Falcatus

Falcatus
Temporal range: 335–318 Ma Middle Viséan - Late Serpukhovian
Specimen in Vienna
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: †Symmoriiformes
Family: †Falcatidae
Genus: †Falcatus
Lund, 1985
Species
  • Falcatus falcatus

Falcatus is an extinct genus of falcatid chondrichthyan which lived during the early Carboniferous Period in Bear Gulch bay in what is now Montana.

Description

Illustration - Falcatus falcatus
Life restoration of female (top) and male (bottom)
Falcatus falcatus male. Lower Carboniferous, Montana, USA

This fish was quite small, only getting to around 25–30 cm or 10-12 inches long. This is about as big as some of the smallest sharks around today, like the pygmy lanternshark. Falcatus was a chondrichthyan known as a "cladodont-toothed stethacanthid holocephalan". The first material known from the genus were the prominent fin spines that curve anteriorly over the head of the animal. When first described in 1883 from the St. Louis Limestone, these remains were given the name Physonemus falcatus. However, in 1985, fossils of a new type of chondrichthyan from Montana were described that displayed a high degree of sexual dimorphism. The same spines that were previously named P. falcatus were found on one of the morphs, identified as the male due to the presence of valvae.

Classification

Despite often being called a shark, Falcatus and its relatives were part of the order Symmoriiformes, which itself was part of the subclass Holocephali. This means that this fish was more closely related to Chimaeras than to true sharks. Other members of its family include Ozarcus from the Carboniferous of Arkansas, and potentially Cretacladoides from the Cretaceous of Austria.

Two Stethacanthus species, S. altonensis and S. productus, lived alongside Falcatus

Paleoecology

The bear gulch limestone is a fossil deposit from the Big Snowy Mountains of Montana. It is a smaller part of the larger St. louis limestone, which dates to the middle carboniferous. During the time, the area was a series of mudflats and lagoons with brackish and freshwater. Many theories have been put forth for the preservation. One is that the creatures sank to the bottom and died of asphyxiation in the oxygen poor waters, being preserved without scavenging took place. Another theory is that the bottom of the bay created mudslides because of heavy rainfall, which rapidly buried the creatures. However, because many of the fish fossils were found with distended gills, this would suggest death by asphyxiation. Falcatus lived alongside many strange creatures like the chondrichthyans Agassizodus, Listracanthus and Delphyodontos. It also lived alongside many ray-finned fish like Discoserra and Paratarrasius. Other fish included the rhabdodermatid Cardiosuctor, the rhizodont Strepsodus, and Hardistiella, one of the oldest known lamprey. The invertebrates of bear gulch were very diverse creatures, like the hoplocarids (relatives of the mantis shrimp), Anderella, which is the youngest known synziphosurine and more enigmatic creatures like the potential gastropod relative Typhloesus, and the "Square objects" which might be sea salps or cnidarians. Other inverts include, mollusks like the nautiloid Tylonautilus, pterioid bivalves which have been found encrusting sargassum like brown algae as well as productid brachiopods, Paleolimulus, phyllocarids and echinoderms like Crinoids, echinoids, sea stars, brittle stars and a many armed starfish called Lepidasterella montanensis.

