Etymology
Cephalopod – meaning ‘head foot’ in Greek, in reference to the animals ‘head’ containing its ‘feet’ (tentacles).
Currently four main groups of cephalopods are known from Richmond and Hughenden:
Nautiloidea – meaning 'sailor' in Greek, referring to the animals ‘sailing’ in their shells.
Ammonoidea – from the name "ammonite", which was inspired by the spiral shape of their fossilized shells resembling a tightly coiled rams' horns. Pliny the Elder (in 79 AD) called fossils of these animals ammonis cornua ("horns of Ammon") because the Egyptian god Ammon (Amun) was typically depicted wearing ram's horns.
Belemnitida – meaning ‘a dart or arrow’ in Greek, referring to the shape of the rostrum.
Vampyromorphida – the name derives from the modern genus Vampyroteuthis meaning ‘vampire squid’ in Greek, referring to the animals’ resemblance to vampires in folklore.
Relationships
Cephalopods, unlike all the other creatures in Kronosaurus Korner’s collections, are invertebrates. These are animals that neither possess nor develop a vertebral column (commonly known as a backbone or spine). The vast majority of animal species on Earth are invertebrates with one estimate putting a figure at 97% of species. Within such a diverse group, cephalopods belong in the phylum Mollusca. These are close cousins of other Lophotrochozoa, such as segmented woms (Annelida), brachiopods (Brachiopoda) and phoronids (Phoronida). The molluscs are the largest marine animal phyla and comprises about 23% of all the named marine organisms. Within the Mollusca the cephalopods are most closely related to the snails (Gastropoda), tusk shells (Scaphopoda) and clams (Bivalvia). All these groups potentially evolved from a monoplacophoran (limpet-like ancestor) at the beginning of the Cambrian (540 million years ago).The cephalopods have a long geological history, with the first ‘true’ cephalopods found in late Cambrian period (495–480 million years ago), and purported stem-group relatives present in the earliest Cambrian soft-body preservation sites (520–515 million years ago). Nautiloids appear to have been the earliest cephalopods, having relatively simple shells. The high point of nautilus evolution was during the Ordovician and Silurian periods (about 505 to 408 million years ago). During this time, giant straight-shelled nautiluses were the only large animals on Earth. Even after their heyday during the Ordovician, nautiluses remained conspicuous (although less important) components of marine invertebrate communities. Several new families evolved during the Mesozoic (252.17–66 million years ago) and Cenozoic eras (66–2.58 million years ago) alongside the various cephalopod groups. Two genera of nautiloid survive to the present day, Nautilus and Allonautilus, this includes the species Nautilus stenomphalus which can be found in nearby Townsville.
The next group to appear where the Ammonoidea. Evolving form an ancestor within the bactritoid nautiloids, the ammonoid cephalopods first appeared in the Devonian (400 million years ago). The ammonoids and nautiloids mainly differ in the internal arrangement of the shell (as discussed below). Ammonoids were extremely abundant especially during the Mesozoic (252.17–66 million years ago). Many genera evolved and ran their course quickly, becoming extinct in a few million years. Due to their rapid evolution and widespread distribution, ammonoids are used by geologists and paleontologists for biostratigraphy (linking rocks with specific geologic time periods). The ammonoids became less abundant during the latter part of the Mesozoic (252.17–66 million years ago), with none surviving into the Cenozoic (66–2.58 million years ago). The last lineages disappeared, along with the dinosaurs, 66 million years ago during the Cretaceous–Paleogene extinction event.
