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The Fossil Hill Member is a Middle Triassic-age rock unit. The Fossil Hill occurs as a member of both the Prida and Favret Formations and outcrops in multiple locations across Northwestern Nevada including the western Humboldt Range, Tobin Range, Augusta Mountains, and China Mountain. Calcareous shale, mudrock, 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-age 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 Ichthyosaurs and a Pistosaur.[2] Other fossils include bony fish, hybodont sharks, and invertebrates with Ceratitid ammonoids being especially abundant.[3]
| Fossil Hill Member | |
|---|---|
| Stratigraphic range: | |
| Type | Geological member |
| Unit of | Prida Formation, Favret Formation |
| Lithology | |
| Primary | Calcareous Shale |
| Other | Limestone |
| Location | |
| Region | Nevada |
| Country |  United States |
| Type section | |
| Named by | Kathryn Nichols and Norman Silberling |
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 caused discontinuous outcrops in 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 near complete specimens from both the Favret and Prida Formations | A large Cymbospondylid ichthyosaur | |
| C. nichollsi[5] | ||||
| C. duelfiri[6] | The smallest species of the genus | |||
| C. youngorum[2] | 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[7] | A medium-sized (5 meter) basal ichthyosaur with dental batteries of button shaped teeth and durophagous feeding strategy. | ||
| O. nettarhynchus[8] | ||||
| Phalarodon | P. fraasi[9] | |||
| P. callowayi[9] | ||||
| Thalattoarchon | T. saurophagis[10] | A large ichthyosaur with large, laterally compressed teeth and interpreted macropredatory habit. |
Sauropterygians
| Genus | Species | Material | Notes | Images |
|---|---|---|---|---|
| Augustasaurus | A. hagdorni[11] | 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 |  |
References
- ^ 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
- ^ a b c 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.
- ^ Various Contributors to the Paleobiology Database. "Fossilworks: Gateway to the Paleobiology Database". Retrieved 09 July 2024.
{{cite web}}: Check date values in:|access-date=(help) - ^ 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.
- ^ FRÖBISCH, NADIA B.; SANDER, P. MARTIN; RIEPPEL, OLIVIER (2006-08). "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.
{{cite journal}}: Check date values in:|date=(help) - ^ 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.
- ^ Sander, P. Martin; Faber, Christiane (2003-12-24). "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.
- ^ Sander, P. Martin; Faber, Christiane (1998-04). "New finds ofOmphalosaurus and a review of Triassic ichthyosaur paleobiogeography". Paläontologische Zeitschrift. 72 (1–2): 149–162. doi:10.1007/BF02987823. ISSN 0031-0220.
{{cite journal}}: Check date values in:|date=(help) - ^ 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.
- ^ 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.
- ^ 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.