Ojo Alamo Formation Explained

Ojo Alamo Formation
Type:Geological formation
Age:Maastrichtian-Danian
~
Period:Danian
Prilithology:Conglomerate, sandstone, shale
Namedfor:Ojo Alamo Spring
Namedby:B. Brown
Year Ts:1910
Region:San Juan Basin, New Mexico
Country: United States
Coordinates:36.3306°N -108.0351°W
Subunits:Naashoibito Member, Kimbeto Member
Underlies:Nacimiento Formation
Overlies:Kirtland Formation

The Ojo Alamo Formation is a geologic formation in New Mexico spanning the Mesozoic/Cenozoic boundary. Non-avian dinosaur fossils have controversially been identified in beds of this formation dating from after the Cretaceous–Paleogene extinction event, but these have been explained as either misidentification of the beds in question or as reworked fossils, fossils eroded from older beds and redeposited in the younger beds.

Description

The Ojo Alamo Formation is divided into two subunits separated by a large unconformity—a gap in the geologic record. The lower Naashoibito member (sometimes considered part of the Kirtland Formation) was deposited during the Maastrichtian age of the Cretaceous period, specifically between about 69-68 million years ago. It overlies the De-na-zin member of the Kirtland formation, though the two are separated by another large unconformity that spans a period of geologic time equivalent to 73-69 million years ago.[1] All dinosaur fossils probably come from this unit.

The upper unit of the Ojo Alamo Formation is the Kimbeto Member, which was deposited mainly during the earliest Cenozoic (Danian age of the Paleogene period), between 66 and 64 million years ago.[1]

Fossils

Dinosaur remains are among the fossils that have been recovered from the formation, though all dinosaur remains come from the lowest part of the formation, the Naashoibito member (sometimes considered part of the Kirtland Formation, which dates to the late Maastrichtian stage of the Cretaceous period).[2]

Some researchers have claimed to find isolated non-avian dinosaur remains in the younger Kimbeto Member. If this is the case, it would represent the only known instance of a non-avian dinosaur population persisting after the Cretaceous–Paleogene extinction event. However, most scientists consider these to have been stratigraphically misinterpreted or reworked from the older Naashoibito member.[3]

Alamo Wash fauna

The following species are known to be present in the Naashoibito Member "Alamo Wash Fauna".[4]

Fish

GenusSpeciesMaterialNotesImages
MyledaphusM. sp.A single toothAn anacoracid elasmobranch. A single tooth (NMMNH P-44485), consisting of a six-sided crown with double roots. Only occurrence of the genus in the Naashoibito Member, but miight actually be from the underlying De-na-zin Member of the Kirtland Formation.
?Squatirhina?S. sp.An isolated toothAn orectolobid elasmobranch. May represent the first and only record of this taxon from the Naashoibito Member.
LepisosteidaeIndeterminateMultiple isolated scalesA gar

Amphibians

Testudines

GenusSpeciesMaterialNotesImages
CompsemysC. sp.Multiple shell fragmentsA pleurosternid testudine. Species-level identification is not possible, but similarities have been noted with Compsemys vafer.
HoplochelysH. sp.A complete plastron and a few fragments
Plastomenuscf. P. sp.Nearly complete right parietalA trionychid testudine. Compares readily to Plastomenus thomasi.
AdocidaeIndeterminateMostly carapace fragmentsAn adocid testudine. Among the attributed material is the holotype of Adocus vigoratus, now considered a nomen dubium.
BasilemysB. sp.Fragments of carapace and plastronA nanhsiungchelyid testudine. Previously Basilemys nobilis, it is now considered a nomen dubium which isn't assignable at the species level.
ParacryptodiraIndeterminateAn incomplete carapace fragmentAn indeterminate paracryptodiran. Similar in shell morphology to Compsemys.
BaenidaeIndeterminateCarapace and skull fragmentsAn indeterminate baenid.
TrionychidaeIndeterminateDozens of specimensAn indeterminate trionychid. A lot of material has been recovered, but it is fragmentary and not able to be defined to the genus level.
TestudinidaeIndeterminateIndeterminate shell and carapace fragments.Indeterminate testudine. Not identifiable to any lower taxonomic rank due to their fragmentary nature.

Squamates

GenusSpeciesMaterialNotesImages
PeneteiusP. sp.A jaw fragment and multiple teethFossil material requires proper documentation.
?Chamops?C. sp.A toothA teiid lizard. The tooth was originally identified as that of a cyprinid fish. Its presence in the Alamo Wash fauna is questionable.

Crocodylians

GenusSpeciesMaterialNotesImages
Brachychampsacf. B. sp.A single toothAn alligatorid. The tooth was previously attributed to Allognathosuchus.
CrocodylidaeIndeterminateA mandibular fragment, multiple teeth and osteoderms.An indeterminate crocodillian of which material has been referred to multiple genera in the past, including Leidyosuchus and Denazinosuchus.

