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Chapter 2
e Fossil Record of Mesozoic and Paleocene
Pennaraptorans
MICHAEL PITTMAN,1 JINGMAI O’CONNOR,2 EDISON TSE,1
PETER MAKOVICKY,3 DANIEL J. FIELD,4 WAISUM MA,5 ALAN H. TURNER,6
MARK A. NORELL,7 RUI PEI,2 AND XING XU2
ABSTRACT
An unabated surge of new and important discoveries continues to transform knowledge of pen-
naraptoran biology and evolution amassed over the last 150+ years. is chapter summarizes prog-
ress made thus far in sampling the pennaraptoran fossil record of the Mesozoic and Paleocene and
proposes priority areas of attention moving forward.
Oviraptorosaurians are bizarre, nonparavian pennaraptorans rst discovered in North America and
Mongolia within Late Cretaceous rocks in the early 20th century. We now know that oviraptorosaurians
also occupied the Early Cretaceous and their unquestionable fossil record is currently limited to Laurasia.
Early Cretaceous material from China preserves feathers and other so tissues and ingested remains
including gastroliths and other stomach contents, while brooding specimens and age-structured, single-
species accumulations from China and Mongolia provide spectacular behavioral insights. Less specialized
early oviraptorosaurians like Incisivosaurus and Microvenator remain rare, and ancestral forms expected
in the Late Jurassic are yet to be discovered, although some authors have suggested Epidexipteryx and
possibly other scansoriopterygids may represent early-diverging oviraptorosaurians.
Long-armed scansoriopterygids from the Middle-Late Jurassic of Laurasia are either early-diverg-
ing oviraptorosaurians or paravians, and some have considered them to be early-diverging avialans.
Known from ve (or possibly six) feathered specimens from China, only two mature individuals
exist, representing these taxa. ese taxa, Yi and Ambopteryx, preserve stylopod-supported wing
membranes that are the only known alternative to the feathered, muscular wings that had been
exclusively associated with dinosaurian ight. us, scansoriopterygid specimens—particularly
those preserving so tissue—remain a key priority for future specimen collection.
Dromaeosaurids and troodontids were rst discovered in North America and Mongolia in Late
Cretaceous rocks. More recent discoveries show that these animals originated in the Late Jurassic,
were strikingly feathered, lived across diverse climes and environments, and at least in the case of
dromaeosaurids, attained a global distribution and the potential for aerial locomotion at small size.
1 Vertebrate Palaeontology Laboratory, Division of Earth and Planetary Science, the University of Hong Kong, Hong Kong.
2 Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology & Paleoanthropology,
Beijing; and CAS Center for Excellence in Life and Paleoenvironment, Beijing.
3 Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN.
4 Department of Earth Sciences, University of Cambridge, Cambridge.
5 School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, U.K.
6 Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY.
7 Division of Paleontology, American Museum of Natural History, New York.
38 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
BACKGROUND
Pennaraptorans are a clade of vaned feathered
coelurosaurian dinosaurs that are comprised of
the Oviraptorosauria, Scansoriopterygidae,
Dromaeosauridae, Troodontidae, and Avialae
(see Pittman et al., in the previous chapter for
additional information). ey include the only
dinosaurs to have evolved ight and the only
ones to have persisted to the present day.
O
Oviraptorosaurian fossils were rst discov-
ered in the 1920s and are now represented by
more than 40 genera spanning a size range across
three orders of magnitude (table 1). e 1920s to
1940s, the 1970s, 1980s, 1990s, and the past 20
years have been key periods in our documenta-
tion of the oviraptorosaurian fossil record, which
is limited to Laurasian continents and dominated
by discoveries from Asia and North America (g.
1). e last 30 years have seen the discovery of
most known oviraptorosaurian taxa, particularly
from the Cretaceous of China and the Late Cre-
taceous of North America and Mongolia. ese
discoveries have greatly broadened our under-
standing of this group, including in regard to the
evolution of their beaked and strangely pneuma-
tized skulls, as well as the origin of brooding in
theropod dinosaurs.
A: is continent is the home of the rst
described oviraptorosaurian species (Osborn,
1924), the eponymous species Oviraptor. Asia is
also home to more than 75% of valid oviraptoro-
saurian genera. e most important sources of
Asian oviraptorosaurians are the Early Creta-
ceous (Hauterivian-Aptian) Jehol Lagerstätte of
northeastern China, the Campanian-Maastrich-
tian Ganzhou oviraptorid fauna of southern
China and Mongolia have yielded the most dromaeosaurid and troodontid specimens and taxa, but
Gondwanan troodontids are almost unknown compared to southern dromaeosaurids, so the delity
of this biogeographical signal is worth further exploration. Discovery of well-preserved Middle-Late
Jurassic material will be crucial for understanding the origin of key dromaeosaurid and troodontid
traits, with the controversial anchiornithines potentially already oering this if their troodontid
status can be solidied.
In line with the preferences of most theropod palaeontologists, birds are dened herein as mem-
bers of Avialae, including stem and crown taxa, whilst Aves herein refers to crown-group birds (see
Pittman et al., chapter 1, for the precise denition of Avialae adopted; elsewhere, typically among
ornithologists, Aves refers to stem and crown taxa whilst Neornithes refers to crown-group birds).
Despite taphonomic bias against avialans in the fossil record, their Early Cretaceous record is fairly
robust largely due to the high taxonomic and ecological diversity preserved within the rich Jehol
deposits of northeastern China. Archaeopteryx (and possibly the controversial Middle-Late Jurassic
anchiornithines) show what some of the earliest birds were like, but better-preserved so tissues
hold the key to understanding their substantially dierent anatomy and ight capabilities to crown-
group birds (Aves).
e Late Cretaceous–early Paleocene fossil record of crown birds is especially poor, and improved
sampling will be necessary to clarify our understanding of avialan survivorship, ecological selectivity,
and recovery across the end-Cretaceous mass extinction. Deposits of Eocene age, such as Messel and
Green River, have been especially useful for documenting the early evolutionary history of crown
birds. However, the discovery of new Cretaceous and/or Palaeogene bird-bearing lagerstätten from
Gondwana will be important for accurately determining ancestral biogeographic patterns.
2020 PITTMAN ET AL.: THE FOSSIL RECORD 39
FIG. 1. Geographic distribution of pennaraptoran theropods illustrated on palaeogeographic globes of the
Late Jurassic (Oxfordian-Tithonian), Early Cretaceous (Berriasian-Albian), and Late Cretaceous (Cenoma-
nian-Maastrichtian). Palaeomaps modied from GPlates (www.gplates.org) (Müller et al., 2018).
40 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
TABLE 1
Oviraptorosaurian fossil record
Continent Geological
Unit Country Period Age Age Reference Taxa Reference
Asia
Jehol Group
(Yixian
Formation;
Jiufotang
Formation)
China Early
Cretaceous
Barremian-
Aptian
Chang et al., 2009, 2017;
Pan et al., 2013
Incisivosaurus, Caudipteryx,
Ningyuansaurus, Protarchaeop-
teryx, Similicaudipteryx (possibly
Incisivosaurus), Xingtianosaurus;
Similicaudipteryx
Ji and Ji, 1997; Ji et al., 1998; 2012;
Zhou et al., 2000; Xu et al., 2002a,
2010a; He et al., 2008; Balano et
al., 2009; Qiu et al., 2019
Nanxiong
Formation China Late
Cretaceous
Campanian-
Maastrichtian
Bureau of Geology and
Mineral
Resources of Jiangxi
Province, 1984
Banji, Corythoraptor,
Ganzhousaurus, Huanansaurus,
Jiangxisaurus, Nankangia,
Tongtianlong
Xu and Han, 2010; Lü et al., 2013a;
Wang et al., 2013a; Wei et al.,
2013; Lü et al., 2015, 2016, 2017
Haoling
Formation China Early
Cretaceous Aptian/Albian Xu et al., 2012a Luoyanggia Lü et al., 2009
Dalangshan
Formation China Late
Cretaceous Maastrichtian
Bureau of Geology and
Mineral Resources of
Guangdong Province,
1988
Heyuannia Lü, 2003
Pingling
Formation China Late
Cretaceous Maastrichtian Zhao et al., 1991 Shixinggia Lü and Zhang, 2005
Qiupa
Formation China Late
Cretaceous
Campanian-
Maastrichtian Jiang et al., 2011 Yul ong Lü et al., 2013b
Gaogou
Formation China Late
Cretaceous
Cenomanian-
Turonian Liang et al., 2009 Beibeilong Pu et al., 2017
Erlian
(Iren Dabasu)
Formation
China Late
Cretaceous
Campanian-
Maastrichtian
van Itterbeeck et al.,
2005; Bonnetti et al.,
2014
Avimimus, Caenagnathasia,
Gigantoraptor
Kurzanov, 1981; Xu et al., 2007;
Yao et al., 2015; Ma et al., 2017
Wulansuhai
(Bayan
Mandahu)
Formation
China Late
Cretaceous Campanian Godefroit et al., 2008 Machairasaurus, Wulatelong Longrich et al., 2010; Xu et al.,
2013b
Wangshi
Group China Late
Cretaceous Campanian An et al., 2016 Anomalipes Yu et al., 2018
Djadokhta
Formation Mongolia Late
Cretaceous Campanian
van Itterbeeck et al.,
2005; Dingus et al.,
2008; Hasegawa et al.,
2009
Avimimus, Citipati, Khaan,
Oviraptor
Osborn, 1924; Kurzanov, 1981;
Clark et al., 2001; Clark et al.,
2002; Balano and Norell, 2012
2020 PITTMAN ET AL.: THE FOSSIL RECORD 41
Continent Geological
Unit Country Period Age Age Reference Taxa Reference
Asia Barun Goyot
Formation Mongolia Late
Cretaceous
Campanian-
Maastrichtian
Gradziński and
Jerzykiewicz, 1974a, b;
Fanti et al., 2012
Ajancingenia/’Ingenia’/Heyuannia
yanshini, Avimimus,
Conchoraptor, Nemegtomaia
Barsbold, 1981; 1986; Longrich et
al., 2010; Fanti et al., 2012;
Funston et al., 2017
Nemegt
Formation Mongolia Late
Cretaceous Maastrichtian
Jerzykiewicz and Russell,
1991; Shuvalov, 2000;
van Itterbeeck et al.,
2005
Avimimus, Elmisaurus,
Gobiraptor; Nemegtomaia,
Nomingia, Rinchenia
Barsbold, 1981, 1986, 2000; Lü et
al., 2004, 2005; Longrich et al.,
2010; Osmólska, 1981; Fanti et al.,
2012; Currie et al., 2015; Funston
et al., 2017; Lee et al., 2019
Bissekty
Formation Uzbekist an Late
Cretaceous Turonian Sues and Averianov,
2014, 2015 Caenagnathasia Currie et al., 1993; Sues and
Averianov, 2015
North
America
Cloverly
Formation U.S. Early
Cretaceous
pre-Aptian-
Albian
Oreska et al., 2013;
Farke et al., 2014 Microvenator Makovicky, 1998
Aguja
Formation U.S. Late
Cretaceous
Campanian-
Maastrichtian
Lehman, 1985; Sankey,
2001 Leptorhynchos Longrich et al., 2013
Two Medicine
Formation U.S. Late
Cretaceous Campanian Rogers et al., 1993;
Foreman et al., 2008 Chirostenotes?Osmólska et al., 2004
Hell Creek
Formation U.S. Late
Cretaceous Maastrichtian
Hoganson and Edward,
2002; Fastovsky and
Bercovici, 2016
Anzu, Chirostenotes?Osmólska et al., 2004; Lamanna et
al., 2014
Kaiparowits
Formation U.S. Late
Cretaceous Campanian
Roberts et al., 2005;
Jinnah et al., 2009;
Zanno et al., 2011
Hagryphus Zanno and Sampson, 2005
Ojo Alamo
Formation U.S. Late
Cretaceous Maastrichtian
Sullivan and Lucas,
2006; Sullivan et al.,
2001
Ojoraptorsaurus Sullivan et al., 2011
Belly River
Formation Canada Late
Cretaceous Campanian Eberth, 2005 Chirostenotes Gilmore, 1924
Dinosaur Park
Formation Canada Late
Cretaceous Campanian Eberth, 2005; Brown et
al., 2013
Caenagnathus, Chirostenotes,
Leptorhynchos
Osmólska et al., 2004; Longrich et
al., 2013; Funston and Currie,
2014; Funston et al., 2015
Horseshoe
Canyon
Formation
Canada Late
Cretaceous
Campanian-
Maastrichtian
EberthandBraman,
2012; Quinney et al.,
2013
Epichirostenotes, Apatoraptor Sullivan et al., 2011; Funston and
Currie, 2016
TABLE 1 continued
42 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
China (Nanxiong Formation) as well as the
southern Mongolian Campanian Djadokhta For-
mation (and the similar Wulansuhai (Bayan
Mandahu) Formation in China), Campanian-
Maastrichtian Barun Goyot Formation, and the
Maastrichtian Nemegt Formation.
