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''Bonapartenykus'' (meaning "
José F. Bonaparte José is a predominantly Spanish and Portuguese form of the given name Joseph. While spelled alike, this name is pronounced differently in each language: Spanish ; Portuguese (or ). In French, the name ''José'', pronounced , is an old vernacul ...
's claw") is a
monospecific In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
alvarezsauroid Alvarezsauroidea is a group of small maniraptoran dinosaurs. Alvarezsauroidea, Alvarezsauridae, and Alvarezsauria are named for the historian Gregorio Álvarez, not the more familiar physicist Luis Alvarez, or his son geologist Walter Alvarez ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
from
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
that lived during the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
(
Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...
-
Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
) in what is now the upper
Allen Formation The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to early Maastrichtian.Salgado et al., 2007 Dinosaur remains are among the fossils that have been recovered from the formati ...
of the
Río Negro Province Río Negro (, ''Black River'') is a province of Argentina, located in northern Patagonia. Neighboring provinces are from the south clockwise Chubut, Neuquén, Mendoza, La Pampa and Buenos Aires. To the east lies the Atlantic Ocean. Its capit ...
. The type and only species, ''Bonapartenykus ultimus'', is known from a nearly articulated but partial skeleton that was found in close association to two incomplete
eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
and several clusters of eggshells belonging to the
oogenus Egg fossils are the fossilized remains of eggs laid by ancient animals. As evidence of the physiological processes of an animal, egg fossils are considered a type of trace fossil. Under rare circumstances a fossil egg may preserve the remains of ...
''
Arriagadoolithus ''Arriagadoolithus'' is the oogenus of fossil eggs which includes the eggs of the alvarezsaurid ''Bonapartenykus''. Fossils of the creature were found in Patagonia; it may have brooded on its eggs. Description ''Arriagadoolithus patagoniensis'' i ...
''. ''Bonapartenykus'' was named in
2012 File:2012 Events Collage V3.png, From left, clockwise: The passenger cruise ship Costa Concordia lies capsized after the Costa Concordia disaster; Damage to Casino Pier in Seaside Heights, New Jersey as a result of Hurricane Sandy; People gather ...
by Federico L. Agnolin, Jaime E. Powell, Fernando E. Novas and Martin Kundrát. ''Bonapartenykus'' has an estimated length of and weight of , making it the largest member of the clade
Alvarezsauroidea Alvarezsauroidea is a group of small maniraptoran dinosaurs. Alvarezsauroidea, Alvarezsauridae, and Alvarezsauria are named for the historian Gregorio Álvarez, not the more familiar physicist Luis Alvarez, or his son geologist Walter Alvarez ...
.


Discovery and Naming

A partial
skeleton A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
of a
theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
with eggs was collected in a surface of approximately 30 m2 in
fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...
sandstones Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) b ...
of the upper
Allen Formation The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to early Maastrichtian.Salgado et al., 2007 Dinosaur remains are among the fossils that have been recovered from the formati ...
in northwestern
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...
,
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. The locality has also produced specimens of hadrosaurids, ankylosaurs, several
titanosaur Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...
sauropods Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
, several
abelisaurids Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are found ...
, indeterminate
tetanurans Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans ar ...
, an incomplete large alvarezsaurid and a large unenlagiid. The skeleton was originally reported and described by Salgado ''et al.'' (2009) as an indeterminate alvarezsaurid. The specimen was later redescribed and named in
2012 File:2012 Events Collage V3.png, From left, clockwise: The passenger cruise ship Costa Concordia lies capsized after the Costa Concordia disaster; Damage to Casino Pier in Seaside Heights, New Jersey as a result of Hurricane Sandy; People gather ...
by Federico L. Agnolin, Jaime E. Powell, Fernando E. Novas and Martin Kundrát. The
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
specimen, MPCA, 1290, consists of a mid-dorsal
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
, both scapulocoracoids, left
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
and
femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
, left pubis articulated with the pubic peduncle of the ilium, the anterior blade of the left ilium, and two partially preserved eggs that were separated from the holotype by less than 20 cm (7.9 inches). Two specimens were referred to ''Bonapartenykus'': MGPIFD-GR 166 and MGPIFD-GR 184, a blade of the left scapula, a left
coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...
, a distal right pubis, four cervical vertebrae and a single caudal vertebra which all belong to the same individual. The eggs of ''Bonapartenykus'' were considered unique enough for them to be given a new parataxonomic name, ''
Arriagadoolithus ''Arriagadoolithus'' is the oogenus of fossil eggs which includes the eggs of the alvarezsaurid ''Bonapartenykus''. Fossils of the creature were found in Patagonia; it may have brooded on its eggs. Description ''Arriagadoolithus patagoniensis'' i ...
'', which was classified in a new
oofamily Egg fossils are the fossilized remains of eggs laid by ancient animals. As evidence of the physiological processes of an animal, egg fossils are considered a type of trace fossil. Under rare circumstances a fossil egg may preserve the remains of ...
, the Arriagadoolithidae, so named for the owner of the site where the discovery was made. The generic name, ''Bonapartenykus'', is derived from the Argentinean
paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
José F. Bonaparte José is a predominantly Spanish and Portuguese form of the given name Joseph. While spelled alike, this name is pronounced differently in each language: Spanish ; Portuguese (or ). In French, the name ''José'', pronounced , is an old vernacul ...
and the
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
word "''onykus''" (claw). The specific name, ''ultimus'', is derived from the Latin word "''ultimus''" (latest), as it is one of the most geologically youngest alvarezsaurid from
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
.


