Calymenina

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Calymenina
Flexicalymene ouzregui from Erfoud, Morocco (length: 7 cm)

Flexicalymene ouzregui from Erfoud , Morocco (length: 7 cm)

Temporal occurrence
Ordovician to Middle Devonian ( Givetian )
485.4 to 382.7 million years
Locations

worldwide

Systematics
Primordial mouths (protostomia)
Molting animals (Ecdysozoa)
Arthropod (arthropoda)
Trilobites (Trilobita)
Phacopida
Calymenina
Scientific name
Calymenina
Swinnerton , 1915

The Calymenina form a suborder of the trilobites - order Phacopida . Members of the Calymenina can be detected at least from the beginning of the Ordovician to the Middle Devonian (from approx. 485.4 to approx. 382.7 million years ago) and achieved worldwide distribution.

External and internal systematics

(after Adrain, 2013)

The Calymenina, next to the Phacopina and the Cheirurina , represent one of the three suborders of the order Phacopida . They are divided into three to five families .

  • Bathycheilidae Přibyl, 1953 : ( Lower to Middle Ordovician ) A small group with only eight known species , which are divided into four genera . The systematic position within the Calymenina is controversial. Some authors see it as an independent family , while others consider the group to be a subfamily of the Calymenidae or integrate the Pharostomatidae as a subfamily in the Bathycheilidae. The Bathycheilidae differ from other representatives of the Calymenina, in particular by the number of their thorax segments (12 instead of the usual 13) and greatly elongated cheek spines.
  • Bavarillidae Sdzuy, 1957 : ( Upper Cambrian to Lower Ordovician) A small monotypical group with only one genus ( Bavarilla ) and three known species. The family has only been little researched and the assignment to the Calymenina is uncertain. Their temporal occurrence is not taken into account here in relation to the temporal occurrence of the Calymenina. In the event that the systematic assignment of the Bavarillidae to the Calymenina should be confirmed, the temporal occurrence of the latter would extend back to the Upper Cambrian.
  • Calymenidae Swinnerton, 1915 : (Lower Ordovician ( Floium ) to Middle Devonian ( Eifelium )) The main group of the Calymenina is extremely species-rich with 33 genera and 316 valid known species. Representatives of the family appear worldwide.
  • Homalonotidae Chapman, 1890 : (Lower Ordovician (Floium) to Middle Devonian ( Givetium )) The family comprises 22 genera with a total of 171 valid species and seems to have been restricted to Gondwana for most of the Ordovician . It then appears around the world from around the Katium . The Homalonotidae were, besides the Calymenidae, the only family that Swinnerton had originally united in 1915 in the subordination of the Calymenina.
  • Pharostomatidae Hupé, 1953 : (Ordovician) This family of 8 genera and a total of 49 known species occurs only in the Ordovician. The Pharostomatidae differ from other representatives of the Calymenina, in particular by the ventrally prickly edge of the cephalon. However, the localization within the Calymenina seems to be based on robust foundations.

These five families are sometimes summarized in the superfamily of the Calymenoidea. However, since the suborder Calymenina, in contrast to the subordination of Phacopina, only contains one superfamily, Calymenina and Calymenoidea are to be regarded as largely identical, apart from their taxonomic rank.

features

Calymene blumenbachii when rolled up as a typical representative of the Calymenidae within the Calymenina

The cephalon is semicircular to subtriangular with mostly gonatoparic, in a few cases also opisthoparic (e.g. Bathycheilidae, some primitive members of the Homalonotidae) facial seams and usually has small, holochroal compound eyes . There is a rostral plate at the bottom of the cephalon. The hypostome is conterminant and in most cases (Calymenidae, Homalonotidae) flatly forked at the rear end. The glabella has four to five lateral lobes and is narrowed towards the front. In comparison to other representatives of the Phacopida, the anterior area of ​​the glabella in particular is not very pronounced. The thorax typically has thirteen segments with rounded pleural ends ; sometimes there are eleven or twelve segments. The pygidium is semicircular to triangular with no spines on the edges.

Digestive tract

In 2015 and 2018, fossil remains of the digestive tract were described in Prionocheilus vokovicensis (Bathycheilidae), Colpocoryphe bohemica (Calymenidae) and Flexicalymene pragensis (Calymenidae). In all three cases there was a similar structure with a central, tubular alimentary canal from which sack-like, paired protuberances ( diverticula ) extend below the head shield and the anterior thoracic segments .

As far as is known, the digestive tract of the Calymenina differs significantly from that of the related Phacopina. In the latter, there is only a tubular digestive tract without paired diverticula, but with a goiter-like thickening immediately below the glabella of the head shield. This goiter-like thickening of the digestive tract is seen in connection with a series of muscle attachment points (“frontal auxiliary impressions”; “FAIs”) on the inside of the head shield. FAIs are unknown among the Calymenina and the relatively flat, forward tapering glabella of the Calymenina would hardly have offered any space for a “goiter” in this area.

