Fossil Hill Member

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Fossil Hill Member
Stratigraphic range: Anisian
TypeGeological member
Unit ofPrida Formation, Favret Formation
Lithology
PrimaryCalcareous Shale
OtherLimestone
Location
RegionNevada
Country
 United States
Type section
Named byKathryn Nichols and Norman Silberling
Not to be confused with Fossil Hill Formation.

The Fossil Hill Member is a Middle Triassic-aged rock unit. The Fossil Hill unit occurs as a member of both the Prida and Favret formations. It outcrops in multiple locations across Northwestern Nevada including the western Humboldt Range, Tobin Range, Augusta Mountains, and China Mountain. Calcareous shale, mudstone, and black limestones are the most common lithologies present within the unit.[1] The member was named for Fossil Hill, Nevada, a locality within the Humboldt Mountains where large quantities of Anisian-aged marine fossils were discovered in the early 20th century. Fossils are common throughout the Fossil Hill, and the unit is well known for preserving the remains of some of the earliest marine reptiles, including several genera of ichthyosaurs and a pistosaur.[2] Other fossils include bony fish, hybodont sharks, and invertebrates with ceratitid ammonoids being especially abundant.[3]

Geology

Stratigraphy

The Favret Formation and the Prida Formation, constitute two of the recognized geological formations within the Star Peak Group, of Northwestern Nevada. The Fossil Hill member links these two formations.

Tectonic fragmentation of the region has broken apart most stratigraphic units of the Star Peak Group. Because of this outcrop discontinuity, the Fossil Hill Member is part of different formations in different parts of the outcrop area.[2] In the Prida Formation, this member outcrops west of the Humboldt Range, and in the Favret Formation, it outcrops in the Augusta Mountains and southern extent of the Tobin Range. Although differing in precise age, the strata assigned to this member form a laterally uniform unit of offshore calcareous rocks. The various occurrences of the Fossil Hill member are also united by a distinct pelagic Anisian paleofauna preserved in the rocks.[1]

The Fossil Hill varies in thickness throughout its outcrops. In the China Mountain and Tobin Range sections, erosion and dolomitization from overlying units have rendered the Fossil Hill usually thin or locally absent. The unit within the Prida Formation varies from 60-120 meters thick while the section in the Augusta Mountains exceeds 200 metres.[1]

Paleobiota

Ichthyosaurs

Genus Species Material Notes Images
Cymbospondylus C. petrinus[4] Multiple specimens of excellent quality from both the Favret and Prida Formations including UCMP 9950, a near-complete specimen from Fossil Hill. A large Cymbospondylid ichthyosaur varying in size from 8-12 meters.
Life restoration of C. petrinus
C. nichollsi[5]
C. duelfiri[6] LACM DI 158109 consists of a nearly complete skull with articulated and disarticulated post cranial material. Diminutive strings of articulated fetal vertebrae in the trunk. The smallest species of the genus at 4.3 meters. Holotype was is among the earliest known viviparous animals.
C. youngorum[7] LACM DI 157871, consists of a large complete skull, some cervical vertebrae, the right humerus as well as fragments of the shoulder girdle. A giant, 17-meter ichthyosaur, the largest known animal up to this point in time.
Omphalosaurus O. nevadanus[8] A medium-sized (5 meter) basal ichthyosaur with dental batteries of button shaped teeth and durophagous feeding strategy.
O. nettarhynchus[9]
Phalarodon P. fraasi[10] A small mixosaur
Life restoration of Phalarodon
P. callowayi[10]
Thalattoarchon T. saurophagis[11] A large ichthyosaur with large, laterally compressed teeth and interpreted macropredatory habit.
Life restoration and size comparison of a T. saurophagis with a human

Sauropterygians

Genus Species Material Notes Images
Augustasaurus A. hagdorni[12] Single specimen. FMNH PR 1974 is a partial articulated skeleton containing the posterior neck, trunk, shoulder girdle, and both forelimbs and a disassociated skull, A pistosauroid from the Favret Formation
Two Augustasaurus hagdorni