Description


Size and distinguishing traits

''Bonapartenykus'' was a large alvarezsaur, measuring long and weighing . Agnolin et al. (2012) diagnosed ''Bonapartenykus'' based on the presence of spinopostzygapophyseal laminae that end abruptly above the
postzygapophyses The articular processes or zygapophyses ( Greek ζυγον = " yoke" (because it links two vertebrae) + απο = "away" + φυσις = " process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vert ...
of the mid-dorsal vertebrae; the underside portion of the coracoid being strongly deflected towards the middle and decorated with delicate but abundant grooves as in ''
Xixianykus ''Xixianykus'' is a genus of alvarezsaurid theropod dinosaur from the late Cretaceous period of China.Xu, X., Wang, D.Y., Sullivan, C., Hone, D.W.E., Han, F.L., Yan, R.H. and Du, F.M. (2010). "A basal parvicursorine (Theropoda: Alvarezsauridae) ...
''; fused scapulocoracoids as in ''
Ceratonykus ''Ceratonykus'' (meaning "horned claw") is a monospecific genus of alvarezsaurid dinosaur from Mongolia that lived during the Late Cretaceous (late Campanian stage, 72.1 Ma) in what is now the Barun Goyot Formation. The type and only species, ''C ...
''; scapula with a very wide notch on the posterior margin of the bone; and a fused ilium and pubis.


