Paleobiota of the Morrison Formation

The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has a wide assortment of taxa represented in its fossil record, including dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish gray, or red. Most of the fossils occur in the green siltstone beds and lower sandstones, relics of the rivers and floodplains of the Jurassic period.

(mostly from Foster [2003], with additional material in the mammal section after [1]; the higher-level classifications will vary as new finds are made.

Contents 1 Amphibians 2 Arthropods 3 Choristoderes 4 Crurotarsans 5 Dinosaurs 6 Fish 7 Lizards 8 Mammals 8.1 Symmetrodonts 8.2 Eutriconodonts 8.3 Multituberculates 8.4 Others 8.5 Dryolestoids 9 Pterosaurs 10 Sphenodonts 11 Turtles 12 See also 13 Footnotes 14 References

Amphibians

According to museum curator John Foster, "frogs are known from several sites in the Morrison Formation but are not particularly well represented."^[1] The history of Morrison anuran discoveries began with the recovery of remains from Reed's Quarry 9 near Como Bluff Wyoming. The new genus Eobatrachus was erected for some of these remains by O. C. Marsh, but the material was later considered non-diagnostic. Decades later another dubious anuran genus, Comobatrachus was erected for addition fragmentary remains. Despite the erection of multiple new names, scientists only recognize two legitimate frog species from the Morrison, Enneabatrachus hechti^[2] and Rhadinosteus parvus.^[3]

In addition to formally named taxa, indeterminate anuran remains have been retrieved from Morrison strata in Colorado, Wyoming, and Utah, with the best specimens found in Dinosaur National Monument and Quarry 9.^[1] Stratigraphically speaking, indeterminate anurans have been found in stratigraphic zones 2 and 4.^[4] Indeterminate anurans with remains diagnostic down to the family level have also been reported from the Morrison. Pelobatids are represented by the illium of an unnamed, indeterminate species.^[5] A specimen has been recovered from Quarry 9 of Como Bluff in Wyoming.^[5] Pelobatids are present in stratigraphic zones 5 and 6.^[4]

Indeterminate salamander remains are present in stratigraphic zones 2, 4, and 5.^[4] A distinctive type of salamander known only as Caudata B is present in stratigraphic zone 6.^[4]

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Name	Species	State	Member	Material	Notes
Comobatrachus[1]	C. aenigmaticus	Wyoming[1]			A dubious genus of prehistoric frog erected by O. C. Marsh to house fragmentary remains recovered from Reed's Quarry 9 near Como Bluff Wyoming.[1] Along with Eobatrachus it was among the earliest frog remains from the formation, although the two dubious genera were erected decades apart.[1]
Comonecturoides[6]	C. marshi[6]	Wyoming[6]		Represented by a single femur.[6]	Considered a nomen dubium because the name is based on non-distinctive remains which cannot be classified in detail.[6]
Enneabatrachus[7]	E. hechti[2]	Utah[8] Wyoming[2]			A small discoglossid frog whose live weight would have only been a few grams.[2]
Eobatrachus[1]	E. agilis	Wyoming[1]			A dubious genus of prehistoric frog erected by O. C. Marsh to house fragmentary remains recovered from Reed's Quarry 9 near Como Bluff Wyoming.[1] Along with Comobatrachus it was among the earliest frog remains from the formation, although the two dubious genera were erected decades apart.[1]
Iridotriton[7]	I. hechti				A basal salamandroid closely related to today's advanced salamanders.
Rhadinosteus[7]	R. parvus[3]	Utah		Known from several slabs of rock which contain multiple partial specimens in association.[3]	A pipoid and possible rhinophrynid, Rhadinosteus parvus was only about 42 mm (1.6 inches) long in life.[3]

Arthropods

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Name	Species	State	Member	Material	Notes
Tektonargus	T. kollaspilus	Colorado	Brushy Basin	Five specimens were reported in the original description of the ichnogenus.

Choristoderes

Name	Species	State	Member	Material	Notes
Cteniogenys[7]	C. antiquus	Colorado Oklahoma South Dakota Utah Wyoming			A champsosaur about 25 to 50 cm in length.

Crurotarsans

Crocodiles of a variety of sizes and habitats were common Morrison animals. Cursorial mesosuchians, or small terrestrial running crocs, included Hallopus victor and "Fruitachampsa callisoni". More derived crocodilians included Goniopholis felix (common), G. gilmorei, G. lucasi, G. stovalli, Hoplosuchus kayi, and Macelognathus vagans.

