Falcatus Explained

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

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 laternshark.[1] Falcatus was a chondricthian known as a "cladodont-toothed stethacanthid holocephalan".[2] 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 condrichthyan 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.[3]

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.[4] Other members of its family include Ozarcus from the Carboniferous of Arkansas,[5] and Cretacladoides from the Cretaceous of Austria.[6]

Paleoecology

See main article: Bear Gulch Limestone.

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.[7] 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.[8] Another theory is that the bottom of the bay created mudslides because of heavy rainfall, which rapidly buried the creatures.[9] However, because many of the fish fossils were found with distended gills, this would suggest death by asphyxiation.[10] Falcatus lived alongside many strange creatures like the chondrichthyans Agassizodus, Listracanthus[11] and Delphyodontos.[12] It also lived alongside many ray-finned fish like Discoserra[13] and Paratarrasius.[14] Other fish included the rhabdodermatid Cardiosuctor,[15] the rhizodont Strepsodus,[16] and Hardistiella, one of the oldest known lamprey.[17] The invertebrates of bear gulch were very diverse creatures, like the hoplocarids, which include modern day mantis shrimp,[18] Anderella, which is the youngest known synziphosurine[19] and more enigmatic creatures like Typhloesus,[20] and the "Square objects" which might be sea salps or cnidarians.[21] Other inverts include, mollusks like the nautiloid Tylonautilus,[22] pterioid bivalves which have been found encrusting sargassum like brown algae[23] as well as productid brachiopods,[24] Paleolimulus,[25] phyllocarids[26] and echinoderms like Crinoids, echinoids, sea stars, brittle stars and a many armed starfish called Lepidasterella montanensis.[27]

References

  1. Web site: A Golden Age of Sharks. elasmo-research.org.
  2. Web site: Bear Gulch - Falcatus falcatus . 2008-09-04 . https://web.archive.org/web/20080821203413/http://www.sju.edu/research/bear_gulch/pages_fish_species/Falcatus_falcatus.php . 2008-08-21 . Fossil Fish of Bear Gulch 2005 by Richard Lund and Eileen Grogan Accessed 2009-01-14
  3. 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. 10.1038/nature13195. 24739974. 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. 10.1080/08912963.2018.1539971. 92392461.
  7. Web site: 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. en. 71. 2. 337–342. 10.1017/S002233600003924X. 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. Geodiversitas. 24. 2. 295–315.
  10. Book: Hagadorn, James W.. Exceptional fossil preservation; a unique view on the evolution of marine life. Columbia University Press. 2002. Bottjer. D.J.. New York. 167–183. Bear Gulch: An Exceptional Upper Carboniferous Plattenkalk. Etter. W.. Hagadorn. J.W.. Tang. C.M.. https://www.researchgate.net/publication/242175100.
  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. en. 27. 1. 1–19. 10.1007/BF00004900. 1573-5133. 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. 1980Sci...209..697L. 10.1126/science.209.4457.697. 17821193. 36858963.
  13. Lund. Richard. 2000. The new Actinopterygian order Guildayichthyiformes from the Lower Carboniferous of Montana (USA). 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. 10.1016/s0016-6995(84)80145-x. 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. en. 98. 2. 739–754. 10.1007/s10641-014-0308-x. 1573-5133. 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. 10.1080/02724634.1983.10011943. 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. Palaeontology. en. 50. 4. 1013–1019. 10.1111/j.1475-4983.2007.00685.x. 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. 1990RSPTB.327..595M. 10.1098/rstb.1990.0102.
  21. Web site: Description of the 'square objects' of the Bear Gulch Limestone, Montana, USA. newhaven.edu.
  22. Cox. Robt S.. 1986. Preliminary report on the age and palynology of the Bear Gulch Limestone (Mississippian, Montana). Journal of Paleontology. en. 60. 4. 952–956. 10.1017/S0022336000043092. 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. en. 63. 5. 578–581. 10.1017/S0022336000041214. 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. 0022-3360. 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. 0022-3360. 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. 0022-3360. 1304921.

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