.e. that some are real and others are contrived terms which attempt to depict a relationship which simply doesn't exist).

If creationists conclude that all salamanders belong to the same "kind" and accept that the variation within salamanders has evolved, this then means that creationists can reconcile an enormous amount of evolution with their religious faith (especially those that believe the earth is only a few thousand years old). Creationists would have difficulty claiming that a relatively small amount of change in one lineage could not occur, even given millions of years, if they accept a far greater amount of evolutionary change as occuring in a few thousand years.

If creationists equate the "kind" with the taxonomic rank of "family" (as many do), this creates an even greater hole in their nonexistent fossil record since each of these "kinds" should date to the first days of life on earth. If there are 9 salamander families, then the fossil record should provide evidence that 9 "kinds" of salamanders have always existed. The smaller the unit which is defined as a "kind", the more difficult it is to argue that frogs which seem to be very similar are as unrelated to each other as they are to trees and insects and people (given that all "kinds" are equally unrelated).

Even if the "kind" is equated with the level of family, an enormous amount of variation would have evolved since the creation of the "kind."

 

IF A SPECIFIC GROUP OF SALAMANDERS WAS DESIGNED TO REPRODUCE IN A CERTAIN WAY WITH A CERTAIN LIFE CYCLE, WHY HAVE SO MANY SALAMANDERS HAD TO REWORK THE DESIGN?

It could be argued that there an animal's style of reproduction needs to be designed because of the complex interactions of anatomical structures, physiological mechanisms, and instincts. However, if such a complex "design" is indeed so "intelligent", then why did so many salamanders rework their designs? In the evolutionary model, some modern salamander groups have kept the ancestral system of reproduction (laying eggs in water to produce an aquatic larval stage) while others have evolved a modified form of reproduction. Since much of this variation occurs within families (and even smaller taxonomic units), most modern creationists would permit this type of evolution in their model. If the original type of reproduction in salamanders was created or designed by direct divine influence, why did it require subsequent evolutionary tinkering in order to fix it and make it workable?

Although the ancestral life cycle seems to have been that of aquatic larvae and terrestrial adults, many salamanders have modified their life cycle and often their reproductive habits as a result. In the family Plethodontidae, there are some species in which larvae undergo direct development on land. While most salamanders of the family Salamandridae have an aquatic larval stage and a terrestrial adult stage, the eastern newt has an aquatic larval stage, a terrestrial eft stage, and an aquatic adult stage. Females of Salamandra salamandra and Mertensiella caucasica give birth to live larvae which are deposited in water while females of Salamndra atra and Mertensiella luschani antalyana give birth to young which have completed their metamorphosis. There are both aquatic and terrestrial members of the family Hynobiidae. Interspecific mating has produced several species consisting only of triploid females in the family Ambystomatidae (Pough, 1998).

Fertilization is internal in Salamandridae, Amphiumidae, Proteidae, Dicamptodonidae, Ambystomatidae, and Plethodontidae and external in Cryptobranchidae and Hynobiidae. Males may perform complex courtship. Although fertilization is internal in most salamanders, male salamanders do not possess a penis. Males guard the eggs in Cryptobranchidae and some species of Hynobiidae; either parent may guard the eggs in Proteidae. Female olms (family Proteidae) may either lay eggs or retain give live birth to a few larvae (which used the eggs of their potential siblings for nourishment). The females of the only other genus in the family lay eggs.

 

IF ANATOMICAL STRUCTURES AND ECOLOGICAL NICHES WERE DIVINELY DESIGNED, WHY HAVE SO MANY FROGS CHANGED THEM?

While ancestral amphibians spent time in both water and on land as do many modern salamanders, some salamanders are fully terrestrial and others are fully aquatic. While most salamanders live just under the soil (and are often found under rocks and logs), some can bury deep into the soil and others can climb trees. Much of this variation can occur within a family of salamanders. Species of the family Plethodontidae have adapted to a diversity of habitats including underground burrowing, terrestrial surface-dwelling, arboreal life in treetops, and fully aquatic lifestyles.

Although amphibians possess lungs, these lungs do not work as well as those of higher vertebrates (in part because the ribs do not reach the sternum and intercostal muscles cannot change the volume of the thoracic cavity). The lungs of lungfish actually are more effective than those of amphibians. Many frogs and salamanders perform a significant amount of their breathing through their skin. In salamders, this cutaneous respiration is so important that the lungs can be reduced or even lost. Lungs have been reduced in some salamanders of the family Hynobiidae (such as Ranodon) and Dicamptodonidae and are lost in other species (Onychodactylus). Lungs have been reduced in the family Rhyacotriton and lost in the family Plethodontidae (Pough, 1998). Giant salamanders possess an extra skin fold near their hindlimbs to create additional surface area for gas exchange. External gills can be retained in adulthood in Proteidae, Sirenidae, and cave-dwelling species of Plethodontidae (Mattison, 1998).
Other significant variations can occur within a family. For example, in the family Plethodontidae, body length ranges from 30 mm in Thorius to 320 mm in Pseudoeurycea belli. Some species are considerably more thin and slender than others. Two subfamilies are recognized and the larger of the two can be divided into a number of tribes; anatomical differences between these groups include the number of larval gill slits, structures associated with the lower jaw and hyoid, and the type of development (Pough, 1998, Mattison, 1998).

There are other traits which vary both within salamander families and between salamander families. Size can vary considerably: the smallest salamanders are a little more than an inch while the largest are more than five feet in length. The two genera of giant salamanders are 2 and 5 feet long. Sirens (Sirenidae) vary from 3 feet to 10 inches. Some species of Hynobiidae possess clawed digits. The salamander family. Newts, brook salamanders, and fire salamanders lack limbs (family Salamandridae) upon hatching, the limbs of cave species (Proteidae and Plethodontidae) are feeble, and the tiny legs of congo eels (Amphiumidae) render them uselss in locomotion. Digits may be fused in tree-living species of Plethodontidae. Larval features are retained in Cryptobranchidae, Proteidae, Sirenidae, and some species of Dicamptodonidae. Proteidae lacks maxillary bones (Pough, 1998, Mattison, 1998).

The Asiatic salamander family Hynobiidae is considered to be the most primitive modern group because of their external fertilization, jaw structure, and the high chromosomal count (40 to 78) because of microchromosomes. Cryptobranchids are related, are known from the Jurassic, and also have a high chromosome count (of 60). Other salamander groups lack microchromosomes and their chromosome numbers typically vary between 34 and 28 (Zhang, 2006).

The olm (Proteidae) lacks eyes and is blind and several cave species of the family Plethodontidae have only vestigial eyes ane are blind (Mattison, 1998).

IS INTELLIGENT DESIGN DESCRIBE A DESIGN WHICH IS ACTUALLY INTELLIGENT?

Most of the variations given above occur within families, a taxonomic group that many to most modern creationists would equate with their term "kind". Creationists accept that evolution can occur within a "kind". If this variation can evolve (and, as the previous paragraphs have illustrated, variation within a salamander family can be significant) then what aspects of the organism are so complex that they could not evolve? If they are designed, then why didn't the original designs work? Why are so many designs necessary? Why did different groups have to alter the original design in similar ways? For example, if it were "intelligent" to design terrestrial salamanders and aquatic salamanders, salamanders with aquatic larvae and salamanders which undergo direct development, why aren't there discrete groups of salamanders which only have those qualities? Would it be intelligent to require direct divine action to fix an aspect of salamander design, only to have to repeat the same repair in additional salamander groups?