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Name	Species	State	Member	Material	Notes	Images
Eutretauranosuchus[7]	E. delfsi	Colorado Wyoming
"Fruitachampsa"[7]	"F. callisoni"	Colorado	Brushy Basin Member Saltwash Member
Goniopholis[7]	G. felix	Colorado
	G. gilmorei	Wyoming
	G. lucasii	Colorado
	G. stovalli	Oklahoma
Hallopus[7]	H. victor	Colorado
Hatcherichnus	H. sanjuanensis	Colorado Utah
	Indeterminate	Utah Wyoming	Saltwash Member
Hoplosuchus[7]	H. kayi	Arizona Utah
Macelognathus[7]	M. vagans	Colorado Wyoming

Dinosaurs

Fish

Although the paleoclimate of the Morrison formation was semiarid with only seasonal rainfall, there were enough bodies of water to support a diverse ichthyofauna.^[9] Although abundant, fish remains are constrained to only certain locations within the formation.^[9] Microvertebrate sites in Wyoming are dominated by fish remains.^[9] Indeterminate ray-finned fish remains have been recovered from Ninemile Hill and a microvertebrate site in the Black Hills.^[9] Found in stratigraphic zones 2, 4, and 5.^[4] Morrison actinopterygians generally have no close modern relatives.^[9] The Wyoming microvertebrate remains are extracted from the sediment by screenwashing.^[9] Paleoniscoid remains are geographically present in the western part of Colorado, where remains have been recovered from "a level above the Mygatt-Moore Quarry."^[9] Largely complete remains of small individuals have been consistently recovered for over 15 years.^[9] So far, Morrison pycnodontoids are represented by a single specimen from Dinosaur National Monument in Utah.^[10] Found in stratigraphic zone 4.^[4] Only a single specimen from Dinosaur National Monument in Utah has been recovered.^[10] Pycnodontoids were "deep-bodied and laterally compressed fish" whose tooth morphology suggest that they preyed on small contemporary invertebrates. They may have resembled modern butterfly fish.^[10] A single tooth is the only known remains.^[10] Dipnoan remains found at a fossil site not far from Cañon City, Colorado.^[9] Remains usually in a state of rather complete preservation.^[9] Halecostome remains are geographically present in the western part of Colorado, where remains have been recovered from "a level above the Mygatt-Moore Quarry."^[9] Largely complete remains of small individuals have been consistently recovered for over 15 years.^[9] Amiid remains found in stratigraphic zones 2, 3, and 4.^[4] Found at a fossil site not far from Cañon City, Colorado.^[9] Remains usually in a state of rather complete preservation.^[9]

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Name	Species	State	Member	Material	Notes	Images
Ceratodus[7]	C. fossanovum[9]				A lungfish genus whose members ranged from 1 to 2 m in length and weights of up to 79 pounds, with most Morrison lungfish being on the smaller end of that range.[9] These species are believed to have had similar diets to extant lungfish like the physically similar modern genus Neoceratodus.[9]
	C. ?frazieri[9]
	C. guentheri[9]
	C. robustus[9]
	Indeterminate.		Brushy Basin Saltwash		Represented by tooth plates.
Hulettia[7]	H. hawesi[11]	Colorado			A small fish of the division Halecostomi about 7.6 cm in length and 5g of live mass which probably preferred quiet water. Its fossils prominently preserve its thick interlocking scales.
cf. Leptolepis[7]	N/A	Colorado[11]		Known only from a single nearly complete skeleton found at Rabbit Valley.[11] Found in stratigraphic zone 5.[4]	A 13 cm (5 inch) fish that was deeper bodied than its co-occurring contemporaries Morrolepis and Hulettia.[11] The Morrison cf. Leptolepis probably had a live mass of about 37g.[11] It is the only teleost fish known from the formation and was morphologically more highly derived than other Morrison fish.[11] It is believed to have fed on contemporary fish and small invertebrates.[11]
Morrolepis[7]	M. schaefferi[12]	Colorado			A palaeoniscoid with forward-set eyes positioned past the front end of the lower jaw. It had a tall dorsal fin set far back on the body and an asymmetrical caudal fin.[12] Adult specimens would reach about 20 cm in length and 113 g (4 oz) in mass.[12]
Potamoceratodus	P. guentheri	Colorado			Once thought to be a species of Ceratodus.