The two other cephalopods found in Richmond (the Belemnitida and Vampyromorphida) collectively belong to a group called the Coleoidea. This group appeared at about the same time as the ammonioids (possibly evolving from a similar common ancestor) and diversified rapidly. The ammonioids and coleoids are very similar, sharing a number of important anatomical traits. However, coleoids differ having an internal shell, whist ammonioids have on an external shell. The Belemnitida are one of the more primitive groups of coleoid, possessed ten arms, no enlarged feeding tentacles, a solid phragmocone made of aragonite and ‘rostrum’ or ‘guard’ made of calcite. They are considered the most successful groups of coleoids, having been very abundant in the seas of the Jurassic and Cretaceous (213 to 66 million years ago). However, like the ammonioids, they went extinct during the Cretaceous–Paleogene extinction event. The other more advanced coleoids found in Richmond are the Vampyromorphida. Little is known of their evolutionary origins, as the group only rarely preserves as fossils. Physically, they somewhat resemble octopuses in lacking a mineralised shell, but the eight arms are united by a web of skin. The vampyromorphs appear to have been moderately diverse during the Jurassic (201.3–145 million years ago) and many of the so-called ‘Jurassic squids’ are in fact vampyromorphs. The early vampyromorphs had shells with chambers that offered neutral buoyancy, but in later species lost this function and the shell became uncalcified. Vampyromorphs and modern octopuses appeared to have diverged during the Late Jurassic (about 140 million years ago). Some of the genera found in Richmond may be more closely related to these early octopuses (e.g. Trachyteuthis), although this suggestion is still continuous. Vampyromorphs continue to survive today with the single modern species (Vampyroteuthis infernalis) living in the oxygen minimum zone (600 to 900 metres deep) of the world's oceans.
Discoveries
Invertebrate fossils have been known in Richmond since the first geologists examined the area in the early 1800’s. However, because invertebrate are perceived as ‘less charismatic’, their discoveries are typically unrecorded, except by scientists. Some of the first cephalopod fossils from Richmond were described between 1867–1928 by the famous palaeontologists Ralph Tate, Robert Etheridge Jr, Robert Etheridge Snr, Sir Frederick McCoy, Julian Tenison-Woods and Dr Frederick Whitehouse. Their work included the naming many of the ammonioids, belemnites and nautiloids species in the region. Following this earlier period of intense discovery, enthusiasm in cephalopod finds faded. Only a few scientific papers were produced (in 1966, 1967 and 1978) by Dr Skwarko, Dr Robert Day and Dr Kenneth McNamara. However, renewed interested in the early 1990’s and 2000’s led researcher to describing new and previously unrecorded species. In particular, their work focused on ammonioids, belemnites and vampyromorphs. This work was done by a number of high profile palaeontologists such as Dr Mary Wade, Dr Don McKenzie, Prof Bob Henderson, Dr Toni William and Prof William Kennedy. Work is still underway, with new species of ammonioid being discovered constantly in the local area.
Geology
Cephalopods from the Early Cretaceous of Queensland are known all throughout the Aptian and Albian (approximately 120–100 million years old) units in the Rolling Downs Group. This includes the Doncaster and Ranmoor members of the Willumbilla Formation, Toolebuc Formation, Allaru Mudstone and Mackunda Formation. However, ammonites are exceptionally rare at the museum’s free fossil hunting sites, likely because the environment was unsuitable for them.
Description
Nautiloids (mainly from the species Eutrephoceras hendersoni) in Richmond are characterized by an involute shell that is 40–50 cm in diameter and smooth. The shell is internally divided into chambers, with the chambered section called the phragmocone. The phragmocone is divided into camerae by simple concave walls called septa. These walls are pierced in the middle by a duct, the siphuncle, which runs along the centre. As nautiloids matures, its body moves forward, sealing the camerae behind it with a new septum. The last fully open chamber, also the largest one, is used as the living chamber. In modern nautiloids the number of camerae increases from around four at the moment of hatching to thirty or more in adults. The tentacles of fossil (and living) nautiloids differ from other cephalopods being both greater in number and lacking suckers, having ‘adhesive ridges’ instead. These tentacles are arranged into two circles and are undifferentiated and retractable.
