This is the first nautiloid specimen I’ve seen in the Matmor Formation (Middle Jurassic, Callovian) after ten years of collecting in it. Our colleague Yoav Avni (Geological Survey of Israel) picked it up during this summer’s fieldwork. It is a beautiful internal mold in which the outer shell has been mostly removed, revealing the radiating lines where the internal walls (septa) intersected the outer shell. These intersections are called sutures. Here we see nice, simple sutures characteristic of nautiloids. Ammonites, on the other hand, can have very complex sutures indeed. Note that some of the outer shell still remains as an orangish layer recrystallized to calcite from the original aragonite. There are two round holes in the foreground. I’d like to think these are tooth marks from a predator, but there is not enough evidence to say that with any seriousness.
This view of the outer edge of the top specimen shows a diagnostic feature of this particular genus: a deep sulcus (channel) running along the venter (periphery). Most nautiloids have a rounded venter, so this characteristic stands out.
This is a side view of another specimen of the same nautiloid, also found by Yoav. The large hole at the center of coiling is called the umbilicus. It is especially large in this Matmor nautiloid. Note again the radiating sutures where the outer wall has been removed.
This nautiloid appears to belong to the genus Paracenoceras Spath 1927. I had to have this beaten into me by a half-dozen cephalopod workers. I thought it looked a lot like Cymatonautilus collignoni Tintant, 1969. If so, it would have been a new occurrence of this rare genus — the closest it has previously been found is in Saudi Arabia. Most importantly, it would have been a range extension for this genus. Previously it has been well documented as having appeared in a very short time interval: the latest early Callovian into the middle Callovian. In the Matmor Formation we found it in a bed in the upper Callovian, specifically subunit 52 in the Quenstedtoceras (Lamberticeras) lamberti Zone. Alas, my dreams of a paper describing this discovery was not to be. Another beautiful idea skewered by reality.
Paracenoceras was described by Leonard Frank Spath (1882-1957) in 1927. Spath was an interesting character. He was a British paleontologist who specialized in ammonites, but also delved into other cephalopods like our nautiloid genus here. He was a BSc graduate of Birkbeck College in 1912, eventually earning a doctorate at the same institution, now known as Birkbeck, University of London. He was a curator in the British Museum (Natural History) for most of his career. He was especially interested precise Jurassic and Cretaceous biostratigraphy using ammonites. He published more than 100 papers and monographs, was elected as a Fellow of the Royal Society, and received the Lyell Medal from the Geological Society of London in 1945. Spath was well known for his biting criticisms of German paleontologists, especially those who worked on ammonites. Turns out that he was keeping a secret from everyone, including his own children: his parents were German! His son (F.E. Spath) discovered this long after his death, publishing an account of his father in 1982. The elder Spath no doubt kept his German heritage secret for the obvious reasons, given his time and place.
References:
Branger, P. 2004. Middle Jurassic Nautiloidea from western France. Rivista Italiana di Paleontologia e Stratigrafia 110: 141-149.
Halder, K. 2000. Diversity and biogeographic distribution of Jurassic nautiloids of Kutch, India, during the fragmentation of Gondwana. Journal of African Earth Sciences 31: 175-185.
Halder, K. and Bardhan, S. 1996. The fleeting genus Cymatonautilus (Nautiloidea): new record from the Jurassic Charl Formation, Kutch, India. Canadian Journal of Earth Sciences 33: 1007-1010.
Kummel, B. 1956. Post-Triassic nautiloid genera. Bulletin of the Museum of Comparative Zoology 114(7): 320-494.
Spath, F.E. 1982. L.F. Spath (1882 – 1957), ammonitologist. Archives of Natural History 11: 103-105.
Tintant, H. 1969. Les “Nautiles à Côtes” du Jurassique. Annales de Paleontologie Invertébrés 55: 53-96.
Tintant, H. 1987. Les Nautiles du Jurassique d’Arabie Saoudite. Geobios 20: 67-159.
Tintant, H. and Kabamba, M. 1985. The role of the environment in the Nautilacea, p. 58-66. In: Bayer, U. and Seilacher, A. (eds.), Sedimentary and Evolutionary Cycles. Lecture Notes in Earth Sciences, vol. 1, Springer (Berlin).