Lizards

Name	Species	State	Member	Material	Notes
Dorsetisaurus[7]		Wyoming			An anguimorph lizard.
Paramacellodus[7]		Colorado Wyoming			A small scincomorph lizard with blunt teeth.
Parviraptor[7]	P. gilmorei	Colorado			An anguimorph lizard.
Saurillodon[7]	Indeterminate	Colorado			A scincomorph lizard whose remains have been found in Middle Jurassic strata in England and Scotland as well as Late Jurassic strata in Portugal in addition to the Morrison formation remains.[13]
Schilleria[7]	S. utahensis[14]	Utah			A small scincomorph lizard of otherwise uncertain evolutionary affinities.[14] It is the only lizard genus endemic to the Morrison Formation.[14]

Mammals

Many types of early mammals are known from the Morrison; almost all of them were small, rodent-like animals. Unclassified types include the digger Fruitafossor windscheffelia. Docodonts included the common genus Docodon, represented by D. victor, D. striatus, and D. superbus, and Peraiocynodon sp. Multituberculates, a common type of early mammal, were represented by Ctenacodon serratus, C. laticeps, C. scindens, "C." brentbaatar, Glirodon grandis, Psalodon fortis, ?P. marshi, P. potens, and Zofiabaatar pulcher. Triconodonts present included Aploconodon comoensis, Conodon gidleyi (AKA Phascolodon and Phascolotheridium), Priacodon ferox, P. fruitaensis, P. gradaevus, P. lulli, P. robustus, Triconolestes curvicuspis, and Trioracodon bisulcus.

Symmetrodonts were represented by Amphidon superstes, Eurylambda aequicrurius (probably Tinodon), and Tinodon bellus (including T. lepidus). Finally, two families of Dryolestoidea were present: Paurodontidae, including Araeodon intermissus, Archaeotrigon brevimaxillus, A. distgamus, Comotherium richi, Euthlastus cordiformis, Foxraptor atrox, Paurodon valens, Pelicopsis dubius, and Tathiodon agilis; and Dryolestidae, including Amblotherium gracilis, Dryolestes obtusus (common genus), D. priscus, D. vorax, Laolestes eminens, L. grandis, and Miccylotyrans minimus.

In 2009, a study by J. R. Foster was published which estimated the body masses of mammals from the Morrison Formation by using the ratio of dentary length to body mass of modern marsupials as a reference. Foster concludes that Docodon was the most massive mammal genus of the formation at 141g and Fruitafossor was the least massive at 6g. The average Morrison mammal had a mass of 48.5g. A graph of the body mass distribution of Morrison mammal genera produced a right-skewed curve, meaning that there were more low-mass genera.^[15]

Symmetrodonts

Name	Species	State	Member	Material	Notes
Amphidon[7]	A. superstes	Wyoming			A small symmetrodont.
Eurylambda	E. aequicrurius	Wyoming			A symmetrodont similar in appearance to Tinodon.
Tinodon[7]	T. bellus	Wyoming			Symmetrodonts.
	T. lepidus	Wyoming

Eutriconodonts

Name	Species	State	Member	Material	Notes
Aploconodon[7]	A. comoensis	Wyoming			An amphilestid eutriconodont.
Comodon[7]	C. gidleyi	Wyoming			An amphilestid eutriconodont slightly larger in size than Aploconodon.
Phascalodon	P. gidleyi	Wyoming
Triconolestes[7]	T. curvicuspis	Utah			An amphilestid eutriconodont similar to Comodon in appearance.
Trioracodon[7]	T. bisulcus	Wyoming			A triconodontid eutriconodont similar to Priacodon.

Multituberculates

Name	Species	State	Member	Material	Notes
Allodon	A. fortis
Ctenacodon[7]	"C." brentbaatar	Wyoming
	C. laticeps	Wyoming
	C. nanus
	C. potens
	C. scindens
	C. serratus	Wyoming
Glirodon[7]	G. grandis	Colorado Utah
Priacodon[7]	P. ferox	Wyoming
	P. fruitaensis	Colorado
	P. gradaevus	Wyoming
	P. lulli	Wyoming
	P. robustus	Wyoming
Psalodon[7]	P. fortis
	?P. marshi
	P. potens
Zofiabaatar[7]	Z. pulcher	Wyoming

Others

Name	Species	State	Member	Material	Notes	Images
Docodon[7]	D. affinis
	D. crassus
	D. striatus
	D. superus
	D. victor
Fruitafossor[7]	F. windscheffeli	Colorado

