Invertebrate paleontology
Invertebrate paleontology (also spelled Invertebrate palaeontology) is sometimes described as Invertebrate paleozoology and/or Invertebrate paleobiology.  
Whether it is considered to be a subfield of paleontology, paleozoology, and/or paleobiology, this discipline is the scientific study of prehistoric invertebrates by analyzing invertebrate fossils in the geologic record.
By invertebrates are meant the non-vertebrate creatures of the kingdom Animalia (or Metazoa) in the biotic domain of Eukaryota.  By phyletic definition, these many-celled, sub-vertebrate animals lack a vertebral column, spinal column, vertebrae, backbone, or long, full-length notochord -- in contrast, of course, to the vertebrates in the one phylum of Chordata.
Relatedly, invertebrates have never had a cartilaginous and/or boney internal skeleton, with its skeletal supports, gill slits, ribs and jaws.  Finally, throughout geologic time, invertebrates have remained non-craniate creatures; that is, they never developed a cranium, nerve-chord brain, skull, or hard protective braincase.

# Invertebrate terminology in science
In the many decades since Jean-Baptiste de Lamarck, a pioneering biologist and evolutionist,  first conceptualized and coined the category "Invertebrata" (between 1793 and 1801) and the term "Biology" (in 1802), zoology has come to recognize that the non-vertebrate category is not a scientifically-valid, monophyletic taxon.  Evolutionary biology and developmental biology (a.k.a. "evo-devo") now consider the term "Invertebrata" to be both polyphyletic and paraphyletic.  Nevertheless, most earth science departments continue to employ this term; and  paleontologists find it both useful and practical in evaluating fossil invertebrates and -- consequently -- invertebrate evolution.
However, there is one contemporary caveat:  Paleobiologists and microbiologists in the 21st century no longer classify one-celled "animal-like" microbes either as invertebrates or as animals. 
For example, the commonly-fossilized foraminifera ("forams") and radiolarians -- zooplankton both formerly grouped under either an animal phylum or animal sub-kingdom called Protozoa ("first animals") -- are now placed in the kingdom or super-kingdom Protista or Protoctista (and thus called protists or protoctists).
Still more recently, the forams and radiolarians are relocated among the non-animal kingdoms of the domain Eukaryota, the taxon which comprises the mostly-unicellular, nuclei-bearing eukaryotes.     
This radical rearrangement of the branches of the phylogenetic tree of life has resulted from the latest findings in genetics, cladistics, and molecular biology. 

### Origins of invertebrate paleontology
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### Modern evolution of invertebrate paleontology
{This section has also been moved to the new article History of invertebrate paleozoology due to limitations on size}

# Invertebrate fossilization
When it comes to the fossil record, soft-bodied and minuscule invertebrates -- such as hydras, jellies, flatworms, hairworms, nematodes, ribbon worms, rotifers and earthworms -- are infrequently fossilized. As a result, paleontologists and other fossil hunters must often rely on trace fossils,  microfossils, or chemofossil residue when scouting for these prehistoric creatures.
Hard-bodied and large invertebrates are much-more commonly preserved; typically as sizeable macrofossils.  These invertebrates are more frequently preserved because their hard parts -- for example, shell, armor, plates, tests, exoskeleton, jaws or teeth -- are composed of silica (silicon dioxide), calcite or aragonite (both forms of calcium carbonate), chitin (a proteinaceous tricalcium phosphate), and/or keratin (an even-more complex protein), rather than the vertebrate bone (tricalcium phosphate) or cartilage of fishes and land-dwelling tetrapods.
The chitinous jaws of annelids (such as the marine scolecodonts) are sometimes preserved as fossils; while many arthropods and inarticulate brachiopods have easily-fossilized hard parts of chitin and/or keratin.  The most common and often-found macrofossils are the very hard calcareous shells of articulate lampshells (that is, the everyday "brachs") and of mollusks (such as the omnipresent clams, snails, mussels and oysters). On the other hand, demosponges (for instance, horny sponges) and hyalosponges (for instance, glass sponges) have occasionally been preserved due to their siliceous or glassy composition.