Ontogenetic development and paleogeographical distribution

Dipleura dekayi as a representative of the Homalonotidae within the Calymenina

The individual larval stages of the Calymenina show, as far as is known, great similarity to those of the Phacopina and the Cheirurina and confirm that they belong to the order of the Phacopida.

The Protaspis larvae of the Calymenina show up to four individual stages of development. Earlier stages of development, for example in the form of a Phaselus larva in the sense of Fortey and Morris, are not known of the Calymenina.

In the case of the protaspis larvae of the trilobites, two basic morphological types are generally distinguished:

  • Non-adult-like Protaspis larvae of the Calymenina are pot-bellied and approximately rounded square in outline. The back armor has only a relatively small, belly-side opening which is largely covered by the relatively oversized hypostome. The back armor has three pointed, conical pairs of spines which, starting from the edge of the armor, protrude ventrodistally (towards the abdomen and away from the center of the body). The hypostome also has a ring of a total of 9 marginal spines. The two lobes of the glabella are divided in two by a sagittal furrow. For the non-adult-like Protaspis larvae, a planktonic and planktotrophic way of life is generally assumed.
  • In contrast, adult-like Protaspis larvae of the Calymenina are flattened on the abdomen and the back armor is generally less arched than in the non-adult-like Protaspis larvae, so that generally a flattened body shape results that is more reminiscent of the adult animals. They carry a multitude of more or less horizontally protruding marginal spines and a relatively small hypostome. There is no sagittal groove in the glabella. For the adult-like Protaspis larvae of the Calymenina, a benthic and either detritotrophic (detritus-eating) or lecithotrophic (nutrition via the yolk originally contained in the egg) is assumed.

Despite all the similarities between the Protaspis larvae of the Calymenina, there are significant differences in the individual development of the Calymenidae and the Homalonotidae. In representatives of the Calymenidae up to four Protaspis larval stages are known, which undergo a metamorphosis from early, non-adult-like to adult-like Protaspis larvae. In the Homalonotidae, however, no non-adult-like Protaspis larvae are known. The adult-like Protaspis larvae are similar to those of the Calymenidae, but unusually large. The non-adult-like larval stages were either already passed through during embryonic development or they did not form an exoskeleton that could be preserved by fossils. Little is known about the ontogeny of the three other families.

Representatives of the Calymenidae were present, especially from the Upper Ordovician, both in warmer waters of lower Paleo latitudes and in cooler regions of higher latitudes. The palaeogeographical distribution of the Homalonotidae in the Ordovician, however, is mainly concentrated in the cooler waters of higher paleo latitudes. In contrast to the three other families of the Calymenina, which became extinct again during the Ordovician, both the Calymenidae and the Homalonotidae survived the Andean-Sahara Ice Age (Middle Ordovician to Lower Silurian with the climax in the Hirnantium , the highest level of the Ordovician). After the end of this ice age, the Calymenidae quickly achieved widespread distribution again, while the Homalonotidae were preferred in the cooler waters of the Malvinokaffrischen province (South America, South Africa and West Antarctica ) until the entire suborder died out .

Chatterton and his co-authors in 1990 saw these two findings, which at first glance appear to be quite different, in direct connection. The apparent lack of planktonic, non-adult-like Protaspis larvae and the relative size of the benthic adult-like Protaspis larvae in the Homalonotidae is in accordance with Thorson's rule (marine benthic invertebrates in warm waters of lower latitudes preferably produce a large number of small eggs from them planktotrophic larvae hatch, while in the colder waters of higher latitudes they usually lay few, but larger eggs from which more developed and larger larval stages hatch) interpreted as an adaptation to survival in the colder waters of higher paleo latitudes.

Trace fossils

Trace fossil of the genus Rusophycus

For Flexicalymene meeki (Calymenidae) and the Ichnotaxon Rusophycus pudicum there is the rare case that a trace fossil can be directly assigned to its causer. Osgood and Drennen see her described as "Type 1" variation of the track Fossils Rusophycus bilobatum from the Silurian of New York is directly related to the Homalonotiden Trimerus delphinocephalus and Rusophycus -like trace fossils from the Devonian of the Rhenish Massif be brought with representatives of Homalonotidae in conjunction .

Way of life

For the representatives of the Calymenina, a nectobenthic (swimming close to the seabed) to epibenthic (on the seabed on the substrate) or semi-epibenthic (partly buried in the substrate) way of life is assumed. The Calymenidae preferred warmer and shallower sea regions, while the Homalonotidae were more likely to be found in colder and / or deeper sea regions.

