Acanthoteuthis
Encyclopedia
Acanthoteuthis is a belemnite
genus, a squid-like cephalopod with an internal shell from the Late Jurassic
Epoch
, related to modern coleoids.
Acanthoteuthus belongs to the belemnoid family Belemnotheutidae in which the pointed rostrum at the back of the phragmocone is lacking.
of Bavaria
, which have small hooklets on their arms, sometimes associated with more or less complete remains of the animal. The hooklets are typically compressed and may be beveled on either or both margins on one side.
Munster characterized three species, A. speciosa, A ferussacii, and A lichtensteinii, chiefly upon the forms of these hooklets. In A lichtensteinii they are smaller than in A speciosa and more circular in transverse section. D'Orbigny united the three under the name A. ferussacii while Wagner regarded A. speciosa as a valid species but saw no essential difference between Munster's A. ferussacii and A.lichtensteinii so united the two under the name ferusscii.
Acanthoteuthis has a distinctive v-shaped ridge on the dorsal side at the back of its internal shell which seems to be analogous to the median keel in the posterior part of the gladius in most recent squids to which the fins are attached. This indicates that Acanthoteuthis also had fins with similar attachment at the posterior end of the animal, and which may have been broadly oval or rhombohidral. The proostracum in front is flat,of considerable width and not likely to have been covered by muscular mantle, which was probably attached to the lateral edges as in recent Vampyroteuthis.
Acanthoteuthis and other belemnotheutids were thought to have been planktonic forms that inhabited the epipelagic and possibly upper mesopelagic zones over the continental shelves and slopes of Mesozoic continental seas.
Belemnoidea
Belemnoids are an extinct group of marine cephalopod, very similar in many ways to the modern squid and closely related to the modern cuttlefish. Like them, the belemnoids possessed an ink sac, but, unlike the squid, they possessed ten arms of roughly equal length, and no tentacles...
genus, a squid-like cephalopod with an internal shell from the Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
Epoch
Epoch (geology)
An epoch is a subdivision of the geologic timescale based on rock layering. In order, the higher subdivisions are periods, eras and eons. We are currently living in the Holocene epoch...
, related to modern coleoids.
Acanthoteuthus belongs to the belemnoid family Belemnotheutidae in which the pointed rostrum at the back of the phragmocone is lacking.
Taxonomy
The genus Acanthoteuthis was founded by R. Wagner and G. Munster for belemnoids, found in the Solnhofen limestoneSolnhofen limestone
The Solnhofen Plattenkalk is a Jurassic Konservat-Lagerstätte that preserves a rare assemblage of fossilized organisms, including highly detailed imprints of soft bodied organisms such as sea jellies...
of Bavaria
Bavaria
Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...
, which have small hooklets on their arms, sometimes associated with more or less complete remains of the animal. The hooklets are typically compressed and may be beveled on either or both margins on one side.
Munster characterized three species, A. speciosa, A ferussacii, and A lichtensteinii, chiefly upon the forms of these hooklets. In A lichtensteinii they are smaller than in A speciosa and more circular in transverse section. D'Orbigny united the three under the name A. ferussacii while Wagner regarded A. speciosa as a valid species but saw no essential difference between Munster's A. ferussacii and A.lichtensteinii so united the two under the name ferusscii.
Characteristics
C. G. Crick (1898) described an Acanthoteuthis, A ferussachi with four pairs of arms, all eight of which have two rows of hooklets. The arms are of unequal length, the longest pair being almost 85 mm long, probably with 14 or 15 hooklets per row. The shortest arms are 32 mm long with another pair with a length of 38 mm, all four having 9 or 10 hooklets per row. The fourth pair are about 55 mm long with 12 or 13 hooklets per row. The pairs are in no particular physiological order other than that they are assumed to be bilaterally symmetrical. Other references, e.g. Catalogue of the Mollusca in the collection of the British museum, describe Acanthoteuthis as having ten, rather unequal arms, with two rows of hooks. The fifth pair seem to be auxiliary and are comparatively short.Acanthoteuthis has a distinctive v-shaped ridge on the dorsal side at the back of its internal shell which seems to be analogous to the median keel in the posterior part of the gladius in most recent squids to which the fins are attached. This indicates that Acanthoteuthis also had fins with similar attachment at the posterior end of the animal, and which may have been broadly oval or rhombohidral. The proostracum in front is flat,of considerable width and not likely to have been covered by muscular mantle, which was probably attached to the lateral edges as in recent Vampyroteuthis.
Paleoecology and lifestyle
The absence of a couterbalancing rostrum indicates that Acanthoteuthis lived head down in a vertical orientation, like Spirula and Mastigoteuthis. and the presence of an ink sack indicates it inhabited the upper 200 m of oceanic waters.Acanthoteuthis and other belemnotheutids were thought to have been planktonic forms that inhabited the epipelagic and possibly upper mesopelagic zones over the continental shelves and slopes of Mesozoic continental seas.
See also
- Belemnite
- List of belemnites
- BelemnotheutisBelemnotheutisBelemnotheutis is an extinct genus of cephalopods which existed from the Middle to Upper Jurassic . They are related to belemnites but differ significantly in morphology. Belemnotheutis fossils are some of the best preserved among coleoids...