Paleobiota of the Morrison Formation

The distinctive banding of the Morrison Formation, a group of rock layers that occur throughout Dinosaur National Monument and the source of fossils like those found at the Dinosaur Quarry.

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]; the higher-level classifications will vary as new finds are made.

Amphibians

A modern frog from the same family as Rhadinosteus parvus, the rhinophrynidae.

According to museum curator John Foster, "frogs are known from several sites in the Morrison Formation but are not particularly well represented." 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 and Rhadinosteus parvus.

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. Stratigraphically speaking, indeterminate anurans have been found in stratigraphic zones 2 and 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. A specimen has been recovered from Quarry 9 of Como Bluff in Wyoming. Pelobatids are present in stratigraphic zones 5 and 6.

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

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

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

Arthropods

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

Name	Species	State	Member	Material	Notes
Eopolis	E. ekdalei	Utah	Brushy Basin	Nests produced by social insects.
Morrisonnepa	M. jurassica	Utah			A hemipteran belonging to the group Nepomorpha.
Parapleurites	P. morrisonensis	Colorado		a forewing.	a grasshopper.
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	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 Diplosaurus ferox, Amphicotylus, 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 taxa are in small text; crossed out taxa are discredited.

Name	Species	State	Member	Material	Notes	Images
Amphicotylus	A. gilmorei	Wyoming				Hallopus Hoplosuchus
	A. lucasii	Colorado
	A. stovalli	Oklahoma
Diplosaurus	D. felix	Colorado
Eutretauranosuchus	E. delfsi	Colorado Wyoming
Fruitachampsa	F. callisoni	Colorado	Brushy Basin Member Saltwash Member
Hallopus	H. victor	Colorado
Hatcherichnus	H. sanjuanensis	Colorado Utah
	Indeterminate	Utah Wyoming	Saltwash Member
Hoplosuchus	H. kayi	Arizona Utah
Macelognathus	M. vagans	Colorado Wyoming
Theriosuchus	T. morrisonensis	Wyoming		A nearly complete left mandible missing teeth.

Dinosaurs

Main article: Dinosaurs of the Morrison Formation

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. Although abundant, fish remains are constrained to only certain locations within the formation. Microvertebrate sites in Wyoming are dominated by fish remains. Indeterminate ray-finned fish remains have been recovered from Ninemile Hill and a microvertebrate site in the Black Hills. Found in stratigraphic zones 2, 4, and 5. Morrison actinopterygians generally have no close modern relatives. The Wyoming microvertebrate remains are extracted from the sediment by screenwashing. Paleoniscoid remains are geographically present in the western part of Colorado, where remains have been recovered from "a level above the Mygatt-Moore Quarry." Largely complete remains of small individuals have been consistently recovered for over 15 years. So far, Morrison pycnodontoids are represented by a single specimen from Dinosaur National Monument in Utah. Found in stratigraphic zone 4. Only a single specimen from Dinosaur National Monument in Utah has been recovered. 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. A single tooth is the only known remains. Dipnoan remains found at a fossil site not far from Cañon City, Colorado. Remains usually in a state of rather complete preservation. Halecostome remains are geographically present in the western part of Colorado, where remains have been recovered from "a level above the Mygatt-Moore Quarry." Largely complete remains of small individuals have been consistently recovered for over 15 years. Amiid remains found in stratigraphic zones 2, 3, and 4. Found at a fossil site not far from Cañon City, Colorado. Remains usually in a state of rather complete preservation.

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

Name	Species	State	Member	Material	Notes	Images
Ceratodus	C. fossanovum				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. These species are believed to have had similar diets to extant lungfish like the physically similar modern genus Neoceratodus.	Ceratodus. Leptolepis.
	C. ?frazieri
	C. guentheri
	C. robustus
	Indeterminate.		Brushy Basin Saltwash		Represented by tooth plates.
Hulettia	H. hawesi	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	N/A	Colorado		Known only from a single nearly complete skeleton found at Rabbit Valley. Found in stratigraphic zone 5.	A 13 cm (5 inch) fish that was deeper bodied than its co-occurring contemporaries Morrolepis and Hulettia. The Morrison cf. Leptolepis probably had a live mass of about 37g. It is the only teleost fish known from the formation and was morphologically more highly derived than other Morrison fish. It is believed to have fed on contemporary fish and small invertebrates.
Morrolepis	M. schaefferi	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. Adult specimens would reach about 20 cm in length and 113 g (4 oz) in mass.
Potamoceratodus	P. guentheri	Colorado			Once thought to be a species of Ceratodus.

Lizards and snakes

Name	Species	State	Member	Material	Notes
Diablophis	D. gilmorei	Colorado			A basal snake. Originally described as a species of Parviraptor, subsequently moved to its own genus.
Dorsetisaurus		Wyoming			An anguimorph lizard.
Paramacellodus		Colorado Wyoming			A small scincomorph lizard with blunt teeth.
Saurillodon	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.
Schillerosaurus	S. utahensis	Utah			A small scincomorph lizard of otherwise uncertain evolutionary affinities. It is the only lizard genus endemic to the Morrison Formation.

Mammaliaforms

Many types of mammaliaform cynodonts, mostly early mammals, are known from the Morrison; almost all of them were small sized animals, though occupying a very large variety of ecological niches, from the more rodent-like multituberculates to the carnivorous eutriconodonts (including the possibly volant Triconolestes) to the anteater-like Fruitafossor. 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, Glirodon grandis, Morrisonodon brentbaatar, Psalodon fortis, ?P. marshi, P. potens, and Zofiabaatar pulcher. Triconodonts present included Amphidon superstes, Aploconodon comoensis, Conodon gidleyi, Priacodon ferox, P. fruitaensis, P. gradaevus, P. lulli, P. robustus, Triconolestes curvicuspis, and Trioracodon bisulcus.