Jehol oviraptorosaurians represent the old-
est unequivocal oviraptorosaurian records, and
the six described taxa include some articulated
specimens preserving feathers, gastroliths, and
stomach contents. e early-diverging ovirap-
torosaurians Incisivosaurus, Protarchaeopteryx,
Similicaudipteryx, Caudipteryx, Xingtianosaurus,
and Ningyuansaurus are the only known toothed
forms and have less specialized skulls compared
to later oviraptorosaurians (Ji et al., 1998; Zhou et
al., 2000; Xu et al., 2002a; Balano et al., 2009; Qiu
et al., 2019). Caudipteryx is known for its penna-
ceous feathered arms, gastroliths, and a tail plume
probably used for display purposes (Ji et al., 1998;
Zhou et al., 2000; Pittman et al., 2013; Persons et
al., 2014). It is known from two species (Ji et al.,
1998; Zhou et al., 2000), although this is contested.
Both specimens were recovered from the ~125
Ma Yixian Formation in Liaoning province, with
both 2-D and 3-D preservations. Two specimens
of Similicaudipteryx, another Yixian Formation
genus, show radical changes to feather morphol-
ogy during ontogeny (Xu et al., 2010a). However,
these two specimens might be specimens of Inci-
sivosaurus (Xu, 2020). Ningyuansaurus possibly
preserves seeds within its body cavity (Ji et al.,
2012). Xingtianosaurus is the most recently named
Jehol genus, which is known from an articulated
postcranial skeleton (Qiu et al., 2019). Luoyang-
gia is an Aptian- to Albian-aged oviraptorid from
the Haoling Formation of Henan, central China,
which was previously thought to be Late Creta-
ceous in age (Lü et al., 2009; Xu et al., 2012a).
e Late Cretaceous Ganzhou fauna of Jiangxi,
southern China, has the greatest known diversity of
oviraptorid oviraptorosaurians with seven reported
genera in the Campanian-Maastrichtian Nanxiong
Formation: Banji, Huanansaurus, Jiangxisaurus,
Tongtianlong, Ganzhousaurus, Nankangia, and
Corythoraptor (Xu and Han, 2010; Lü et al., 2013a,
2015, 2016, 2017; Wang et al., 2013a; Wei et al.,
2013). Embryos of an oviraptorid have also been
recovered from this formation (Wang et al., 2016a).
Heyuannia is an oviraptorid genus described from
a partial skeleton from the Maastrichtian
Dalangshan Formation of Guangdong, southern
China (Lü, 2003). “Ingenia,” or Ajancingenia yan-
shini, from the Campanian-Maastrichtian Barun
Goyot Formation of southern Mongolia (Barsbold,
1981; Easter, 2013) has been referred to this genus
as a second species, H. yanshini, but this involves a
very large geographical and temporal separation
between species (Funston et al., 2017). Shixinggia is
another described Guangdong oviraptorid from the
Maastrichtian Pingling Formation (Lü and Zhang,
2005). Yu long is a chicken-sized oviraptorid repre-
sented by excellent fossil material from the Upper
Cretaceous Qiupa Formation of Henan, central
China (Lü et al., 2013b), while Beibeilong is a cae-
nagnathid known from a perinate skeleton and
some eggs from the Cenomanian-Turonian Gaogou
Formation of the same province (Pu et al., 2017).
Anomalipes is a recently reported caenagnathid
from the Campanian Wangshi Group of Shandong
Province, known only from hind-limb elements
(Yu et al., 2018). e largest known oviraptorosau-
rian—the caenagnathid Gigantoraptor—was recov-
ered in the northernmost frontier of China from
the Campanian-Maastrichtian Erlian (Iren Dabasu)
Formation of Nei Mongol (Inner Mongolia) (Xu et
al., 2007). is is also the locality for one of the
smallest oviraptorosaurians, Avimimus, which was
rst reported from similarly aged rocks in Mongo-
lia (Kurzanov, 1981), although these assignments
would benet from review, as they may represent
dierent taxa. e Campanian Wulansuhai (Bayan
Mandahu) Formation, also in the Gobi Desert
region, is the home to the oviraptorids Machai-
rasaurus and Wulatelong and some other indeter-
minate oviraptorid material (Longrich et al., 2010;
Xu et al., 2013b).
Mongolian oviraptorosaurians are dominated
by oviraptorids, with three genera from the Cam-
panian Djadokhta Formation (Oviraptor, Citipati,
and Khaan) (Osborn, 1924; Clark et al., 2001,
2002; Balano and Norell, 2012), four genera from
2020 PITTMAN ET AL.: THE FOSSIL RECORD 43
the Maastrichtian Nemegt Formation (Gobiraptor,
Nomingia, Rinchenia, and Nemegtomaia) (Bars-
bold, 1986; Barsbold et al., 2000; Lü et al., 2004,
2005; Fanti et al., 2012; Funston et al., 2017; Lee et
al., 2019) and three from the Campanian-Maas-
trichtian Barun Goyot Formation (“Ingenia”/
Ajancingenia/Heyuannia yanshini, Conchoraptor,
and Nemegtomaia [also from the Nemegt]; see
Fanti et al., 2012, for details of Maastrichtian por-
tion) (Barsbold, 1981; 1986; Longrich et al., 2010;
Funston et al., 2017). Several skeletons are known
for Khaan and Citipati from the rich fossil beds of
Ukhaa Tolgod, including brooding specimens,
single species group associations and embryos
(Norell et al., 1995, 2001; Clark et al., 2001).
Avimimus is a small, early-diverging ovirap-
torosaurian closer to Caenagnathidae and Ovi-
raptoridae that is known from multiple
formations in Mongolia, including the Djad-
okhta, Nemegt, and Barun Goyot (Kurzanov,
1981; Longrich et al., 2010). Elmisaurus is a cae-
nagnathid from the Nemegt Formation (Osmól-
ska, 1981; Currie et al., 2016). e holotype of
the caenagnathid Caenagnathasia is a pair of
dentaries from a single individual recovered
from the Turonian Bissekty Formation of Uzbeki-
stan (Currie et al., 1993). A partial dentary
referred to Caenagnathasia is known from the
Erlian (Iren Dabasu) Formation of Nei Mongol,
China (Yao et al., 2015). Few caenagnathid skull
elements have been reported in Asia; these are
from the perinate Beibeilong and the mandible of
Gigantoraptor and a similarly sized specimen
from the Gobi Desert (Xu et al., 2007; Tsuihiji et
al., 2015; Ma et al., 2017; Pu et al., 2017).
N A: e early-diverging cae-
nagnathid Microvenator was recovered from the
Aptian-Albian Cloverly Formation and is a his-
torically important specimen and likely that of a
juvenile. It is the continent’s oldest oviraptoro-
saurian (Makovicky and Sues, 1998). Late Cre-
taceous caenagnathids dominate the North
American oviraptorosaurian fossil record. Chiro-
stenotes, currently known from the species C.
pergracilis, was the rst discovered caenagnathid
as well as the rst described North American
oviraptorosaur (Gilmore, 1924). e Campanian
Dinosaur Park Formation of Canada is the most
important source of North American caenag-
nathids including Chirostenotes (also referred to
possible material in the Campanian Two Medi-
cine and Maastrichtian Hell Creek formations of
the northern United States [Osmólska et al.,
2004]), Leptorhynchos (Longrich et al., 2013)
(also the Campanian-Maastrichtian Aguja For-
mation of the southern United States) as well as
Caenagnathus, the caenagnathid that lends its
name to the clade (Currie et al., 1993). Hagry-
phus is a caenagnathid from the Campanian
Kaiparowits Formation of Utah, known from
forelimb material (Zanno and Sampson, 2005).
Moving into the latest Cretaceous, Epichiroste-
notes and Apatoraptor are caenagnathids from
the Campanian-Maastrichtian Horseshoe Can-
yon Formation of Canada. Both have preserved
skull elements, and the holotype of Apatoraptor
is a largely articulated partial skeleton. Ojorap-
torsaurus is a caenagnathid known from pubic
bones recovered from the Maastrichtian Ojo
Alamo Formation of the southwestern United
States (Sullivan et al., 2011; Funston and Currie,
2016). Anzu is the largest described caenag-
nathid from North America and is one of the
best-preserved North American oviraptorosau-
rians (Lamanna et al., 2014). It is known from
the Maastrichtian Hell Creek Formation of
North and South Dakota (Lamanna et al., 2014).
Fossil eggshell material and undescribed skeletal
material from the top of the Cedar Mountain
Formation (Cenomanian-Turonian) of Utah
represents an even larger taxon that was simi-
larly sized to Gigantoraptor (Makovicky et al.,
2015; Tucker et al., 2020).
E: Oviraptorosaurians are poorly
known from Europe with representation from
only isolated postcranial material (Naish et al.,
2001; Csiki and Grigorescu, 2005) whose refer-
rals have been subsequently challenged (Csiki et
al., 2010; Allain et al., 2014).
Isolated elements from Cretaceous strata of
Gondwana have been interpreted as deriving
from oviraptorosaurians, but these records have
44 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
not withstood subsequent reevaluation. An iso-
lated cervical from the Maastrichtian El Brete
Formation of Argentina was described as an
oviraptorosaurian (Frankfurt and Chiappe,
1999), but has since been reinterpreted as a
noasaurid theropod (Agnolín and Martinelli,
2007). Elements from the Lower Cretaceous
Otway Group of Australia described as an ovi-
raptorosaurian lower jaw fragment and dorsal
vertebra (Currie et al., 1996), have since been
attributed to Unenlagiinae or other theropod
clades (Agnolín et al., 2010). To date, no unam-
biguous records of oviraptorosaurians from
Gondwanan continents exist.
