Arms Calyx Stem Scale

Transcription

1 Name: Answers Geology 1023 Lab #11, Winter 2014 Lab day: Tu W Th Mesozoic & Cenozoic invertebrates life forms, and hominids This week s laboratory will complete the study of the major invertebrate fossil groups by focusing on the echinoderms (stelleroids, echinoids, crinoids, and blastoids), molluscs (clams, snails, and cephalopods) and bryozoans. We will also have a brief look at hominid and primate fossil skulls and some of the parameters used in the study of hominid evolution. Phylum Echinodermata: Echinoderms include sea stars, sand dollars, sea urchins, sea cucumbers, and crinoids ( sea lilies ). Echinoderms all show 5-fold symmetry best shown by sea stars. However, close examination shows that one of the 5-fold rays is different and, strictly speaking, echinoderms are bilaterally symmetrical some obviously so (e.g., Micraster). Class Echinoidea (Sea urchins): Echinoids are hemispherical or disc-shaped (sand dollars) with 5-fold symmetry around the apex of the hemisphere (or disc). They are mobile and benthic. Many have spines (urchins). Some burrow into sediment (e.g. sand dollars). They are not abundant in fossil record but are best preserved in late Mesozoic and Cenozoic rocks. Class Stelleroidea (Sea stars and brittle stars): Five-rayed, benthic, mobile forms that are rare in the fossil record. Class Crinoidea ( sea lilies ): Sessile benthic forms consisting of a globular body (calyx) of tightly fitting calcite plates with five-fold radial symmetry and branching, tree-like arms. The calyx is attached to the seafloor by a stem of variable length. The stems consist of stacked, circular or pentagonal calcite plates called columnals. The arms also consist of calcite plates, which are usually very small and are rarely preserved. Occasionally the calyx is preserved intact, but typically the plates disarticulate after death. Separated columnals are the most common crinoid fossil. Rock that consists mostly of crinoid debris is called crinoidal limestone. 1. Study and compare the labelled drawing of a generalized crinoid (in handout) with the lab display specimens Make a drawing of one specimen, with scale. Label arms, calyx and stem. Variable drawing showing: Arms Calyx Stem

2 Mesozoic & Cenozoic Life & Hominids Winter 2014 Page 2 of 7 2. Display specimen 304 is a limestone made of crinoid debris. a) What part(s) do you recognise (use handlens)? b) What proportion of the grains is derived from crinoids? c) Thus, what is the name for this kind of limestone? Columnals and stems >50% Crinoidal limestone 3. Echinoid specimens , 339, 340 have 2 different symmetries. Make a labelled drawing of a bilateral form with a scale and indicate its plane of symmetry and name. Drawing of echinoid showing: Bilateral symmetry Name 4. Examine display specimen 302 (sea star). Does it truly have 5-fold symmetry? No, bilateral 5. Draw a labelled sketch of specimen 302 with a scale showing its symmetry. Drawing of sea-star showing: Bilateral symmetry (one arm shorter than others)