Postcrania

The mid-dorsal vertebrae has diapophyses and parapophyses that are worn, with the former lacking its distal ends. As in other alvarezsaurids, the centrum of the mid-dordsal vertebrae lack pleurocoels. Unlike ''
Haplocheirus ''Haplocheirus'' is a genus of theropod dinosaur. Upon its description, it was considered the oldest alvarezsauroid, predating all other members by about 63 million years. This has subsequently been questioned. A 2019 study considered ''Haploch ...
'' and ''
Patagonykus ''Patagonykus'' (meaning "Patagonian claw") is a genus of theropod dinosaur from the Upper Cretaceous of Argentina. This alvarezsauroid was discovered in exposures of the Portezuelo Formation (Turonian- Coniacian) of the Rio Neuquén Subgroup i ...
'', the centrum has a cranial articular surface that is deeply concave with a sharp bony margin that surrounds it, which might be procoelous. The neural spine is proportionally taller than in Mononykini, but also resembles the condition seen in basal alvarezsauroids such as ''Haplocheirus''. As in ''
Mononykus ''Mononykus'' ( , sometimes ; meaning "one claw") is a genus of alvarezsaurid dinosaur that lived during the Late Cretaceous in what is now Asia on the Nemegt Formation, about 70 million years ago. ''Mononykus'' was a very small theropod, estim ...
'' and ''Patagonykus'', both the prespinal and postspinal fossae are very deep. A unique feature of ''Bonapartenykus'' is the spinopostzygapophyseal laminae ending abruptly above the rear margin of the postzygapophyses. The mid-dorsal vertebrae has neural canals that are wide and prezygapophyses that shows a subcircular contour and a shallow concavity at its caudal margin. As in ''Patagonykus'', the parapophyses connect to the margins of the cranial articular surface through a small ridge and the diapophyse connect to the parapophyses by a deep ridge. The centrodiapophyseal lamina was craniocaudally wider than in other alvarezsaurids, based on the preserved portions. The postzygapophyses are
ellipsoidal An ellipsoid is a surface that may be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface;  that is, a surface that may be defined as the z ...
in contour in dorsal view and show a notched caudal margin. The postzygapophyses are transversely wide and cranicaudally shortened, but lacks a lateroventral projection. As in ''
Alvarezsaurus ''Alvarezsaurus'' (; "Alvarez's lizard") is a genus of alvarezsaurid dinosaur from the Late Cretaceous, living in Argentina approximately 86 - 83 million years ago. It was a small dinosaur, measuring long and weighing approximately . It was fou ...
'', the scapular blade is medially deflected, unlike other alvarezsaurids that have a straight
scapular blade The scapular (from Latin ''scapulae'', "shoulders") is a Western Christian garment suspended from the shoulders. There are two types of scapulars, the monastic and devotional scapular, although both forms may simply be referred to as "scapular ...
. However, as in other alvarezsaurids, both the cranial and caudal margins are almost parallel. Along the caudal margin of the scapular blade is a well-developed notch. As in
Maniraptora Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoros ...
,
Oviraptorosauria Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or wi ...
and other Alvarezsauridae, the
acromion In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade). Together with the coracoid process it extends laterally over the shoulder joint. The acro ...
is subtriangular in shape. The
glenoid fossa The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from el, gléne, "socket", reflecting the shoulder joint's ball-and-socket form. It is a sha ...
is oriented towards the posterior and sides, with the scapular portion being lateromedially expanded and wider than the coracoidal portion, as well as perpendicular to the main axis of the coracoid. Similar to
Paraves Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the avial ...
, the ventral half of the coracoid is strongly medially flexed. The coracoid lacks a bicipital tubercle and is transversely thick at the cranial margin. The coracoidal foramen is wide and rounded in contour, and possesses several ridges near the caudal margin which may correspond to
muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
attachment points. Along the side margins of the coracoid are a smooth surface towards the sides and upper side and a directed margin towards the middle and underside. This feature is similar in condition to that of ''Patagonykus'' but differs by the middle portion of the coracoid not being as strongly inflected towards and the surface of the side show only isolated and poorly developed grooves. The faintly defined ridge of ''Ceratonykus'' is very poorly and is restricted to the posterior end of the coracoid which is unlike that of ''Bonapartenykus''. Agnolin ''et al.'' (2012) noted that the ventral half of the coracoid is deflected towards the middle, with an extremely thin medial rear that is slightly wrapping upwards which probably correlates with some kind of
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
cornification, but does not correlate with a cornified sheath due to the absence of oblique neurovascular foramina. The coracoid is extremely elongate and ends at an acute end which restricted articulation with the sternum. Alvarezsaurids like ''Bonapartenykus'' may have had a flat and wide breast based on a combination of characteristics like a continuous subhorizontal surface with formed by the medial deflection of the coracoids with the sternal plate. Unlike ''Patagonykus'', the pubic shaft of ''Bonapartenykus'' is more compressed towards the sides and narrower from front to back. As in derived alvarezsaurids, the pubic shaft lacks the caudal sulcus for the ischial articulation. The distal end of the pubic shaft possesses a small ridge on its cranial margin, which is absent in more derived alvarezsaurids, but shows a distal pubic boot on the pubis. The pubic boot appears to be rounded in side view on the rear margin. A small portion of the right ilium is preserved. The pubic pedicle is compressed towards the middle and sides. The pubic pedicle is also strongly fused with the pubis, which is a characteristic unique among alvarezsaurids, along with a reduced cuppedicus fossa. The cuppedicus fossa is shallow and elongate with a low, wide, and smooth ridge being present above it. The
femoral head The femoral head (femur head or head of the femur) is the highest part of the thigh bone (femur). It is supported by the femoral neck. Structure The head is globular and forms rather more than a hemisphere, is directed upward, medialward, and a l ...
was separated from the
greater trochanter The greater trochanter of the femur is a large, irregular, quadrilateral eminence and a part of the skeletal system. It is directed lateral and medially and slightly posterior. In the adult it is about 2–4 cm lower than the femoral head.Stan ...
by a cleft as indicated by the base of the cranial trochanter. The femoral head was similar in general size and proportions to ''Patagonykus''. In lateral view, a large, sculptured bulge is present on the femur, which may correspond to muscle attachment points. The
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
is very short and robust, while the tibial shaft is bowed towards the sides. Towards the sides of the base of the
cnemial crest The cnemial crest is a crestlike prominence located at the front side of the head of the tibiotarsus or tibia in the legs of many mammals and reptiles (including birds and other dinosaurs). The main extensor muscle of the thigh In human anat ...
, a small bump is present and the distal end is strongly scraped by friction or erosion.


