Chambers Tuff

Chambers Tuff
Chambers Tuff
Stratigraphic range: mid-late Eocene (late Duchesnean - early Chadronian, 38.29 - 37.14 Ma) PreꞒ Ꞓ O S D C P T J K Pg N Pal. Eocene Oligo. Miocene P P
Type	Formation
Unit of	Vieja Group
Underlies	Bracks Rhyolite
Overlies	Buckshot Ignimbrite
Lithology
Primary	sandstone, siltstone, conglomerate, tuff
Location
Region	Texas
Country	United States
Type section
Named by	DeFord (1958)

The Chambers Tuff (or Chambers Tuff Formation) is a geological formation in the Trans-Pecos area of Texas. It preserves fossils dating back to the Eocene epoch, across the boundary between the Duchesnean and Chadronian North American land mammal ages. The Chambers Tuff is the middle of three fossil-bearing sedimentary formations in the Vieja Group, alongside the older Colmena Tuff and younger Capote Mountain Tuff.

Geology

Though named as a tuff (airborne ash deposit), most of the Chambers Tuff actually represents water-carried sediments. Most of it comprises multicolored fine-grained sediments, alongside coarse gray conglomerates and a few marker beds with legitimate ash content. The lower marker bed is a soft pale-colored tuff about 100–175 feet above the base of the Chambers Tuff as a whole. The upper marker bed is a tough layer of sanidine-based dark red sandstone higher in the section. A third marker bed, another red sandstone layer, is occasionally found near the top of the Chambers Tuff.

Radiometric (⁴⁰Ar/³⁹Ar) dating has not been attempted for the Chambers Tuff itself, but it is possible for the volcanic layers which bracket it. Depending on the study, the underlying Buckshot Ignimbrite has been dated to anywhere between 38.29 ± 0.16 Ma and 37.68 ± 0.06 Ma. The overlying Bracks Rhyolite is dated to anywhere between 37.14 ± 0.08 Ma and 36.67 ± 0.04 Ma.

Paleobiota

Mammal fossils are found at two particular local faunas in the Chambers Tuff, both found in Presidio County:

The Porvenir local fauna occurs in the lower layers of the Chambers Tuff, below the lower marker bed and up to 100 feet above it. It corresponds to the late Duchesnean NALMA and an early part of magnetostratigraphic chron C17n.
The Little Egypt local fauna occurs in the higher layers of the Chambers Tuff, exposed at sites such as Reeves Bonebed and Chalk Gap Draw. It corresponds to the earliest Chadronian NALMA and magnetostratigraphic chron C17n.1n. The Rancho Gaitan local fauna, in Chihuahua, Mexico, is very close to the Little Egypt local fauna in age and environment. Natural endocasts (brain molds) are abundant in the Reeves bonebed.

Mammals

Artiodactyla

Artiodactyls of the Chambers Tuff
Genus / Taxon	Species	Local fauna	Notes	Images
Aclistomycter	A.? dunagani	Little Egypt	An early aclistomycterine merycoidodontid (oreodont). Previously considered a species of Merycoidodon.
Aclistomycter	A. middletoni	Porvenir	An early aclistomycterine merycoidodontid (oreodont).
Agriochoerus	A. antiquus	Porvenir, Little Egypt	An agriochoerid (claw-bearing oreodont relative).
Archaeotherium	A. cf. A. mortoni	Porvenir, Little Egypt	An entelodont (boar-like relative of hippos).
Bathygenys	B. reevesi	Little Egypt	An early oreonetine merycoidodontid (oreodont).
Brachyhyops	B. wyomingensis	Porvenir	An entelodont (boar-like relative of hippos).
Eotylopus	E. cf. reedi	Little Egypt	An oromerycid (early camel).
Hendryomeryx	H. defordi	Porvenir	A leptomerycid. Previously considered a species of Leptomeryx.
Heteromeryx	H. dispar	Porvenir	An early protoceratid.
Hidrosotherium	H. transpecoensis	Porvenir	A leptomerycid.
Oromeryx	O. sp.	Porvenir	An oromerycid (early camel).
Poabromylus	P. kayi	Porvenir	An early protoceratid.
Protoreodon	P. pumilus	Porvenir	An agriochoerid (claw-bearing oreodont relative).
Pseudoprotoceras	P. minor	Porvenir	An early protoceratid. Previously considered a species of Poabromylus.

