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Removed Omphalosaurus nettarhynchus from table as it was found in the early Triassic lower member of the Prida and not the Fossil Hill
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{{Short description|Triassic geologic unit}}
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{{Infobox rockunit|name=Fossil Hill Member|image=|caption=|type=[[Geological member]]|age={{Geological range|Anisian}}|prilithology=Calcareous [[Shale]]|otherlithology=[[Limestone]]|namedfor=|namedby=Kathryn Nichols and Norman Silberling|region=[[Nevada]]|country=<br />{{USA}}|coordinates=|unitof=[[Prida Formation]], [[Favret Formation]]|subunits=|underlies=|overlies=|thickness=|extent=|area=|map=|map_caption=|period=Triassic}}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|Humboldt Range,]] [[Tobin Range]], [[Augusta Mountains]], and China Mountain. Calcareous shale, mudrock, and black limestones are the most common [[Lithology|lithologies]] present within the unit.<ref name=":0">{{Citation |last=Nichols |first=K. M. |title=Stratigraphy and Depositional History of the Star Peak Group (Triassic), Northwestern Nevada |date=1977 |work=Geological Society of America Special Papers |volume=178 |pages=1–74 |url=https://pubs.geoscienceworld.org/books/book/301/chapter/3795487/ |access-date=2024-07-09 |publisher=Geological Society of America |language=en |doi=10.1130/spe178-p1 |isbn=978-0-8137-2178-1 |last2=Silberling |first2=N. J.}}</ref>The member was named for Fossil Hill, [[Nevada]], a locality within the [[Humboldt Range|Humboldt Mountains]] where large quantities of [[Anisian]]-age marine [[Fossil|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 [[Pistosauroidea|Pistosaur]].<ref name=":1">{{Cite journal |last=Sander |first=P. Martin |last2=Griebeler |first2=Eva Maria |last3=Klein |first3=Nicole |last4=Juarbe |first4=Jorge Velez |last5=Wintrich |first5=Tanja |last6=Revell |first6=Liam J. |last7=Schmitz |first7=Lars |date=2021-12-24 |title=Early giant reveals faster evolution of large body size in ichthyosaurs than in cetaceans |url=https://www.science.org/doi/10.1126/science.abf5787 |journal=Science |language=en |volume=374 |issue=6575 |doi=10.1126/science.abf5787 |issn=0036-8075}}</ref> Other fossils include bony fish, [[Hybodontiformes|hybodont]] sharks, and [[Invertebrate|invertebrates]] with [[Ceratitida|Ceratitid ammonoids]] being especially abundant.<ref>{{Cite web |last=((Various Contributors to the Paleobiology Database)) |title=Fossilworks: Gateway to the Paleobiology Database |url=http://www.fossilworks.org/cgi-bin/bridge.pl?action=home}}</ref>
{{Infobox rockunit|name=Fossil Hill Member|image=|caption=|type=[[Geological member]]|age={{Geological range|Anisian}}|prilithology=Calcareous [[Shale]]|otherlithology=[[Limestone]]|namedfor=|namedby=Kathryn Nichols and Norman Silberling|region=[[Nevada]]|country=<br />{{USA}}|coordinates=|unitof=[[Prida Formation]], [[Favret Formation]]|subunits=|underlies=|overlies=|thickness=|extent=|area=|map=|map_caption=|period=Triassic}}
{{Distinguish|Fossil Hill Formation}}
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The '''Fossil Hill Member''' is a [[Middle Triassic]]-aged rock unit. The Fossil Hill unit occurs as a member of both the [[Prida Formation|Prida]] and [[Favret Formation|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 [[Lithology|lithologies]] present within the unit.<ref name=":0">{{Citation |last1=Nichols |first1=K. M. |title=Stratigraphy and Depositional History of the Star Peak Group (Triassic), Northwestern Nevada |date=1977 |work=Geological Society of America Special Papers |volume=178 |pages=1–74 |url=https://pubs.geoscienceworld.org/books/book/301/chapter/3795487/ |access-date=2024-07-09 |publisher=Geological Society of America |language=en |doi=10.1130/spe178-p1 |isbn=978-0-8137-2178-1 |last2=Silberling |first2=N. J.}}</ref> The member was named for Fossil Hill, [[Nevada]], a locality within the [[Humboldt Range|Humboldt Mountains]] where large quantities of [[Anisian]]-aged marine [[Fossil|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 [[genus|genera]] of ichthyosaurs and a [[Pistosauroidea|pistosaur]].<ref name=":1">{{Cite journal |last1=Sander |first1=P. Martin |last2=Griebeler |first2=Eva Maria |last3=Klein |first3=Nicole |last4=Juarbe |first4=Jorge Velez |last5=Wintrich |first5=Tanja |last6=Revell |first6=Liam J. |last7=Schmitz |first7=Lars |date=2021-12-24 |title=Early giant reveals faster evolution of large body size in ichthyosaurs than in cetaceans |url=https://www.science.org/doi/10.1126/science.abf5787 |journal=Science |language=en |volume=374 |issue=6575 |doi=10.1126/science.abf5787 |issn=0036-8075}}</ref> Other fossils include bony fish, [[Hybodontiformes|hybodont]] sharks, and [[Invertebrate|invertebrates]] with [[Ceratitida|ceratitid ammonoids]] being especially abundant.<ref>{{Cite web |last=((Various Contributors to the Paleobiology Database)) |title=Fossilworks: Gateway to the Paleobiology Database |url=http://www.fossilworks.org/cgi-bin/bridge.pl?action=home}}</ref>


