Nacimiento Formation
Geologic formation in New Mexico
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The Nacimiento Formation is a sedimentary rock formation in the San Juan Basin of western New Mexico (United States).[1] It is dated to approximately 61.0–65.7 million years ago, corresponding to the early and middle Paleocene. The formation has yielded numerous fossil assemblages from the interval following the Cretaceous–Paleogene extinction event, which have been used to study biotic recovery and the early diversification of mammals after the extinction.[1]
| Nacimiento Formation | |
|---|---|
| Stratigraphic range: Paleocene ~ | |
The badlands below Angel Peak are made up of Nacimiento Formation rocks | |
| Type | Formation |
| Underlies | San Jose Formation |
| Overlies | Ojo Alamo Formation |
| Thickness | 254 m (833 ft) |
| Lithology | |
| Primary | Shale |
| Other | Siltstone, sandstone |
| Location | |
| Coordinates | 36.0126977°N 106.9855481°W |
| Region | New Mexico |
| Country | United States |
| Type section | |
| Named for | Nacimiento (now Cuba, New Mexico) |
| Named by | J.H. Gardner |
| Year defined | 1910 |
  Nacimiento Formation (the United States)  Nacimiento Formation (New Mexico) | |
Description
The Nacimiento Formation is a heterogeneous nonmarine formation composed of shale, siltstone, and sandstone,[2] deposited in floodplain, fluvial and lacustrine settings,[3] and made up of sediment shed from the San Juan uplift to the north and the Brazos-Sangre de Cristo uplift to the east.[4] It was deposited mostly between ~65.7 and ~61 million years ago, during the early and middle Paleocene.[5] The climate was humid and warm to hot[6] and stable, but with a distinct dry season.[7] This unit interbeds with the underlying Ojo Alamo Formation but is separated by an unconformity from the overlying San Jose Formation.[3]
The Nacimiento Formation is divided into several subunits known as members. In outcrops in southern areas of the formation, the Puercan fauna is found in the Arroyo Chijuillita Member, the Torrejonian fauna is found in the Ojo Encino Member, and the uppermost Escavada Member lacks age-diagnostic fossils.[1] In northern outcrops, the two lower members are indistinguishable, and are called the "main body".[5] Above them are two more informal members. These preserve a younger, Tiffanian fauna.[8] The Puercan and Torrejonian faunas are further subdivided into several biostratigraphic zones.[5]
Fossils
Many fossils are known from the Nacimiento Formation, although bone is often altered into phosphatic concretions.[9] Fossils belonging to a number of different organisms have been found here, including: plants (mostly dicotyledonous angiosperms),[6][10] gastropods, freshwater bivalves,[11] cartilaginous fish and bony fish, salamanders, turtles, champsosaurs, amphisbaenians, lizards, snakes, crocodilians,[12] birds,[13] and a variety of archaic mammals. Mammalian groups represented include multituberculates,[14] plesiadapiforms,[15] didelphid marsupials, insectivorans, carnivorans, taeniodonts, mesonychians, condylarths, and cimolestans.[1] Fossil remains found in the formation support the validity of the genus Thylacodon and the species T. montanensis.[16]
These fossils provide important clues to the impact of the Cretaceous–Paleogene extinction event on mammals[16] and to the recovery, evolution, and turnover of mammals shortly after the event. The formation and its fossils provide a particularly clear record of the To2-To3 turnover event, allowing the timing of the event to be constrained to between 62.59 and 62.47 million years ago. The event may have been associated with climate change or with the rapid development of a river system across the San Juan basin, which caused a temporary pause in sediment deposition that separates the Nacimiento Formation from the San Jose Formation.[17]
Fossil content
Based on the Paleobiology Database:[18]
Color key
|
Notes Uncertain or tentative taxa are in small text; |
Actinopterygii