Ammonioid shells are striking similar to those of nautiloids. However, the groups differs in the postion of the siphuncle and the arrangement of septa. In ammonioid the siphuncle runs along the periphery of the shell and the septa are highly fluted at the edges (with leaf-like pattrens). Some species of Richmond ammonioid also possess ribbed or lobbed ornamentation, making it easier to differentiate them from nautiloids. Size is highly variable with some species getting up to 1.5 m in diameter, compared to other that are less than 1 cm. Unfortunately the soft body parts of ammonioid have never been preserved in any detail. The jaw, however, are sometime founds as calcitic plates. These are termed aptychi (in the case of a pair of plates) or anaptychus (in the case of a single plate). Anaptychi are relatively rare as fossils and only occur in ammonites from the Mesozoic era.
Belemnites in Richmond are typically known from part of the internal skeleton called a ‘rostrum’ or a ‘guard’ .This would have been a solid structure at the posterior (back) of the animal in life. The rostrum is usually a dark colour, 2–8 cm bullet-shaped object, with grooves along the sides that are used to identify species. The rostrum would have been attached to a chambered conical shell known as the phragmocone. The space between the phragmocone and the rostrum is known as the alveolus. At the forward part of the phragmocone is a thin, fragile spoon-shaped structure known as the proostracum which is almost never found. Fossils which preserve the soft parts of belemnites indicate that they had ten hooked tentacles, an ink sac, a hard beak, tail fins, and large eyes. Well preserved specimens have even retained evidence of strong muscular fibers in the mantle, suggesting that they were very powerful swimmers.
Vampyromorphs remains from Richmond are often found as thin, blade-like objects called ‘gladii’. These can be white, blue and black in colour with an iridescent sheen and distinct growth lines. Some can measure up to 1.5 m long, although the majority range between 50–100 cm in length. Originally this structure would have been made of chitin (an organic polymer) and placed inside the mantle of the animal (like a cuttlefish bone). However after the animal died the ‘gladii’ was released and floated to seafloor where chemical reaction altered the chitin, replacing it calcium phosphate (the same substances that makes up our bones). We know from soft tissue preserved in similar species that these vampire squid can reach a maximum total length around 2–3 m, comparable with some smaller marine reptiles. A webbing of skin connected their eight arms, each lined with rows of fleshy spines or cirri. Only the distal half of the arms (farthest from the body) had suckers. Adults may have also had a pair of large fins projecting from the lateral sides of the mantle. These fins were used as the primary means of propulsion: "flying" through the water by flapping their fins.
Palaeobiology
Much of what we know about fossil nautiloids come from studying their modern relatives. It is likely that the Richmond nautiloids were scavengers and opportunistic predators, eating small crustaceans and carrion (dead animals). Instead of vision, the animal is thought to have used smell as its primary sense for foraging. Unlike many other cephalopods, fossil nautiloids did not have well developed vision, as their eye lacks a solid lens. Instead, nautiloids had a simple pinhole eye open to the environment, which only allows for the creation of very blurry image imagery. It has been suggested they may have used their vision to keep track of predators. This included animals like Kronosaurus, as demonstrated through fossilised shells with large punctures wounds representing tooth marks. Little is known about the biology of ammonites and their close relatives. Nonetheless, much has been determined by examining their shells. It is tempting to think that they occupied same ecological niches as fishes; however, this is unlikely given their difficulty in maintaining high swimming speeds. Much more likely is that they occupied a variety of niches comparable to those occupied by modern crustaceans, and molluscs (like the plankton-feeding ‘glass squids’). Only a few species of ammonites from Richmond might have been active, open water predators, such as the large genus Tropaeum. Some of the stranger ‘heteromorphic ammonites’ (with U-shaped shells) may have lived as part of the plankton (drifting with currents), or hooked onto floating objects. Dense accumulations of these ‘heteromorphic ammonites’ in shallow water deposits around the area suggests that they likely preferred to live in coastal environments. Belemnites likely filled the same ecological roles as modern squid, eating molluscs, fish and crustacean. This is supported by finds of their sharp hooklets used for grasping prey and highly recurved beak used for tearing flesh. Platypterygius australis fossils are often found alongside the remains of belemnites in Richmond, suggesting a predator-prey relationship. Occasionally the fossilised stomach contents of other related ichthyosaurs from England and Germany are discovered with belemnite hooks, but rarely are rostra. This suggests that either the unpalatable rostra were regurgitated after being eaten or that the head was the only part of the belemnite to be devoured. Vampyromorphs are exceptionally rare as fossils and almost nothing is known about their palaeobiology. It seems highly unlikely that they would feed like modern ‘vampire squid’, using two retractile filaments in order to capture detritus. Based on their size (up to 6 metres) it has been suggested that their ecology was more similar to the modern colossal squid (Mesonychoteuthis hamiltoni). They may have feed on large fish, other celphalopods and possibly small marine reptiles (like turtles).There is some indirect evidence that these ancient vampyromorphs may have even lived close to the surface. This come from a specimen that has been discovered with bite marks, likely caused by a shallow water marine reptile (e.g. Kronosaurus).