== Geology ==
== Geology ==
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The [[Favret Formation]] and the [[Prida Formation]], constitute two of the recognized [[Geological formation|geological formations]] within the [[Star Peak Group]], of Northwestern Nevada. The Fossil Hill member links these two formations.
The [[Favret Formation]] and the [[Prida Formation]], constitute two of the recognized [[Geological formation|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.<ref name=":1" /> In the Prida Formation, this member outcrops west of the [[Humboldt Range]], and in the Favret Formation, it [[Outcrop|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.<ref name=":0" />
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.<ref name=":1" /> In the Prida Formation, this member outcrops west of the [[Humboldt Range]], and in the Favret Formation, it [[Outcrop|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.<ref name=":0" />


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.<ref name=":0" />
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.<ref name=":0" />
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| rowspan="4" |''[[Cymbospondylus]]''
| rowspan="4" |''[[Cymbospondylus]]''
|''C. petrinus''<ref>{{Cite journal |last=Akamatsu |first=N. |last2=Nakajima |first2=H. |last3=Ono |first3=M. |last4=Miura |first4=Y. |date=1975-09-15 |title=Increase in acetyl CoA synthetase activity after phenobarbital treatment |url=https://pubmed.ncbi.nlm.nih.gov/15 |journal=Biochemical Pharmacology |volume=24 |issue=18 |pages=1725–1727 |doi=10.1016/0006-2952(75)90013-1 |issn=0006-2952 |pmid=15}}</ref>
|''C. petrinus''<ref>{{Cite journal |last1=Akamatsu |first1=N. |last2=Nakajima |first2=H. |last3=Ono |first3=M. |last4=Miura |first4=Y. |date=1975-09-15 |title=Increase in acetyl CoA synthetase activity after phenobarbital treatment |url=https://pubmed.ncbi.nlm.nih.gov/15 |journal=Biochemical Pharmacology |volume=24 |issue=18 |pages=1725–1727 |doi=10.1016/0006-2952(75)90013-1 |issn=0006-2952 |pmid=15}}</ref>
|Multiple near complete specimens from both the Favret and Prida Formations
|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
|A large Cymbospondylid ichthyosaur varying in size from {{convert|8-12|m|ft}}.
|[[File:Cymbospondylus petrinus SW Small.png|thumb|center|280px|Life restoration of ''C. petrinus'']]
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|''C. nichollsi''<ref>{{Cite journal |last=FRÖBISCH |first=NADIA B. |last2=SANDER |first2=P. MARTIN |last3=RIEPPEL |first3=OLIVIER |date=2006 |title=A new species of Cymbospondylus (Diapsida, Ichthyosauria) from the Middle Triassic of Nevada and a re-evaluation of the skull osteology of the genus |url=http://dx.doi.org/10.1111/j.1096-3642.2006.00225.x |journal=Zoological Journal of the Linnean Society |volume=147 |issue=4 |pages=515–538 |doi=10.1111/j.1096-3642.2006.00225.x |issn=1096-3642}}</ref>
|''C. nichollsi''<ref>{{Cite journal |last1=FRÖBISCH |first1=NADIA B. |last2=SANDER |first2=P. MARTIN |last3=RIEPPEL |first3=OLIVIER |date=2006 |title=A new species of Cymbospondylus (Diapsida, Ichthyosauria) from the Middle Triassic of Nevada and a re-evaluation of the skull osteology of the genus |url=http://dx.doi.org/10.1111/j.1096-3642.2006.00225.x |journal=Zoological Journal of the Linnean Society |volume=147 |issue=4 |pages=515–538 |doi=10.1111/j.1096-3642.2006.00225.x |issn=1096-3642}}</ref>
| FMNH PR2251, from the Favret Formation, consists of the back half of a skull, the first 28 vertebrae, several ribs, and part of the shoulder girdle
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| Mid-sized species of ''Cymbospondylus'', estimated to be about {{convert|7.6|m|ft}} long
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| [[File:Cymbospondylus nichollsi FMNH.jpg|thumb|center|250px|The holotype of ''C. nichollsi'' on display at the Field Museum]]