Dinosaurs

GenusSpeciesMaterialNotesImages
Dineobellator[5] D. notohesperus
Ojoraptorsaurus[6] O. boereiPossibly a nomen dubium[7]
CaenagnathidaeIndeterminate
OrnithomimidaeIndeterminate
RichardoestesiaR. sp.
TroodontidaeIndeterminate
Tyrannosauruscf. T. sp.
Alamosaurus[8] A. sanjuanensis
Glyptodontopelta[9] G. mimus
AnkylosauridaeIndeterminateNoted to be similar to Euoplocephalus and Ankylosaurus
AnkylosauriaIndeterminate
HadrosauridaeIndeterminate
Lambeosaurini[10] IndeterminateNoted as being similar to Corythosaurus and Hypacrosaurus
CeratopsidaeIndeterminate
Ojoceratops[11] O. fowleri

Mammals

GenusSpeciesMaterialNotesImages
Alphadoncf. A. marshi
AlphadontinaeIndeterminate
Essonodon[12] E. browni
Glasbiuscf. G. sp.
MesodmaM. formosa
Meniscoessuscf. M. sp.
MultituberculataIndeterminate
Pediomyidaecf. Indeterminate

History of investigation

The formation was named by Barnum Brown in 1910 for exposures near Ojo Alamo springs in the San Juan Basin.[13] Baltz et al. reassigned the lower beds to the Kirtland Formation in 1966, but this has not been generally accepted.[14]

See also

Further reading

Notes and References

  1. Sullivan, R.M., and Lucas, S.G. 2006. "The Kirtlandian land-vertebrate "age" – faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America." New Mexico Museum of Natural History and Science, Bulletin 35:7-29.
  2. Williamson, T.E. and Weil, A. (2008). "Metatherian mammals from the Naashoibito Member, Kirtland Formation, San Juan Basin, New Mexico and their biochronologic and paleobiogeographic significance. Journal of Vertebrate Paleontology, 28: 803-815.
  3. Sullivan. RM. No Paleocene dinosaurs in the San Juan Basin, New Mexico. Geological Society of America Abstracts with Programs. 35. 5. 15. 2003. 2007-07-02. 2011-04-08. https://web.archive.org/web/20110408155457/http://gsa.confex.com/gsa/2003RM/finalprogram/abstract_47695.htm. dead.
  4. Jasinski, S. E., Sullivan, R. M., & Lucas, S. G. (2011). Taxonomic composition of the Alamo Wash local fauna from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member) San Juan Basin, New Mexico. Bulletin, 53, 216-271.
  5. Jasinski . Steven E. . Sullivan . Robert M. . Dodson . Peter . New Dromaeosaurid Dinosaur (Theropoda, Dromaeosauridae) from New Mexico and Biodiversity of Dromaeosaurids at the end of the Cretaceous . Scientific Reports . 2020-03-26 . 10 . 5105 . 5105 . 10.1038/s41598-020-61480-7 . 32218481 . 7099077 . 2020NatSR..10.5105J . free .
  6. Robert M. Sullivan, Steven E. Jasinski and Mark P.A. Van Tomme . 2011 . A new caenagnathid Ojoraptorsaurus boerei, n. gen., n. sp. (Dinosauria, Oviraptorosauria), from the Upper Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico . Fossil Record 3. New Mexico Museum of Natural History and Science Bulletin . 53 . 418–428.
  7. Funston . G. F. . Williamson . T. E. . Brusatte . S. L. . 2024 . A caenagnathid tibia (Theropoda: Oviraptorosauria) from the upper Campanian Kirtland Formation of New Mexico . . 105856 . in press . 10.1016/j.cretres.2024.105856 .
  8. Gilmore . Charles W. . A new sauropod dinosaur from the Ojo Alamo formation of New Mexico (with two plates) . Smithsonian Miscellaneous Collections . 1922 . 72 . 14 . 1–9 . 23 October 2020.
  9. T.L. Ford. (2000). "A review of ankylosaur osteoderms from New Mexico and a preliminary review of ankylosaur armor", In: S. G. Lucas and A. B. Heckert (eds.), Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin 17: 157-176
  10. Web site: Jasinski. Steven E.. Sullivan. Robert M.. Lucas. Spencer G.. Spielmann. Justin A.. The first "lambeosaurin" (Dinosauria, Hadrosauridae, Lambeosaurinae) from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico: further implications for the age of the Alamo Wash local fauna. www.researchgate.com. 21 August 2016.
  11. Robert M. Sullivan and Spencer G. Lucas, 2010, "A New Chasmosaurine (Ceratopsidae, Dinosauria) from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico", In: Ryan, M.J., Chinnery-Allgeier, B.J., and Eberth, D.A. (eds.) New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium, Bloomington, Indiana University Press, 656 pp.
  12. Willamson . Thomas M. . Weil . Anne . Metatherian Mammals from the Naashoibito Member, Kirtland Formation, San Juan Basin, New Mexico and Their Biochronologic and Paleobiogeographic Significance . Journal of Vertebrate Paleontology . 12 September 2008 . 28 . 3 . 803–815 . 19 November 2020 . Taylor & Francis, Ltd.. 10.1671/0272-4634(2008)28[803:MMFTNM]2.0.CO;2 . 20491004 . 140555450 .
  13. Brown, Barnum, 1910, The Cretaceous Ojo Alamo beds of New Mexico with description of the new dinosaur genus Kritosaurus: American Museum of Natural History Bulletin, v. 28, art. 24, p. 267-274.
  14. Baltz, E.H., Ash, S.R., and Anderson, R.Y., 1966, History of nomenclature and stratigraphy of rocks adjacent to the Cretaceous-Tertiary boundary, western San Juan basin, New Mexico, IN Shorter contributions to general geology, 1965: U.S. Geological Survey Professional Paper, 524-D, p. D1-D23.