Coleoids and Nautiloids
Octopods and Nautiloids of the Western Interior Sea
In addition to the more common fossils of ammonoid shells, deposits laid down by the Cretaceous Western Interior Sea hold the fossils of two more groups of cephalopods. One of these groups is the nautiloids whose members have rounded and tightly coiled external shells divided into chambers. Their simple shell sutures separate them at a glance from the elaborate shell divisions of ammonites. Coleoids, on the other hand, are the lineage containing modern squid, octopuses, and cuttlefish. These animals do not have an external shell and as a result the fossil record for these animals is made up mostly of smaller hard elements from the internal parts of their bodies and occasionally the remains of hook-like structures from their arms and tentacles. Most members of this second group are thought to have been active hunters much like their living relatives.
Coleoid Anatomy
Internal and External Tissues
Coleoids have soft bodies which are organized around a muscular mantle which surrounds the internal organs. By drawing water into the mantle cavity and forcing it through the flexible funnel of the hyponome, many coleoids can push themselves through the water using a process which somewhat resembles jet propulsion. They have complex eyes and their mouths are surrounded by a sharp beak. Inside of their mouths they have a radula which is used to break up their food. Coleoids have a series of muscular arms covered in suckers and/or hooks. Squids and cuttlefish generally have eight arms plus two elongated feeding tentacles, whereas octopods have eight arms and no separate tentacles. Unlike nautiloids, coleoids do not have a large external shell. Some still have an internal shell, such as the squid’s gladius or the cuttlefish’s chambered cuttlebone, while some octopods have a set of small hard structures beneath their mantles which are called stylets. Belemnites, another type of coleoid, have bullet shaped rostra at the very tips of their bodies in front of their fins. Many of the larger extinct muensterellid coleoids who are fairly well represented in the fossil record from this time period had internal gladii and external anatomies which at first look a lot like those of squids, although they are now currently considered to be a group of stem-octopods.
(BELOW) A labeled diagram of the external anatomy of the muensterellid coleoid Muensterella showing the features seen in many types of Cretaceous stem-octopods
(BELOW) The hard tissue elements of the body of a squid, including a large elongated gladius and a small beak
(BELOW) The hard tissue elements found in today's octopi. Not all octopi have stylets but these represent the last remaining portions of the shells which were found in basal cephalopods. In Cretaceous stem-octopods, the mantle usually houses a large gladius which appears roughly similar to that of a squid.
(BELOW) The hard tissue elements found in extinct belemnite cephalopods. In addition to the fossils of the solid rostrum, some of these animals are known from fossils which preserve the remains of hook-like structures on their arms.
(Browse by subclass)
Belemnites
Temporal Range: 234 million years ago - 66 million years ago
Geographic Range: Worldwide distribution
Genera in the Western Interior Sea: Actinocamax, Belemnitella
Diet: Active pelagic predator, small fish and invertebrates
Belemnites are a group of cephalopods who first show up during the Triassic period and were some of the most abdundant pelagic mollusks of the Mesozoic era. They are best known from fossils of their rostra, which are bullet-shaped hard tissue elements positioned in front of the animal's side fins in life. Belemnites would have appeared very similar to squid from the outside, although the long rostral proifiles of some belemnites groups would have given them a distinctive elongated and pointed appearance which is not seen in any type of extant cephalopod. These animals most likely dissapeared during the end-Cretaceous extinction,
(BELOW) A pair of belemnite rostrum fossils on display the the KU Natural History Museum. The rostra of different types of belemnites can vary a lot between different families, both in terms of their cross-sections and the presence/absence of grooves or furrows along the margins of the structure.​
Enchoteuthis
Temporal Range: Early and Late Cretaceous, Albian - Campanian stages
Geographic Range: Central North America, Australia
Species: E. melanae, E. tonii, E. cobbani
Diet: Active pelagic predator, small fish and invertebrates
Enchoteuthis was a large stem-octopod which lived out in the open waters of the Western Interior Sea. These animals are mostly known from gladius fossils of an elongated spear-like internal structure that supported its mantle. Because fossils usually preserve only this structure, scientists know little about its softer anatomy, including its arms and possible tentacles. It used to be restored to appear similar to a living giant squid but more recent findings have shown that it probably was more similar to the smaller Muensterella. It had a torpedo-shaped body, short fins, eight arms and no long tentacles. It likely fed upon small to medium-sized fishes, cephalopods and possibly even small marine reptiles. Most fossils formerly assigned to the more famous genus Tusotheuthis are now classified under the Enchoteuthis genus.