S
Scansoriopterygids are a bizarre group of early-
diverging Laurasian oviraptorosaurians or paravi-
ans, known only from the Middle and Late
Jurassic Haifanggou Formation and Late Jurassic
Tiaojishan Formation of north China so far
(~168–155 Ma) (Czerkas and Yuan, 2002; Zhang
et al., 2002; Zhang et al., 2008a; Turner et al., 2012;
Brusatte et al., 2014; Xu et al., 2015a; Wang et al.
2019a; Pei et al., in press) (g. 1; table 2). Known
from ve (or six: O’Connor and Sullivan, 2014)
feathered Chinese specimens, only one denitive
and possibly two somatically mature individuals
exist. Two of these specimens (Yi qi and Ambop-
teryx longibrachium) possess feathered, membra-
nous wings (Xu et al., 2015a; Wang et al., 2019a)
and one possesses a pygostyle (Wang et al., 2019a).
Epidendrosaurus and Epidexipteryx are two well-
accepted genera, but Scansoriopteryx may be the
same genus as Epidendrosaurus. e Early Creta-
ceous Zhongornis, originally described as a bird
(Gao et al., 2008), may be a scansoriopterygid
instead (O’Connor and Sullivan, 2014), but this
has been contested (Rashid et al., 2018). e
notion that scansoriopterygids are early-branch-
ing avialans (Xu et al., 2011a; Czerkas and Feduc-
cia, 2014) has been replaced by anatomical
evidence grouping some or all scansoriopterygids
with oviraptorosaurians (Turner et al., 2012;
Agnolín and Novas, 2013; Brusatte et al., 2014; Pei
TABLE 2
Scansoriopterygid fossil record
Continent Geological
Unit Country Period Age Age Reference Taxa Reference
Asia
Haifanggou
and Tiaojishan
formations
China
Middle–
Late
Jurassic
Kimmeridgian-
Bathonian
Liu et al., 2012;
Wang et al.,
2013c; Sullivan et
al., 2014; Tian et
al., 2015
Ambopteryx, Epidendrosaurus,
Epidexipteryx, Scansoriopteryx
(possibly a synonym of
Epidendrosaurus), Yi, possibly
Zhongornis
Czerkas and Yuan, 2002; Zhang et
al., 2002; Gao et al., 2008; Zhang et
al., 2008a; O’Connor and Sullivan,
2014; Xu et al., 2015b; Rashid et al.,
2018; Wang et al., 2019a
2020 PITTMAN ET AL.: THE FOSSIL RECORD 45
TABLE 3
Dromaeosaurid fossil record
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
Asia Bayan Gobi
Formation China Early
Cretaceous Aptian-Albian Pittman et al., 2015 IVPP V22530 Pittman et al., 2015
Jehol Group
(Yixian Formation;
Jiufotang
Formation)
China Early
Cretaceous
Barremian-
Aptian
He et al., 2004; Chang et
al., 2009, 2017; Pan et al.,
2013
Changyuraptor
Graciliraptor,
Sinornithosaurus,
Tianyuraptor,
Zhenyuanlong,
Zhongjianosaurus;
Microraptor, Wul ong
Xu et al., 1999, 2000, 2003; Xu
and Wang, 2004a; Hwang et al.,
2002; Longrich and Currie, 2009;
Zheng et al., 2009; Gong et al.,
2012; Han et al., 2014; Lü and
Brusatte, 2015; Xu and Qin, 2017;
Pei et al., 2014; Poust et al., 2020
Wulansuhai/Bayan
Mandahu
Formation
China Late
Cretaceous Campanian Godefroit et al., 2008 Linheraptor, Velociraptor
osmolskae
Godefroit et al., 2008; Xu et al.,
2010b, 2015a
Qiupa Formation China Late
Cretaceous
Campanian-
Maastrichtian Jiang et al., 2011 Luanchuanraptor Lü et al., 2007
Bayan Shireh
Formation Mongolia Late
Cretaceous
Cenomanian-
Santonian
Shuvalov, 2000; van
Itterbeeck et al., 2005;
Kurumada et al., 2020
Achillobator Perle et al., 1999
Djadokhta
Formation Mongolia Late
Cretaceous Campanian
van Itterbeeck et al.,
2005; Dingus et al., 2008;
Hasegawa et al., 2009
Halszkaraptor,
Mahakala, Tsaagan,
Velociraptor mongoliensis
Osborn, 1924; Norell et al.,
2006; Turner et al., 2007b, 2011;
Cau et al., 2017
Barun Goyot
Formation Mongolia Late
Cretaceou
Campanian-
Maastrichtian
Gradzinski and
Jerzykiewicz, 1974a,
1947b; Fanti et al., 2012
Hulsanpes (possibly not
a dromaeosaurid)
Osmólska, 1982; Turner et al.,
2012; Cau and Madzia, 2018
Nemegt Formation Mongolia Late
Cretaceous Maastrichtian
Jerzykiewicz and Russell,
1991; Shuvalov, 2000; van
Itterbeeck et al., 2005
Adasaurus Barsbold, 1983
Öösh Formation Mongolia Early
Cretaceous
Berriasian-
Barremian Turner et al., 2007c Shanag Turner et al., 2007c
Jinju Formation South
Korea
Early
Cretaceous Aptian Kim et al., 2018 suspected
microraptorine tracks Kim et al., 2018
Bissekty Formation Uzbekistan Late
Cretaceous Turonian Sues and Averianov,
2014, 2015 Itemirus Kurzanov, 1976; Sues and
Averianov, 2014
46 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
TABLE 3 continued
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
Europe Jydegaard
Formation Denmark Early
Cretaceous
Berriasian-
Valanginian
Bonde and Christiansen,
2003 Dromaeosauroides
Bonde and Christiansen 2003;
Christiansen and Bonde, 2003
Lulworth
Formation U.K. Early
Cretaceous Berriasian Milner, 2002 Nuthetes
Owen, 1854; Milner, 2002;
Sweetman 2004; Rauhut et al.,
2010
Wessex Formation U.K. Early
Cretaceous Barremian Howse and Milner 1993 Ornithodesmus
Seeley, 1887; Howse and Milner,
1993; Norell and Makovicky,
1997
Grés à Reptiles
Formation France Late
Cretaceous
Campanian-
Maastrichtian Walker et al., 2007 Pyroraptor Allain and Taquet, 2000; Turner
et al., 2012
Sebeş Formation Romania Late
Cretaceous Maastrichtian Brusatte et al., 2013 Balaur Csiki et al., 2010; Brusatte et al.,
2013
South
America Allen Formation Argentina Late
Cretaceous
Campanian-
Maastrichtian Armas and Sánchez, 2015 Austroraptor Novas et al., 2009; Currie and
Paulina-Carabajal, 2012
Candeleros
Formation Argentina Late
Cretaceous
Cenomanian-
Turonian Leanza et al., 2004 Buitreraptor Makovicky et al., 2005; Novas et
al., 2018; Gianechini et al., 2018
Portezuelo
Formation Argentina Late
Cretaceous
Turonian-
Coniacian Calvo et al., 2007 Neuquenraptor,
Unenlagia, Pamparaptor
Novas and Puerta, 1997; Calvo
et al., 2004; Makovicky et al.,
2005; Novas and Pol, 2005;
Porri et al., 2011; Brissón Egli
et al., 2017; Novas et al., 2018
Huincul Formation Argentina Late
Cretaceous
Cenomanian-
Turonian
Garrido, 2010; Motta et
al., 2020
Overoraptor (nonavialan
paravian, possibly unen-
lagiine dromaeosaurid)
Motta et al., 2020
Los Blanquitos
Formation Argentina Late
Cretaceous Maastrichtian Martínez and Novas,
2006 Unquillosaurus
Powell, 1979; Novas and
Agnolín, 2004; Martínez and
Novas, 2006
North
America
Dinosaur Park
Formation Canada Late
Cretaceous Campanian Eberth, 2005; Brown et
al., 2013
Dromaeosaurus,
Hesperonychus,
Saurornitholestes
Matthew and Brown, 1922; Sues,
1978; Currie, 1995; Longrich
and Currie, 2009; Turner et al.,
2012; Currie and Evans, 2020
2020 PITTMAN ET AL.: THE FOSSIL RECORD 47
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
North
America
Horseshoe Canyon
Formation Canada Late
Cretaceous
Campanian-
Maastrichtian
EberthandBraman,
2012; Quinney et al.,
2013
Atrociraptor Currie and Varricchio, 2004
Wapiti Formation Canada Late
Cretaceous Campanian Bell and Currie, 2015 Boreonykus Bell and Currie, 2015
Antlers Formation U.S. Early
Cretaceous Aptian-Albian Brinkman et al., 1998 Deinonychus Brinkman et al., 1998
Cedar Mountain
Formation U.S. Early
Cretaceous
Barremian?-
Aptian Senter et al., 2012 Utahraptor, Yurgovuchia Kirkland et al., 1993; Senter et
al., 2012
Cloverly Formation U.S. Early
Cretaceous
pre-Aptian–
Albian
Oreska et al., 2013; Farke
et al., 2014 Deinonychus Ostrom, 1969
Hell Creek
Formation U.S. Late
Cretaceous Maastrichtian
Hoganson and Edward,
2002; Fastovsky and
Bercovici, 2016
Acheroraptor,
Dakotaraptor
Evans et al., 2013; DePalma et
al., 2015
Morrison
Formation U.S. Late
Jurassic
Kimmeridgian-
Tithonian
Trujillo and Kowallis,
2015 teeth of dromaeosaurids? Foster and Heckert, 2011
Ojo Alamo
Formation U.S. Late
Cretaceous Maastrichtian
Sullivan and Lucas, 2006;
Sullivan et al., 2001;
Jasinski et al., 2020
Dineobellator Jasinski et al., 2020
Two Medicine
Formation U.S. Late
Cretaceous Campanian Rogers et al., 1993;
Foreman et al., 2008 Bambiraptor Burnham et al., 2000
Africa Maevarano
Formation Madagascar Late
Cretaceous Maastrichtian Rogers et al., 2013 Rahonavis Forster et al., 1998; Makovicky
et al., 2005
Wadi Milk
Formation Sudan
Early to
Late
Cretaceous
Albian-
Cenomanian Turner et al., 2012 Wadi Milk
dromaeosaurid Rauhut and Werner, 1995
Antarctica Snow Hill Island
Formation –Late
Cretaceous Maastrichtian Case et al., 2007
Imperobator (indeter-
minate deinonychosaurian
material or nondromaeo-
saurid paravian)
Case et al., 2007; Turner et al.,
2012; Ely and Case, 2019
TABLE 3 continued
48 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
et al., in press) or as early-branching paravians
(Turner et al., 2012; Godefroit et al., 2013a, 2013b;
Xu et al., 2015a; Wang et al., 2019a).
D
Dromaeosaurid fossils have been found on
almost all modern continental landmasses
including members that appear to have had
volant capabilities (Turner et al., 2012; Pei et al.,
in press; g. 1; table 3).
