E.S.C.O.N.I.

       PALEONTOLOGY STUDY GROUP MEETING

                                February 16, 2002

Chairman John Good called the meeting to order and all attendees introduced themselves. John mentioned that Jim Fairchild had copies of "Creature Corner" available for purchase at the introductory special price of $5. After the Show March 3 the price will go up to $8. He also has copies of the Mazon Creek plant and animals books for sale. Show Chairman Dave Bergmann then reported that it is two weeks to our Show and set up will begin on Friday March 1 at 12:30 to skirt tables. Case setup and vendor set up can start by about 3:00. Set up will close at 7:30 pm promptly. Set up can also start at 7:30 am on Saturday March 2 until opening at 10:00. We need more displays, and cases and locks are available from Chicagoland. Show Chairman Sheila Bergmann needs help with security at the door before opening on both days and could use more demonstrators. John said that the Paleo cases would be South Dakota material and Illinois non-Mazon fossils. Kathy Dedina suggested that we have a third case for "Creature Corner" with some of the fossils around the book. Field Trip Chair John Good then talked about future field trips. Burpee PaleoFest is coming up next weekend in Rockford. March 23 and 24 is the Braceville trip with no helmets needed and kids allowed. There will be a 9:00 am meeting time. Adults must carefully supervise their young children on trips. MAPS will be the field trip for April from April 12 to 14 in Macomb Illinois. A side trip to Keokuk for geodes will be added to that weekend. Andy Hay reported that there were no new developments at Mazon Creek. April 1^st (instead of the usual March 1^st) will be the opening date this year. Big Field Trip is to South Dakota and Nebraska with John Good and Dave Bergmann leading it for a week each (probably the 2^nd and 3^rd week of June). There are good museums and fossils and minerals to collect. Rob Sula’s Paleo Prospectors also runs good trips out in that area for a fee. Other trip plans are being looked at by John.

Future Paleontology Group Meetings

March 16           Traces by Karen Nordquist to coincide with MAPS topic)

April 20              CANCELED; NO MEETING!!

May 18               Fish by Irene Broede

AMMONOIDS with John Catalani

Ammonoids and nautiloids are both within cephalopods, but are in very different branches. Ammonites as we know them evolved in either the Late Triassic or Early Jurassic, but ammonoids have been known since the Devonian. Ammonoids grew incredibly quickly and died incredibly quickly.

John showed a table differentiating ammonoids (A) from nautiloids (N). The septa of A s convex to the aperture (neck in) and is concave (neck out) for N. The siphuncle size of A are small and located on the outer margin of the shell and for N are small to very large and variable in location. The sutures of A are complex and for N are simple. The whorl of A are compressed and for N are compressed to depressed. The shell of A are thin and for N are thick (which strengthens the shell as it dives deep). Deposits of shell material within the shell or in the siphuncle is absent for A and varies from absent to heavy for N (total weight up to 1,000 to 2,000 pounds). The muscles in A are long and weak and for N are short and strong (allows quick movement). A new theory says that A uses its body to fit into the convolutions of the sutures to build the next one. The old theory was that the convolutions were to add strength to the shell (which is now known to be untrue). The growth of A is fast with only one reproductive cycle and for N is slow with many cycles. The life span of A is short (less than a year) and is long for N (up to 30 years). The Nautilus has fur on its outside which falls off after death. The umbilicus is the central tight coils.

There is a part of nautiloids that are found in Solnhofen specimens called the aptychus. In the Nautilus it serves as an operculum that can be pulled across the shell opening for protection. It is part fleshy and part calcareous and falls off at death. In the ammonoids there are parts that are like lower jaws (some are enormous) whose function is not known. It could be used to mash food (Nautilus can take off your finger), but may have folded up over the aperture from the bottom to protect.

The shells of ammonites are usually compressed – shortened from side to side, not top to bottom (depressed). The ammonite sutures have lobes and saddles and their shapes determine the species. The simple sutures are common in the Devonian and are called goniatitic with pointed lobes and rounded saddles. Cerititic are more crenellated lobes. The most complex are ammonitic with detailed lobes and saddles. The reason for the complex sutures is unknown. It was believed that it was for withstanding pressure. But the simple sutures of the Nautilus are actually much stronger. It was certainly not strong enough to withstand a mososaur bite. There are five current theories to explain the complex sutures. First was the strengthening against hydrostatic pressures. Second the enlarged surface could improve physiological functions (?). Third, the greater weight with more shell was helping buoyancy and control. Fourth, the marginal folding secures the body to the shell during formation of new septa. Fifth, it forms recesses for storage of cameral liquid to improve buoyancy adjustments. The fourth is the most logical. The small siphuncle would have difficulty removing fluid to move quickly. Ammonoids could refill relatively quickly (Nautilus can not). Nautilus stays down in the depths during the day and comes up to feed at night when it is safer.

