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. found in stratigraphic zone 4. Found at a fossil site not far from
Cañon City, Colorado. The history of Morrison anuran discoveries began with the recovery of remains from 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 based on additional fragmentary remains. Despite the erection of multiple new names, only two frog species are currently recognised from the Morrison:
Enneabatrachus hechti Pelobatids are present in stratigraphic zones 5 and 6.
but subsequently moved to the new genus Diablophis'' by Michael Caldwell et al. in 2015, with extra material also being reported from Utah's Cisco Mammal Quarry, and
Schillerosaurus, originally described as "Schilleria" and reported from Dinosaur National Monument by Evans and Dan Chure in 1999. It is thought that their counterparts from the Morrison Formation would have occupied a similar
niche due to their morphological similarities. Anguimorph lizards most likely hunted small vertebrates, and
Diablophis is thought to have done so too. Prey items would have included the other squamates from the formation as well as its large diversity of small
mammals. All squamates might have been prey for the larger predators of the Morrison Formation, including the abundant theropod dinosaurs and crocodilians.
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.
Choristoderes 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.
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.
Dinosaurs 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,
Comodon 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 Eutriconodonts Multituberculates Others Dryolestoids ==See also==