(BELOW) A large fossil gladius (center frame) from the Cretaceous period of Kansas on display at the KU Natural History Museum. This particular fossil is well over 3 feet long and most likely comes from an Enchoteuthis
Muensterella
Temporal Range: 155 million years ago - 90 million years ago
Geographic Range: Texas, parts of Europe, Antarctica
Species: M. scutellaris, M. spinosa
Diet: Active pelagic predator, small fish and invertebrates
Muensterella was an extinct coleoid which would have looked a lot like a cuttlefish or bobtail squid, despite more fossil evidence pointing towards it being closer to octopuses and vampire squids. Aside from the more common fossils of their gladii, some fossils of these animals found in fine-grained limestone preserve traces of soft tissue, including the remains of tentacles and even internal organs. The genus is unusually well documented compared with many other prehistoric coleoids which typically begin to decompose shortly after death and leave behind very few hard remains.
Niobrarateuthis
Temporal Range: 89 million years ago
Geographic Range: Kansas
Species: N. bonneri
Diet: Active pelagic predator, small fish and invertebrates
Niobrarateuthis was a muensterellid stem-octopod which had a gladius with a wide, spoonlike end called the patella. This characteristic links the animal to early relatives of modern octopuses. However, its complete appearance remains uncertain because delicate structures such as the arms, eyes, beak, and muscles were rarely fossilized. Exact size estimates for these animals are difficult to make but it may have grown to be around 3 feet long.
Nautiloid Anatomy
Internal and External Tissues
Nautiloids are cephalopods whose bodies are mostly covered in shells which may be coiled, curved, or straight. Living nautiluses in the family nautilidae have tightly coiled shells and have bodies which occupy the largest outer living chamber. Their heads and many small tentacles come out of the aperture of the shell while a strong and leathery hood covers the upper portion of the head and seals the shell entrance when the animal retreats inside. Unlike squid and octopus arms, these appendages do not have any suckers. They do not have the complex eyes seen in coleoid cephalopods and instead have more simple pinhole eyes.
(BELOW) A labeled diagram of the external anatomy of a nautiloid. Older nautiloid groups often had straight shells but by the Cretaceous period, the surviving family Nautilidae tended to only have tightly coiled shells.
Family Nautilidae
Temporal Range: Triassic period - Present
Diet: Scavengers, remains of fish, crustaceans, other invertebrates
Genera in the Western Interior Sea: Stenzeloceras, Eutrephoceras, Cymatoceras
Nautilidae is the only surviving family of nautiloids and comprises most of the nautiloid genera known from the Late Cretaceous. The shells of these animals form a flat coil and, like the shells of ammonoids, contain chambers separated by walls called septa. The nautilid itself lives in the outermost chamber, whereas the inner chambers hold gas and liquid and are connected to a tube-like siphuncle which adjusts the fluid balance of the shell to help the animal control its buoyancy. Nautiloids were already much less common in the Cretaceous period than they had been in earlier time periods. They may have managed to survive the end-Cretaceous extinction event by taking shelter in deep waters.
Lifestyle: Near-benthic, tend to swim near ocean floor
(BELOW) The genus Stenzeloceras from the Late Cretaceous, Campanian stage. Found in Alabama. Species in the Western Interior Sea: S. sinuosum
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(BELOW) The genus Cymatoceras from the Late Jurassic to the Oligocene epoch. Species found in the Western
Interior Sea: C. texana. Found in Texas
(BELOW) The genus Eutrephoceras from the Early Cretaceous to the Pliocene epoch. Species found in the Western
Interior Sea: E. dekayi. Found in Montana, South Dakota, Mississippi, Alabama, Texas, Tennessee
Suggested References: Coleoids, Nautiloids
Brinster, K. F. (1970).” Molluscan Paleontology of the Pierre Shale (Upper Cretaceous), Bowman County, North Dakota (MS).” University of North Dakota.
Everhart, M.J. (2017). “Oceans of Kansas - A Natural History of the Western Interior Sea,” Second Edition. Indiana University Press, 460 pp.
Green, R.G. (1977). “Niobrarateuthis walkeri, a new species of teuthid from the Upper Cretaceous Niobrara Formation of Kansas”. Journal of Paleontology 51(5):992-995.
Jeletzky, J.A. (1961). “Actinocamax from the Upper Cretaceous Benton and Niobrara Formations of Kansas.” Journal of Paleontology 35(3):505-53
Kauffman, E.G., Sageman, B.B., Kirkland, J.I., Elder, W.P., Harries, P.J. and Villamil, T. (1993). “Molluscan biostratigraphy of the Cretaceous Western Interior Basin, North America”. pp. 397-434 in Caldwell, W.G.E and Kauffman, E.G. (eds.), Evolution of the Western Interior Basin.
Kauffman, E.G. (2004). “Mosasaur predation on Upper Cretaceous nautiloids and ammonites from the United States Pacific Coast.” Palaios 19(1):96-100.
Larson, N. L; Jorgensen, S.D ; Farrar, R. A. & Larson, P. L. (1997). “Ammonites and the Other Cephalopods of the Pierre Seaway”. Geoscience Press, Inc. p. 44
Selden, P. A., ed. 2009. Treatise on Invertebrate Paleontology. Part L, Mollusca 4, Revised, vol. 2. The University of Kansas Paleontological Institute. Lawrence, Kansas