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|''C. duelfiri''<ref>{{Cite journal |last=Klein |first=Nicole |last2=Schmitz |first2=Lars |last3=Wintrich |first3=Tanja |last4=Sander |first4=P. Martin |date=2020-04-20 |title=A new cymbospondylid ichthyosaur (Ichthyosauria) from the Middle Triassic (Anisian) of the Augusta Mountains, Nevada, USA |url=http://dx.doi.org/10.1080/14772019.2020.1748132 |journal=Journal of Systematic Palaeontology |volume=18 |issue=14 |pages=1167–1191 |doi=10.1080/14772019.2020.1748132 |issn=1477-2019}}</ref>
|''C. duelfiri''<ref>{{Cite journal |last1=Klein |first1=Nicole |last2=Schmitz |first2=Lars |last3=Wintrich |first3=Tanja |last4=Sander |first4=P. Martin |date=2020-04-20 |title=A new cymbospondylid ichthyosaur (Ichthyosauria) from the Middle Triassic (Anisian) of the Augusta Mountains, Nevada, USA |url=http://dx.doi.org/10.1080/14772019.2020.1748132 |journal=Journal of Systematic Palaeontology |volume=18 |issue=14 |pages=1167–1191 |doi=10.1080/14772019.2020.1748132 |bibcode=2020JSPal..18.1167K |issn=1477-2019}}</ref>
|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
|The smallest species of the genus at {{convert|4.3|m|ft}}. Holotype is among the earliest known viviparous animals.
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|''C. youngorum''<ref name=":12">{{Cite journal |last1=Sander |first1=P. Martin |last2=Griebeler |first2=Eva Maria |last3=Klein |first3=Nicole |last4=Juarbe |first4=Jorge Velez |last5=Wintrich |first5=Tanja |last6=Revell |first6=Liam J. |last7=Schmitz |first7=Lars |date=2021-12-24 |title=Early giant reveals faster evolution of large body size in ichthyosaurs than in cetaceans |url=https://www.science.org/doi/10.1126/science.abf5787 |journal=Science |language=en |volume=374 |issue=6575 |doi=10.1126/science.abf5787 |issn=0036-8075}}</ref>
|''C. youngorum''<ref name=":1" />
|LACM DI 157871, consists of a large complete skull, some [[cervical vertebrae]], the right [[humerus]] as well as fragments of the [[shoulder girdle]].
|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.
|A giant, {{convert|17|m|ft}} long ichthyosaur, the largest known animal up to this point in time.
| [[File:Cymbospondylus youngorum skull.jpg|thumb|center|250px|The skull of ''C. youngorum'' on display]]
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| rowspan="2" |''[[Omphalosaurus]]''
|''[[Omphalosaurus]]''
|''O. nevadanus''<ref>{{Cite journal |last=Sander |first=P. Martin |last2=Faber |first2=Christiane |date=2003 |title=The Triassic marine reptile Omphalosaurus : osteology, jaw anatomy, and evidence for ichthyosaurian affinities |url=http://www.tandfonline.com/doi/abs/10.1671/6 |journal=Journal of Vertebrate Paleontology |language=en |volume=23 |issue=4 |pages=799–816 |doi=10.1671/6 |issn=0272-4634}}</ref>
|''O. nevadanus''<ref>{{Cite journal |last1=Sander |first1=P. Martin |last2=Faber |first2=Christiane |date=2003 |title=The Triassic marine reptile Omphalosaurus : osteology, jaw anatomy, and evidence for ichthyosaurian affinities |url=http://www.tandfonline.com/doi/abs/10.1671/6 |journal=Journal of Vertebrate Paleontology |language=en |volume=23 |issue=4 |pages=799–816 |doi=10.1671/6 |bibcode=2003JVPal..23..799S |issn=0272-4634}}</ref>
|Multiple specimens from both the Fossil Hill locality and the Favret formation.
|
|A medium-sized (5 meter) basal ichthyosaur with dental batteries of button shaped teeth and durophagous feeding strategy.
|A medium-sized—{{convert|5|m|ft}}—basal ichthyosaur with dental batteries of button shaped teeth and durophagous feeding strategy.
| [[File:Omphalosaurus Holotype.jpg|thumb|center|250px|An illustration of the ''O. nevadanus'' holotype]]
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|-