References

  1. ↑ "A Golden Age of Sharks". elasmo-research.org.
  2. ↑ "Bear Gulch - Falcatus falcatus". Archived from the original on 2008-08-21. Retrieved 2008-09-04. Fossil Fish of Bear Gulch 2005 by Richard Lund and Eileen Grogan Accessed 2009-01-14
  3. 1 2 The morphology of Falcatus falcatus (St. John and Worthen), a Mississippian stethacanthid chondrichthyan from the Bear Gulch Limestone of Montana. Journal of Vertebrate Paleontology 5(1):1-19.
  4. ↑ Coates, M., Gess, R., Finarelli, J., Criswell, K., Tietjen, K. 2016. A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes. Nature. doi: 10.1038/nature20806
  5. ↑ Alan Pradel; John G. Maisey; Paul Tafforeau; Royal H. Mapes; Jon Mallatt (2014). "A Palaeozoic shark with osteichthyan-like branchial arches". Nature. 509 (7502): 608–611. doi:10.1038/nature13195. PMID 24739974. S2CID 3504437.
  6. ↑ Iris Feichtinger; Andrea Engelbrecht; Alexander Lukeneder; Jürgen Kriwet (2018). "New chondrichthyans characterised by cladodont-like tooth morphologies from the Early Cretaceous of Austria, with remarks on the microstructural diversity of enameloid". Historical Biology: An International Journal of Paleobiology. 32 (6): 1–14. doi:10.1080/08912963.2018.1539971. S2CID 92392461.
  7. ↑ "Bear Gulch Limestone Fossil Lagerstätte". fossilmuseum.net.
  8. ↑ Grogan, Eileen D.; Lund, Richard (1997). "Soft tissue pigments of the Upper Mississippian chondrenchelyid, Harpagofututor volsellorhinus (Chondrichthyes, Holocephali) from the Bear Gulch Limestone, Montana, USA". Journal of Paleontology. 71 (2): 337–342. doi:10.1017/S002233600003924X. ISSN 0022-3360.
  9. ↑ Grogan, Eileen D.; Lund, Richard (2002). "The geological and biological environment of the Bear Gulch Limestone (Mississippian of Montana, USA) and a model for its deposition" (PDF). Geodiversitas. 24 (2): 295–315.
  10. ↑ Hagadorn, James W. (2002). "Bear Gulch: An Exceptional Upper Carboniferous Plattenkalk". In Bottjer, D.J.; Etter, W.; Hagadorn, J.W.; Tang, C.M. (eds.). Exceptional fossil preservation; a unique view on the evolution of marine life. New York: Columbia University Press. pp. 167–183.
  11. ↑ Lund, Richard (1990-01-01). "Chondrichthyan life history styles as revealed by the 320 million years old Mississippian of Montana". Environmental Biology of Fishes. 27 (1): 1–19. doi:10.1007/BF00004900. ISSN 1573-5133. S2CID 13249799.
  12. ↑ Lund, Richard (1980-08-08). "Viviparity and Intrauterine Feeding in a New Holocephalan Fish from the Lower Carboniferous of Montana". Science. 209 (4457): 697–699. Bibcode:1980Sci...209..697L. doi:10.1126/science.209.4457.697. PMID 17821193. S2CID 36858963.
  13. ↑ Lund, Richard (2000). "The new Actinopterygian order Guildayichthyiformes from the Lower Carboniferous of Montana (USA)" (PDF). Geodiversitas. 22 (2): 171–206.
  14. ↑ Lund, Richard; Melton, William G. Jr. (1982). "A new actinopterygian fish from the Mississippian Bear Gulch Limestone of Montana". Palaeontology. 25 (3): 485–498.
  15. ↑ Lund, Richard; Lund, Wendy (1984). "New genera and species of coelacanths from the Bear Gulch Limestone (Lower Carboniferous) of Montana (U.S.A.)". Geobios. 17 (2): 237–244. doi:10.1016/s0016-6995(84)80145-x. ISSN 0016-6995.
  16. ↑ Lund, Richard; Greenfest-Allen, Emily; Grogan, Eileen D. (2015-02-01). "Ecomorphology of the Mississippian fishes of the Bear Gulch Limestone (Heath formation, Montana, USA)". Environmental Biology of Fishes. 98 (2): 739–754. doi:10.1007/s10641-014-0308-x. ISSN 1573-5133. S2CID 14850973.
  17. ↑ Janvier, Philippe; Lund, Richard (1983). "Hardistiella montanensis n. gen. et sp. (Petromyzontida) from the Lower Carboniferous of Montana, with remarks on the affinities of the lampreys". Journal of Vertebrate Paleontology. 2 (4): 407–413. doi:10.1080/02724634.1983.10011943. ISSN 0272-4634.
  18. ↑ Factor, David F.; Feldmann, Rodney M. (11 October 1985). "Systematics and paleoecology of malacostracan arthropods in the Bear Gulch Limestone (Namurian) of Central Montana". Annals of Carnegie Museum. 54 (10): 319–356.
  19. ↑ Moore, Rachel A.; McKenzie, Scott C.; Lieberman, Bruce S. (2007). "A Carboniferous synziphosurine (Xiphosura) from the Bear Gulch Limestone, Montana, USA" (PDF). Palaeontology. 50 (4): 1013–1019. doi:10.1111/j.1475-4983.2007.00685.x. ISSN 1475-4983.
  20. ↑ Conway Morris, Simon (1990-04-12). "Typhloesus wellsi (Melton and Scott, 1973), a bizarre metazoan from the Carboniferous of Montana, U. S. A". Philosophical Transactions of the Royal Society of London. B, Biological Sciences. 327 (1242): 595–624. Bibcode:1990RSPTB.327..595M. doi:10.1098/rstb.1990.0102.
  21. ↑ "Description of the 'square objects' of the Bear Gulch Limestone, Montana, USA" (PDF). newhaven.edu.
  22. ↑ Cox, Robt S. (1986). "Preliminary report on the age and palynology of the Bear Gulch Limestone (Mississippian, Montana)". Journal of Paleontology. 60 (4): 952–956. doi:10.1017/S0022336000043092. ISSN 0022-3360.
  23. ↑ McRoberts, Christopher A.; Stanley, George D. (1989). "A unique bivalve–algae life assemblage from the Bear Gulch Limestone (Upper Mississippian) of central Montana". Journal of Paleontology. 63 (5): 578–581. doi:10.1017/S0022336000041214. ISSN 0022-3360.
  24. ↑ Schram, Frederick R.; Horner, John (1978). "Crustacea of the Mississippian Bear Gulch Limestone of Central Montana". Journal of Paleontology. 52 (2): 394–406. ISSN 0022-3360. JSTOR 1303712.
  25. ↑ Schrams, Frederick R. (1979). "Limulines of the Mississippian Bear Gulch Limestone of Central Montana, USA". Transactions of the San Diego Society of Natural History. 19 (6): 67–74.
  26. ↑ Schram, Frederick R.; Horner, John (1978). "Crustacea of the Mississippian Bear Gulch Limestone of Central Montana". Journal of Paleontology. 52 (2): 394–406. ISSN 0022-3360. JSTOR 1303712.
  27. ↑ Welch, James R. (1984). "The Asteroid, Lepidasterella montanensis n. sp., from the Upper Mississippian Bear Gulch Limestone of Montana". Journal of Paleontology. 58 (3): 843–851. ISSN 0022-3360. JSTOR 1304921.