| Boney Fish of the Nacimiento Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Lepisosteidae indet. | Torrejonian | A gar of uncertain affinities. | ||||
Amphibians
| Amphibians of the Nacimiento Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Habrosaurus | H. dilatus | Torrejonian | A sirenid salamander. |  | ||
Reptiles
Crocodyliformes
| Crocodyliformes of the Nacimiento Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Akanthosuchus | A. langstoni | Puercan & Torrejonian | An alligatorid. |  | ||
| Listrognathosuchus | L. multidentatus | Torrejonian | An alligatoroid. | |||
| Navajosuchus | L. mooki | Puercan & Torrejonian | An alligatorid. |  | ||
Turtles
| Turtles of the Nacimiento Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Adocus | A. hesperius | Puercan | An adocid turtle. |  | ||
| A. onerosus | Torrejonian | |||||
| Axestemys | A. montinsana | Puercan[19] | A softshell turtle. |  | ||
| Compsemys | C. victa | Puercan/Torrejonian | A compsemydid turtle. | |||
| "Emys" | "E." sp. | Puercan/Torrejonian | A pond turtle. | |||
| Hutchemys | H. acupictus | Puercan[19] | A plastomenid stem-softshell turtle. | |||
| Hoplochelys | H. crassa | Puercan/Torrejonian | A kinosternoid turtle. Type locality of species. | |||
| Neurankylus | N. cf. eximius | Puercan | A baenid turtle. Type locality of N. torrejonensis. |  | ||
| N. torrejonensis | Torrejonian, potentially Puercan | |||||
| Plastomenus | P. vegetus | Puercan | A plastomenid stem-softshell turtle.[20] |  | ||
| "Platypeltis" | "P." antiqua | Torrejonian | A stem-softshell turtle. Nomen dubium.[19] | |||
| "Trionyx" (=Paleotrionyx) | "T." eloisae | Puercan | A softshell turtle. Type locality of species.[19] | |||
| "T." reesidei | ||||||
| "T." singularis |  | |||||
Squamates
| Squamates of the Nacimiento Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Glyptosaurinae indet. | Puercan & Torrejonian | A glyptosaurine anguid of uncertain affinities. | ||||
| Helagras | H. prisciformis | Puercan | A snake, the largest known Early Paleocene snake.[21] | |||
| Machaerosaurus | M. torrejonensis | Torrejonian | A glyptosaurine anguid. | |||
| Odaxosaurus | O. piger | Puercan | A glyptosaurine anguid. | |||
| Parodaxosaurus | P. sanjuanensis | Torrejonian | A glyptosaurine anguid. | |||
| Plesiorhineura | P. tsentasi | Torrejonian | A rhineurid worm lizard. | |||
| Proxestops | P. silberlingii | Puercan & Torrejonian | A glyptosaurine anguid. | |||
Birds
| Birds of the Nacimiento Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
| Tsidiiyazhi | T. abini | Torrejonian | A relative of the mousebirds.[22] | |||
Mammals
Primary based on Kondrashov and Lucas (2015), with changes where necessary:[23]
Archaic Ungulates
| 'Condylarths' of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Anisonchus | A. sectorius | Torrejonian 1–3 | A periptychid | |
| Carsioptychus [24] | C. coarctatus | Puercan 2–3 | A periptychid originally described as a species of the genus Periptychus. | |
| Conacodon | C. cophater | Puercan 2–3 | A periptychid | |
| C. entoconus | Puercan 2 | |||
| C. kohlbergeri | Puercan 2 | |||
| Ectoconus | E. ditrigonus | Puercan 2–3 | A periptychid | |
| Haploconus | H. augustus | Torrejonian 1–2 | A periptychid | |
| Hemithlaeus | H. kowalewskianus | Puercan 2 | A periptychid | |
| Mithrandir[25] | M. gillianus | Puercan 2–3 | A periptychid originally described as a species of the genus Anisochus. | |
| Oxyacodon | O. agapetillus | Puercan 2 | A periptychid | |
| O. apiculatus | Puercan 2–3 | |||
| O. priscilla | Puercan 2 | |||
| Periptychus | P. carinidens | Torrejonian 1–3 | A periptychid | |
Arctocyonia
| Arctocyonians of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Arctocyon | A. corrugatus | Torrejonian 2 | An arctocyonid | |
| A. ferox | Torrejonian 2–3 | |||
| Chriacus | C. baldwini | Torrejonian 2–3 | An arctocyonid |  |
| C. orthogonius | Torrejonian | |||
| C. pelvidens | Torrejonian 2–3 | |||
| Colpoclaenus | C. procyonoides | Torrejonian 3 | An arctocyonid | |