Dryolestoids

Name	Species	State	Member	Material	Notes
Amblotherium[7]	A. gracilis	Colorado			A small Dryolestid dryolestoid.
Araeodon[7]	A. intermissus	Utah Wyoming			A paurodontid dryolestoid, somewhat smaller than Archaeotrigon and Paurodon.
Archaeotrigon[7]	A. brevimaxillus	Wyoming			Paurodontid dryolestoids similar in appearance to Paurodon.
	A. distagmus
Comotherium[7]	C. richi	Wyoming			A paurodontid dryolestoid.
Dryolestes[7]	D. obtusus				Dryolestid dryolestoids.
	D. priscus	Wyoming
	D. tenax
Euthlastus[7]	E. cordiformis	Wyoming			A paurodontid dryolestoid.
Foxraptor[7]	F. atrox	Wyoming			A paurodontid dryolestoid similar in size to Paurodon.
Herpetairus	H.
Kepolestes	K.	Colorado
Laolestes[7]	L. eminens				Common Dryolestid dryolestoids.
	L. grandis
Malthacolestes	M.
Melanodon	M.
Miccylotyrans	M. minimus	Morrison			A Dryolestid dryolestoid.
Paurodon[7]	P. valens	Wyoming			A paurodontid dryolestoid.
Pelicopsis	P. dubius	Wyoming			A paurodontid dryolestoid.
Tathiodon[7]	T. agilis	Wyoming			A paurodontid dryolestoid.

Pterosaurs

Pterosaurs are very uncommon fossils in the Morrison, because the fragility of their thin walled bones often prevented their remains from being preserved.^[16] Despite being uncommon they are geographically widespread;^[17] indeterminate pterosaur remains have been found in stratigraphic zones 2 and 4-6.^[4] In addition to indeterminate remains, several species have been identified from both the rhamphorhynchoids (long-tailed pterosaurs) and pterodactyloids (short-tailed pterosaurs).^[16] Since the 1970s and 80s, pterosaur finds have become more common, but are still rare.^[16] Most Morrison pterosaurs have been found in marine and shoreline deposits.^[16] Pterosaur tracks have been found in both the Tidwell and Saltwash members.^[16] Morrison pterosaurs probably lived on fish, insects and scavenged dinosaur carcasses.^[16]

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Name	Species	State	Member	Material	Notes
Comodactylus[7]	C. ostromi	Wyoming	Brushy Basin	1 specimen.	Nomen dubium
Dermodactylus[7]	D. montanus	Wyoming	Brushy Basin	1 specimen.	Nomen dubium
Harpactognathus[7]	H. gentryii	Wyoming	Brushy Basin	1 specimen.	A large rhamphorhynchoid with a wingspan of about 2.5 m and live mass of about 1.5 kg (3.3 lbs).[18] Harpactognathus was related to the Solnhofen genus Scaphognathus.[18]
Kepodactylus[7]	K. insperatus	Colorado	Brushy Basin	1 specimen.	A large pterodactyloid with a 2.5 m (8 foot) wingspan and a live weight of about 1.5 kg (3 lbs).[19] Kepodactylus may be related to the Asian dsungaripteroid pterosaurs.[19]
Laopteryx[17]	L. priscus	Wyoming	Brushy Basin	1 specimen.	Nomen dubium initially misidentified as a bird.
Mesadactylus[7]	M. ornithosphyos	Colorado	Brushy Basin
Pteraichnus[20]	P. saltwashensis'*	Arizona Oklahoma	Saltwash
Utahdactylus[7]	U. kateae	Utah	Tidwell	1 specimen.	Nomen dubium. All that can be said for certain about its identity is that it is a diapsid reptile.

Sphenodonts

Name	Species	State	Member	Material	Notes
Eilenodon[7]	E. robustus	Colorado			A sphenodontian of relatively large size.
Opisthias[7]	O. rarus	Colorado Utah Wyoming			A sphenodontian similar in appearance to the modern Tuatara
Theretairus[7]	T. antiquus	Wyoming			A small sphenodontian.

Turtles

Turtles (Testudines) are very common fossils in the Morrison, due to their bony shells. The most common were Glyptops plicatus (very common) and Dinochelys whitei (also common, but not as common as Glyptops). Also present were Dorsetochelys buzzops and Uluops uluops.

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Name	Species	State	Member	Material	Notes
Chelonipus		Colorado Utah	Saltwash Member
Compsemys	C. plicatulus	Colorado
Dinochelys[7]	D. whitei	Colorado Utah Wyoming
Dorsetochelys[7]	D. buzzops
Glyptops[7]	G. plicatulus	Colorado Wyoming
	G. ornatus	Wyoming
	G. utahensis	Utah
Uluops[7]	U. uluops	Wyoming

See also

• List of dinosaur-bearing rock formations
• Molluscs
• Synthesis
• lacustrine carbonates

Footnotes

References

• Foster, J. (2007). Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. 389pp. ISBN 978-0-253-34870-8.
• Lockley, M.; Harris, J.D.; and Mitchell, L. 2008. "A global overview of pterosaur ichnology: tracksite distribution in space and time." Zitteliana. B28. p. 187-198. ISSN 1612 - 4138.