References
Cook, A. G. 2012. Cretaceous faunas and events, northern Eromanga Basin, Queensland. Episodes 35, 153–159.
Day, R. E. 1969 The Early Cretaceous of the Great Artesian Basin. In Stratigraphy and Palaeontology Essays in Honour of Dorothy Hill (Ed. Campbell, K. S. W.) pp. 140–173. Australian National University Press Canberra.
Etheridge Jr, R. 1909. Lower Cretaceous fossils from the sources of the Barcoo, Ward and Nive Rivers, south central Queensland. Part II: Cephalopoda. Records of the Australian Museum 7: 235–240.
Henderson, R. A. 1990. Late Albian ammonites from the Northern Territory, Australia. Alcheringa 14: 109–148.
Henderson, R. A., Crampton, J. S., Dettmann, M. E., Douglas, J. G., Haig, D., Shafik, S., Stilwell, J. D., and Thulborn, R. A. 2000. Biogeographical observations on the Cretaceous biota of Australasia. Memoirs of the Association of Australian Palaeontologists 23: 355–404.
Henderson, R. A., and Kennedy, W. J. 2002. Occurrence of the ammonite Goodhallites goodhalli (J. Sowerby) in the Eromanga Basin, Queensland: an index species for the late Albian (Cretaceous). Alcheringa 26, 233–247.
Henderson, R. A., and McKenzie, E. D. 2002. Idanoceras, a new heteromorph ammonite genus from the Late Albian of Eastern Australia. Journal of Paleontology 76: 906–909.
Ludbrook, N. H. 1966. Cretaceous biostratigraphy of the Great Artesian Basin in South Australia. Geological Survey of South Australia, Bulletin 40: 1–223.
McKenzie, E. D., Rozefelds, A. C., and Deacon, P. 2014. An ancyloceratid ammonite from the Aptian Maryborough Formation, Queensland, Australia, and synonymy of Australiceras Whitehouse with Tropaeum Sowerby. Alcheringa 38: 256–265.
McNamara, K. J. 1978. Myloceras (Ammonoidea) from the Albian of central Queensland. Alcheringa, 2: 231–242.
Moore, C. 1870. Australian Mesozoic geology and palaeontology. Quarterly Journal of the Geological Society 26: 226–261.
Price, G. D., Williamson, T., Henderson, R. A., & Gagan, M. K. 2012. Barremian–Cenomanian palaeotemperatures for Australian seas based on new oxygen-isotope data from belemnite rostra. Palaeogeography, Palaeoclimatology, Palaeoecology 358: 27–39.
Wade, M. 1993. New Kelaenida and Vampyromorpha: Cretaceous squid from Queensland. Memoirs of the Association Australasian Paleontologists 15: 353–374.
Whitehouse, F. W. 1926. The Cretaceous Ammonoidea of eastern Australia. Memoirs of the Queensland Museum 8: 195–242
Williamson, T. 2006. Systematics and biostratigraphy of Australian Early Cretaceous belemnites with contributions to the timescale and palaeoenvironmental assessment of the early Australian Early Cretaceous system derived from stable isotope proxies. PhD thesis, James Cook University.