Foraminifera photo by D. B. Scott           Ostracode:  Heterocypris      Radiolarian shown with
           Centre for Marine Geology, Dalhousie    fretensis, Photo by Alison     permission from the Univ.
           Univ., Halifax, Nova Scotia, Canada       J. Smith, Kent State Univ.   Cal. Mus. Paleo. at Berkeley
 
 

Introduction

    This week we will explore the realm of the very tiny fossils, the microfossils.  Microfossils may be small, but they are tremendously useful to paleontologists.  This is because microfossils are 1) so abundant that statistics can be applied to their distributions; 2) tiny samples yield thousands of specimens, and 3) many can be used not only for paleoecological information but also for geochemical information (stable and radiogenic isotope data, trace elements, heavy metals...many possibilities here to explore). There are MANY important groups of microfossils, but we will be looking at only three groups today:  the Foraminifera and the Radiolaria (both groups are Protistans) and the Ostracoda (microscopic crustaceans).  If you are intrigued by these fossils, you might want to consider a Micropaleontology course someday.

Kingdom Protista
Phylum Sarcomastigophora
Subphylum Sarcodina
Class Granuloreticulosa
Order Foraminiferida  Foraminifera Cambrian-Recent

The forams are marine protists with a fossil record that extends back to the Cambrian.  These single-celled organisms are an important part of the food chain in the oceans-they are zooplankton, feeding on diatoms and other microorganisms, and some groups also harbor symbiotic algae.  Most are benthic, but an important group, the Order Globigeriina, are planktonic and used in paleoclimate and oxygen isotope studies of the ocean.  Fossil forams from Cambrian rocks had shells composed simply of an organic tube with various sand grains glued to it (agglutinated shell).  However, by late Paleozoic time, several types of shell appeared, including a very large form, rice-grain shaped, belonging to the Fusulinid forams (be sure to look at these in the type collection).  Foram protists move and capture prey using pseudopodia called reticulopodia.  The shell, known as a "test" is species specific in its design, and is the basis for an enormous literature on the biostratigraphic applications of forams.  Most foram shells are composed of calcium carbonate or agglutinated sand grains, but the wall structures and designs are quite elaborate and varied.  Looking carefully at a foram, you will be able to see the opening in the shell (the aperture), and the individual chambers and suture lines of the shell.  Note that some are planispirally coiled, others are trochispiral, as in snail shell coils, and still others are composed of linear rows of chambers (uniserial-one row, biserial, 2 rows, or triserial, 3 rows).  In life, the cellular material extends throughout the entire test, and continues in a layer around the outside of the test as well.  Also, in life many of these forams have long, delicate spines that are later broken off after death.
 
 

Examine the forams in the teaching collection and draw any two slides/specimens, labelling the aperture, chamber(s), and suture lines

Foram shell (test) shapes, image shown with permission from the
University of California Museum of Paleontology

Photo Credit:  D.B. Scott, Centre for Marine Geology, Dalhousie University, Halifax, Nova Scotia, Canada
 
 
 

Kingdom Protista
Phylum Sarcomastigophora
Subphylum Sarcodina
Class Granuloreticulosa
Subclass Radiolaria Cambrian-Recent

    The Radiolaria are also microscopic marine protists that range throughout the world oceans.  However, the shells of these protists are not made of calcium carbonate, but instead are composed of opaline silica (hydrated silica).  These are about half the size of forams, ranging in size from 60 to about 200 microns. Radiolarians show strong vertical stratification in ocean waters to depths of 1,000 m, and are also highly abundant:  enough so to produce what is known as "radiolarian ooze" sediments on the ocean floor!  Their abundance is strongly tied to deep ocean upwelling, where nutrients and dissolved silica are abundant.  Some radiolarians can live in nutrient poor water by keeping symbiotic algae (just as some forams do).  Two common radiolarian Orders are the Spumellaria (radial-spherical symmetry) and the Nasellaria (conical symmetry).  Radiolarians are important microfossils in paleoclimate analysis, and have been used to reconstruct oxygen isotope records of the past conditions of the oceans, just as has been done with forams.
 
 

Examine the radiolarians in the teaching collection and draw a radiolarian shown on the Radiolarian strewn slides.  Indicate whether it is a Nasellarian or Spumellarian radiolarian.

Nasellarian            Spumellarian 
 

Here is a Nasellarian radiolarian (conical symmetry) and a Spumellarian (spherical symmetry).  Images shown with permission from the University of California Museum of Paleontology.
 
 

Kingdom Animalia
Phylum Arthropoda
Subphyum Crustacea
Class Ostracoda Ordovician-Recent

    The ostracodes are microcrustaceans that produce a hinged calcite shell, often ornamented, in which they can completely close themselves up.  They live in every aquatic environment, from marine to freshwater to groundwater to wetlands, with the exception of very acidic water.  They are slightly larger than the forams (typically 500-700 microns), and can also be used as both paleoecological and geochemical data in paleoenvironmental and paleoclimatic reconstructions.  The shell is commonly preserved, although often disarticulated into two valves.  When examining these bean shaped valves, look for the adductor muscle scars.  Other scars are sometimes visible, including the dorsal muscle scars.  Ostracodes are sensitive to temperature and salinity in the deep ocean, and are used to map the changing position of water masses through time.  In fresh water environments, ostracodes are sensitive to water composition as well as temperature.  Their rapid speciation, wide distribution, and commonly preserved valves make them excellent index species.
 
  To see images of non-marine ostracodes in the NANODe (North American Non-Marine Ostracode Database, click here.
 

 
 

Examine the ostracodes in the teaching collection and pick any two slides, drawing an ostracode valve from them.  Label the Dorsal and Ventral sides, and the muscle scar patterns (if visible).