3 Mesozoic & Cenozoic Life & Hominids Winter 2014 Page 3 of 7 Phylum Mollusca: A very diverse group of invertebrates containing many extinct classes, three of which are important fossils and also account for most aquatic invertebrates alive today. These are Class Bivalvia (modern clams, mussels), Class Gastropoda (snails) and Class Cephalopoda (octopus, squid and Nautilus). Class Bivalvia: Bivalves are aquatic and live in both fresh and salt water. All are benthic, some are sessile (e.g., mussels), others burrow into soft sediment (e.g., clams, razor-shells), and others bore into harder substrates (including rock and wood, e.g., shipworms ). Bivalves have a hinged, calcareous, bivalved shell. Bivalves use a single set of muscles to close the shell and an elastic ligament to open it. Thus, on the death of the organism the valves pop open. As a result, fossil bivalves are usually preserved as separated shells (or parts thereof). Brachiopods, in contrast, use two sets of muscles to open and close their shells and are commonly preserved intact. IF a bivalve species has a plane of symmetry it passes between the valves (in contrast to the brachiopods). Some bivalves are asymmetrical (e.g., oysters). Class Gastropoda: Gastropods (snails) are the most abundant molluscs today (> 100,000 known species). They are found in terrestrial and aquatic (fresh and salt water) environments. Aquatic gastropods are mobile, benthic forms and are both carnivores and herbivores. Typically, gastropods have a single shell that is coiled in a helical (screw) spiral. A few species have planar spirals. The shell is not chambered (c.f. cephalopods). Some forms do not have shells (e.g., the common garden slug) and some do not have coiled shells. Gastropods are important Mesozoic fossils. Class Cephalopoda: Cephalopods are tentacle-bearing invertebrates that include octopus and squid. Cephalopods are pelagic and move rapidly. Most are predators. Note also that cephalopods are the largest invertebrates (e.g., modern giant squid as well as many fossil forms). Modern cephalopods do not have an external skeleton with one exception, Nautilus. The important fossil forms have a shell, which is divided into chambers by cross-cutting walls (septa). The shell is commonly coiled though there are some straight forms (most of which are early forms). The organism secreted new chambers as it grew and the soft tissues occupied the last (largest) chamber. In contrast to gastropods, cephalopod shells are usually coiled in a plane (planispiral) not a helix. Where septa and outer wall join, suture lines develop. Suture lines can have simple or complex shapes and that variability makes distinguishing species relatively easy. In addition, suture lines showed marked changes with evolution. Thus, cephalopods are extremely important zone fossils in the Mesozoic. Sutures in shelled cephalopods are described by holding the cephalopod with the plane of

4 Mesozoic & Cenozoic Life & Hominids Winter 2014 Page 4 of 7 symmetry (coiling) vertical and with the aperture on top and pointing away. Viewed this way, sutures are variably wavy lines that are symmetrical across the plane of symmetry (see morphology handout). Cephalopods are divided into three orders. Two orders are shelled cephalopods and the distinction is based on the suture shape. Shelled cephalopods are divided as follows: 1. Order Nautiloidea: Sutures are straight or gently curved. 2. Order Ammonoidea: Sutures have complex crenulated shapes. The third order is different. 3. Order Belemnoidea. Belemnites were similar to the modern squid. They had an internal skeleton (modern squid have cuttlebones ). Belemnites (all extinct) had an internal, translucent, honey-brown, bullet-shaped, rod of calcite called a guard. The guard is very distinctive in shape and colour. Well-preserved guards show a conical opening at one end called the phragmocone. 6. Display specimen 317 is a modern bivalve, Mercenaria. Using your handout as a guide, draw a sketch with scale. Label at least 3 of: teeth/sockets, ligament area, muscle scars, palial line, and palial sinus. Drawing of bivalve showing (at least three of): Teeth/sockets, ligament pit, muscle scars, palial line, palial sinus 7. Give two features of 317 that indicate it is a clam not a brachiopod. Two of: Not symmetrical, ligament pit, no pedicle opening, one set of muscle scars, 8. Two of the fossil specimens in your specimen drawer are bivalves. Which ones are they? F17 F24 One of: Not symmetrical across shell, muscle scars, etc.

5 Mesozoic & Cenozoic Life & Hominids Winter 2014 Page 5 of 7 What feature(s) indicate that they are bivalves not brachiopods? 9. Specimens 308, 309, 310, and 312 are snails. Draw a sketch of one of them with scale. Label the apical angle, an important distinguishing feature. (See morphology handout). Drawing of snail showing: Apical angle 10. Specimen 310, and F19 (from your drawer) is a snail, but both are somewhat unusual for snails in one respect. What is it? Coiled in a plane not a helix. 11. Specimens and are cephalopods. List which one(s) is (are): Nautiloids: 322, 326(?), 343 Ammonoids: 323, 324, 325, 326(?), 327, 329, 341, 342, 344, 345 Belemnites: Note that specimen 323 is somewhat unusual for a cephalopod. What feature makes it so? [Hint: this is the reverse of question 10.] Coiled in a slight helix. Phylum Bryozoa: Bryozoans are colonial, mostly marine, tentacle-bearing, filter-feeding, benthic invertebrates. Individuals are very small or microscopic. Each individual secretes it own individual, calcareous or chitinous tubes (zoecia) that joins with others to form a twig-like,