|''O. nettarhynchus''<ref>{{Cite journal |last=Sander |first=P. Martin |last2=Faber |first2=Christiane |date=1998 |title=New finds of Omphalosaurus and a review of Triassic ichthyosaur paleobiogeography |url=http://link.springer.com/10.1007/BF02987823 |journal=Paläontologische Zeitschrift |language=en |volume=72 |issue=1-2 |pages=149–162 |doi=10.1007/BF02987823 |issn=0031-0220}}</ref>
|
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| rowspan="2" |''[[Phalarodon]]''
| rowspan="2" |''[[Phalarodon]]''
|''P. fraasi''<ref name=":2">{{Cite journal |last=Schmitz |first=Lars |last2=Sander |first2=P. Martin |last3=Storrs |first3=Glenn W. |last4=Rieppel |first4=Olivier |date=2004-03-10 |title=New Mixosauridae (Ichthyosauria) from the Middle Triassic of the Augusta Mountains (Nevada, USA) and their implications for mixosaur taxonomy |url=http://www.schweizerbart.de/papers/pala/detail/270/100781/New_Mixosauridae_Ichthyosauria_from_the_Middle_Tri?af=crossref |journal=Palaeontographica Abteilung A |language=en |volume=270 |issue=4-6 |pages=133–162 |doi=10.1127/pala/270/2004/133 |issn=0375-0442}}</ref>
|''P. fraasi''<ref name=":22">{{Cite journal |last1=Schmitz |first1=Lars |last2=Sander |first2=P. Martin |last3=Storrs |first3=Glenn W. |last4=Rieppel |first4=Olivier |date=2004-03-10 |title=New Mixosauridae (Ichthyosauria) from the Middle Triassic of the Augusta Mountains (Nevada, USA) and their implications for mixosaur taxonomy |url=http://www.schweizerbart.de/papers/pala/detail/270/100781/New_Mixosauridae_Ichthyosauria_from_the_Middle_Tri?af=crossref |journal=Palaeontographica Abteilung A |language=en |volume=270 |issue=4–6 |pages=133–162 |doi=10.1127/pala/270/2004/133 |bibcode=2004PalAA.270..133S |issn=0375-0442}}</ref>
|Multiple specimens from the Fossil Hill and Augusta Mountain localities
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|A small, {{convert|1|m|ft}} long mixosaur
|
| rowspan="2" |[[File:PhalarodonDB15.jpg|thumb|center|250px|[[Paleoart|Life restoration]] of ''Phalarodon'']]
|
|-
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|''P. callowayi''<ref name=":2" />
|''P. callowayi''<ref name=":22" />
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|
|
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| Holotype found in the same beds as ''[[Augustasaurus]]''
|-
|-
|''[[Thalattoarchon]]''
|''[[Thalattoarchon]]''
|''T. saurophagis''<ref>{{Cite journal |last=Fröbisch |first=Nadia B. |last2=Fröbisch |first2=Jörg |last3=Sander |first3=P. Martin |last4=Schmitz |first4=Lars |last5=Rieppel |first5=Olivier |date=2013-01-07 |title=Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks |url=http://dx.doi.org/10.1073/pnas.1216750110 |journal=Proceedings of the National Academy of Sciences |volume=110 |issue=4 |pages=1393–1397 |doi=10.1073/pnas.1216750110 |issn=0027-8424}}</ref>
|''T. saurophagis''<ref>{{Cite journal |last1=Fröbisch |first1=Nadia B. |last2=Fröbisch |first2=Jörg |last3=Sander |first3=P. Martin |last4=Schmitz |first4=Lars |last5=Rieppel |first5=Olivier |date=2013-01-07 |title=Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks |journal=Proceedings of the National Academy of Sciences |volume=110 |issue=4 |pages=1393–1397 |doi=10.1073/pnas.1216750110 |doi-access=free |pmid=23297200 |issn=0027-8424|pmc=3557033 |bibcode=2013PNAS..110.1393F }}</ref>
|[[FMNH]] PR 3032, consists of a major part of the [[skull]] and the [[axial skeleton]], including parts of the [[pelvic girdle]] and rear [[Flipper (anatomy)|flippers]]
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|A large ichthyosaur with large, laterally compressed teeth and interpreted macropredatory habit.
|A large ichthyosaur with large, laterally compressed teeth and interpreted macropredatory habit.
|[[File:Thalattoarchon_saurophagis.jpg|thumb|center|250px|[[Paleoart|Life restoration]] and size comparison of a ''T. saurophagis'' with a human]]
|
|}
|}


