Snow Hill Island Formation

The Snow Hill Island Formation is an Early Maastrichtian geologic formation found on James Ross Island, James Ross Island group, Antarctica.^[1] Remains of a paravian theropod Imperobator antarcticus^[2] have been recovered from it, as well as the elasmarian ornithopods Trinisaura santamartaensis, "Biscoveosaurus" and Morrosaurus antarcticus, the ankylosaurian Antarctopelta oliveroi, and the shark Notidanodon sp. Alongside these described genera are also the remains of indeterminate elasmosaurids,^[3] lithostrotian titanosaurs and an indeterminate pterosaur.^[4]

Snow Hill Island Formation
Stratigraphic range: Late Campanian-Early Maastrichtian 71.2–70.8 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Artist's reconstruction of the paleoenvironment of the Snow Hill Island Formation.
Type	Geological formation
Unit of	Marambio Group
Sub-units	Gamma & Herbert Sound Members
Underlies	Lopez de Bertodano Formation
Overlies	Santa Marta Formation
Lithology
Primary	Sandstone
Other	Mudstone
Location
Coordinates	63.9°S 57.9°W / -63.9; -57.9
Approximate paleocoordinates	61.8°S 68.5°W / -61.8; -68.5
Region	James Ross Island, James Ross Island group
Country	Argentine Antarctica, British Antarctic Territory, Chilean Antarctic Territory
Geologic map of Seymour Island, Antarctica with Snow Hill Island Formation in dark green

In the Herbert Sound Member of the Snow Hill Island Formation, bivalves, ammonites, and fish were found.^[5]

Fossil content

Invertebrates

Corals

Genus	Species	Presence	Material	Notes	Images
Fungiacyathus	F. deltoidophorus	Karlsen Cliffs Member.[6]	Imprints	A Scleractinian Coral	Specimen of the same genus
Scleractinia	Unidentifiable	Karlsen Cliffs Member.[6]	Imprints

Arthropoda

Genus	Species	Presence	Material	Notes	Images
Angarestia	A. australensis	East side of Leal Bluff	Specimens[7]	A Glypheidae lobster
Cristafrons	C. praescientis	East side of Leal Bluff	Specimens[7]	A Raninidae crab
Hadrocarcinus	H. wrighti	East side of Leal Bluff	Specimens[7]	A Necrocarcinidae crab
Hoploparia	H. stokesi	East side of Leal Bluff; Humps Island	Specimens[7]	A Clawed lobster

Mollusks

Genus	Species	Presence	Material	Notes	Images
Cymatoceras	C. spp.	Santa Marta Cove	Shells[8]	A Nautilid
Diplomoceras	D. cylindraceum	Day Nunatak	Shells[8]	A Diplomoceratidae Ammonite	Reconstruction
	D. lambi	Day Nunatak; Cape Lamb	Shells[8]
Eutrephoceras	E. spp.	Day Nunatak	Shells[8]	A Nautilid
Gunnarites	G. antarcticus	Vega Island; Day Nunatak; Santa Marta Cove	Shells[4][9][8]	A Kossmaticeratidae Ammonite
Jacobites	J. crofti	Day Nunatak	Shells[8]	A Kossmaticeratidae Ammonite
Maorites	M. seymourianus	Day Nunatak; Al's Bird Site; Vega Island	Shells[8]	A Kossmaticeratidae Ammonite
Oistotrigonia	O. pygoscelium	Day Nunatak	Shells[8]	A Pterotrigoniidae bivalve
Pinna	P. frenexiae	Day Nunatak	Shells[8]	A Pinnidae bivalve	Extant specimen
	P. anderssoni	Day Nunatak	Shells[8]
Pseudophyllites	P. loryi	Day Nunatak	Shells[8]	A Tetragonitidae Ammonite
Struthiochenopus	S. hurleyi	Day Nunatak	Shells[8]	An Aporrhaidae gastropod

