Heteropetalus

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Heteropetalus
Temporal range: Serpukhovian
Heteropetalus elegantulus Bear Gulch Montana USA.jpg
Well-preserved specimen of H. elegantulus
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Holocephali
Order:† Debeeriiformes
Family:† Debeeriidae
Genus:† Heteropetalus
Lund, 1977
Species:
†H. elegantulus
Binomial name
†Heteropetalus elegantulus
Lund, 1977

Heteropetalus is a genus of chondrichthyan from the Mississippian age Bear Gulch Limestone of Montana, United States. One species, H. elegantulus, is known. [1] Known fossils of Heteropetalus are exceptionally well preserved, displaying details of the soft tissue anatomy such as the eyes and an opercular cover over the gills. [2] Heteropetalus is a member of the family Debeeriidae and the order Debeeriiformes. [3]

Contents

Discovery and naming

Heteropetalus elegantulus was named in 1977 by paleontologist Richard Lund, based on several fossil specimens collected from the Serpukhovian-stage Bear Gulch Limestone of Fergus County, Montana. The holotype (specimen based on which the species is named) is housed at the University of Montana Museum of Paleontology, and is designated MV 2778. [1]

Description

The mouth was positioned subterminally (opened at the front of the snout) and may have had a form of lips, although these were not supported by labial cartilages (skeletal elements in the lips of sharks). While the palatoquadrates (upper jaws) were initially interpreted as hyostylic and mobile in the genus' description, [1] further research has shown them to have instead been autodiastylic, meaning they are attached tightly to the skull and are immobile. [2] [3] Behind the skull were four gill arches, which were covered by a soft operculum. [1] [2] [4] The animal had a scaleless, fusiform body and a diphycercal tail fin. A fin spine protruded from the front of the single long dorsal fin that ran down the length of the body. The species grew to 12 centimeters (4.7 in) in total length. [1]

Heteropetalus was sexually dimorphic, and the males had a larger, modified dorsal fin which supporting a hook. [1]

Classification

When first described, the genus was identified as a member of the order Petalodontiformes. Later research by the paleontologist Rainer Zangerl instead found a tentative relation between Heteropetalus and Desmiodus , and the two were classified together in the order Desmiodontiformes. [5] [6] The genus Desmiodus and the order Desmiodontiformes have subsequently fallen out of use, however. [6] The most recent research by Richard Lund and Eileen Grogan has placed Heteropetalus in the order Debeeriiformes and the family Debeeriidae, due to similarities with the genus Debeerius . [3] [7]

Paleobiology and paleoecology

Life reconstruction of Heteropetalus elegantulus Heteropetalus elegantulus 3.jpg
Life reconstruction of Heteropetalus elegantulus

The hook-like structure on the dorsal fin of male Heteropetalus likely functioned as a clasper, and was used to grab females during mating. [1]

Like many other benthic fish known from the Bear Gulch Limestone, specimens of Heteropetalus were preserved by loose, fine sediments rapidly burying them during mudslides. The H. elegantulus buried by the mud then died by asphyxiation, as indicated by the blood vessels in their fossilized gills, and were preserved in exceptional detail. [2] [4]

References

  1. 1 2 3 4 5 6 7 Lund, Richard (1977-09-30). "A new petalodont (Chondrichthyes, Bradyodonti) from the Upper Mississippian of Montana". Annals of the Carnegie Museum. 46: 129––155. doi: 10.5962/p.330526 .
  2. 1 2 3 4 Grogan, Eileen; Lund, Richard (1995). "Pigment patterns; soft anatomy and relationships of Bear Gulch Chondrichthyes (Namurian E2b; Lower Carboniferous; Montana; USA)(Namurian E2b; Lower Carboniferous; Montana; USA)" . Geobios. Premiers Vertandébrandés et Vertandébrandés Infandérieurs. 28: 145–146. doi:10.1016/S0016-6995(95)80102-2.
  3. 1 2 3 Grogan, Eileen D.; Lund, Richard (2000). <219::aid-jmor1>3.3.co;2-t "Debeerius ellefseni (Fam. Nov., Gen. Nov., Spec. Nov.), an autodiastylic chondrichthyan from the Mississippian Bear Gulch Limestone of Montana (USA), the relationships of the chondrichthyes, and comments on gnathostome evolution". Journal of Morphology. 243 (3): 219. doi:10.1002/(sici)1097-4687(200003)243:3<219::aid-jmor1>3.3.co;2-t. ISSN   0362-2525.
  4. 1 2 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): 341. ISSN   0022-3360.
  5. ↑ Zangerl, Rainer (1981). Chondrichthyes 1: Paleozoic Elasmobranchii (Handbook of Paleoichthyology). Friedrich Pfell (published January 1, 1981). pp. 62–63. ISBN   978-3-89937-045-4.
  6. 1 2 Lund, Richard; Grogan, Eileen D. (2004). "Five new euchondrocephalan Chondrichthyes from the Bear Gulch Limestone (Serpukhovian, Namurian E2b) of Montana, USA". Recent Advances in the Origin and Radiation of Early Vertebrates: 505–531. ISBN   3-89937-052-X.
  7. ↑ Nelson, Joseph S.; Grande, Terry; Wilson, Mark V. H. (2016). Fishes of the world (5th ed.). Hoboken, New Jersey: John Wiley & Sons. p. 50. ISBN   978-1-118-34233-6.


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