Carnivora

Carnivorans of the Chambers Tuff
Genus / Taxon	Species	Local fauna	Notes	Images
Angelarctocyon	A. australis	Porvenir	An indeterminate amphicyonid ("bear-dog"). Previously considered a species of Miacis.
Brachyrhynchocyon	B. dodgei	Little Egypt	A daphoenine amphicyonid ("bear-dog"). Formerly known as Daphoenocyon dodgei.
Daphoenictis	D. sp.	Porvenir	A daphoenine amphicyonid ("bear-dog").
Daphoenus	D. lambei	Porvenir	A daphoenine amphicyonid ("bear-dog").
Feliformia	indet.	Little Egypt	An unusual snout fragment with a deep premaxilla, broad incisors, and large canines. Potentially a new species of felid (cat) or nimravid ("false saber-toothed cat").
Gustafsonia	G. cognita	Little Egypt	An indeterminate amphicyonid ("bear-dog"). Previously considered a species of Miacis.

Eulipotyphla

Eulipotyphlans of the Chambers Tuff
Genus / Taxon	Species	Local fauna	Notes	Images
Centetodon	C. chadronensis	Porvenir	A geolabidid.
Apternodus	A. iliffensis	Porvenir	An apternodontid.

Hyaenodonta

Hyaenodonts of the Chambers Tuff
Genus / Taxon	Species	Local fauna	Notes	Images
Hemipsalodon	H. viejaensis	Porvenir	A hyainailourid.
Hyaenodon	H. crucians	Porvenir	A hyaenodontid.
	H. cf. horridus	Little Egypt
	H. montanus	Porvenir
Ischnognathus	I. savagei	Porvenir	A hyainailourid.

Leptictida

Leptictids of the Chambers Tuff
Genus / Taxon	Species	Local fauna	Notes	Images
Leptictis	L. douglasi	Porvenir	A leptictid.
Leptictis	L. wilsoni	Little Egypt	A leptictid.

Perissodactyla

Perissodactyls of the Chambers Tuff
Genus / Taxon	Species	Local fauna	Notes	Images
Colodon	C. stovalli	Porvenir, Little Egypt	A helaletid (early tapir).
Duchesneodus	D. uintensis	Porvenir	A large horned brontothere.
Haplohippus	H. texanus	Porvenir	An early horse.
Hyracodon	H. primus	Porvenir, Little Egypt	A hyracodontid (lightly-built, pony-like rhino).
Metamynodon	M. chadronensis	Porvenir	An amynodontid (hippo-like rhino).
Mesohippus	M. texanus	Porvenir, Little Egypt	An early three-toed horse.
Penetrigonias	P. dakotensis	Porvenir	An early hornless rhinocerotid (rhino). Reports of Trigonias-like fossils probably represent this species.
Protitanops	P. curryi	Porvenir, Little Egypt	A large horned brontothere. Texan fossils of this species were previously described under the dubious name "Menodus bakeri".
Schizotheroides	S. jackwilsoni	Porvenir, Little Egypt	An enigmatic perissodactyl with teeth similar to hyracodontids.
Subhyracodon?	S.? sp.	Porvenir	An early hornless rhinocerotid (rhino). Formerly known as Caenopus.
Toxotherium	T. hunteri	Porvenir, Little Egypt	An enigmatic perissodactyl with a short, broad skull and rhino-like teeth.

Primates

Primates of the Chambers Tuff
Genus / Taxon	Species	Local fauna	Notes	Images
Rooneyia	R. viejaensis	Porvenir	An omomyid (early tarsier relative)

Rodentia

Rodents of the Chambers Tuff
Genus / Taxon	Species	Local fauna	Notes	Images
Adjidaumo	A. cf. A. minutus	Porvenir	An eomyid.
Ardynomys	A. occidentalis	Porvenir, Little Egypt	A cylindrodontid.
Aulolithomys	A. bounites	Porvenir	An eomyid.
Aulolithomys	A. cf. A. bounites	Little Egypt	An eomyid.
Cylindrodon	C. fontis	Little Egypt	A cylindrodontid.
Dolocylindrodon	D. texanus	Porvenir, Little Egypt	A cylindrodontid. Previously considered a species of Pseudocylindrodon.
Eutypomys	E. inexpectatus	Porvenir, Little Egypt	A eutypomyid.
Ischyromys	I. blacki	Porvenir	An ischyromyine ischyromyid.
Litoyoderimys	L. lustrorum	Porvenir	An eomyid. Previously considered a species of Yoderimys.
Microparamys	M. perfossus	Porvenir	A paramyine ischyromyid.
Pseudocylindrodon	P. neglectus	Porvenir, Little Egypt	A cylindrodontid.
Pseudotomus	P. cf. P. petersoni	Porvenir	A paramyine ischyromyid. Previously considered a species of Ischyrotomus.
Pseudotomus	P. johanniculi	Porvenir, Little Egypt	A paramyine ischyromyid. Previously considered a species of Manitsha.
Quadratomus	Q. gigans	Porvenir	A paramyine ischyromyid. Previously considered a species of Leptotomus.
cf. Simimys	cf. Simimys sp. indet.	Porvenir	A simimyid.
Viejadjidaumo	V. magniscopuli	Porvenir	An eomyid.

