Lab 2: Morphological variability in Fossils

Use Textbook Chapters 2 and 3 (possibly chapters for the specific Phyla as well, see below)

Goals of this lab: Start to familiarize yourself with the types on characters used to recognize species/genera in fossils belonging to different Phyla of animals. Think about the chances of these characters surviving in fossils.

There are 5 trays with fossils (labeled Mollusca 1; Mollusca 2; Brachiopoda; Echinodermata 1; Echinodermata 2). For each of these answer the following questions:

• Into how many morphological groups can you separate these fossils? (number must be less than number of specimens present.
• What characters of the fossils did you use to distinguish these morphological groups (e.g., length, color, presence of spines, etc.)?
• Which of these characters could be or is influenced by fossilization processes?
• And, thinking back to last week: how are the fossils preserved?

What are these fossils?

• Mollusca 1 (Chapter 15): Recent bivalve shells collected on the beach at Sanibel Island, Florida.
  • There are 5 different species (and genera) in this collection: the turkey wing (Arca zebra -the rather wide shells with straight hingeline and dark brown-white stripes), the ponderous arc (Noetia ponderosa; most common specimens, white, some with black material on outside valve, straight hinge line), the broad-banded cardita (Carditamera floridana; broad ribs, curved hingeloine, light brown and white; width larger than height of valve), the prickly cockle (Trachycardium egmontianum: fairly light colored, width somewhat less than height of valve, spines) and Van Hynig's cockle (Dinocardium robustum vanhynigi ; large shells, width somewhat less than height of valve, lively browb/yellow colors, smooth shell. Used to distinguish these: the length-width ratio of the shell, the nature of the hinge between the two shells (shape of hinge-line straight or curved; presence and shape of 'teeth' and corresponding 'sockets' in the hinge, the presence/absence of spines on the shell, and the color of the shells. Note that color does not fossilize well: the ponderous arc as well as the turkey wing have a layer of organic matter (periostracum) on the outside of the shell which wears off. The small spines on the prickly cockle can easily be abraded when shells are moved around by the waves. The colors may (and will) fade. The hard parts only are preserved; the shells are not attached to their counterparts (thus only a part of the organism is present); original composition. Note that even recent shells show damage done by abrasion of the shells by waves; boring by various organisms.
• Mollusca 2 (Chapter 15): Pliocene snails collected in Florida.
  • There are 5 species (and genera) present in these snails. Two species of Conus (C. adversarius and C. apium), as well as Busycon planulatum, Scaphella floridana, and Fasciolaria tulipa. They are distinguished by the shape of the 'tube' in cross section, the angle of the apex of the shell (top); the height of the spire. The specimens all have lost most of their color; hard parts only are preserved, of the whole organism, but the aragonite has been recrystallized to calcite (which you can not see). The two species of Conus are not easy to split on morphology: C. apius has a more triangular top, C. adversarius a more board, flat top with only very little central 'peak'), but there are intermediate specimens. Busycon planulatum is the whelk, braod, flaring tube, long 'spine' in the center, where the sipho was. Fasciolaria tulipa is the snail with broader tube of the remaining two, and the central spine. Scaphella floridana has the compressed tube. Note that most specimens are right-coiling; there are only a few left-coiling among the Conus specimens.
• Brachiopoda (Chapter 13): Paleozoic brachiopoda, Devonian, Ohio.
  • There are at least 5 genera/species preserved: Mediospirifer, (the large, thick specimens, biconvex; width of shells larger than height of shells; with the very pronounces sulcus, the bend in the lower edge of the shells); Spirifer, (the smaller specimens, biconvex; straight hingeline, width much larger than height of shells; pronounces sulcus); Atrypa (biconvex, curved hinge line, height and width of shells similar, some specimens with weak sulcus), Rafinesquia (very flat, concavo-convex but with flat convex side, straight hinge line, height and width of shells similar; no sulcus) and Strophomena (flat, straight hingeline, concavo-convex with convex side rounded; no sulcus). Characters used: length/width ratio of the shell; the shape of the hinge line (straight/curved); whether both shells are convex (biconvex shells) or whether one is concave (concavo-convex shell); the degree of convexity/concavity; and the presence or absence of a 'sulcus', which is a depression on one side, a bulge on the other part in the middle of the shell. The shells are preserved in doubles, thus representing the complete hard parts of the animals. They are probably recrystallized. Some people would recognize more than 1 species of Spirifer, based on presence/absence of long spines on the outer edges of the hinge line. These spines, however, commonly break off, so that absence of this feature can not be used to reliably subdivide the specimens.
• Echinodermata 1 (Chapter 16): Sea urchins. Most specimens are Cretaceous (Surrey, England), one is from the Jurassic of Germany, and several are recent (Mediterranean and Pacific).
  • There are three genera represented: Cidaris (Jurassic, Recent; mouth and anus central; one species with very fine, thin knobs for spines, one species with very large knobs); Holaster (Cretaceous; mouth and anus off center; one species has height larger than width, one species has width larger than height) and Spatanga (Cretaceous; height smaller than width, mouth and anus central). Characters used: the location of the mouth (central or towards one side at the bottom of the fossil), the position of the anus (central or to one side on the top of the fossil). Note that if mouth/anus are central, the sea urchin has five-sided symmetry. If the mouth and anus are at the side, the animal has bilateral (two-sided) symmetry. In addition, we use the ratio of height and length (or width) of the urchin and the length-width ratio, as well as the surface view: smooth or with knobs (to which spines were attached during the life of the animal). Recent and Jurassic forms have central mouth and anus; recent forms preserved original hard parts of most of the skeleton (but pieces missing in the middle around mouth and anus), Jurassic probably still original or recrystallized. Most Cretaceous forms original material; one shows replacement by opaline silica (chert). Note that during fossilization the location of mouth and anus may be lost: covered in sediment, broken off. In addition, some specimens are cracked/deformed by overload of sediment.
• Echinodermata 2 (Chapter 16): An extinct group of Echinodermata (blastoids) from the Carboniferous of Kentucky.
  • These all belong to the same genus (Pentremites), very common during the Carboniferous. They were, in life, rather like a crinoid: standing on a long, slender stalk (broken off), and with thin, fragile arms (broken off). They can not be subdivided into different morphological groups because the thin stem and arms have broken off, and many specimens have been deformed (flattened) so that differences in height/width can not be ascertained. Hard parts of part of the organism preserved; recrystallized.