Tinodontids were represented by Eurylambia aequicrurius (probably Tinodon), and Tinodon bellus (including T. lepidus). Finally, two families of Dryolestoidea were present: Paurodontidae, including Comotherium richi, Euthlastus cordiformis, Paurodon valens, 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 mammaliaform 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.

Tinodontids

Name	Species	State	Member	Material	Notes
Eurylambia	E. aequicrurius	Wyoming			A tinodontid similar in appearance to Tinodon.
Tinodon	T. bellus	Wyoming			Tinodontids.
	T. lepidus	Wyoming

Eutriconodonts

Name	Species	State	Member	Material	Notes
Amphidon	A. superstes	Wyoming			A small amphidontid.
Aploconodon	A. comoensis	Wyoming			An amphilestid eutriconodont.
Comodon	C. gidleyi	Wyoming			An amphilestid eutriconodont slightly larger in size than Aploconodon.
Phascalodon	P. gidleyi	Wyoming
Triconolestes	T. curvicuspis	Utah			A volaticotherian eutriconodont.
Trioracodon	T. bisulcus	Wyoming			A triconodontid eutriconodont similar to Priacodon.

Multituberculates

Name	Species	State	Member	Material	Notes
Ctenacodon	C. laticeps	Wyoming
	C. scindens
	C. serratus	Wyoming
Glirodon	G. grandis	Colorado Utah
Morrisonodon	M. brentbaatar	Wyoming
Priacodon	P. ferox	Wyoming
	P. fruitaensis	Colorado
	P. grandaevus	Wyoming
	P. lulli	Wyoming
	P. robustus	Wyoming
Psalodon	P. fortis
	P. marshi
	P. potens
Zofiabaatar	Z. pulcher	Wyoming

Others

Name	Species	State	Member	Material	Notes
Docodon	D. victor
Fruitafossor	F. windscheffeli	Colorado			Fruitafossor

Dryolestoids

Name	Species	State	Member	Material	Notes
Amblotherium	A. gracilis	Colorado			A small Dryolestid dryolestoid.
	A. megistodon	Wyoming
Araeodon	A. intermissus	Utah Wyoming			A paurodontid dryolestoid, somewhat smaller than Archaeotrigon and Paurodon. Considered to be a junior synonym of Paurodon valens by Averianov and Martin (2015).
Archaeotrigon	A. brevimaxillus	Wyoming			Paurodontid dryolestoids similar in appearance to Paurodon. Both species were considered to be junior synonyms of Paurodon valens by Averianov and Martin (2015).
	A. distagmus
Comotherium	C. richi	Wyoming			A paurodontid dryolestoid.
Dryolestes	D. obtusus				Dryolestid dryolestoids.
	D. priscus	Wyoming
	D. tenax
Euthlastus	E. cordiformis	Wyoming			A paurodontid dryolestoid.
Foxraptor	F. atrox	Wyoming			A paurodontid dryolestoid similar in size to Paurodon. Considered to be a junior synonym of Paurodon valens by Averianov and Martin (2015).
Herpetairus	H.
Kepolestes	K.	Colorado
Laolestes	L. eminens				Common Dryolestid dryolestoids.
	L. grandis
Malthacolestes	M.
Melanodon	M.
Miccylotyrans	M. minimus	Morrison			A Dryolestid dryolestoid.
Paurodon	P. valens	Wyoming			A paurodontid dryolestoid.
Pelicopsis	P. dubius	Wyoming			A paurodontid dryolestoid. Considered to be a junior synonym of Paurodon valens by Averianov and Martin (2015).
Tathiodon	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. Despite being uncommon they are geographically widespread; indeterminate pterosaur remains have been found in stratigraphic zones 2 and 4-6. In addition to indeterminate remains, several species have been identified from both the rhamphorhynchoids (long-tailed pterosaurs) and pterodactyloids (short-tailed pterosaurs). Since the 1970s and 80s, pterosaur finds have become more common, but are still rare. Most Morrison pterosaurs have been found in marine and shoreline deposits. Pterosaur tracks have been found in both the Tidwell and Saltwash members. Morrison pterosaurs probably lived on fish, insects and scavenged dinosaur carcasses, or even foraged for prey, and activally hunted; they are fairly ecologically diverse, ranging from small hawking insectivore Mesadactylus to the raptorial Harpactognathus.

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

Name	Species	State	Member	Material	Notes
Comodactylus	C. ostromi	Wyoming	Brushy Basin	1 specimen.	Nomen dubium
Dermodactylus	D. montanus	Wyoming	Brushy Basin	1 specimen.	Nomen dubium
Harpactognathus	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). Harpactognathus was related to the Solnhofen genus Scaphognathus.
Kepodactylus	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). Kepodactylus may be related to the Asian dsungaripteroid pterosaurs.
Laopteryx	L. priscus	Wyoming	Brushy Basin	1 specimen.	Nomen dubium initially misidentified as a bird.
Mesadactylus	M. ornithosphyos	Colorado	Brushy Basin
Pteraichnus	P. saltwashensis'*	Arizona Oklahoma	Saltwash
Utahdactylus	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	E. robustus	Colorado			A sphenodontian of relatively large size.
Opisthias	O. rarus	Colorado Utah Wyoming			A sphenodontian similar in appearance to the modern Tuatara
Theretairus	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 taxa are in small text; crossed out taxa are discredited.

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

Insects

Insects are very rare in the Morrison Formation and only two have been described to date.

Name	Species	State	Member	Material	Notes
Morrisonnepa	M. jurassica	Utah			A nepomorphan of uncertain placement
Parapleurites	P. morrisonensis	Colorado			A Locustopsid orthopteran

See also

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

Footnotes

Bibliography

• 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