# Footnotes
-   Correspondingly, the one-celled "plant-like" organisms -- a group of mostly simple algae once known as Protophyta ("first plants") -- are now also placed among the protists and/or the non-plant eukaryotes.  So too are the "plant-like" fungi, which have been discovered to be far-more "animal-like" (genetically speaking) than the early naturalists would have ever suspected.
-   For the new locus of the multi-celled animals in the "tree of life", see especially the tree diagrams on pp. 45, 78 and 555 of Joel Cracraft and Michael J. Donaghue, editors (2004) of Assembling the Tree of Life (Oxford, England: Oxford University Press ), 592 pages.  ISBN 0195172345.   And for even less technical and superbly-illustrated evolutionary trees, see The Variety of Life:  A Survey and a Celebration of All the Creatures That Have Ever Lived by Colin Tudge (20002), an easy-to-read 704-page book also published by the Oxford University Press.  ISBN 0198604262.

# Further reading
Although these books are not footnoted in this article, the following are well-illustrated, well-organized -- and often well-worn -- guides to invertebrate (and sometimes other) fossils:
- Paolo Arduini (1987), Simon and Schuster's Guide to Fossils (Old Tappan, New Jersey: Fireside), 320 pages.  ISBN 0671631322.
- James R. Beerbower (1968).  Search for the Past: An Introduction to Paleontology (Englewood Cliffs, New Jersey: Prentice-Hall), 512 pages.
- British Museum of Natural History (1969).  British Palaeozoic Fossils (London, England: British Museum of Natural History).
- Euan N. K. Clarkson (1998).  Invertebrate Palaeontology and Evolution (London, England: Allen and Unwin), 468 pages.  ISBN 9780632052387.
- Peter Doyle (1996), Understanding Fossils: An Introduction to Invertebrate Paleontology (Hoboken, New Jersey: John Wiley & Sons), 426 pages.  ISBN 0471963518.
- Carroll Lane Fenton and Mildred Adams Fenton (1958); updated by Patricia Vickers Rich and Thomas Hewitt Rich (1997).  The Fossil Book: A Record of Prehistoric Life (Garden City, New York: Doubleday and Courier Dover Publishing), from 482 to 760 pages.  ISBN 0486293718.
- W. R. Hamilton and others (1974).  A Guide to Minerals, Rocks and Fossils (London, England: Hamlyn Publishing Group Ltd.), 320 pages.
- W. B. Harland (1967).  The Fossil Record (London, England: Geological Society of London), 827 pages.
- V. Lehmann and G. Hillmer (1983).  Fossil Invertebrates (Cambridge, England: Cambridge University Press).
- Harold L. Levin (1998), Ancient Invertebrates and Their Living Relatives (Boston: Prentice-Hall), 358 pages.  ISBN 9780137489558.
- William H. Matthews III (1962).  Fossils: An Introduction to Prehistoric Life (New York: Barnes and Noble), 337 pages.
- Helmut Mayr (1992).  A Guide to Fossils (New York: Longman, Harlow).
- Raymond C. Moore and others (1952).  Invertebrate Fossils (New York: McGraw-Hill), 776 pages.  ISBN 00704302.
- J. W. Murray, editor (1985).  Atlas of Invertebrate Macrofossils (Princeton: Princeton University Press), 256 pages.
- Douglas Palmer (2004), Fossils (London, England: Dorling Kindersley).
- Frank H. T. Rhodes and others (1962).  Fossils: A Guide to Prehistoric Life (New York: Golden Nature Guide), 242 pages.
- Henry Woodburn Shimer and Robert Rakes Shrock (1944/1983).  Index Fossils of North America (Cambridge, Massachusetts: Massachusetts Institute of Technology Press), 837 pages.
- Robert Rakes Shrock and W. H. Twenhofel (1953).  Invertebrate Paleontology (New York: McGraw-Hill).
- Ronald Singer (2000), Encyclopedia of Paleontology (London, England: Routledge), 1,467 pages.  ISBN 1884964966.
- Ida Thompson (1982/2004).  National Audubon Society Field Guide to North American Fossils (New York: Alfred A. Knopf), 846 pages.
- Cyril Walker and David Ward (2002).  Smithsonian Handbook of Fossils (London, England: Dorling Kindersley), 320 pages.