Review of the Major Animal Fossil Makers

Not all clades of organisms produce preservable hard parts. Soft bodied organisms CAN produce fossils under special (konservat-lagersätten) situations, but these are vanishingly rare.

Main hard substances found in organisms:


List of some of the major clades producing common body fossils:
(Classifications used here largerly follow these on the UMCP website)

Animalia ("Metazoa" under one definition of that term): Will list these groups in more detail!


Porifera (sponges): (Cambrian - rec.)

  • Likely paraphyletic
  • "Parazoan"-grade organisms, benthic sessile epifaunal suspension feeders
  • Hard parts include spicules made of aragonite, silica, and spongin
  • Spongin doesn't fossilize readily. Various important fossil clades of sponges are all calcareous (except for hexactinellids).
  • Volumetrically significant in reef environments.
  • NEXT

    Probably ancient sponges:


    Cnidaria (corals, hydroids, jellyfish, anemones) (Ediacaran - rec.) The majority are soft bodied with practically no fossil record. (But not the occasional trace fossil left by a resting anemone or jellyfish.)
  • Benthic epifaunal sessile suspension feeders
  • Cnidarians with hard calcareous skeletons commonly called "corals."
  • Dominant groups in the fossil record:



    Bryozoa (AKA "Ectoprocts": (Ordovician - rec.)

  • Exclusively colonial, benthic, epifaunal, sessile suspension feeders
  • Some forms lack hard skeleton; those that have them are calcareous
  • Minor components of many reef systems


    Brachiopoda: (Cambrian - rec.)

  • Solitary benthic suspension feeders, strictly marine
  • Two hard valves surrounding most body tissue
  • Hard parts are calcium phosphates in lingulates, calcite in craniids and articulates
  • Phenomenal fossil record; modern diversity much lower than Paleozoic diversity


    E. Mollusca: (Cambrian - rec.)

  • Extremely significant, extremely diverse clade of (almost all motile) animals
  • Most forms have shells (single, double, or eight) made of aragonite (i.e. calcareous)
  • Major clades are:


    F. Arthropoda: (Cambrian - rec.)

  • Extremely common, diverse clade of (predominantly) motile animals
  • Majority have exoskeleton of chitin; some forms have calcified skeletons
  • Grow by ecydysis, so a single individual produces many potential fossils
  • Major clades include:



    G. Echinodermata: (Cambrian - rec.)

  • Calcitic skeleton, unique "water vascular system" to control feeding tube feet
  • Strictly marine, macroscopic, almost all epifaunal
  • Five-fold body symmetry in all but most primitive forms
  • Ancestrally suspension feeders; later forms include some grazers and predators
  • Several major groups with substantial fossil record:


    Graptolithina, or "graptolites": (Cambrian - Pennsylvanian)

  • Colonial benthic or planktonic suspension feeders
  • Hemichordates related to acorn worms and pterobranchs (may actually be a clade of pterobranchs)
  • Strictly mid-Paleozoic, important index fossils
  • Hard parts are collagen


    Conodonta: (Cambrian - Triassic)

  • Known as exceptionally valuable Paleozoic and early Mesozoic index fossils, but until late 20th century, no one knew what they were. (I.e. neither what kind of animal nor what part.)

  • Hard parts (apparatus) are calcium phosphate, formed mouth parts


    Craniata - deuterostomes with heads: (Cambrian - Recent)

  • Basalmost forms have few hard parts
  • Primitive forms have exoskeleton of bone, endoskeleton of cartilage
  • Derived forms ossify the endoskeleton and deossify the exoskeleton
  • Many separate bones in the body

    The fossil record contains diverse jawless craniates in addition to hagfish and lampreys (whose record is very poor). Traditionally lumped together as "ostracoderms" (paraphyletic):

    Gnathostomata - craniates with heads: (Silurian - Recent) include:


    Bony Fish

    Osteichthyan survey: The diversity of "fish" breaks down into two groups:

    This course regards the terrestrial sarcopterygians and transitional forms with particular interest.


    Tetrapoda: (Mississippian - Recent) Sarcopterygians with fingers and toes.

    Within Tetrapoda, there is a rich record for:


    Amniota - the land vertebrates

  • Proliferation of land vertebrates in two major groups:


  • Sauropsida: Reptiles.