Vertebrates

Fish

Genus	Species	Presence	Material	Notes	Images
Albuliformes	Indeterminate	Santa Marta Cove	Isolated vertebra, IAA-IRJ2000-24[10]
Antarctichthys	A. longipectoralis	Santa Marta Cove	MN 7838-V, single and incomplete specimen[11]	A Dercetidae fish
Apateodus	cf. A. sp.	Santa Marta Cove	teeth[10]	Alepisauriformes fish
Callorhinchus	C. sp.	Santa Marta Cove	teeth[4][12]	A Chimaera
	Cf. C. sp.	Cape Lamb	teeth[4][12]
Centrophoroides	C. sp.	Santa Marta Cove	Teeth[4][12]	A Squalidae shark
Chimaera	C. zangerli	Santa Marta Cove, James Ross Island.	Teeth[4]	A chimaera.	Extant member of the genus
Chlamydoselachus	C. thompsoni	Santa Marta Cove, James Ross Island.	Complete dentition.[10]	A frilled shark.	Extant member of the genus
Cretalamna	C. appendiculatta	Santa Marta Cove	Teeth.[12]	An Otodontidae shark
Edaphodon	E. snowhillensis	Herbert Sound Member.[13]	MLP 13- I-26-1, Complete dentition.[13]	A large species of chimaera.
Enchodus	E. sp.	Santa Marta Cove	IAA-IRJ2000-32, IAA-IRJ2000-33, teeth[10]	Enchodontidae fish	Restoration
Ichthyodectiformes	Indeterminate	Vega island	MLP 15-XI-7-11, body scale patch[4]
Lamniformes	Indeterminate	Santa Marta Cove	(IAA-IRJ2000-9 to IAA-IRJ2000-10, BAS DJ.172.11, teeth[10]
Notidanodon	N. dentatus	Santa Marta Cove; Vega Island	(MLP 95-IV-1), lateral tooth embedded in the hosting rock[4]	A cow shark.
	N. sp.	Santa Marta Cove[14]
Paraorthacodus	P. antarcticus	Santa Marta Cove	IAA-IRJ2000-19; BAS DJ.136.2, teeth[10]	A Synechodontiform
Rhinochimaeridae	Indeterminate	Santa Marta Cove	teeth[12]
Scapanorhynchus	S. spp.	Santa Marta Cove	IAA-IRJ2000-11[10]	A Mitsukurinidae shark	Reconstruction
	Cf. S. sp.	Santa Marta Cove	teeth[4]
Sphenocephalidae	Indeterminate	False Island Point	DJ. 360.8, small, incomplete, and poorly-preserved specimen that lack its skull and the anterior part of the body.[4]
Sphenodus	S. sp.	Santa Marta Cove	IAA-IRJ2000-17 and IAA-IRJ2000-18, teeth[10]	An Orthacodontid
Squatina	S. cf.hassei	Santa Marta Cove	IAA-IRJ2000-10-IAA-IRJ2000-16[10]	An Angelshark	Extant member of the genus

Pterosaurs

Genus	Species	Presence	Material	Notes	Images
Pterodactyloidea	gen. et sp. Indet.	Camp Lamb, Vega Island.	MN 7801-V, a wing metacarpal IV.[15]	A pterosaur with an estimated wingspan of 4 to 5 meters.[15]

