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]
Portland Formation | |
---|---|
Stratigraphic range: Hettangian-Sinemurian ~ | |
Type | Geological formation |
Unit of | Agawam Group, Newark Supergroup |
Sub-units | Turners Falls Sandstone & Mount Toby Formation |
Overlies | East Berlin Formation |
Lithology | |
Primary | Sandstone |
Other | Mudstone, siltstone, limestone |
Location | |
Coordinates | 42.3°N 72.5°W |
Approximate paleocoordinates | 24.0°N 18.6°W |
Region | Connecticut, Massachusetts |
Country | USA |
Extent | Deerfield & Hartford Basins |
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]
Vertebrate paleofauna
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] | 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[13] | R. gracilis | The last surviving redfieldiiform fish. | ||||
Semionotus[13] | S. sp. | A semionotid fish. |
Invertebrate paleofauna
Insects | ||||||
---|---|---|---|---|---|---|
Genus | Species | Location | Stratigraphic position | Material | Notes | Images |
Holcoptera | H. schlotheimi[14] | A coptoclavid beetle. | ||||
H. giebeli[15] | ||||||
Orthoptera sp.[15] | An indeterminate orthopteran. | |||||
Blattaria sp.[15] | An indeterminate cockroach. |
See also
References
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