References

1 2 3 4 5 6 7 Tomiya, Susumu; Tseng, Zhijie Jack (2016). "Whence the beardogs? Reappraisal of the Middle to Late Eocene ' Miacis ' from Texas, USA, and the origin of Amphicyonidae (Mammalia, Carnivora)". Royal Society Open Science. 3 (10) 160518. Bibcode:2016RSOS....360518T. doi:10.1098/rsos.160518. ISSN 2054-5703. PMC 5098994. PMID 27853569.
1 2 3 4 5 6 J. A. Wilson. (1977). "Stratigraphic Occurrence and Correlation of Early Tertiary Vertebrate Faunas Trans-Pecos Texas. Part I: Vieja Area." Texas Memorial Museum Bulletin 25:1-42
1 2 3 Prothero, Donald R. (1996-06-13), "Magnetostratigraphy of the Eocene-Oligocene transition in Trans-Pecos Texas", in Prothero, Donald R.; Emry, Robert J. (eds.), The Terrestrial Eocene-Oligocene Transition in North America (1 ed.), Cambridge University Press, pp. 189–198, doi:10.1017/cbo9780511665431.010, ISBN 978-0-521-43387-7, retrieved 2026-08-01
↑ Kelly, T.S.; Murphey, P.C.; Walsh, S.L. (2012). "New records of small mammals from the middle Eocene Duchesne River Formation, Utah, and their implications for the Uintan–Duchesnean North American Land Mammal Age transition." Paludicola 8: 208–251.
1 2 Nyborg, Torrey; Lander, E. Bruce (2022-03-14), "Vertebrate paleontology and Cenozoic depositional environments of Death Valley National Park, California, USA", Field Excursions from Las Vegas, Nevada: Guides to the 2022 GSA Cordilleran and Rocky Mountain Joint Section Meeting, Geological Society of America, pp. 1–22, doi:10.1130/2022.0063(01), ISBN 978-0-8137-0063-2, retrieved 2026-08-02
↑ Prothero, Donald R.; Swisher III, Carl C. (1992), "2. Magnetostratigraphy and Geochronology of the Terrestrial Eocene-Oligocene Transition in North America", Eocene-Oligocene Climatic and Biotic Evolution, Princeton University Press, pp. 46–73, doi:10.1515/9781400862924.46, ISBN 978-1-4008-6292-4, retrieved 2026-08-29{{citation}}: CS1 maint: work parameter with ISBN (link)
1 2 Wilson, John Andrew (1986-12-24). "Stratigraphic Occurrence and Correlation of Early Tertiary Vertebrate Faunas, Trans-Pecos Texas: Agua Fria–Green Valley Areas". Journal of Vertebrate Paleontology. 6 (4): 350–373. Bibcode:1986JVPal...6..350W. doi:10.1080/02724634.1986.10011630. ISSN 0272-4634. JSTOR 4523112.
↑ Macrini, Thomas E. (2009-12-12). "Description of a digital cranial endocast of Bathygenys reevesi (Merycoidodontidae; Oreodontoidea) and implications for apomorphy-based diagnosis of isolated, natural endocasts". Journal of Vertebrate Paleontology. 29 (4): 1199–1211. Bibcode:2009JVPal..29.1199M. doi:10.1671/039.029.0413. ISSN 0272-4634.
1 2 3 4 5 Wilson, John A. (1971). "Early Tertiary Vertebrate Faunas, Vieja Group, Trans-Pecos Texas, Agriochoeridae and Merycoidodontidae". Bulletin of the Texas Memorial Museum, University of Texas at Austin. 18: 1–83.
1 2 Wilson, J.A. (1974). "Early Tertiary vertebrate faunas, Vieja Group and Buck Hill Group, Trans-Pecos Texas: Protoceratidae, Camelidae, Hypertragulidae." Texas Memorial Museum Bulletin 23:1-34.
1 2 3 4 5 6 7 8 9 10 E. P. Gustafson (1986). "Carnivorous mammals of the Late Eocene and Early Oligocene of Trans-Pecos Texas." Texas Memorial Museum Bulletin 33:1-66
1 2 Hunt, Robert M. (1996-06-13), "Amphicyonidae", in Prothero, Donald R.; Emry, Robert J. (eds.), The Terrestrial Eocene-Oligocene Transition in North America (1 ed.), Cambridge University Press, pp. 476–485, doi:10.1017/cbo9780511665431.024, ISBN 978-0-521-43387-7, retrieved 2026-08-01
1 2 3 4 5 6 7 8 Wilson, J.A.; Schiebout, J.A. (1984). "Early Tertiary Vertebrate Faunas, Trans-Pecos Texas: Ceratomorpha Less Amynodontidae." The Pearce-Sellards Series, Texas Memorial Museum 39:1-47.
↑ Wilson, J.A.; Schiebout, J.A. (1981). "Early Tertiary Vertebrate Faunas Trans-Pecos Texas: Amynodontidae." The Pearce-Sellards Series, Texas Memorial Museum 33:1-62.
↑ Forsten, A.; McGrew, P.O. (1971). "Early Tertiary Vertebrate Faunas, Vieja Group, Trans-Pecos Texas: Equidae." The Pearce-Sellards Series, Texas Memorial Museum 18:1-16.
↑ Prothero, Donald R. (2005). The evolution of North American rhinoceroses. Cambridge: Cambridge university press. ISBN 978-0-521-83240-3.
↑ Mihlbachler, Matthew; Prothero, Donald (2021). "Eocene (Duchesnean and earliest Chadronian) brontotheres (Brontotheriidae), Protitanops curryi and cf. Parvicornus occidentalis, from west Texas and Mexico". Palaeontologia Electronica. doi:10.26879/944.
↑ Schiebout, Judith A. (1977). "Schizotheroides (Mammalia: Perissodactyla) from the Oligocene of Trans-Pecos Texas". Journal of Paleontology. 51 (3): 455–458. ISSN 0022-3360. JSTOR 1303676.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 A. E. Wood. (1974). "Early Tertiary vertebrate faunas, Vieja Group Trans-Pecos Texas: Rodentia". Texas Memorial Museum Bulletin 21:1-112