Dinosaurs

Genus	Species	Presence	Material	Notes	Images
Antarcticavis	A. capelambensis[16]	Cape Lambe Member, Vega Island.	A partial skeleton (SDSM 78147) consists of two thoracic vertebrae, the sternum keel, the right coracoid and shoulder blade, the sternal part of the left coracoid, the right upper arm, parts of the left upper arm, the proximal right ulna, the proximal left ulna and radius (articulated), the proximal right carpometacarpus, the proximal left carpometacarpus, the distal left carpometacarpus, the synsacrum, the right and left thighs, the proximal right tibiotarsus, the right and left distal tibiotarsus, and the proximal right tarsometatarsus.	An avialan of uncertain phylogenetic placement.
Antarctopelta	A. oliveroi	Santa Marta Cove[17]	A partial skeleton (MLP 86-X-28-1) consists of three isolated teeth, part of the lower jaw with another tooth in situ, some other skull fragments, vertebrae of the neck, back, hips and tail, some shoulder and hip bones (scapula, ilium) a thigh bone (femur), foot and hand bones (five metapodials and two phalanges), and numerous pieces of armor.[17][14]	A parankylosaur
"Biscoveosaurus"	Indeterminate	Cape Lamb Member.[18][19]	NHMUK PV R 36760, dentaries, teeth, a braincase, parts of the maxillae, forelimb elements, assorted vertebrae, and the pectoral girdle.	An ornithopod.
Elasmaria	Indeterminate	Santa Marta Cove	Two isolated ungual phalanges (MLP 07-III-2-1 and MLP 07-III-2-2)[4]
	Indeterminate	Fortress Hill	limb, foot[20]
	Indeterminate	Vega Island	BMNH BAS R.2450[9]
Gaviiformes	Indeterminate	Vega Island	MLP 98-I-10-47: incomplete tarsometatarsus; MLP 98-I-10-50: incomplete right tarsometatarsus; MLP 98-I-10-51: proximal end of left femur[21]
Imperobator	I. antarcticus	Cape Lamb Member, Naze Peninsula.[22]	A single specimen that contains skull fragments possibly from the premaxilla, maxilla, and dentary as well as a caudal vertebra, teeth, and pedal elements, UCMP 276000.[20][23]	A potential Unenlagiinae paravian
Lithostrotia	Indeterminate	Loma Verde, near Santa Marta Cove	11-II-20-1, incomplete middle caudal vertebra[24]
Morrosaurus	M. antarcticus	Cape Lamb Member.[25]	Fragmentary right hind limb.[25]	An elasmarian ornithopod.
Neornithes	Indeterminate	Vega Island	MLP 98-I-10-25, left tarsometatarsus[4]
Ornithurae[26]	Indeterminate	Cape Lamb	AMNH FARB 30920, thoracic vertebra
Theropoda	Indeterminate	Cape Lamb	MLP 15-I-7-2, isolated pedal phalax (digit III?)[4]
Trinisaura	T. santamartaensis	Santa Marta Cove, in the lower levels of the formation.[27]	MLP08-III-1-1, disarticulated and partial skeleton that includes one incomplete dorsal vertebra, three sacral centra, seven caudal vertebrae; two incomplete dorsal rib shafts, one proximal haemal arch, incomplete right scapulocoracoid, incomplete right humerus, two metacarpals, both ilia, right pubis, right ischium, right femur, right distal tibia, incomplete metatarsal III, first phalanx of pedal digit III, two phalanges of pedal digit IV, and indeterminate fragments.	An elasmarian ornithopod.

Plesiosaurs

Genus	Species	Presence	Material	Notes	Images
Aristonectinae	Indeterminate	Santa Marta Cove	SGO.PV.6579, fragmentary postcranial skeleton preserving eight fragmentary caudal centra, two articular propodial heads (likely femora), an epipodial (likely a fibula), ventral portion of the right ilium, partial left pubis, and several rib portions[28]
Elasmosauridae	Indeterminate	Monolithic Lake; Santa Marta Cove	"MLP 11-II-20-4, one cervical vertebra preserving a partial rib; MLP 86-X-28-3, two cervical vertebrae; MLP 86-X-28-(2–6), 10 posterior cervical vertebrae articulated with three pectoral vertebrae, part of two dorsal vertebrae, ribs, and indeterminate fragments."[29]
	Indeterminate	Santa Marta Cove	SGO.PV.6508, one isolated cervical vertebral centrum[28]
	Indeterminate	W Santa Marta Cove	MN 7820-V, four vertebral centra and fragments of another six centra[30]
	Indeterminate	Cape Lamb	MLP 98-I-10-20, an incomplete postcranial skeleton (juvenile)[31]
	Indeterminate	Vega Island	SDSM 78156 (a nearly complete, articulated torso, partial paddles, and neck and tail sections)[32]
Plesiosauria	Indeterminate	The Naze	DJ.355.140, half of large water-worn vertebra, either anterior trunk or distal cervical vertebra[33]
Plesiosauroidea	Indeterminate	The Naze; Cape Lamb	MLP 78-XI-1-2; MLP 78-XI-1-1, vertebrae and fragments[34]
Vegasaurus	V. molyi	Cape Lamb member, Vega Island.	MLP 93-I-5-1, postcranial skeleton preserving a complete cervical region with 54 cervical vertebrae, three pectoral vertebrae, 17 dorsal vertebrae, three sacral vertebrae, anterior and medial caudal vertebrae, pectoral and pelvic girdles, forelimbs and hind limbs, ribs, and gastroliths.[35]	A plesiosaur.
Weddellonectia	Indeterminate	Cape Lamb	MLP 15-I-7-6, partial skull comprising caudal half of pterygoids, basisphenoid, basioccipital, squamosal, exoccipitalopisthotic; cervical, dorsal, sacral and caudal centra; cervical and dorsal ribs, partially preserved coracoid, two partially preserved propodials.[36]
	Indeterminate	Cape Lamb	AMNH FARB 30877 is a largely articulated partial skeleton[37]