N A: In 1922, Dromaeosaurus,
from the Campanian Dinosaur Park Formation of
Alberta, Canada, was the rst dromaeosaurid to
be described. It lends its name to the clade and is
known from partial cranial and very fragmentary
postcranial material (Matthew and Brown, 1922;
Currie, 1995). e Dinosaur Park Formation has
also yielded Saurornitholestes, a relatively completely
known taxon thought to be from only one species,
Saurornitholestes langstoni (Sues, 1978; Turner et
al., 2012). is taxon lacked a proper diagnosis
until recently and is likely represented by mul-
tiple partial skeletons. Recently, an exquisite skull
and skeleton from Dinosaur Provincial Park were
recovered allowing for a revised diagnosis (Currie
and Evans, 2020). Evidence of tooth-marked bones
and a broken tip of a tooth still embedded in a bone
suggest that this taxon ate azhdarchid pterosaurs on
occasion (Currie and Jacobsen, 1995). Hesperony-
chus elizabethae is known from a single incomplete
pelvis and referred pedal bones recovered from the
Dinosaur Park Formation (Longrich and Currie,
2009. is taxon is North America’s only named
microraptorine and the youngest one worldwide
by almost 45 million years (Longrich and Cur-
rie, 2009). Atrociraptor marshalli is a fragmentary
taxon recovered from the similarly aged Horse-
shoe Canyon Formation from the same part of
Canada (Currie and Varricchio, 2004). It consists
of a partial rostrum, including both premaxillae, a
right maxilla, and both dentaries. e snout of this
dromaeosaurid appears to be quite short and deep,
given the abbreviated nature of the facial process
of the maxilla. Across the border in neighboring
Montana, the Campanian Two Medicine Forma-
tion is home to the relatively well-preserved drom-
aeosaurid Bambiraptor (Burnham et al., 2000). e
holotype of Bambiraptor feinbergi is quite small and
typically considered a juvenile to subadult (Cur-
rie and Varricchio, 2004; Norell and Makovicky,
2004). However, attempts at histologically sampling
the single known skeleton of this taxon have been
unsuccessful. It is possible that Bambiraptor is a
juvenile specimen of Saurornitholestes (Burnham et
al., 2000; Norell and Makovicky, 2004): both taxa
lack detailed and adequate diagnoses and dier
only in the length of the suborbital process of the
frontal, a feature that is undoubtedly inuenced by
ontogeny. Furthermore, the Bambiraptor feinbergi
type specimen is known to be a chimera, as there
are elements of three dierent similarly sized lower
legs included in the holotype. e youngest North
American dromaeosaurids are from the Maastrich-
tian Hell Creek and Ojo Alamo formations of the
United States. From the Hell Creek Formation: the
velociraptorine Acheroraptor temertyorum, which is
known from a complete right maxilla and a referred
right dentary (Evans et al., 2013) as well as the sig-
nicantly larger Dakotaraptor steini, which was
originally described as a dromaeosaurine (DePalma
et al., 2015), but recently recovered as a velocirap-
torine (Pei et al., in press). From the Ojo Alamo
Formation: the velociraptorine Dineobellator noto-
hesperus, which is known from fragmentary cra-
nial and postcranial material (Jasinski et al., 2020).
Deinonychus, Utahraptor, and Yurgovuchia are the
oldest widely accepted dromaeosaurids from North
America with an Aptian/Albian age for the former
(Ostrom, 1969) and a Barremian age for the latter
two taxa (Kirkland et al., 1993; Senter et al., 2012).
Deinonychus and Utahraptor are known from a
large amount of material, much of it undescribed
(personal commun., J. Kirkland), and Utahraptor
ostrommaysorum remains the largest dromaeosau-
rid known. Yurgovuchia doellingi is represented by
associated postcranial remains. e oldest record
of Dromaeosauridae in North America relates to
controversial fragmentary material from the Late
Jurassic Morrison Formation (Heckert and Foster,
2011). Deinonychus antirrhopus remains the best-
2020 PITTMAN ET AL.: THE FOSSIL RECORD 49
represented dromaeosaurid from North America.
It is known from at least eight partially articulated
and disarticulated skeletons from the Cloverly and
Antlers formations. A partial egg associated with
an adult has also been recovered (Grellet-Tinner
and Makovicky, 2006). e osteology of this taxon
was described in detail in Ostrom’s monograph
(Ostrom, 1969) and has been revisited by subse-
quent studies (Norell and Makovicky, 1997, 1999;
Norell et al., 2006).
A: Velociraptor, arguably the most famous
dromaeosaurid, was the second dromaeosaurid to
be described, in 1924 (Osborn, 1924). It is one of
the best-known genera, with several complete or
near-complete skeletons, and lends its name to the
subfamily Velociraptorinae. Velociraptor was recov-
ered from the Campanian Djadokhta Formation
of southern Mongolia, which is among the most
productive strata for dromaeosaurids anywhere
on Earth. Several specimens of Velociraptor tell us
much about its palaeobiology. e famous “ght-
ing dinosaurs” appears to preserve Velociraptor
attacking a large Protoceratops (Kielan-Jaworowska
and Barsbold, 1972). Another specimen shows the
presence of quill knobs on the ulna (Turner et al.,
2007a), and yet another preserves stomach contents
that include the remains of a pterosaur (Currie and
Jacobsen, 1995). A second species, V. osmolskae, is
known from paired maxillae and a le lacrimal
described from similar rocks across the border in
Nei Mongol, China (Wulansuhai (Bayan Mandahu)
Formation) (Godefroit et al., 2008). is appears to
be a valid taxon despite the paucity of its preserved
fossil material (Turner et al., 2012). Djadokhta
Formation outcrops at Ukhaa Tolgod have yielded
Tsaagan mangas, a velociraptorine larger than Velo-
ciraptor (Norell et al., 2006) that is closely related to
Linheraptor exquisitus, with a nearly complete holo-
type skeleton from the Wulansuhai Formation (Xu
et al., 2010b, 2015b). e Djadokhta Formation has
also yielded the earliest diverging noneudromaeo-
saurian dromaeosaurid Mahakala omnogovae,
which is known from a partial skeleton including
the back of the skull (Turner et al., 2007b; Turner
et al., 2011). It was recovered from the Tögrögiin
Shiree locality in Mongolia. Recent work described
an additional dromaeosaurid from the Djadokhta
Formation, Halszkaraptor escuilliei, and recovered
it as the sister taxon to Mahakala, although parts
of the sole specimen have been forged (Cau et
al., 2017). Hulsanpes is another enigmatic speci-
men purported to be a dromaeosaurid (Osmólska,
1982). It is from the Campanian -Maastrichtian
Barun Goyot Formation at the Khulsan locality in
Mongolia. It consists only of a partial right metatar-
sus and pes (and possibly an associated braincase).
Although considered a dromaeosaurid by recent
analyses (Cau et al., 2017; Cau and Madzia, 2018),
because of the extremely fragmentary nature of
the material this identication has been repeatedly
challenged (Turner et al., 2012).
e Gobi Desert has yielded a number of taxa
occupying other parts of the Late Cretaceous: Achil-
lobator from the Cenomanian-Santonian Bayan
Shireh Formation (Perle et al., 1999) and Adasaurus
from the Maastrichtian Nemegt Formation (Bay-
ankhongor) of southwestern Mongolia (Barsbold,
1983). Adasaurus was only recently well gured
and described (Turner et al., 2012). IGM 100/20 is
the only specimen considered to be Adasaurus and
is known from a partial skull and postcranial skel-
eton. Additional cranial and postcranial remains
(IGM 100/22 and 100/23) likely pertain to a dier-
ent taxon from the older Baynshiree Formation.
Shanag is the only Early Cretaceous Mongolian
dromaeosaurid, belonging to the Berriasian-Barre-
mian Öösh Formation (Turner et al., 2007c).
In contrast, China has a large number of Early
Cretaceous forms, but fewer Late Cretaceous ones.
The Barremian-Aptian Yixian Formation and
Aptian Jiufotang Formation of northeastern China,
which yield part of the Jehol Biota, are home to
many microraptorines, a non-eudromaeosaurian
subclade that is known only from one fragmentary
specimen outside Asia (Longrich and Currie, 2009).
Despite their name, microraptorines were not all
small and appear to be reasonably large ancestrally
(Pei et al., in press). eir well-known arm and
leg feathers are exemplied in the group’s name-
sake Microraptor, where they are extremely long
and are thought to have enabled volant capabili-
ties, although this remains an area of intense study
50 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
(Dyke et al., 2013; Dececchi et al., 2016; Pei et al.,
in press). Microraptor is from the Aptian Jiufotang
Formation and is known from three species M.
zhaoianus, M. gui, and M. hanqingi (Xu et al., 2000,
2003; Gong et al., 2012); however, the status of M.
gui (Senter et al. 2004) and M. hanqingi have been
questioned (Turner et al., 2012; Pei et al., 2014). e
other known Jiufotang microraptorine is Wul ong
(Poust et al., 2020). e Yixian Formation has the
microraptorines Changyuraptor (Han et al., 2014),
Graciliraptor (Xu and Wang, 2004a), Sinornitho-
saurus (Xu et al., 1999), Zhongjianosaurus (Xu and
Qin, 2017) and the larger seemingly early-diverging
forms Tianyuraptor and Zhenyuanlong (Zheng et
al., 2009; Lü and Brusatte, 2015; Pei et al., in press).
Microraptorines are otherwise rare in Asia: IVPP
V22530 is from the younger Aptian-Albian Bayan
Gobi Formation of Nei Mongol, northern China
(Pittman et al., 2015) and suspected microrapto-
rine tracks have been discovered in the Aptian Jinju
Formation of Gyeongsangnamdo, South Korea
(Kim et al., 2018). Shanag is possibly a microrapto-
rine as well, as found in some phylogenetic analyses
(Gianechini et al., 2018). Luanchuanraptor, known
from a partial skeleton, was discovered from the
Campanian-Maastrichtian Qiupa Formation of
Henan, central China (Lü et al., 2007), and a recent
analysis found it closely related to its Late Creta-
ceous Mongolian relative Velociraptor (Pei et al., in
press). Tracks of two dierently sized coeval dei-
nonychosaurs have been found in the Barremian-
Aptian Tianjialoue Formation of Shandong, eastern
China, but the identity of their makers remains elu-
sive (Li et al., 2008a).
A small partial braincase forms the type of
Itemirus medullaris from the Turonian Bissekty
Formation of Uzbekistan, which was originally
described as an earlier-diverging theropod (Kur-
zanov, 1976). More recently, two phylogenetic
analyses have recovered it as a velociraptorine
(Longrich and Currie, 2009) and dromaeosau-
rine (Sues and Averianov, 2014).
E: Variraptor was named as a dromaeo-
saurid from the Late Campanian–Early Maas-
trichtian Grès à Reptiles Formation of France
(LeLoeu and Buetaut, 1998). However, it was
shown to lack dromaeosaurid synapomorphies
and was superseded by Pyroraptor (Late Cam-
panian–Early Maastrichtian of La Boucharde,
France) as the only known Late Cretaceous Euro-
pean dromaeosaurid taxon (Allain and Taquet,
2000; Turner et al., 2012). Prior to the discovery
of Pyroraptor, only indeterminate Late Creta-
ceous dromaeosaurid material had been known
in Europe (Allain and Taquet, 2000) from else-
where in France (Buetaut et al., 1986; LeLoeu
et al., 1992; LeLoeu and Buetaut, 1998) and
from Portugal (Antunes and Sigogneau, 1992)
and Romania (Weishampel and Jianu, 1996).