[:9-1] 1 2 3 4 5 6 7 Tomiya, Susumu; Tseng, Zhijie Jack (2016). "Whence the beardogs? Reappraisal of the Middle to Late Eocene ' Miacis ' from Texas, USA, and the origin of Amphicyonidae (Mammalia, Carnivora)". Royal Society Open Science. 3 (10) 160518. Bibcode:2016RSOS....360518T. doi:10.1098/rsos.160518. ISSN 2054-5703. PMC 5098994. PMID 27853569.

[:10-2] 1 2 3 4 5 6 J. A. Wilson. (1977). "Stratigraphic Occurrence and Correlation of Early Tertiary Vertebrate Faunas Trans-Pecos Texas. Part I: Vieja Area." Texas Memorial Museum Bulletin 25:1-42

[:0-3] 1 2 3 Prothero, Donald R. (1996-06-13), "Magnetostratigraphy of the Eocene-Oligocene transition in Trans-Pecos Texas", in Prothero, Donald R.; Emry, Robert J. (eds.), The Terrestrial Eocene-Oligocene Transition in North America (1 ed.), Cambridge University Press, pp. 189–198, doi:10.1017/cbo9780511665431.010, ISBN 978-0-521-43387-7, retrieved 2026-08-01

[4] Kelly, T.S.; Murphey, P.C.; Walsh, S.L. (2012). "New records of small mammals from the middle Eocene Duchesne River Formation, Utah, and their implications for the Uintan–Duchesnean North American Land Mammal Age transition." Paludicola 8: 208–251.