| Desmatoclaenus | D. dianae | Puercan 2–3 | An arctocyonid | |
| D. protogonoides | Puercan 2–3 | |||
| Deuterogonodon | D. montanus | Torrejonian 1–2 | An arctocyonid | |
| Loxolophus | L. hyattianus | Puercan 2–3 | An arctocyonid | |
| L. pentacus | Puercan 2–3 | |||
| L. priscus | Puercan 3 | |||
| Prothryptacodon | P. ambiguus | Torrejonian 3 | An arctocyonid | |
| Tricentes | T. subtrigonus | Torrejonian 1–3 | An arctocyonid | |
Carnivorans
| Carnivorans of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Bryanictis | B. paulus | Torrejonian 2 | A viverravid carnivoran | |
| Intyrictis | I. vanvaleni | Torrejonian 2 | A viverravid carnivoran | |
| Protictis | P. haydenianus | Torrejonian 2–3 | A viverravid carnivoran | |
| P. minor | Torrejonian 2 | |||
| P. simpsoni | Torrejonian 2 | |||
Cimolesta
| Cimolestans of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Acemeodon | A. secans | Torrejonian 2–3 | A cimolestid cimolestan | |
| Betonnia | B. tsosia | Puercan 2–3 | A cimolestid cimolestan | |
| Chacopterygus | C. minutus | Puercan 2–3 | A cimolestid cimolestan | |
| Palaeoryctes | P. puercensis | Torrejonian 2–3 | A palaeoryctid cimolestan | |
| Puercolestes | P. simpsoni | Puercan 2–3 | A cimolestid cimolestan | |
Dermoptera
| Dermopterans of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Mixodectes | M. malaris | Torrejonian 2–3 | A mixodectid dermopteran | |
| M. pungens | Torrejonian 3 | |||
Eutheria Incertae sedis
| Other Eutherians of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Deltatherium[26] | D. dandreae | Torrejonian 2–3 | A eutherian mammal of unknown placement | |
| D. fundaminis | Torrejonian 4–5 | |||
Leptictida
| Leptictidans of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Prodiacodon | P. puercensis | Torrejonian 1–3 | A leptictiid leptictidan | |
Mesonychians
| Mesonychians of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Ankalagon | A. saurognathus | Torrejonian 2–3 | A mesonychid mesonychian | |
| Carcinodon | C. antiquus | Puercan 3 | A triisodontid mesonychian | |
| C. olearyi | Puercan 2–3 | |||
| C. simplex | Puercan 2 | |||
| Dissacus | D. navajovius | Torrejonian 2–3 | A mesonychid mesonychian | |
| Eoconodon | E. coryphaeus | Puercan 2–3 | A triisodontid mesonychian | |
| E. gaudrianus | Puercan 2 | |||
| E. ginibitohia | Puercan 2 | |||
| Goniacodon | G. levisanus | Torrejonian 2–3 | A triisodontid mesonychian | |
| Oxyclaenus | O. cuspidatus | Torrejonian 2–3 | A triisodontid mesonychian | |
| Triisodon | T. crassicuspis | Torrejonian 2 | A triisodontid mesonychian | |
| T. quivirensis | Torrejonian 2 | |||
Metatheria
| Metatherians of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Peradectes | P. coprexeches | Torrejonian 2–3 | A peradectid metatherian | |
| P. minor | Puercan 2–3 | |||
| Swaindelphys | S. encinensis | Torrejonian 2 | A herpetotheriid metatherian | |
| S. johnsoni | Torrejonian 3 | |||
| Thylacodon | T. pusillus | Puercan 2–3 | A herpetotheriid metatherian | |
Multituberculata
| Multituberculates of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Anconodon | A. gidleyi | Torrejonian 2 | A neoplagiaulacid multituberculate | |
| Catopsalis | C. fissidens | Torrejonian 2 | A taeinolabid multituberculate | |
| C. foliatus | Puercan 2 | |||
| Ectypodus | E. szalayi | Torrejonian 2 | A neoplagiaulacid multituberculate | |
| Eucosmodon | E. americanus | Puercan 2 | An eucosmodontid multituberculate | |
| E. molestus | Torrejonian 2 | |||
| E. primus | Puercan 2 | |||
| Kimbetohia | K. campi | Puercan 2 | A ptilodontid multituberculate | |
| Kimbetopsalis[27] | K. simmonsae | Puercan 2 | A taeinolabid multituberculate | |
| Krauseia | K. clemensi | Torrejonian 2 | A neoplagiaulacid multituberculate | |
| Liotomus | L. vanvaleni | Puercan 2 | A cimolodontid multituberculate | |
| Mesodma | M. formosa | Puercan 2 | A neoplagiaulacid multituberculate | |
| M. thompsoni | Puercan 2 | |||
| Mimetodon | M. krausei | Torrejonian 2 | A neoplagiaulacid multituberculate | |
