Dactylioceras

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Dactylioceras
Temporal range: Pliensbachian–Toarcian [1]
Dactylioceras 01.jpg
Dactylioceras (Dactylioceras) athleticum
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Family: Dactylioceratidae
Subfamily: Dactylioceratinae
Genus: Dactylioceras
Hyatt, 1867

Dactylioceras was a widespread genus of ammonites from the Lower Jurassic period, [1] approximately 180 million years ago (mya). [2] Like many other ammonites, the genus Dactylioceras is extremely important in biostratigraphy, being a key index fossil for identifying their region of the Jurassic. It had a nearly cosmopolitan distribution during the time it existed.

Contents

Etymology

The name Dactylioceras comes from the Greek dactyl, meaning “finger”, and keras, meaning "horn" and refers to the shell's branching ribs.

Description

Dactylioceras are generally small, averaging 65 millimetres (2.6 in) in diameter. They have a strong, ribbed shell. The ribs are slightly inclined forward, running over the outer edge, and either simple or forking at outer end. Though they eventually died out 180 mya, their style of ribbing was copied by numerous subsequent ammonite genera until the whole group became extinct 66 million years ago with the dinosaurs.

Ecology

Dactylioceras probably lived by scavenging on the sea floor. Mass mortality specimens of Dactylioceras are common, and perhaps suggest that these ammonites may often have died shortly after spawning. The dead shells were probably gently washed up into a shell bank on the margins of the Lower Jurassic seas. Flow tank experiments show that Dactylioceras was probably a slow swimmer. It was likely prey for larger marine animals at the time including several belemnites.

Distribution

Dactylioceras has been collected from almost every continent, and was one of the most successful ammonite lineages ever. They are abundant throughout Europe, with exceptionally fine specimens found in England and Germany.

Subgenera

Currently, 3 or 4 subgenera are considered to be valid. Number differs on authors opinions.

Species

Species within the genus Dactylioceras include: [2]

Digital artist's recreation Dactylioceras NT.jpg
Digital artist's recreation
Dactylioceras (Orthodactylites) helianthoides Dactylioceras helianthoides - National Museum of Nature and Science, Tokyo - DSC07012.JPG
Dactylioceras (Orthodactylites) helianthoides
Dactylioceras (Orthodactylites) semicelatum Dactylioceras semicelatum - Naturhistorisches Museum, Braunschweig, Germany - DSC05126.JPG
Dactylioceras (Orthodactylites) semicelatum
Dactylioceras (Dactylioceras) commune Dactylioceratidae - Dactylioceras commune.JPG
Dactylioceras (Dactylioceras) commune

Dactylioceras commune has shells reaching a diameter of 9–11 centimetres (3.5–4.3 in). Usually the average diameter reach about 24.1 millimetres (0.95 in), while the average width is 8.20 millimetres (0.323 in). [2]

In these small but strong shells ribs run straight or are slightly convex across the venter. These ribs are quite coarse on the outer whorls and finer on the inner whorls. The whorl section is as round as a circle. [6] [7] [8]

Fossils of this species have been found in Lower Jurassic, Toarcian age of Canada, France, Italy, Russia, Serbia and Montenegro, United Kingdom and United States. [2]

References

  1. 1 2 Sepkoski, Jack (2002). "Sepkoski's Online Genus Database" . Retrieved 2014-05-28.
  2. 1 2 3 4 Dactylioceras on the Paleobiology Database.
  3. M. K. Howarth 2013. Treatise on Invertebrate Paleontology, Part L, Revised, Volume 3B, Chapter 4: Psiloceratoidea, Eoderoceratoidea, Hildoceratoidea.
  4. Bardin, J., I. Rouget, M. Benzaggagh, F.T. Fürsich, and F. Cecca. 2014. Lower Toarcian (Jurassic) ammonites of the South Riffian ridges (Morocco): systematics and biostratigraphy. Journal of Systematic Palaeontology. doi:10.1080/14772019.2014.937204.(published online 20.08.2014).
  5. KOVÁCS, Zoltán. "Toarcian Dactylioceratidae (Ammonitina) from the Gerecse Mts (Hungary)." (2014): 45-77.
  6. The Whitby Ammonite or a Whole lot of variation
  7. Europeana
  8. "Ammonites". Archived from the original on 2015-04-14. Retrieved 2015-04-28.