See also

References

  1. ^ a b c Nichols, K. M.; Silberling, N. J. (1977), "Stratigraphy and Depositional History of the Star Peak Group (Triassic), Northwestern Nevada", Geological Society of America Special Papers, vol. 178, Geological Society of America, pp. 1–74, doi:10.1130/spe178-p1, ISBN 978-0-8137-2178-1, retrieved 2024-07-09
  2. ^ a b Sander, P. Martin; Griebeler, Eva Maria; Klein, Nicole; Juarbe, Jorge Velez; Wintrich, Tanja; Revell, Liam J.; Schmitz, Lars (2021-12-24). "Early giant reveals faster evolution of large body size in ichthyosaurs than in cetaceans". Science. 374 (6575). doi:10.1126/science.abf5787. ISSN 0036-8075.
  3. ^ Various Contributors to the Paleobiology Database. "Fossilworks: Gateway to the Paleobiology Database".
  4. ^ Akamatsu, N.; Nakajima, H.; Ono, M.; Miura, Y. (1975-09-15). "Increase in acetyl CoA synthetase activity after phenobarbital treatment". Biochemical Pharmacology. 24 (18): 1725–1727. doi:10.1016/0006-2952(75)90013-1. ISSN 0006-2952. PMID 15.
  5. ^ FRÖBISCH, NADIA B.; SANDER, P. MARTIN; RIEPPEL, OLIVIER (2006). "A new species of Cymbospondylus (Diapsida, Ichthyosauria) from the Middle Triassic of Nevada and a re-evaluation of the skull osteology of the genus". Zoological Journal of the Linnean Society. 147 (4): 515–538. doi:10.1111/j.1096-3642.2006.00225.x. ISSN 1096-3642.
  6. ^ Klein, Nicole; Schmitz, Lars; Wintrich, Tanja; Sander, P. Martin (2020-04-20). "A new cymbospondylid ichthyosaur (Ichthyosauria) from the Middle Triassic (Anisian) of the Augusta Mountains, Nevada, USA". Journal of Systematic Palaeontology. 18 (14): 1167–1191. doi:10.1080/14772019.2020.1748132. ISSN 1477-2019.
  7. ^ Sander, P. Martin; Griebeler, Eva Maria; Klein, Nicole; Juarbe, Jorge Velez; Wintrich, Tanja; Revell, Liam J.; Schmitz, Lars (2021-12-24). "Early giant reveals faster evolution of large body size in ichthyosaurs than in cetaceans". Science. 374 (6575). doi:10.1126/science.abf5787. ISSN 0036-8075.
  8. ^ Sander, P. Martin; Faber, Christiane (2003). "The Triassic marine reptile Omphalosaurus : osteology, jaw anatomy, and evidence for ichthyosaurian affinities". Journal of Vertebrate Paleontology. 23 (4): 799–816. doi:10.1671/6. ISSN 0272-4634.
  9. ^ Sander, P. Martin; Faber, Christiane (1998). "New finds of Omphalosaurus and a review of Triassic ichthyosaur paleobiogeography". Paläontologische Zeitschrift. 72 (1–2): 149–162. doi:10.1007/BF02987823. ISSN 0031-0220.
  10. ^ a b Schmitz, Lars; Sander, P. Martin; Storrs, Glenn W.; Rieppel, Olivier (2004-03-10). "New Mixosauridae (Ichthyosauria) from the Middle Triassic of the Augusta Mountains (Nevada, USA) and their implications for mixosaur taxonomy". Palaeontographica Abteilung A. 270 (4–6): 133–162. doi:10.1127/pala/270/2004/133. ISSN 0375-0442.
  11. ^ Fröbisch, Nadia B.; Fröbisch, Jörg; Sander, P. Martin; Schmitz, Lars; Rieppel, Olivier (2013-01-07). "Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks". Proceedings of the National Academy of Sciences. 110 (4): 1393–1397. doi:10.1073/pnas.1216750110. ISSN 0027-8424.
  12. ^ Sander, P. Martin; Rieppel, Olivier C.; Bucher, Hugo (1997-09-04). "A new pistosaurid (Reptilia: Sauropterygia) from the Middle Triassic of Nevada and its implications for the origin of the plesiosaurs". Journal of Vertebrate Paleontology. 17 (3): 526–533. doi:10.1080/02724634.1997.10010999. ISSN 0272-4634.
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