Fortey and Owens assume a predator and / or scavenger diet and mainly refer to the conterminant, forked hypostome and the connection with some taxa of the Rusophycus trace fossils, which are often, if not always, the dwellings of ground living, worm-like creatures cut off. However, many Rusophycus fossils can also be interpreted as traces of detritus eaters and the finding is in some contradiction with the shape of the digestive tract, which also points to detritus eaters.

Individual evidence

  1. ↑ a b H. H. Swinnerton: Suggestions for a revised classification of trilobites. In: Geological Magazine , Vol. 2, pp. 487–496 & 538–545, 1915. (digitized version )
  2. ↑ a b c J. M. Adrain: A synopsis of Ordovician trilobite distribution and diversity. In: DAT Harper & T. Servais (Eds.): Early Palaeozoic Biogeography and Palaeogeography. - The Geological Society of London - Memoirs, Vol. 38, pp. 297–336, 2013. (digitized version )
  3. ↑ J.-L. Henry: Trilobites ordoviciens du Massif Armoricain. In: Mémoires de la Société Géologique et Minéralogique de Bretagne , Vol. 22, pp. 1-250, 1980.
  4. ^ RA Fortey: Classification. In HB Whittington (Ed.): Treatise on invertebrate paleontology. , Part O, Arthropoda 1, Trilobita, revised, pp. O289-302, Geological Society of America and University of Kansas, Boulder and Lawrence, 1997.
  5. ↑ a b c d R. A. Fortey & RM Owens: Feeding Habits in Trilobites. In: Palaeontology , Vol. 42, Part 3, pp. 429-465, 1999. (digitized version )
  6. ↑ a b c R. Lerosey-Aubril, Th. A. Hegna & S. Olive: Inferring internal anatomy from the trilobite exoskeleton: the relationship between frontal auxiliary impressions and the digestive system. In: Lethaia , Vol. 44, Issue 2, Pp. 166-184, 2011. doi : 10.1111 / j.1502-3931.2010.00233.x
  7. ^ O. Fatka & P. ​​Budil: Digestive structures in the Middle Ordovician trilobite Prionocheilus Rouault 1847, from the Barrandian area of ​​Czech Republic. In: Geologica Acta , Vol. 16, No. 1, pp. 65-73, 2018. doi : 10.1344 / GeologicaActa2018.16.1.4
  8. ^ O. Fatka, P. Budil & M. David: Digestive structures in Ordovician trilobites Colpocoryphe and Flexicalymene from the Barrandian area of ​​Czech Republic. In: Estonian Journal of Earth Sciences , Vol. 64, No. 4, pp. 255–266, 2015. (digitized version )
  9. ^ RA Fortey & SF Morris: Discovery of Nauplius-like Trilobite Larvae. In: Palaeontology , Vol. 21, Part 4, pp. 823-833 & Plate 94, 1978. (digitized version )
  10. ↑ a b c d e f g B. DE Chatterton, DJ Siveter, GD Edgecombe & AS Hunt: Larvae and Relationships of the Calymenina (Trilobita). In: Journal of Paleontology , Vol. 64, No. 2, pp. 255-277, 1990. (digitized version )
  11. ↑ St. E. Speyer & BDE Chatterton: Trilobite larvae and larval ecology. In: Historical Biology , Vol. 3, Issue 1-2, pp. 27-60, 1989. (Abstract)
  12. ^ G. Thorson: Reproductive and larval ecology of marine bottom invertebrates. In: Biological Reviews , Vol. 25, Issue 1, pp. 1-45, 1950. doi : 10.1111 / j.1469-185x.1950.tb00585.x
  13. ^ RG Osgood Jr .: Trace Fossils of the Cincinnati Area. In: Palaeontographica Americana , Vol. VI, No. 41, pp. 281-438, 1970. (digitized version )
  14. ^ RG Osgood Jr. & WT Drennen III .: Trilobite Trace Fossils from the Clinton Group (Silurian) of East-Central New York State. In: Bulletin of American Paleontology , Vol. 287, pp. 299-348, 1975. (digitized version )
  15. ↑ K.-W. Wenndorf: Homalonotinae (Trilobita) from the Rhenish Lower Devonian. In: Palaeontographica , Department A, Vol. 211, 184 S., 1990.
  16. ↑ a b M. M. Key Jr., GA Schumacher, LE Babcock, RC Frey, WP Heimbrock, St. H. Felton, DL Cooper, WB Gibson, DG Scheid & SA Schumacher: Paleoecology of Commensal Epizoans Fouling Flexicalymene (Trilobita) from the Upper Ordovician, Cincinnati Arch Region, USA. In: Journal of Paleontology , Vol. 84, Issue 6, pp. 1121–1134, 2010 (digitized version )

Web links

Commons : Calymenina  - collection of images, videos and audio files