Despite being represented by only extremely
fragmentary remains, the unique biogeography
of Pyroraptor and its near contemporaneous-
ness with Late Cretaceous taxa from neighbor-
ing continents (Campanian and Maastrichtian of
Provence, France) made it an important taxon
(Allain and Taquet, 2000). Understanding of Late
Cretaceous European dromaeosaurids dramati-
cally increased with the discovery of Balaur, a
more complete partial skeleton of an island-
dwelling velociraptorine from the Maastrichtian
Sebeş Formation of Alba county, Romania (Csiki
et al., 2010; Brusatte et al., 2013). e animal is
perhaps most distinctive for its double sickle claw
on the foot, due to the unusual hypertrophy of
the rst pedal ungual in addition to the typically
enlarged and trenchant second pedal ungual
of dromaeosaurids and other deinonychosaurs.
Although recently argued to be an avialan (Cau
et al., 2015), its status as a velociraptorine was
recently rearmed (Pei et al., in press).
Knowledge of Early Cretaceous European
dromaeosaurids is sparse and supercial. Reexami-
nation of historic reptilian tooth and fragmentary
jaw material from the Berriasian Lulworth Forma-
tion of the U.K. led to Nuthetes being reassigned
as a dromaeosaurid taxon (Milner, 2002), and then
being narrowed to the subfamily Velociraptorinae
(Sweetman, 2004). However, this assignment was
later contested by one of the original authors as
possible tyrannosaurid material instead (Rauhut et
al., 2010). Six fused sacral vertebrae from the Ber-
riasian-Barremian Wessex Formation of the U.K.
2020 PITTMAN ET AL.: THE FOSSIL RECORD 51
TABLE 4
Troodontid fossil record
Continent Geological Unit Country Period Age Age Reference Taxa Reference
Asia Ejinhoro
Formation China Early
Cretaceous Aptian-Albian Sereno, 2010 Sinornithoides Russell and Dong, 1993
Huajiying
Formation China Early
Cretaceous
Hauterivian-
Barremian Pan et al., 2013 Jinfengopteryx Ji et al., 2005
Majiacun
Formation China Late
Cretaceous
Coniacian-
Santonian Tan et al., 2015 Xixiasaurus Lü et al., 2010
Wulansuhai/
Bayan Mandahu
Formation
China Late
Cretaceous Campanian Godefroit et al., 2008 Linhevenator, Philovenator Xu et al., 2011b, 2012b
Jehol Group
(Yixian
Formation)
China Early
Cretaceous
Barremian-
Aptian
Chang et al., 2009,
2017; Pan et al., 2013
Daliansaurus, Jianianhualong,
Liaoningvenator, Mei, Sinovenator,
Sinusonasus, Yixianosaurus (possibly
an avialan)
Xu et al., 2002b, 2017; Xu
and Wang, 2003, 2004b;
Xu and Norell, 2004;
Chang et al., 2017; Shen
et al., 2017a, 2017b; Yin
et al., 2018
Kallamedu
Formation India Late
Cretaceous Maastrichtian Goswami et al., 2013 troodontid tooth Goswami et al., 2013
Khamareen Us
locality Mongolia Early
Cretaceous Cenomanian Makovicky and
Norell, 2004 MPC-D 100/44
Barsbold et al., 1987;
Makovicky and Norell,
2004
Khamaryn Ar
locality Mongolia Early
Cretaceous
Barremian-
Albian
Tsuihiji et al., 2016;
Lucas, 2006 MPC-D 100/140 Tsuihiji, et al., 2016
Djadokhta
Formation Mongolia Late
Cretaceous Campanian
van Itterbeeck et al.,
2005; Dingus et al.,
2008; Hasegawa et
al., 2009
Almas, Byronosaurus, Gobivenator,
Saurornithoides
Osborn, 1924; Norell et
al., 2000; Makovicky et
al., 2003; Bever and
Norell, 2009; Tsuihiji et
al., 2014; Pei et al., 2017a
Nemegt
Formation Mongolia Late
Cretaceous Maastrichtian
Jerzykiewicz and
Russell, 1991;
Shuvalov, 2000; van
Itterbeeck et al., 2005
Borogovia, Tochisaurus, Zanabazar
Barsbold, 1974;
Osmólska, 1987;
Kurzanov and Osmólska,
1991; Norell et al., 2009
52 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
Continent Geological Unit Country Period Age Age Reference Taxa Reference
Asia Kakanaut
Formation Russia Late
Cretaceous Maastrichtian Herman et al., 2016 Troodon ?Godefroit et al., 2009
Udurchukan
Formation Russia Late
Cretaceous Maastrichtian Averianov and Sues,
2007 Troodon ?Averianov and Sues, 2007
Dzharakuduk
Formation Uzbekistan Late
Cretaceous Cenomanian Averianov and Sues,
2007 Urbacodon Averianov and Sues, 2007
North
America
Dinosaur Park
Formation Canada Late
Cretaceous Campanian Eberth, 2005; Brown
et al., 2013
Latenivenatrix, Polyodontosaurus/
Stenonychosaurus/Troodon ?
Gilmore, 1932; Sternberg,
1932; Brown et al., 2013;
Evans et al., 2017; van
der Reest and Currie,
2017
Horseshoe
Canyon
Formation
Canada Late
Cretaceous
Campanian-
Maastrichtian
EberthandBraman,
2012; Quinney et al.,
2013
Albertavenator, Troodon Ryan et al., 1998; Evans
et al., 2017
Old Man
Formation Canada Late
Cretaceous Campanian Eberth, 2005 Troodon Ryan and Russell, 2001
Scollard
Formation Canada
Late
Cretaceous-
Palaeogene
Maastrichtian-
Palaeocene
Khidir and
Catuneanu, 2010 Troodon Weishampel et al., 2004
St. Mary River
Formation Canada Late
Cretaceous Maastrichtian Jackson and
Varricchio, 2017 Troodon Weishampel et al., 2004
Wapiti Formation Canada Late
Cretaceous
Campanian-
Maastrichtian Fanti et al., 2013 Troodon Ryan and Russell, 2001
El Gallo
Formation Mexico Late
Cretaceous Campanian López-Conde et al.,
2018 Troodon Weishampel et al., 2004
Cedar Mountain
Formation U.S. Early
Cretaceous
Berremian?-
Aptian Senter et al., 2012 Geminiraptor Senter et al., 2010
Dakota Formation U.S.
Early to
Late
Cretaceous
Albian-
Cenomanian Barclay et al., 2015 Troodon Eaton et al., 1999
Ferris Formation U.S.
Late
Cretaceous–
Palaeogene
Maastrichtian-
Palaeocene
Lillegraven and
Eberle, 1999 Troodon Lillegraven and Eberle,
1999
TABLE 4 continued
2020 PITTMAN ET AL.: THE FOSSIL RECORD 53
Continent Geological Unit Country Period Age Age Reference Taxa Reference
North
America
Hell Creek
Formation U.S. Late
Cretaceous Maastrichtian
Hoganson and
Edward, 2002;
Fastovsky and
Bercovici, 2016
Troodon Fastovsky and Bercovici,
2016
Judith River
Formation U.S. Late
Cretaceous Campanian Lawver and Jackson,
2017 Troodon Leidy, 1856; Varricchio
and Jackson, 2004
Kaiparowits
Formation U.S. Late
Cretaceous Campanian
Roberts et al., 2005;
Jinnah et al., 2009;
Zanno et al., 2011
Tal os, Troodon Eaton et al., 1999; Zanno
et al., 2011
Kirtland
Formation U.S. Late
Cretaceous Campanian Sullivan and Lucas,
2006 ‘Saurornitholestes’ Sullivan, 2006; Evans et
al., 2014
Lance Formation U.S. Late
Cretaceous Maastrichtian Elżanowski et al.,
2000 Pectinodon/Troodon ?Carpenter, 1982
Morrison
Formation U.S. Late Jurassic Kimmeridgian-
Tithonian
Trujillo and
Kowallis, 2015 Hesperornithoides, Koparion Chure, 1994; Hartman et
al., 2019
Prince Creek
Formation U.S. Late
Cretaceous Maastrichtian Fiorillo et al., 2016 Troodon Fiorillo et al., 2016
Wahwea p
Formation U.S. Late
Cretaceous Campanian Moran et al., 2010 Troodon Eaton et al., 1999
Two Medicine
Formation
U.S./
Canada
Late
Cretaceous Campanian Rogers et al., 1993;
Foreman et al., 2008 Troodon ?Foreman et al., 2008
Europe Painten Formation Germany Late Jurassic Tithonian Foth and Rauhut,
2017
Ostromia (anchiornithine; possibly
an early-diverging avialan) Foth and Rauhut, 2017
Antarctica Snow Hill Island
Formation –Late
Cretaceous Maastrichtian Case et al., 2007
Imperobator (indeterminate
deinonychosaurian material or
nondromaeosaurid paravian)
Case et al., 2007; Turner
et al., 2012; Ely and Case,
2019
TABLE 4 continued
54 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
form the type of Ornithodesmus cluniculus (Seeley,
1887), which probably belongs to a dromaeosau-
rid (Norell and Makovicky, 1997; Naish and Mar-
till, 2007). However, this specimen has a complex
taxonomic history including past identications as
a bird, pterosaur, troodontid, and earlier-diverging
theropod (Anonymous, 1887; Seeley, 1887; Howse
and Milner, 1993; Naish et al., 2001). Dromaeosau-
roides bornholmensis is a taxon known from a tooth
from the Early Cretaceous of Denmark (Bonde and
Christiansen, 2003).
A: Rahonavis ostromi of the Maastrichtian
Maevarano Formation (Rogers et al., 2013) of Mad-
agascar’s Mahajanga Basin was rst described as an
avialan (Forster et al., 1998) as supported by others
(Agnolín and Novas, 2013; Cau, 2018; Novas et al.,
2018). However, it has also been recognized as one
of the rst discovered Gondwanan dromaeosaurids
(Makovicky et al., 2005; Turner et al., 2012; Pei et
al., in press), which we follow in this volume. A
dromaeosaurid from the Albian-Cenomanian
Wadi Milk Formation of Sudan (Dromaeosauridae
incertae sedis (Turner et al., 2012)) is the rst and
only African record reaching into the Early Creta-
ceous (Rauhut and Werner, 1995).
S A: e discovery of Unenlagia
from the Turonian-Coniacian Portezuelo Forma-
tion of Patagonia, Argentina (Calvo et al., 2007)
provides strong support that dromaeosaurids were
not exclusively Laurasian, but occupied Gondwana
as well (Novas and Puerta, 1997). is landmark
discovery was followed by recognition of a second
species, U. paynemili, in addition to the original U.
comahuensis from the same formation (Calvo et
al., 2004) as well as the new genus Neuquenraptor
(Novas and Pol, 2005). However, the latter might
be a junior synonym of Unenlagia (Makovicky et
al., 2005), but this remains unclear (Brissón Egli
et al., 2017). Buitreraptor from the Cenomanian-
Turonian Candeleros Formation of Patagonia
extended the South American record of dromaeo-
saurids into the earliest Late Cretaceous (Makov-
icky et al., 2005) and also provided evidence for
a monophyletic Unenlagiinae in Gondwana,
while Austroraptor demonstrated that their record
extended to the end of the Cretaceous (Campan-
ian-Maastrichtian Allen Formation) (Novas et al.,
2009) and solidied Patagonia, Argentina, as a
hotspot for dromaeosaurid fossils. Pamparaptor is
based on a deinonychosaurian foot from the Port-
ezuelo Formation that is distinct from specimens
of Unenlagia (Porri et al., 2011). is material
has possible unenlagiine anities, but does not
nest exclusively with that clade in phylogenetic
analyses (Gianechini et al., 2018). Overoraptor of
the Cenomanian-Turonian Hiuncul Formation of
Patagonia is known from fragmentary postcranial
material (Motta et al., 2020). Described as a para-
vian, it was recovered as a stem avialan in a phylo-
genetic analysis (Motta et al., 2020). However, the
closeness of its phylogenetic position to contempo-
raneous Patagonian unenlagiine dromaeosaurids as
well as its highly modied deinonychosaurian digit
II-2, suggests that Overoraptor might instead be an
unenlagiine. Unquillosaurus is based on a le pubis
from the Maastrichtian Los Blanquitos Formation
of Patagonia (Powell, 1979). It may be a dromaeo-
saurid (Martínez and Novas, 2006) and was previ-
ously proposed as an indeterminate maniraptoran
theropod (Novas and Agnolín, 2004) and as an
earlier-diverging theropod (Powell, 1979). South
American records outside Argentina are rare, but
possible unenlagiine elements have been reported
from the Late Cretaceous Bauru group of Brazil
(Candeiro et al., 2012; Delcourt and Grillo, 2017).
