Dactylioceras
| Dactylioceras Temporal range: Pliensbachian–Toarcian[1] | |
|---|---|
 | |
| D. athleticum | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Subclass: | Ammonoidea |
| Order: | Ammonitida |
| Family: | Dactylioceratidae |
| Genus: | Dactylioceras Hyatt, 1867 |
Dactylioceras was a widespread genus of ammonite from the Lower Jurassic period,[1] approximately 172 million years ago (mya).[2]
Etymology
The name Dactylioceras comes from the Greek dactyl, meaning “finger”, and refers to the shell’s branching ribs.
Description
Dactylioceras are generally small, averaging 65 millimetres (2.6 in) in diameter. They has 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.
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. Like many other ammonites, the genus Dactylioceras is extremely important in biostratigraphy, being a key index fossil for identifying their region of the Jurassic.
Species
Species within the genus Dactylioceras include:[2]
- D. alpestre
- D. angumum
- D. annuliferum
- D. athleticum Simpson, 1855
- D. attenuatum
- D. commune Sowerby, 1815
- D. comptum
- D. consimile Buckman, 1926
- D. crassescens Simpson, 1855
- D. crassifactum
- D. crassiusculum Simpson, 1855
- D. crosbeyi
- D. gracile Simpson, 1843
- D. kanense
- D. marioni
- D. polymorphum Fucini, 1935
- D. praepositum Buckman, 1927
- D. pseudocommune
- D. semiannulatum
- D. simplex Fucini, 1935
- D. temperatum Buckman, 1927
- D. tenuicostatum
- D. toxophorum Buckman, 1926
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. [3][4][5]
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
- ↑ 1.0 1.1 Sepkoski, Jack (2002). "Sepkoski's Online Genus Database". Retrieved 2014-05-28.
- ↑ 2.0 2.1 2.2 2.3 Dactylioceras on the Paleobiology Database.
- ↑ The Whitby Ammonite or a Whole lot of variation
- ↑ Europeana
- ↑ Ammonites
- Lehmann, U. "The jaws and radula of the Jurassic ammonite Dactylioceras". Palaeontology 22: 265–271. http://palaeontology.palass-pubs.org/pdf/Vol%2022/Pages%20265-271.pdf.