Mosasaurs

Genus	Species	Presence	Material	Notes	Images
Liodon	L. sp.	Cape Lamb	Teeth[4]	A Mosasaur
	Cf. L. sp.	Cape Lamb	Teeth[4]
Mosasaurus	M. cf. M. lemonnieri	Cape Lamb	Teeth[4]	A Mosasaur
Plioplatecarpus	cf. P. sp.	Cape Lamb	MLP 93-I-3-5, small tooth[31]
Taniwhasaurus[38]	T. antarcticus	Santa Marta Cove; Al's Bird Site	IAA 2000-JR-FSM-1, containing a skull measuring 72 cm (28 in) long, teeth, some vertebrae, and rib fragments.	A tylosaur.	Taniwhasaurus
	cf. T. antarcticus	Al's Bird Site	MLP 93-I-3-7, a tooth crown[39]
Tylosaurinae	Indeterminate	Vega Island	Juvenile skull[40]

Plants

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.

During the Campanian–Maastrichtian, the Antarctic Peninsula supported temperate, humid forests dominated by podocarps, araucarian conifers, and a diversifying group of angiosperms. Key angiosperm families included Nothofagaceae, Monimiaceae, Cunoniaceae, Proteaceae, Myrtaceae, Lauraceae, Atherospermataceae, Winteraceae, and extinct Sassafras-like forms.^[41][42] Another important group is Asteraceae, with Dasyphyllum-like pollen, the oldest fossils ever found for the family.^[43] Ferns such as Osmundaceae and Gleicheniaceae formed part of the understorey. Fossil evidence (wood, pollen, leaves) comes mainly from Seymour, Vega, James Ross, and Snow Hill islands. Forests were structurally similar to modern Valdivian temperate forests. The flora reflects a transition from gymnosperm-dominated to mixed angiosperm-conifer ecosystems under polar greenhouse conditions.^[41][44]

Taxa	Species	Locality	Material	Notes	Images
Agathoxylon	A. pseudoparenchymatosum	Seymour Island; Caleta Santa Marta	Fossil specimens[45]	An Araucariaceae Conifer
	A. arayai	Caleta Santa Marta; Byers Peninsula	Fossil specimens[46]
Araucaria	A. antarctica	Cape Lamb	Cone and wood[47]	An Araucariaceae Conifer	Extant representatives of the genus
Eucryphiaceoxylon	E. eucryphioides	Day Nunatak	A fossilized specimen (IAA-Pb 1022)[48]	A member of the angiosperm family Cunoniaceae.
Longexylon	L. oliveroi	Day Nunatak	A fossilized specimen (IAA-Pb 1021).[48]	A member of the angiosperm family Lauraceae.
Microcachryxylon	M. gothani	Cerro Naze	Fossil specimens[46]	A Podocarpaceae Conifer
Millerocaulis	M. santamartaensis	Santa Marta Cove	LPPB 15252 (hand specimen) and LPpm 1404 to 1411 (microscope slides).[49]	A member of the family Osmundaceae.
Nothofagoxylon	N. scalariforme	Seymour Island	Fossil specimens[45]	A member of the angiosperm family Nothofagaceae.
Nothofagus	N. "sp. 1"	Vega Island	Fossil leaves (IAA-Pb 539, IAA-Pb 541)[50]	A member of the angiosperm family Nothofagaceae.	Extant Nothofagus specimen
Phyllocladoxylon	P. antarcticum	Seymour Island; Brandy Bay	Fossil specimens[45]	A Podocarpaceae Conifer
Podocarpoxylon	P. "sp. 1"	Caleta Santa Marta	Fossil specimens[46]	A Podocarpaceae Conifer
	P. "sp. 2"	Caleta Santa Marta	Fossil specimens[46]
	P. "sp. 3"	Caleta Santa Marta	Fossil specimens[46]

See also

• List of fossiliferous stratigraphic units in Antarctica
• List of dinosaur-bearing rock formations
• Sobral Formation
• South Polar region of the Cretaceous