A: Two isolated teeth associated
with a partial le foot and fragments from the
right foot from the Maastrichtian Snow Hill Island
Formation of James Ross Island, Antarctica were
referred to Dromaeosauridae (Case et al., 2007).
ese were subsequently reinterpreted as indeter-
minate deinonychosaurian material (Turner et al.,
2012). Ely and Case (2019) have recently described
this specimen as Imperobator antarcticus, and
recovered it as a nondromaeosaurid paravian.
T
Troodontids were rst recognized in the late
19th century in North America and it is on that
continent and in Asia where most fossils have
been found (g. 1; table 4). Troodontids are oth-
2020 PITTMAN ET AL.: THE FOSSIL RECORD 55
erwise scarce and have been traditionally thought
of as a Laurasian group, but a single tooth now
suggests that troodontids were possibly present
in Gondwana (g. 1; table 4).
N A: e rst troodontid genus
Troodon was given to a tooth discovered in the
Campanian Judith River Formation of Montana
in the mid-19th century (Leidy, 1856). Originally
thought to belong to a fossil lizard and then a
pachycephalosaur, this is one of three historic
North American troodontid genera, alongside
Polyodontosaurus (Gilmore, 1932) andStenony-
chosaurus (Sternberg, 1932). North American
Campanian- and Maastrichtian-aged troodontids
have experienced a prolonged period of taxo-
nomic instability, including the role of Troodon as
a wastebasket taxon (see Zanno et al., 2011, for
further details) once it was recognized as a thero-
pod (Sternberg, 1945). Campanian material
referred to this genus comes from the Judith
River Formation (Lawver and Jackson, 2017) as
well as the Dinosaur Park (Brown et al., 2013)
and Oldman formations of Alberta, Canada
(Ryan and Russell, 2001), the Two Medicine For-
mation of Alberta, Canada, and Montana (Fore-
man et al., 2008), the Kaiparowits and Wahweap
formations of Utah (Eaton et al., 1999), the El
Gallo Formation of Baja California, Mexico
(Weishampel et al., 2004) and the Campanian-
Maastrichtian Wapiti, Horseshoe Canyon and St.
Mary River formations of Alberta, Canada (Ryan
et al., 1998; Ryan and Russell, 2001). e Two
Medicine material includes eggs, some with
embryos, and nests (Varricchio and Jackson,
2016) as well as skeletons. Troodon has been
reported from Maastrichtian strata including the
Ferris Formation of Wyoming (Lillegraven and
Eberle, 1999), the Hell Creek Formation of Mon-
tana, Wyoming, North Dakota, and South Dakota
(Fastovsky and Bercovici, 2016), the Prince Creek
Formation of Alaska (Fiorillo et al., 2016), the
Lance Formation of Wyoming (Carpenter, 1982),
and the Scollard Formation of Alberta, Canada
(Weishampel et al., 2004). Troodon has even been
assigned to material from the Lower Cretaceous
Dakota Formation of Utah (Eaton et al., 1999),
although this rock unit, now known as the Natu-
rita Formation, has been reassigned to the early
Late Cretaceous (Tucker et al., 2020). Material
from the Dinosaur Park Formation has been
assigned a dierent species name, T. inequalis,
from the original T. formosus (Currie, 2005). e
discovery of Talo s , a partial postcranial skeleton
from the Campanian Kaiparowits Formation of
Utah, provided a chance to reappraise North
American troodontid material, which led to the
suggestion that Troodon is a nomen dubium and
support for the genus Pectinodon (Longrich,
2008; Zanno et al., 2011). e latter, known from
teeth and juvenile skeletal material from the
Maastrichtian Lance Formation of Wyoming, was
originally described as an additional species of
Troodon, T. bakkeri (Carpenter, 1982). Continued
eorts to address the taxonomic confusion aris-
ing from North America’s problematic, highly
fragmentary historic holotypes led to the resur-
rection of the genus Stenonychosaurus for some
troodontid skeletal material from the Dinosaur
Park Formation (Evans et al., 2017). is analysis
was supported by subsequent work that assigned
some of this Stenonychosaurus material to the
new genus Latenivenatrix (van der Reest and
Currie, 2017). Albertavenator was named from a
distinctive partial le frontal recovered from the
Maastrichtian Horseshoe Canyon Formation of
Alberta, Canada (Evans et al., 2017). “Saurornit-
holestes” robustus from the Campanian Kirtland
Formation of San Juan Basin, New Mexico, is an
indeterminate troodontid frontal (Evans et al.,
2014), originally referred to a new species of the
dromaeosaurid Saurornitholestes (Sullivan, 2006).
Geminiraptor, an incomplete maxilla from the
Cedar Mountain Formation of Utah is arguably
one of the most important North American
troodontid specimens because, as the only Early
Cretaceous record, it provides a crucial point of
comparison with better-known Chinese contem-
poraries (Senter et al., 2010). A tooth that is the
holotype ofKoparion (Chure, 1994), and the par-
tial articulated skeleton that forms the type of
Hesperornithoides miessleri (Hartman et al., 2019)
are possible Jurassic troodontid records, both
56 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
from the Morrison Formation of the western
United States.
A: e Gobi Desert of Mongolia provided
the rst Asian record of troodontids: Saurorni-
thoides from the Campanian Djadokhta Forma-
tion of southern Mongolia (Osborn, 1924). Its
reasonably complete skull and partial postcra-
nium was particularly important in the early
days of troodontid research. is animal was
known from one species, S. mongoliensis, that
was later joined by a second species, S. junior,
from the younger Maastrichtian Nemegt For-
mation (Barsbold, 1974), although S. junior is
now ascribed to Zanabazar (Norell et al., 2009).
Other Djadokhta taxa include Byronosaurus,
which is known from a large amount of cranial
material and some postcranial material (Norell
et al., 2000; Makovicky et al., 2003) including,
perhaps, two perinates (Bever and Norell, 2009;
but see Pei et al., 2017a). Gobivenator and Almas
are well-preserved, recently described speci-
mens from this formation, with Gobivenator
one of the best three-dimensionally preserved
troodontids in existence (Tsuihiji et al., 2014;
Pei et al., 2017a). Linhevenator tani, known
from a partial, eroded skeleton, was discovered
from the similar Campanian Wulansuhai
(Bayan Mandahu) Formation across the border
in Nei Mongol, northern China (Xu et al.,
2011b, 2012b). A single leg from the same for-
mation was originally identied as a juvenile
Saurornithoides specimen (Currie and Peng,
1993) and was later assigned to the new taxon
Philovenator (Xu et al., 2012b). Mongolia and
Russia provide the latest Cretaceous records.
Borogovia and Tochisaurus are known from
fragmentary hind-limb elements (Osmólska,
1987; Kurzanov and Osmólska, 1991), and like
Zanabazar, were recovered from the Maastrich-
tian Nemegt Formation of southern Mongolia.
“Troodon” records from the Maastrichtian
Kakanaut and Udurchukan formations of Rus-
sia are expected to belong to one or more new
genera given the recent revisions to Troodon
taxonomy in North America (Averianov and
Sues, 2007; Zanno et al., 2011; Evans et al.,
2017; van der Reest and Currie, 2017). A single
tooth from the Maastrichtian Kallamedu For-
mation of India potentially represents the only
troodontid record from Gondwana (Goswami
et al., 2013), despite the group being known for
over 150 years. Occurrences from China and
Uzbekistan extend the Asian troodontid record
back into the earliest Late Cretaceous as well as
the Early Cretaceous, providing the only
described taxa from these time intervals world-
wide. Xixiasaurus is from the Coniacian-Santo-
nian Majiacun Formation (Lü et al., 2010) of
Henan, China, and Urbacodon is from the
Cenomanian Dzharakuduk Formation of Navoi
Viloyat, Uzbekistan (Averianov and Sues, 2007).
e Early Cretaceous troodontid record of Asia
is well represented in China by at least eight
named genera. e oldest record is Jinfengop-
teryx from the Hauterivian-Barremian Huajiy-
ing (Qiaotou) Formation of Hebei, China, that
was originally described as an avialan and
whose stomach may contain preserved seeds (Ji
et al., 2005; Pan et al., 2013). Sinovenator, Mei,
Sinusonasus, Daliansaurus, Liaoningvenator,
and Jianianhualong were all discovered from the
Barremian-Aptian Yixian Formation of north-
ern China (Xu et al., 2002b, 2017; Xu and
Norell, 2004; Xu and Wang, 2004b; Pan et al.,
2013; Chang et al., 2017; Shen et al., 2017a,
2017b). is formation and the Djadokhta For-
mation represent the most important sources of
troodontid material globally. Sinovenator was
the rst troodontid reported from the Yixian
Formation (Xu et al., 2002b). Initially repre-
sented by a partial skull and a few incomplete
postcranial skeletons (Xu et al., 2002b), later
material included a partial skull with a well-
preserved braincase (Yin et al., 2018). Mei was
rst described on the basis of an exquisitely-
preserved skeleton with a bird-like sleeping
posture, which is arguably the most complete
Early Cretaceous troodontid specimen known
(Xu and Norell, 2004; Pan et al., 2013).