Classification

Agnolin ''et al.'' (2012) originally placed ''Bonapartenykus'' within
Alvarezsauridae Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...
, within the clade Patagonykinae as sister taxon to ''
Patagonykus ''Patagonykus'' (meaning "Patagonian claw") is a genus of theropod dinosaur from the Upper Cretaceous of Argentina. This alvarezsauroid was discovered in exposures of the Portezuelo Formation (Turonian- Coniacian) of the Rio Neuquén Subgroup i ...
''. Makovicky, Apesteguía and Gianechini (2012) found it to be in a
polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...
with ''
Alnashetri ''Alnashetri'' is an extinct genus of alvarezsaurid coelurosaurian theropod dinosaur known from the early Late Cretaceous ( Cenomanian stage) of La Buitrera, Río Negro Province, Argentina. It contains one known species, ''Alnashetri cerropolici ...
'', ''Patagonykus'', and a clade containing more deeply nested taxa such as ''
Linhenykus ''Linhenykus'' is an extinct genus of alvarezsaurid theropod dinosaur from the Late Cretaceous of Inner Mongolia, China. It is the most basal known member of the Parvicursorinae. The genus gets its name from Linhe, a city near the site where t ...
'', ''
Mononykus ''Mononykus'' ( , sometimes ; meaning "one claw") is a genus of alvarezsaurid dinosaur that lived during the Late Cretaceous in what is now Asia on the Nemegt Formation, about 70 million years ago. ''Mononykus'' was a very small theropod, estim ...
'' and '' Albinykus''. However, Xu ''et al.'' (2018) positioned it as a basal
Alvarezsauroidea Alvarezsauroidea is a group of small maniraptoran dinosaurs. Alvarezsauroidea, Alvarezsauridae, and Alvarezsauria are named for the historian Gregorio Álvarez, not the more familiar physicist Luis Alvarez, or his son geologist Walter Alvarez ...
, sister taxon to ''Patagonykus'' and '' Achillesaurus'', which was also recovered by Fowler ''et al.'' (2020). ''Bonapartenykus'' has also been recovered as sister taxon to ''Patagonykus'' and Alvarezsauridae by Qin ''et al.'' (2019), and sister taxon to only ''Patagonykus'' outside of Alvarezsauridae by Averianov & Lopatin (2022a) and Averianov & Lopatin (2022b). A phylogenetic analysis conducted by Fowler ''et al.'' (2020) is reproduced below. The results of an earlier analysis by Agnolin ''et al.'' (2012) are reproduced below.