[:1-5] 1 2 Nyborg, Torrey; Lander, E. Bruce (2022-03-14), "Vertebrate paleontology and Cenozoic depositional environments of Death Valley National Park, California, USA", Field Excursions from Las Vegas, Nevada: Guides to the 2022 GSA Cordilleran and Rocky Mountain Joint Section Meeting, Geological Society of America, pp. 1–22, doi:10.1130/2022.0063(01), ISBN 978-0-8137-0063-2, retrieved 2026-08-02

[6] Prothero, Donald R.; Swisher III, Carl C. (1992), "2. Magnetostratigraphy and Geochronology of the Terrestrial Eocene-Oligocene Transition in North America", Eocene-Oligocene Climatic and Biotic Evolution, Princeton University Press, pp. 46–73, doi:10.1515/9781400862924.46, ISBN 978-1-4008-6292-4, retrieved 2026-08-29{{citation}}: CS1 maint: work parameter with ISBN (link)

[:18-7] 1 2 Wilson, John Andrew (1986-12-24). "Stratigraphic Occurrence and Correlation of Early Tertiary Vertebrate Faunas, Trans-Pecos Texas: Agua Fria–Green Valley Areas". Journal of Vertebrate Paleontology. 6 (4): 350–373. Bibcode:1986JVPal...6..350W. doi:10.1080/02724634.1986.10011630. ISSN 0272-4634. JSTOR 4523112.

[8] Macrini, Thomas E. (2009-12-12). "Description of a digital cranial endocast of Bathygenys reevesi (Merycoidodontidae; Oreodontoidea) and implications for apomorphy-based diagnosis of isolated, natural endocasts". Journal of Vertebrate Paleontology. 29 (4): 1199–1211. Bibcode:2009JVPal..29.1199M. doi:10.1671/039.029.0413. ISSN 0272-4634.

[:12-9] 1 2 3 4 5 Wilson, John A. (1971). "Early Tertiary Vertebrate Faunas, Vieja Group, Trans-Pecos Texas, Agriochoeridae and Merycoidodontidae". Bulletin of the Texas Memorial Museum, University of Texas at Austin. 18: 1–83.

[:11-10] 1 2 Wilson, J.A. (1974). "Early Tertiary vertebrate faunas, Vieja Group and Buck Hill Group, Trans-Pecos Texas: Protoceratidae, Camelidae, Hypertragulidae." Texas Memorial Museum Bulletin 23:1-34.

[:15-11] 1 2 3 4 5 6 7 8 9 10 E. P. Gustafson (1986). "Carnivorous mammals of the Late Eocene and Early Oligocene of Trans-Pecos Texas." Texas Memorial Museum Bulletin 33:1-66

[:16-12] 1 2 Hunt, Robert M. (1996-06-13), "Amphicyonidae", in Prothero, Donald R.; Emry, Robert J. (eds.), The Terrestrial Eocene-Oligocene Transition in North America (1 ed.), Cambridge University Press, pp. 476–485, doi:10.1017/cbo9780511665431.024, ISBN 978-0-521-43387-7, retrieved 2026-08-01

[:19-13] 1 2 3 4 5 6 7 8 Wilson, J.A.; Schiebout, J.A. (1984). "Early Tertiary Vertebrate Faunas, Trans-Pecos Texas: Ceratomorpha Less Amynodontidae." The Pearce-Sellards Series, Texas Memorial Museum 39:1-47.

[14] Wilson, J.A.; Schiebout, J.A. (1981). "Early Tertiary Vertebrate Faunas Trans-Pecos Texas: Amynodontidae." The Pearce-Sellards Series, Texas Memorial Museum 33:1-62.

[15] Forsten, A.; McGrew, P.O. (1971). "Early Tertiary Vertebrate Faunas, Vieja Group, Trans-Pecos Texas: Equidae." The Pearce-Sellards Series, Texas Memorial Museum 18:1-16.

[16] Prothero, Donald R. (2005). The evolution of North American rhinoceroses. Cambridge: Cambridge university press. ISBN 978-0-521-83240-3.

[17] Mihlbachler, Matthew; Prothero, Donald (2021). "Eocene (Duchesnean and earliest Chadronian) brontotheres (Brontotheriidae), Protitanops curryi and cf. Parvicornus occidentalis, from west Texas and Mexico". Palaeontologia Electronica. doi:10.26879/944.

[18] Schiebout, Judith A. (1977). "Schizotheroides (Mammalia: Perissodactyla) from the Oligocene of Trans-Pecos Texas". Journal of Paleontology. 51 (3): 455–458. ISSN 0022-3360. JSTOR 1303676.

[:17-19] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 A. E. Wood. (1974). "Early Tertiary vertebrate faunas, Vieja Group Trans-Pecos Texas: Rodentia". Texas Memorial Museum Bulletin 21:1-112