6 Mesozoic & Cenozoic Life & Hominids Winter 2014 Page 6 of 7 branching, or frond-like colony called a zoarium. The colonies commonly have a lacy sheet-like structure (fenestrate), and may exist separately or be an encrustation on other organisms (including plants). One form (Archimedes) occurs as a lacy sheet twisted in a corkscrew shape. Many forms are featureless but velvety small mounds or encrustations on rocks, seaweed and other sessile organisms. 13. Display samples 278 to 281 are bryozoans. Examine them and then look at the specimens in your sample drawer. Using the display specimens and the identification charts indicate which specimens in your drawer are bryozoa (there are four, including a modern one). F7 F8 F9 F23 Humans (and their nearest relatives). In paleoanthropology (study of fossil humans and their relatives), we must classify hominid species on the basis of aspects of their skeleton. We must be aware however, that much of what makes (or made) humans different from their ancestors and modern related species is not readily seen in our skeletons. We focus particularly on the one aspect that does seem to show the most difference, the size and shape of the skull. Paleoanthropologists use a wide variety of skull measurements to distinguish between various species of hominids. We will make a few measurements (and calculate ratios) to compare the 11 skulls in our collection. Of particular importance are: braincase size, whether the foramen is under the skull or at its back, the presence (and size) of brow ridges, the slope of the forehead, etc. The diagram at the left shows some of the dimensions we will use to calculate various ratios. a. The condylar position index (CPI) = CD/CE x 100. C is the occipital condyle, a boney knob beside the foramen (the hole where the spinal chord emerges from the skull). The CPI is highest in humans (where the foramen is far forward). b. The angle of the forehead, J, is measured relative to the plane of the eye sockets (orbits). In modern humans this is around 20, in apes and more ancient humans the forehead slopes backwards considerably (i.e., J is larger). c. Eyebrow ridges (supraorbital torus) are a prominent feature of ape and many hominid skulls. The function of the ridge seems to be to distribute the forces associated with chewing a largely vegetarian diet. d. Apes and some early hominids have/had a bony crest along the top of the skull (sagittal crest). This is present in forms that had very large jaw muscles (for a vegetarian diet perhaps). Some modern humans have a relict of this, a sagittal keel. Looking face-on (and provided they are bald) they have a pointy-headed appearance (e.g., Patrick Stewart, a.k.a. Jean-Luc Picard).

7 Mesozoic & Cenozoic Life & Hominids Winter 2014 Page 7 of 7 e. Many apes and other primates have large canine teeth. The larger canine requires a gap (called a canine diastema) in the opposing jaw into which it fits. Enlarged canines and associated diastemas disappeared early in humans. 14. Measure the CPI and forehead angle for the specimens. Indicate if brow ridges are Absent, Slight, Prominent or Extreme. Indicate if the specimen has a sagittal crest (Y/N). Determine (if possible) if there are Enlarged canine teeth ( 50% larger than the other teeth) and if there is an associated canine Diastema. Some of the specimens are damaged and don t show every feature (particularly the teeth and any associated diastemas). Skull # H01 H02 H03 H04 H05 H06 H07 H08 H09 H10 H11 CPI (condylar position index) 4.5/12.5 x 100 = /11.5 x 100 = /12.5 x 100 =30 50 cannot measure 6/14 x 100 = /9.5 x 100 = /11.5 x 100 = /11.5 x 100 = /10.5 x 100 = /15.5 x 100 = /19.5 x 100 =20 40 Angle of forehead Indices/traits Brow ridges (Absent, Slight, Prominent, Extreme) Sagittal crest (Y/N) Enlarged canines, canine Diastema (or Neither) E N E S N No P N cannot see E Y cannot see P E Y No S N No P N No S P N No A N No P E Y E+D E Y E+D