Paleoenvironment

''Bonapartenykus'' is known from fluvial sandstones of the upper Allen Formation which have been dated to the
Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...
to
Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...
stages of the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
period. The Allen Formation represents a range of environments such as ephemeral
lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...
, aeolian and
fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...
systems to coastal marine environments that developed into
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...
and
tidal flat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal fl ...
s. In 2015, Armas and Sánchez described the relationship of the coastal environment with wind systems of the Allen Formation and concluded the formation represents a hybrid coastal system of tidal flats with a large storm influence in some areas linked to aeolian systems. The fauna of the Allen Formation consists of the
titanosaur Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...
sauropods Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
''
Bonatitan ''Bonatitan'' is a genus of titanosaurian dinosaur from the Late Cretaceous Allen Formation of Argentina. It was named in 2004. Description The type species is ''Bonatitan reigi'', first described by Martinelli and Forasiepi in 2004. The s ...
'', '' Menucocelsior'', '' Panamericansaurus'', ''
Rocasaurus ''Rocasaurus'' (meaning "General Roca lizard") is a genus of titanosaurian sauropod that lived in South America. ''Rocasaurus'' was discovered in Argentina in 2000, within the Allen Formation which is dated to be middle Campanian to early Maastr ...
''Salgado, L. and C. Azpilicueta. (2000). Un nuevo saltasaurino (Sauropoda, Titanosauridae) de la provincia de Río Negro (Formacíon Allen, Cretácico Superior), Patagonia, Argentina. ''Ameghiniana'' 37 (3):259-264. and an indeterminate species of ''
Aeolosaurus ''Aeolosaurus'' (; "Aeolus' lizard") is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now South America. Like most sauropods, it would have been a quadrupedal herbivore with a long neck and tail. ''Aeolos ...
'', the
hadrosaurid Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which inclu ...
ornithopods Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world ...
''
Bonapartesaurus ''Bonapartesaurus'' (meaning "Bonaparte's lizard", named after José Bonaparte) is an extinct genus of herbivorous ornithopod dinosaur belonging to Hadrosauridae, which lived in the area of modern Argentina during the Campanian and Maastrichtia ...
'', '' Kelumapusaura'', '' Lapampasaurus'' and '' Willinakaqe'', an indeterminate
nodosaurid Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous period in what is now North America, South America, Europe, and Asia. Description Nodosaurids, like their close relatives the ankylosaurids, we ...
, the
abelisaurid Abelisauridae (meaning "Abel's lizards") is a family (or clade) of ceratosaurian theropod dinosaurs. Abelisaurids thrived during the Cretaceous period, on the ancient southern supercontinent of Gondwana, and today their fossil remains are foun ...
theropods Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ca ...
'' Niebla '' and ''
Quilmesaurus ''Quilmesaurus'' is a genus of carnivorous abelisaurid theropod dinosaur from the Patagonian Upper Cretaceous (Campanian stage) of Argentina. It was a member of Abelisauridae, closely related to genera such as ''Carnotaurus''. The only known rema ...
'', the large unenlagiid
paravian Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the aviala ...
''
Austroraptor ''Austroraptor'' ( ) is a genus of large dromaeosaurid dinosaur that lived during the Late Cretaceous Period in what is now Argentina. ''Austroraptor'' was a large-sized, moderately-built, ground-dwelling, bipedal carnivore, estimated at in len ...
'', the
avialans Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally use ...
''
Lamarqueavis ''Lamarqueavis'' is an extinct genus of prehistoric birds from the Cimolopterygidae known from Late Cretaceous-aged rocks from Argentina, Canada, and the United States. The type species, ''L. australis'', was named in 2010 and is based on the ho ...
'' and ''
Limenavis ''Limenavis'' is a prehistoric bird genus from the Late Cretaceous. It lived about 70 million years ago, around the Campanian-Maastrichtian boundary. Known from several broken bones, the remains of the only known species ''Limenavis patagonica'' ...
'',Clarke and Chiappe, 2001. "A new carinate bird from the Late Cretaceous of Patagonia (Argentina)". ''American Museum Novitates''. 3323, 1-23. the
azhdarchid Azhdarchidae (from the Persian word , , a dragon-like creature in Persian mythology) is a family of pterosaurs known primarily from the Late Cretaceous Period, though an isolated vertebra apparently from an azhdarchid is known from the Early Cre ...
pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 to ...
''
Aerotitan ''Aerotitan'' is a genus of large azhdarchid pterosaur known from the Late Cretaceous period (Maastrichtian stage) of what is now the Allen Formation of the Neuquén Basin in northern Patagonia, Argentina. Discovery and naming The type speci ...
'', the rhynchocephalian ''
Lamarquesaurus ''Lamarquesaurus'' is an extinct genus of sphenodontian from the Late Cretaceous (Campanian) of Patagonia. It is known from a single species, ''Lamarquesaurus cabazai''. This genus and species is represented by MML-PV-42, a well-preserved right ...
'', and the
plesiosaur The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared ...
''
Kawanectes ''Kawanectes'' (meaning "Kawas swimmer") is a genus of elasmosaurid plesiosaur, a type of long-necked marine reptile, that lived in the marginal marine ( estuarine) environment of Late Cretaceous Patagonia. It contains one species, ''K. lafquen ...
''.


References

{{Portal bar, Dinosaurs, Cretaceous, Paleontology Alvarezsaurs Campanian life Maastrichtian life Late Cretaceous dinosaurs of South America Cretaceous Argentina Fossils of Argentina Allen Formation Fossil taxa described in 2012 Taxa named by Jaime Powell Taxa named by Fernando Novas