The Great
Tree of Life

Tree of Life for Fossil Collectors

The affinities of all beings of the same class have sometimes been represented by a great tree.

Charles Darwin, 1959

The geological time scale with links to paleobiologyThe evolution of life describes along the geological time scaleThe Earth's evolvement over geologic timeFamous fossil sites described with links to representative fossilsPhylogenetics and classification of life

Galleries of fossils according to location and classificationTheory, examples and misconceptions of evolution

Science articlesGlossary of terms in paleontology, biology, evolution, etc.

Click here to start climbing The Great Tree of Life

"The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species . . . The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs; and this connexion of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups . . . From the first growth of the tree, many a limb and branch has decayed and dropped off, and these lost branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and which are known to us only from having been found in a fossil state . . . As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all a feebler branch, so by generation I believe it has been with the Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications" (Charles Darwin, 1859).

A tree is inherently hierarchical, as is the great "Tree of Life". Its boughs are analogous to the higher Linnean rankings, i.e., the domains, kingdoms, phyla, classes, etc. Smaller branches correspond to middle rankings, i.e., the orders, families and genera. At the end of the many branches are the twigs, the uncountable species, some 99% of which are extinct. The great Tree of Life is real. It is a phylogenetic tree representing the unique ancestral history of each and every creature. Darwin believed that all creatures on Earth might have originated from a single common ancestor so that each species through geological history fit somewhere in an overarching metaphorical tree:

"From the first dawn of life, all organic beings are found to resemble each other in descending degrees, so they can be classed in groups under groups."

So too does modern biology believe all life began with a common ancestor.

Darwin further believed that the classification of living creatures, extinct and extant, should be based on phylogeny:

"I believe that the arrangement of the groups within the class, in due subordination and relation to the other groups, must be strictly genealogical in order to be natural."

Setting aside the supernatural, so too does modern biology and zoology.

However, the dream of placing all the boughs, branches and twigs in their rightful place is a formidable task, and doing it accurately is intractable. Even with the ability to fully sequence the genomes of related creatures, accurately unfolding the lineage of related creatures might only be done to a limited statistical certainty. If we consider the beloved trilobite, extinct for hundreds of million of years, where we will never have DNA, the uncertainties in classification rise enormously. Despite rigorous if not painful descriptive protocols used by invertebrate paleotologists for trilobites, the precepts of decent with modification allow morphological change without evolution and evolution without morphological change, such trilobite classification will forever be highly confounded. Decent with modification also allows multiple evolutionary paths to a common morphological end. With all confounders considered, the metaphorical tree for subphylum trilobita will forever be shrouded with great mystery. Recently, the concept of a single unifying, hierarchical tree has been challenged by sequence studies that suggest lateral transfer of genes may further confound lineage among species.

Fossil Museum presents one structure for the Tree of Life, but since the museum is devoted to collectable fossils, we will not venture far down some boughs of the tree, will not venture at all down many branches, and in the end, will not cover many twigs of life. The data presented will concentrate on the areas where the fossil record is most rich, where the collector can hope to obtain specimens, and where we can provide photographs.

The number of known living species on earth sets somewhere below 2,000,000. A review of the literature shows that in the 1970's, estimates of the actual number of extant species ranged from 10,000,000 to 100,000,000, with 30,000,000 being a reasonable average. In this post-genomic era, with bacterium included, and extrapolating back 3.5 billion years knowing what we now know about the ratio of extinct to extant species in some families, an astonishing 4 trillion species of life can be conjectured to have existed over geologic time.