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|''[[Augustasaurus]]''
|''[[Augustasaurus]]''
|''A. hagdorni''<ref>{{Cite journal |last=Sander |first=P. Martin |last2=Rieppel |first2=Olivier C. |last3=Bucher |first3=Hugo |date=1997-09-04 |title=A new pistosaurid (Reptilia: Sauropterygia) from the Middle Triassic of Nevada and its implications for the origin of the plesiosaurs |url=http://dx.doi.org/10.1080/02724634.1997.10010999 |journal=Journal of Vertebrate Paleontology |volume=17 |issue=3 |pages=526–533 |doi=10.1080/02724634.1997.10010999 |issn=0272-4634}}</ref>
|''A. hagdorni''<ref>{{Cite journal |last1=Sander |first1=P. Martin |last2=Rieppel |first2=Olivier C. |last3=Bucher |first3=Hugo |date=1997-09-04 |title=A new pistosaurid (Reptilia: Sauropterygia) from the Middle Triassic of Nevada and its implications for the origin of the plesiosaurs |url=http://dx.doi.org/10.1080/02724634.1997.10010999 |journal=Journal of Vertebrate Paleontology |volume=17 |issue=3 |pages=526–533 |doi=10.1080/02724634.1997.10010999 |bibcode=1997JVPal..17..526S |issn=0272-4634}}</ref>
|Single specimen. [[FMNH]] PR 1974 is a partial articulated skeleton containing the posterior neck, trunk, shoulder girdle, and both forelimbs and a disassociated skull,
|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
|A pistosauroid from the Favret Formation
|[[File:Augustasaurus_BW.jpg|right|thumb|[[Paleoart|T]]<nowiki/>wo ''Augustasaurus hagdorni'']]
|[[File:Augustasaurus_BW.jpg|right|thumb|[[Paleoart|T]]<nowiki/>wo ''Augustasaurus hagdorni'']]
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|}
=== Pseudosuchians ===
{| class="wikitable"
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|+
!Genus
!Species
!Material
!Notes
!Images
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|-
|''[[Benggwigwishingasuchus]]''
| ''B. eremicarminis''<ref name=S24>{{Cite journal|last1=Smith|first1=N.D.|last2=Klein|first2=N.|last3=Sander|first3=M.P.|last4=Schmitz|first4=L.|year=2024|title=A new pseudosuchian from the Favret Formation of Nevada reveals that archosauriforms occupied coastal regions globally during the Middle Triassic|journal=Biol. Lett.|volume=20|issue=7|doi=10.1098/rsbl.2024.0136|pmid=38982977 |doi-access=free|pmc=11286145}}</ref>
|A single, mostly complete skeleton (LACM-DI 158616)
|A [[poposauroid]] [[pseudosuchian]] from the [[Favret Formation]], specimen was probably a terrestrial animal washed out to sea<ref name=S24 />
| [[File:Benggwigwishingasuchus.jpg|thumb|center|180px|Photos and diagrams of the holotype]]
|}
|}


