MAY 2003
Longest Nautiloid Found in Arkansas
Three undergrads from the University of Arkansas have found a 325 MY old fossil that is 8 feet long. This is the longest actinoceratoid nautiloid in the world. The previous record holder is a 7 foot 2 inch (about 2.5 meters) one found near there in 1963. It is identified as belonging to the extinct species Rayonnoceras solidiforme that lived in a shallow sea. The geology professor of the discoverers, Walter Manger, feels that this specimen confirms his theory that this is a pathological giant. He believes that they would have lived like modern squid, mating, laying eggs and dying within a 3 or 4 year lifetime. However, these giant animals would have been made sterile by parasitic trematodes and lived for decades since their energy was not used up with reproduction. Now there are 2 specimens that support this. They believe that they have the whole shell with the last living chamber and it is in pretty good shape. In addition they may know the sex if the fossil animals were like their modern relatives. In modern nautiloids the females have a wider aperture. If this holds true then they have just found a female, because the aperture of the 1963 fossil is a third as wide as this new one.
Review of Amazing Chinese Cretaceous Ecosystem
A review article in Nature by Zhou et al discusses the extraordinary Early Cretaceous Jehol Group with its array of wonderful well preserved fossils. They range from the feathered dinosaurs and early birds, to basal angiosperms and primitive mammals. They include the Yixian and Jiufotang Formations of northeastern China’s Liaoning Province that reveal the “Jehol Biota”. It is difficult for the researchers to keep up with descriptions of all that is being found. The biota includes representatives of all the major clades of terrestrial and freshwater vertebrates, a variety of invertebrates and a diverse flora. It shows an incredible picture of the entire ecosystem that is rare. During the Mesozoic this area was a landmass away from marine influence. Regional volcanism along with numerous shallow lakes during that time probably accounts for the excellent preservation and the good dating of the formations. The climate was probably semi-arid with relatively low moisture. Finding articulated shells, vertebrate skeletons, land plants with stems and associated leaves indicates low energy lacustrine locations with little transporting of material. There are ash tufts from volcanic activity above the layers where mass mortality beds are found. These factors allowed for the formation of Konservat-Lagerstatten conditions even preserving soft tissue features. These include stomach contents, wing membranes and color patterns, feathers, fur, and skin impressions. The dating has been contentious settling in the Late Jurassic Early Cretaceous time. The authors have settled on a date range of 18 MY from 128 to 110 MYA (Early Cretaceous). Many of the specimens show that feathers did not evolve for flight and shows a wide diversity of birds in the Jehol fauna. In addition 6 genera of mammals (insectivores and carnivores) are known including Eomaia that extends the range of eutherians into the Early Cretaceous. Invertebrates are the most abundant and remain largely undescribed. They include insects, spiders, crustaceans, bivalves and gastropods. Flies with long tubular mouthpieces suggest nectar-producing angiosperms. The flora is conifer dominated with some bryophytes, lycopsids, ferns ginkos and possible early angiosperms (including 3 species of Archaefructus a possible stem-group angiosperm). Many of the closest relatives of many of these fossils are from the Late Jurassic leading some to believe that it may have been a refugium based upon its isolation from the rest of Laurasia at that time. Because of the presence of some Late Cretaceous fossils like tyrannosauroids and therizinosauroids it may also have been a center of diversification for some of them. It is believed that this isolation ended in the Early Cretaceous and this may help explain the mixed biota. One of the biggest problems with this area is the illegal collecting that is stealing many specimens from scientific research. Another is that the discoveries are outstripping the rate of description. This site provides a unique picture of an intact ecosystem and will yield exciting results for years to come.
World’s Biggest Trilobite Is From Canada – Isotelus rex
Finally it is in print - an article by Rudkin et al. in the Journal of Paleontology details the largest trilobite ever found at 700 mm (2.3 ft). Because of its size it is called Isotelus rex and it is almost complete. This is the one that the Field Museum and Wendy Taylor are supposed to get a cast of some day. It is at the Royal Ontario Museum in Toronto and is dated to the Upper Ordovician at about 440 MYA. It is also interesting to compare it to other large arthropods, some fossil and some recent. Compare it to a large reconstructed New York eurypterid at 1.3 m (4.3 ft); a reconstructed Arthropleurid (millipede) at 1 m (3.3 ft); a spider Macrocheira kaempferi at 300 mm (1 ft); and a generalized lobster at 500 mm (1.6 ft).
This fossil brings to mind the whole question about how some of these animals got so big. This trilobite is probably the largest and most massive body of any arthropod. Most of the other large animals had tapered bodies or long appendages. In the Carboniferous (as we know) some dragonfly wingspans reached up to 700 m (2.3 ft) and Megarachne servinei reached a size of 340 mm (1.1 ft) from the front appendages to the base of the abdomen. Large size has been thought to be constrained by many factors such as strength of the cuticle, respiratory efficiency, and complex molt cycles among others. It would also depend on food supply, species interaction, temperature and oxygen availability. Many believe that gigantism is most often found in cold waters with more dissolved oxygen, but this trilobite was found in a warm shallow setting. The high oxygen level of the Carboniferous (35% compared to today’s 21%) is thought by some to explain the large terrestrial arthropods. Some studies show that during the Ordovician oxygen levels were lower at about 15% and CO2 levels were above today’s levels. This might help explain their larger sizes since in warmer climates it is easier to precipitate and maintain calcified skeletons. It is possible that Isotelus rex could get large by molting rapidly with an elevated metabolism and readily available calcium carbonate. The issue of extinction also comes up because some feel that when animals get larger they are more susceptible to climate changes and thus more easily go extinct. However, at this point more believe that the extinction of trilobites in general comes from the vulnerability of their early life stages. Isotelus and many other trilobite species go through an early larval stage called protaspid with a long planctic stage before metamorphosis to their benthic stage. This early stage may have been vulnerable to the newly arriving cold waters at the end of the Ordovician. Another interesting fact about this new giant animal is that it did not have many signs of encrusting organisms on its surface. Could it have possessed some antifouling property or did it live a life partially buried which would discourage organisms from attaching (and also facilitate burial and preservation)? It is a very interesting specimen.
Karen Nordquist, ESCONI Paleontology Study Group
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Field Museum of Natural History
SVP Society for Vertebrate Paleontology
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