The Portland Formation is a geological formation in Connecticut and Massachusetts in the northeastern United States. It dates back to the Early Jurassic period. The formation consists mainly of sandstone laid down by a series of lakes (in the older half of the formation) and the floodplain of a river (in the younger half). The sedimentary rock layers representing the entire Portland Formation are over 4 kilometres (2.5 mi) thick and were formed over about 4 million years of time, from the Hettangian age (lower half) to the late Hettangian and Sinemurian ages (upper half).

In 2016, the paleontologist Robert E. Weems and colleagues suggested the Portland Formation should be elevated to a geological group within the Newark Supergroup (as the Portland Group), and thereby replacing the former name "Agawam Group". They also reinstated the Longmeadow Sandstone as a formation (within the uppermost Portland Group); it had earlier been considered identical to the Portland Formation.

Dinosaur coprolites are known from the formation. This formation and the underlying East Berlin Formation are well-known for its numerous well-preserved dinosaur tracks, which represent ornithischians, theropods, and sauropodomorphs, which are preserved at sites such as Dinosaur Footprints Reservation. Other tracks are also known representing animals such as pseudosuchians, turtles, and temnospondyls.

Dinosaurs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Anchisaurus	A. polyzelus	Connecticut Massachusetts		Several specimens.	A relatively small basal Sauropodomorph. Many Otozoum tracks in the formation that may belong to Anchisaurus could have been made by potentially even larger specimens of the genus.
Podokesaurus	P. holyokensis	Massachusetts		Partial postcranial skeleton.	A coelophysoid theropod. The only specimen was destroyed in a fire.
Neotheropoda sp.		Massachusetts		Partial humerus.	Estimated to have been 9 meters long, and possibly a semiaquatic piscivore.
Theropoda sp.		Connecticut		Bones and tracks attributed to "Anchisauripus"

Non-dinosaur archosaurs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Stegomosuchus	S. longipes	Hine's Quarry, Longmeadow		Partial postcranial skeleton.	Originally Stegomus. A small armored "protosuchian" crocodyliform.
Pterosauria sp.		South Hadley, Massachusetts		Partial Wrist and tooth.	Non-pterodactyloid pterosaur estimated to have a wingspan of 40 cm.

Fish
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Acentrophorus	A. chicopensis				Material initially referred to the genus Acentrophorus. Most researchers consider the species distinct from Acentrophorus.
Redfieldius	R. gracilis				The last surviving redfieldiiform fish.
Semionotus	S. sp.				A semionotid fish.

Insects
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Holcoptera	H. schlotheimi				A coptoclavid beetle.
	H. giebeli
Orthoptera sp.					An indeterminate orthopteran.
Blattaria sp.					An indeterminate cockroach.

• List of dinosaur-bearing rock formations

• Weishampel, David B.; Dodson, Peter; Osmólska, Halszka, eds. (2004). The Dinosauria, 2nd edition. Berkeley: University of California Press. ISBN 0-520-24209-2. Retrieved 2019-02-21.