Sinusonasus, Daliansaurus, and Liaoningvenator
all have a similar size as Sinovenator, and each
of them were reported from a single, near com-
2020 PITTMAN ET AL.: THE FOSSIL RECORD 57
TABLE 5
Mesozoic avialan fossil record
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
Asia
Haifanggou and
Tiaojishan
formations
China Middle-Late
Jurassic
Bathonian-
Oxfordian
Gao and Shubin,
2012; Liu et al.,
2012; Wang et
al., 2013c;
Sullivan et al.,
2014; Tian et al.,
2015
Anchiornis, Aurornis (possibly a
synonym of Anchiornis), Caihong,
Eosinopteryx, Pedopenna, Serikornis,
Xiaotingia (possibly all troodontids)
Xu and Zhang, 2005; Xu et al.,
2009, 2011a; Hu et al., 2009, 2018;
Godefroit et al., 2013a, 2013b;
Lefèvre et al., 2017; Pei et al.,
2017b
Dabeigou Formation China Early Cretaceous Hauterivian-
Barremian
Zhang et al.,
2008b Jinguofortis, Eoconfuciusornis Zhang et al., 2008b; Wang et al.,
2018
Huajiying
Formation China Early Cretaceous Hauterivian-
Barremian Pan et al., 2013
Archaeornithura, Cruralispennia,
Eoconfuciusornis, Eopengornis,
Hebeiornis (Ves co rn is ), Jibeinia,
Orienantius, Protopteryx
Hou, 1997a; Zhang and Zhou,
2000; Zhang et al., 2004; Jin et al.,
2008; Wang et al., 2014a,,, 2015a,
2017; Pan et al., 2016; Zheng et
al., 2017; Navalón et al., 2018,
Chiappe et al., 2019a; Liu et al.,
2019
Qiaotou Formation China Early Cretaceous Barremian Wang et al.,
2010 Shenqiornis Wang et al., 2010
Jehol Group (Yixian
Formation; Jiufotang
Formation)
China Early Cretaceous Barremian-Aptian
Chang et al.,
2009, 2017; Pan
et al., 2013
Archaeorhynchus, Changchengornis,
Confuciusornis, D alingheornis, Dingavis,
Eoenantiornis, Eogranivora,
Grabauornis, Gretcheniao,
Hongshanornis, Iteravis, Jeholornis,
Jixiangornis (likely a synonym of
Jeholornis), Junornis, Liaoningornis,
Longicrusavis, Longirostrav is, Mirusavis,
Monoenantiornis, Paraprotopteryx,
Sapeornis , Shanweiniao, Sulcavis,
Tianyuornis, Xinghaiornis, Ya ng av is ,
Yan orn is , Zhongornis (possibly a
scansoriopterygian)
Hou et al., 1995, 1996, 1997b,
1999a, 1999b, 2002, 2004; Hou,
1996, 1997b; Chiappe et al., 1999,
2007, 2014, 2019b; Ji et al., 1999,
2002a, 2002b; Xu et al., 1999;
Zhang et al., 2006, 2009; Zhou
and Zhang, 2005, 2006a, 2006b;
Gao et al., 2008, 2012; O’Connor
et al., 2009, 2010, 2011a, 2013,
2016c; Li et al., 2010; Wang et al.,
2013d, 2013e, 2019c; ; Zheng et
al., 2007, 2013, 2014, 2018;
Dalsätt et al., 2014; Lefèvre et al.,
2014; Zhou et al., 2014a; Hu and
O’Connor, 2017; Liu et al., 2017;
Wang and Zhou, 2018
58 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
Asia Alethoalaornis, Archaeorhynchus,
Bellulornis, Bohaiornis, Boluochia,
Cathayornis (Largirostrornis,
Longchengornis), Chaoyangia,
Chiappeavis, Chongmingia,
Confuciusornis, D alianraptor (might be
a chimera), Dapingfangornis,
Eocathayornis, Fortunguavis, Gracilornis,
Houornis, Huoshanornis, Jeholornis
(Shenzhouraptor), Jianchangornis,
Linyior nis, Longipteryx, Longusunguis,
Mengciusornis, Parabohaiornis,
Parahongshanornis, Parapengornis,
Pengornis, Piscivoravis,
Piscivorenantiornis, Pter ygornis,
Rapaxav is, Sapeorni s, Schizooura,
Shangyang, Shengjingornis, Sinornis,
Songlingornis, Xi angornis, Yan or nis,
Yixianornis, Yuanjiawaornis,
Zhongjianornis, Zhouornis
Sereno and Rao, 1992; Zhou et
al., 1992, 2004, 2008, 2009, 2010,
2012, 2013, 2014; Hou and
Zhang, 1993; Zhou, 1995, 2002;
Hou, 1997a; Hou et al., 2002;
Czerkas and Ji, 2002; Ji et al.,
2002a; Zhou and Hou, 2002;
Zhou and Zhang, 2001, 2002a,
2002b, 2003a, 2003b,, 2006a;
Gong et al., 2004; Dalsätt et al.,
2006;; Li et al., 2006, 2007, 2008,
2010a, 2010b, 2011, 2012, 2014b;
Morschhauser et al., 2009; Yuan,
2010; Hu et al., 2010, 2011, 2015a,
2015b; Li and Hou,
2011O’Connor et al., 2011a, 2012,
2016a; Pu et al., 2013; Wang et al.,
2010b, 2014b, 2014d, 2014e,
2016b, 2016c, 2016d, 2019d;
Zhang et al., 2001, 2013; Wang
and Zhou, 2018, 2019
Jingchuan
Formation China Early Cretaceous Barremian-Aptian? Lockley et al.,
2012
Otogornis (originally assigned to the
Yijinhuoluo Formation),
enantiornithines
Hou, 1994; Li et al., 2008b; Zhang
et al., 2010; Wang and Liu, 2015
Xiagou Formation China Early Cretaceous Aptian O’Connor et al.,
2016b
Avi ma ia , Changmaornis, Dunhuangia,
Feitianius, Gansus, Jiuquanornis,
Qiliania, Yumenornis
Hou and Liu, 1984; You et al.,
2006, 2010; Ji et al., 2011; Wang
et al., 2013b, 2013f, 2015b;
O’Connor et al., 2016b; Bailleul et
al., 2019
Jiangdihe Formation China Late Cretaceous Turonian-Santonian Wang et al.,
2014c Parvavi s Wang et al., 2014c
Qiupa Formation China Late Cretaceous Campanian-
Maastrichtian Jiang et al., 2011 enantiornithines Xu et al., 2011c
Kuwajima
Formation Japan Early Cretaceous Barremian Sano and Yabe,
2017 enantiornithines Matsuoka et al., 2002
TABLE 5 continued
2020 PITTMAN ET AL.: THE FOSSIL RECORD 59
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
Asia Kitadani Formation Jap an Early Cretaceous Aptian Sano and Yabe,
2017 Fukuipteryx Imai et al., 2019
Sinuiju series North Korea Early Cretaceous -Gao et al., 2009 confuciusornithiforms, enantiornithines Gao et al., 2009
“Burmese Amber” Myanmar Late Cretaceous Cenomanian Xing et al., 2017 enantiornithines; Elektorornis Xing et al., 2016, 2017, 2019a,b,c
Khodzhakul Svita Uzbekistan Early Cretaceous Albian Kurochkin, 2000 Horezmavis Kurochkin, 2000
Bissetky Formation Uzbekistan Late Cretaceous Coniacian Panteleev, 2018 enantiornithines, ornithuromorphs
(Zhyraor nis)
Nessov, 1984; Kurochkin, 2000;
Panteleev, 2018
“Kushmurun” Kazakhstan Late Cretaceous Maastrichtian Dyke et al., 2006 Asiahesperornis Nessov and Prizemlin, 1991;
Dyke et al., 2006
Ilek Formation Russia Early Cretaceous Barremian-Aptian O’Connor et al.,
2014 Evgenavis, Mystiornis Kurochkin et al, 2011; O’Connor
et al., 2014
Rybuskha Formation Russia Late Cretaceous Campanian Kurochkin, 2000 Hesperornis Marsh, 1872; Kurochkin, 2000
“Ouadi al Gabour” L ebanon Late Cretaceous Cenomanian Cau and
Arduini, 2008 Enantiophoenix Cau and Arduini, 2008
Andaikhudag
Formation Mongolia Early Cretaceous Hauterivian-
Barremian
Zelenkov and
Averianov, 2016 Ambiortus, Holbotia
Kurochkin, 1982; O’Connor and
Zelenkov, 2013; Zelenkov and
Averianov, 2016
Barun Goyot
Formation Mongolia Late Cretaceous Campanian-
Maastrichtian
Gradziński and
Jerzykiewicz,
1974a, 1974b
Gobipteryx, Hollanda, nests of
enantiornithines?
Elżanowski, 1974; Elżanowski,
1977; Bell et al., 2010; Varricchio
and Barta, 2015
Djadokhta
Formation Mongolia Late Cretaceous Campanian?
van Itterbeeck et
al., 2005; Dingus
et al., 2008;
Hasegawa et al.,
2009
Apsarav is, Gobipteryx, nests of
enantiornithines?
Chiappe et al., 2001; Norell and
Clarke, 2001; Varricchio and
Barta, 2015
Nemegt Formation Mongolia Late Cretaceous Maastrichtian?
Jerzykiewicz and
Russell, 1991;
Shuvalov, 2000;
van Itterbeeck et
al., 2005
Brodavis, Gurilynia, Judinornis
Nessov and Borkin, 1983;
Kurochkin, 1999; Martin et al.,
2012
Australia Wonthaggi
Formation Australia Early Cretaceous Barremian-Aptian Close et al., 2009 enantiornithines Rich et al., 1999; Close et al., 2009
TABLE 5 continued
60 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
Australia Toolebuc Formation Australia Early Cretaceous Albian Close et al., 2009 enantiornithines Molnar, 1986
Griman Creek
Formation Australia Early Cretaceous Albian Close et al., 2009 enantiornithines Molnar, 1999
Europe
Solnhofen
Limestone
(Altmühltal
Formation)
Germany Late Jurassic Tithonian Rauhut et al.,
2018 Archaeopteryx
Owen, 1863; Dames, 1884; Heller,
1959; Wellnhofer, 1974, 1988,
1993, 2009; Mayr et al., 2005;
Wellnhofer and Röper, 2005;
Tischlinger, 2009; Foth et al.,
2014; Rauhut et al., 2018; Kundrát
et al., 2019.