Smooth shells like Placentaceras show the convolutions beautifully. Others have ornamentation to break up the flow of water flowing around it to reduce friction and allow faster movement. It may also strengthen the shell a little. It may also cause the shell to crack along the ridges rather than crack the whole shell causing certain loss of whole shell.

The soft parts are not known well. There have been some preserved siphuncles found in some fossils. There is an organic coating over all of the septa and other parts. There are also muscle scars found on the insides of some of the shells showing their position. The ammonite muscles are very thin and long running the length of the shell. The nautilus muscles are short and dense in the front of the shell. They rock as they move because of the strong short muscle movements. Some think some ammonites could take their whole body outside of the shell. Orthoceras are the long shelled ammonoids and they have 10 arms rather than the 90 for some nautiloids. There are really only 8 arms so the other two are tentacles. There is one theory that says that some ammonoids had fleshy outside coverings instead of an internal animal. John was not sure of the evidence in support for this strange theory. Another interesting animal (Czekanowskites) from Siberia was found on a large slab with about 700 specimens with 3 different forms but only one species (some compressed and some depressed shell forms). This was probably a mass mortality slab that happened after spawning which supports the one species theory. Many species spawn once in large quantities and then die. This shows intraspecific variation.

Under growth and reproduction, most shelled cephalopods grow to maturity and stop growing, but Nautilus can mate once a year for 10 to 15 years after maturity was reached. Adult Nautilus can have 30-36 chambers over 20 years of growth. Some ammonites contain many more chambers. Female Nautilus lay about 12 eggs at a time (largest egg of any invertebrate at 25 mm in diameter). They have 7 chamber when they hatched. Ammonites laid many thousand of eggs with a protoconch and they went up to the plankton to feed. They reproduced only once in a spawning orgy and then died. It is not known whether fertilization was internal or external. Some ammonoid eggs may have been kept in the female shells. Most squid live only one year (not sure about giant squid).

The male shell is a little wider to accommodate the male organ. In some species the female is much larger than the male – the macroconch compared to the microconch. The paper nautilus is actually an egg case for a tiny ammonoid.

Many thought that the ammonite was sluggish like a gastropod. They did not see how they could be good swimmers with such small openings to the outside. Heteromorphs could not swim at all. Ammonoids were probably better at vertical movements following plankton. Ammonoids do not have siphons like nautiloids. There were several vertical shelled ammonoids like baculites and they were usually pictured that way. Heteromorphs change the form of their shells as they grow. They might start as a coil and then grow a straight shell. They were probably not very mobile.

Ammonoids evolved in the Lower Middle Devonian and suffered several crises at the end of the Devonian, another at the end of the Permian, one at the start of the Jurassic and then disappeared at the K/T. Why are the ammonoids gone? There are several theories. The first was poor shell design with their fast growth and thin shell being a weakness with some strong predators around. Second was ecological because they were specialist that were subject to environmental changes. Nautilus is a generalist that can eat anything. Ammonoids are more specialists. Third is the reproductive theory. If ammonites had only one spawn and then died and the young stayed up with the plankton, they were susceptible. Nautiloids lived deep and kept their young deeper for long periods of time. Then when the asteroid hit at the K/T it formed a "caldron of seething death". The shallow living ammonites were vulnerable with the plankton killed off and the water acidified to dissolve their shells. But many of the nautiloids would have been down deep and survived. So this last theory may be the strongest one to explain what happened. The nautiloids were plentiful in some areas of the world like they are today, but the ammonites were all over the world with their fast and prolific reproduction. John then explained many of the specimens that he brought which illustrated much of the information he had discussed.

Many members described the ammonite specimens that they brought. The Bergmanns, Dave Liss, Bob Beadle, Andy Hay, and Dick Ade all showed their fossils. The meeting adjourned for refreshments from John Good and Eileen Mizerk.

Respectfully Submitted Karen Nordquist, Secretary

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