==See also==
*[[List of fossiliferous stratigraphic units in Nevada]]
== References ==
== References ==
{{reflist}}
<references responsive="1"></references>

{{Chronostratigraphy of Nevada}}

[[Category:Triassic geology of Nevada]]
[[Category:Geologic formations of the United States]]
[[Category:Natural history of Nevada]]
[[Category:Stratigraphy of Nevada]]
[[Category:Triassic System of North America]]
[[Category:Shale formations]]
[[Category:Fossiliferous stratigraphic units of North America]]
[[Category:Anisian Stage]]

Revision as of 05:59, 23 August 2024

Fossil Hill Member
Stratigraphic range: Anisian
TypGeological member
Unit ofPrida Formation, Favret Formation
Lithology
PrimäreCalcareous Shale
OtherLimestone
Standort
RegionNevada
Land
 Vereinigte Staaten
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 metres (26–39 ft).
Life restoration of C. petrinus
C. nichollsi[5] FMNH PR2251, from the Favret Formation, consists of the back half of a skull, the first 28 vertebrae, several ribs, and part of the shoulder girdle Mid-sized species of Cymbospondylus, estimated to be about 7.6 metres (25 ft) long
The holotype of C. nichollsi on display at the Field Museum
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 metres (14 ft). Holotype 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 metres (56 ft) long ichthyosaur, the largest known animal up to this point in time.
The skull of C. youngorum on display
Omphalosaurus O. nevadanus[8] Multiple specimens from both the Fossil Hill locality and the Favret formation. A medium-sized—5 metres (16 ft)—basal ichthyosaur with dental batteries of button shaped teeth and durophagous feeding strategy.
An illustration of the O. nevadanus holotype
Phalarodon P. fraasi[9] Multiple specimens from the Fossil Hill and Augusta Mountain localities A small, 1 metre (3.3 ft) long mixosaur
Life restoration of Phalarodon
P. callowayi[9] Holotype found in the same beds as Augustasaurus
Thalattoarchon T. saurophagis[10] FMNH PR 3032, consists of a major part of the skull and the axial skeleton, including parts of the pelvic girdle and rear flippers 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[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
Two Augustasaurus hagdorni

Pseudosuchians

Genus Species Material Notes Images
Benggwigwishingasuchus B. eremicarminis[12] A single, mostly complete skeleton (LACM-DI 158616) A poposauroid pseudosuchian from the Favret Formation, specimen was probably a terrestrial animal washed out to sea[12]
Photos and diagrams of the holotype

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. Bibcode:2020JSPal..18.1167K. 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. Bibcode:2003JVPal..23..799S. doi:10.1671/6. ISSN 0272-4634.
  9. ^ 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. Bibcode:2004PalAA.270..133S. doi:10.1127/pala/270/2004/133. ISSN 0375-0442.
  10. ^ 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. Bibcode:2013PNAS..110.1393F. doi:10.1073/pnas.1216750110. ISSN 0027-8424. PMC 3557033. PMID 23297200.
  11. ^ 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. Bibcode:1997JVPal..17..526S. doi:10.1080/02724634.1997.10010999. ISSN 0272-4634.
  12. ^ a b Smith, N.D.; Klein, N.; Sander, M.P.; Schmitz, L. (2024). "A new pseudosuchian from the Favret Formation of Nevada reveals that archosauriforms occupied coastal regions globally during the Middle Triassic". Biol. Lett. 20 (7). doi:10.1098/rsbl.2024.0136. PMC 11286145. PMID 38982977.
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