The Portland Formation is a geological formation in Connecticut and Massachusetts in the northeastern United States.^[1] It dates back to the Early Jurassic period.^[2] 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).^[3]

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.^[4]

Dinosaur coprolites are known from the formation.^[2] 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.^[2][5] Other tracks are also known representing animals such as pseudosuchians, turtles, and temnospondyls.^[6]

Dinosaurs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Anchisaurus[2]	A. polyzelus[2]	Connecticut[2] Massachusetts[2]		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.[7]
Podokesaurus[2]	P. holyokensis	Massachusetts		Partial postcranial skeleton.[8]	A coelophysoid theropod. The only specimen was destroyed in a fire.
Neotheropoda sp.[9]		Massachusetts		Partial humerus.	Estimated to have been 9 meters long, and possibly a semiaquatic piscivore.
Theropoda sp.[10]		Connecticut		Bones and tracks attributed to "Anchisauripus"

Non-dinosaur archosaurs
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Stegomosuchus[11]	S. longipes	Hine's Quarry, Longmeadow		Partial postcranial skeleton.	Originally Stegomus. A small armored "protosuchian" crocodyliform.
Pterosauria sp.[12]		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[13]	A. chicopensis				Material initially referred to the genus Acentrophorus. Most researchers consider the species distinct from Acentrophorus.
Redfieldius[14]	R. gracilis				The last surviving redfieldiiform fish.
Semionotus[14]	S. sp.				A semionotid fish.

Insects
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Holcoptera	H. schlotheimi[15]				A coptoclavid beetle.
	H. giebeli[16]
Orthoptera sp.[16]					An indeterminate orthopteran.
Blattaria sp.[16]					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.