| Neoplagiaulax | N. macintyrei | Puercan 2 | A neoplagiaulacid multituberculate | |
| N. macrotomeus | Torrejonian 2 | |||
| Parectypodus | P. trovessartianus | Torrejonian 2 | A neoplagiaulacid multituberculate | |
| Ptilodus | P. mediaevus | Torrejonian 2–3 | A ptilodontid multituberculate | |
| P. tsosiensis | Puercan 2 | |||
| Stygimys | S. teilhardi | Torrejonian 2 | An eucosmodontid multituberculate | |
| Taeniolabis | T. simmonsae | Puercan 3 | A taeinolabid multituberculate | |
| T. taoensis | Puercan 3 |  | ||
Palaeanodonta
| Palaeanodonta of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Escavadodon | E. zygus | Torrejonian 3 | An escavadodontid palaeanodont | |
Panperissodactyla
| Panperissodactyls of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Bomburodon | B. priscus | Puercan 2–3 | A hyopsodontid | |
| Choeroclaenus | C. turgidunculus | Puercan 2–3 | A hyopsodontid | |
| Chacomylus | C. sladei | Puercan 3 | A hyopsodontid | |
| Litomylus | L. osceolae | Torrejonian 2–3 | A hyopsodontid | |
| Mioclaenus | M. turgidus | Torrejonian 1–3 | A hyopsodontid | |
| Promioclaenus | P. wilsoni | Puercan 2–3 | A hyopsodontid | |
| Protoselene | P. bombadili | Puercan 2–3 | A hyopsodontid | |
| P. opisthacus | Torrejonian 2–3 | |||
| Tetraclaenodon | T. puercensis | Torrejonian 1–3 | A phenacodontid | |
| Tiznatzinia | T. vanderhoofi | Puercan 2–3 | A hyopsodontid | |
Pantodonts
| Pantodonts of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Pantolambda | P. bathmodon | Torrejonian 3 | A pantolambdid pantodont |  |
| P. cavirictum | Torrejonian 2–3 |  | ||
| P. intermedium | Torrejonian 2 | |||
Pantolesta
| Pantolestans of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Coriphagus | C. encinensis | Torrejonian 2–3 | A pentacodontid pantolestan | |
| Pentacodon | P. inversus | Torrejonian 2 | A pentacodontid pantolestan | |
| P. occultus | Torrejonian 3 | A pentacodontid pantolestan | ||
Plesiadapiforms
| Plesiadapiforms of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Anasazia | A. williamsoni | Torrejonian 2 | A palaechthonid plesiadapiform | |
| Palaechthon | P. woodi | Tiffanian 1 | A palaechthonid plesiadapiform | |
| Paromomys | P. libedianus | Torrejonian 2 | A paromomyid plesiadapiform | |
| Picrodus | P. calgariensis | Torrejonian 2 | A picrodontid plesiadapiform | |
| Plesiolestes | P. nacimienti | Torrejonian 2–3 | A palaechthonid plesiadapiform | |
| P. torrejonius | Torrejonian 2 | |||
| Torrejonia | T. wilsoni | Torrejonian 3 | A palaechthonid plesiadapiform | |
Taeniodonta
| Taeniodonts of the Nacimiento Formation | ||||
|---|---|---|---|---|
| Genus | Species | Stratigraphic position | Notes | Images |
| Conorystes | C. comma | Torrejonian 2–3 | A conoryctid taeniodont | |
| Conoryctella | C. pattersoni | Torrejonian 2 | A conoryctid taeniodont | |
| Huerfanodon | H. torrejonius | Torrejonian 2 | A conoryctid taeniodont | |
| Onychodectes | O. tisonensis | Puercan 2–3 | A conoryctid taeniodont | |
| Psittacotherium | P. multifragum | Torrejonian 2–3 | A stylinodontid taeniodont | |
| Wortmania | W. otariidens | Puercan 2–3 | A stylinodontid taeniodont | |
Molluscs
Bivalves
| Bivalves of the Nacimiento Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Gastropods
| Gastopods of the Nacimiento Formation | ||||||
|---|---|---|---|---|---|---|
| Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
History of investigation
Edward Drinker Cope described the fossils during the Wheeler Survey.[28]
Workers in the early 1900s divided the rocks of the Nacimiento Formation into two formations, the lower Puerco Formation and the upper Torrejon Formation.[13] This was rejected on the grounds that there were no lithological differences between the two, only differences in fossil faunas, making determination of which formation was present in a given area impossible if fossils could not be found.[9] The Puerco and Torrejon were retained as zones within the Nacimiento Formation, and their faunas became the basis of the Puercan and Torrejonian North American Land Mammal Ages.[29]