Painten Formation Germany Late Jurassic Tithonian Foth and
Rauhut, 2017
Ostromia (anchiornithine; possibly a
troodontid; formerly Haarlem
Archaeopteryx)
Foth and Rauhut, 2017
Mörnsheim
Formation Germany Late Jurassic Tithonian Foth and
Rauhut, 2017 Archaeopteryx Tischlinger, 2009; Kundrát et al.,
2019
La Pedrera de
Rubies Lithographic
Limestones
Formation
Spain Early Cretaceous Barremian Szwedo and
Ansorge, 2015 Noguerornis, enantiornithines Lacasa-Ruiz, 1989; Sanz et al.,
1997
Calizas de la
Huérguina
Formation
Spain Early Cretaceous Barremian
Buscalioni and
Fregenal-
Martínez, 2010
Concornis, Eoalulavis, Iberomesornis
Sanz and Bonaparte, 1992; Sanz
and Buscalioni, 1992; Sanz et al.,
1996, 2002; Sereno, 2000; Navalón
et al., 2015
Melovatskaya
Formation Russia Late Cretaceous Cenomanian Kurochkin et al.,
2007 Cerebravis Kurochkin et al., 2007
Csehbánya
Formation Hungary Late Cretaceous Santonian Dyke and Ösi,
2010 Bauxitornis Dyke and Ösi, 2010
Grès à Reptiles
Formation France Late Cretaceous Campanian-
Maastrichtian
Walker et al.,
2007 Gargantuavis, Martinavis Buetaut, 1998; Walker et al.,
2007
“Fox-Amphoux
basin” France Late Cretaceous Maastrichtian? Buetaut et al.,
1995 unnamed taxon Buetaut et al., 1995
TABLE 5 continued
2020 PITTMAN ET AL.: THE FOSSIL RECORD 61
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
Europe Sebeş Formation Romania Late Cretaceous Maastrichtian Brusatte et al.,
2013 nests and bones of enantiornithines Dyke et al., 2012
“Hateg Basin” Romania Late Cretaceous Maastrichtian Wang et al.,
2011 enantiornithines Wang et al., 2011
Maastricht
Formation Belgium Late Cretaceous Maastrichtian Keutgen, 2018 Ichthyornis-like bird, Asteriornis Dyke et al., 2002; Field et al.,
2020
South
America Crato Formation Brazil Early Cretaceous Aptian
de Souza
Carvalho et al.,
2015
enantiornithines; Cratoavis (valid?) Naish et al., 2007; de Souza
Carvalho et al., 2015
Portezuelo
Formation Argentina Early Cretaceous Turonian-
Coniacian
Agnolín et al.,
2006 ornithuromorph Agnolín et al., 2006
Bajo de la Carpa
Formation Argentina Late Cretaceous Santonian Fernández et al.,
2013
Neuquenornis, Patagopteryx, nests with
embryonic remains
Alvarenga and Bonaparte, 1992;
Chiappe and Calvo, 1994;
Schweitzer et al., 2002; Fernández
et al., 2013
Las Curtiembres
Formation Argentina Late Cretaceous Campanian Novas et al.,
2010 Intiornis Novas et al., 2010
Allen Formation Argentina Late Cretaceous Campanian-
Maastrichtian
Armas and
Sánchez, 2015 Limenavis Clarke and Chiappe, 2001
Los Alamitos
Formation Argentina Late Cretaceous Campanian-
Maastrichtian
Agnolín and
Martinelli, 2009 Alamitornis Agnolín and Martinelli, 2009
Bauru Group Brazil Late Cretaceous Campanian-
Maastrichtian Nava et al., 2015 enantiornithines Nava et al., 2015
Quiriquina
Formation Chile Late Cretaceous Campanian-
Maastrichtian Olson, 1992 Neogaeornis Lambrecht, 1929; Olson, 1992;
Mayr, 2016
Lecho Formation Argentina Late Cretaceous Maastrichtian Walker and
Dyke, 2009
Elbretornis, Enantiornis, Lectavis,
Martin avis, Yungavolucris,
Soroavisaurus
Walker, 1981; Chiappe, 1993;
Walker et al., 2007; Walker and
Dyke, 2009
La Colonia
Formation Argentina Late Cretaceous Maastrichtian Lawver et al.,
2011 enantiornithines Lawver et al., 2011
North
America Ashville Formation Canada Late Cretaceous Cenomanian Tokaryk et al.,
1997 Pasquiaornis Tokaryk et al., 1997
TABLE 5 continued
62 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
North
America
Belle Fourche
Formation Canada Late Cretaceous Cenomanian Clarke, 2004 Ichthyor nis-like material Clarke, 2004
Woodbine
Formation U.S. Late Cretaceous Cenomanian Tykoski and
Fiorillo, 2010 Flexomornis Tykoski and Fiorillo, 2010
Kaskapau Formation Canada Late Cretaceous Turonian Clarke, 2004 Ichthyor nis-like material Clarke, 2004
“Canadian Arctic
circle” Canada Late Cretaceous Turonian Bono et al., 2016 Tingmiatornis Bono et al., 2016
Mancos Shale
Formation U.S. Late Cretaceous Turonian Clarke, 2004 Ichthyornis Lucas and Sullivan, 1982; Clarke,
2004
Austin Chalk
Formation U.S. Late Cretaceous Coniacian-
Santonian Clarke, 2004 Ichthyornis Clarke, 2004
Niobrara Formation U.S. Late Cretaceous Coniacian-
Campanian
Da Gama et al.,
2014
Apatornis, Baptornis, Hesperornis,
Iaceornis, Ichthyor nis, Parahesperornis,
hesperornithiforms
Marsh, 1872, 1877, 1880; Martin
and Tate, 1976; Martin, 1984;
Clarke, 2004; Bell and Chiappe,
2015; Field et al., 2018b
Belly River Group Canada Late Cretaceous Campanian Longrich, 2009 ornithurines Longrich, 2009
Dinosaur Park
Formation Canada Late Cretaceous Campanian Brown et al.,
2013 enantiornithines Buetaut, 2010
Northumberland
Formation Canada Late Cretaceous Campanian McLachlan et
al., 2017 Maaqwi Morrison et al., 2005; McLachlan
et al., 2017
La Bocana Roja
Formation Mexico Late Cretaceous Campanian Peecook and
Sidor, 2015 Alex ornis Brodkorb, 1976
Kaiparowits
Formation U.S. Late Cretaceous Campanian Zanno et al.,
2011 Mirarce Atterholt et al., 2018
Mooreville Chalk
Formation U.S. Late Cretaceous Campanian Clarke, 2004 Halimornis, Ichthyornis Chiappe et al., 2002; Clarke, 2004;
Field et al., 2018b
Two Medicine
Formation U.S. Late Cretaceous Campanian Foreman et al.,
2008 Gettyia Atterholt et al., 2018
TABLE 5 continued
2020 PITTMAN ET AL.: THE FOSSIL RECORD 63
Continent Geological Unit Countr y Period Age Age Reference Taxa Reference
North
America Pierre Shale U.S. Late Cretaceous Campanian-
Maastrichtian
Aotsuka and
Sato, 2016 hesperornithiforms Bell and Chiappe, 2015
Frenchman
Formation Canada Late Cretaceous Maastrichtian Martin et al.,
2012
enantiornithines, hesperornithiforms,
ornithurines
Longrich et al., 2011; Martin et
al., 2012
“Canadian Arctic
Circle” Canada Late Cretaceous Maastrichtian Hou, 1999 Canadaga Hou, 1999
Hell Creek
Formation U.S. Late Cretaceous Maastrichtian Fastovsky and
Bercovici, 2016
Avisaurus, hesperornithiforms,
ornithurines
Brett-Surman and Paul, 1985;
Longrich et al., 2011
Lance Formation U.S. Late Cretaceous Maastrichtian Elzanowski et
al., 2000 ornithurines Longrich et al., 2011
Africa Maevarano
Formation Madagascar Late Cretaceous Maastrichtian Rogers et al.,
2013 Vorona, enantiornithines, Rahonavis?
Forster et al., 1996; O’Connor and
Forster, 2010; Agnolín and Novas,
2013
Antarctica López de Bertodano
Formation –Late Cretaceous Maastrichtian Olivero et al.,
2007
Veg av is , Polarornis; Ichthyornis -like
material
Zinsmeister, 1985; Noriega and
Tambussi, 1995; Chatterjee, 2000;
Clark et al., 2005a
Snow Hill Island
Formation –Late Cretaceous Maastrichtian Cordes-Person,
2020
Antarcticavis; Imperovator
(indeterminate deinonychosaurian
material or nondromaeosaurid
paravian)
Case et al., 2007; Turner et al.,
2012; Ely and Case, 2019; Cordes-
Person, 2020
TABLE 5 continued
64 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
A
e fossil record of stem birds (those mem-
bers of Avialae falling outside the crown group
Aves; alternatively crown group birds are referred
to as Neornithes, with Aves consisting of stem
and crown birds) has rapidly expanded since the
1980s (table 5). Prior to this, the record of Meso-
zoic birds consisted almost entirely of the Late
Jurassic Archaeopteryx from the Solnhofen Lime-
stone of southern Germany (Owen, 1863) and
the Late Cretaceous “Odontornithes” (ornithu-
rines Ichthyornis and the Hesperornithiformes)
from marine deposits in North America (Marsh,
1880), with little to no evidence documenting
the evolution of the avian postcranium from the
primitive condition in Archaeopteryx to the
nearly modern condition in Ichthyornis (g. 1;
table 5). Since the 1980s the number of species
has more than doubled and the number of speci-
mens has increased more than tenfold. In addi-
tion to the overwhelming collections uncovered
in the Jehol Lagerstätte of northeastern China,
important specimens have been discovered in
Cretaceous deposits all over the world (O’Connor
et al., 2011a) (g. 1).
A: e greatest concentration of non-avian
avialan fossils is found in Asia. More than half of
all known species of Cretaceous birds are from
the Early Cretaceous Hauterivian - Aptian Jehol
lagerstätten, preserved in northeastern China,
which occurs in three successive formations (and
their stratigraphic equivalents): the Huajiying,
Yixian, and Jiufotang formations, deposited from
about 131 to 120 Ma (Zhou and Zhang, 2006a;
Pan et al., 2013). is includes the only lineage
of long bony-tailed birds other than the Archae-
opterygiformes, the Jeholornithiformes (Zhou
and Zhang, 2002a); almost the entire record of
non-ornithothoracine pygostylians, including
the Sapeornithiformes, Confuciusornithiformes,
and the Jinguofortisidae (Hou et al., 1995; Zhou
and Zhang, 2002b; Wang et al., 2016b, 2018); and
the earliest-known record of the Enantiornithes
and Ornithuromorpha (together Ornithothora-
ces) in the Huajiying Formation (Zhang and
plete skeleton (Xu and Wang, 2004b; Shen et al.,
2017a, 2017b). Jianianhualong is only known
from a single attened specimen from the Yix-
ian Formation, which preserves the rst record
of asymmetrical feathers in troodontids (Xu et
al., 2017). Sinornithoides is known from the
Aptian-Albian Ejinhoro Formation of Nei Mon-
gol, China, based on a near complete skeleton
(Russell and Dong, 1993). Across the border in
Mongolia, unnamed Early Cretaceous troodon-
tids have been reported, including the well-
known “Early Cretaceous troodontid” MPC-D
100/44 and MPC-D 100/140 (Barsbold et al.,
1987; Tsuihiji et al., 2016).
In northeastern China, the Middle Jurassic
Bathonian Haifanggou Formation yields Pedo-
penna (Xu and Zhang, 2005), while the Late Juras-
sic Oxfordian Tiaojishan Formation yields
Anchiornis, Auronis, Caihong, Eosinopteryx,
Serikornis, and Xiaotingia (Xu et al., 2008, 2011a;
Godefroit et al., 2013a, 2013b; Lefèvre et al., 2017;
Hu et al., 2018). ese taxa have been proposed as
members of the Anchiornithinae, a controversial
clade of long-tailed, early-diverging paravians.
Anchiornithines were rst described as early avia-
lans, but their phylogenetic placement lacks con-
sensus (Hu et al., 2009; Lee and Worthy, 2011; Xu
et al., 2011a; Agnolín and Novas, 2013; Godefroit
et al., 2013a, 2013b; Foth and Rauhut, 2017;
Lefèvre et al., 2017; Pei et al., 2017b, in press). If
they are troodontids as recovered in some recent
works, they would be the oldest fossils of these
animals (Hu et al., 2009). Hesperornithoides, from
the Morrison Formation of Wyoming, is also a
potential Jurassic troodontid (Hartman et al.,
2019). Two Early Cretaceous taxa from the Yixian
Formation, Liaoningvenator and Yixianosaurus,
have been recovered as anchiornithines and are
the only anchiornithine taxa besides Ostromia
(previously an archaeopterygid) that have been
found outside the Tiaojishan Formation (Cau et
al., 2017; Foth and Rauhut, 2017; Shen et al.,
2017b). However, the phylogenetic placement of
Yixianosaurus remains controversial (Dececchi et
al., 2012; Xu et al., 2013a; Cau et al., 2017; Foth
and Rauhut, 2017; Lefèvre et al., 2017).
2020 PITTMAN ET AL.: THE FOSSIL RECORD 65
Zhou, 2000; Wang et al., 2014a, 2015). We adopt
the node-based denition for the Ornithuromor-
pha because of the preference of our authors:
Euornithes Sereno et al. 1998 is the stem-based
denition. Two species of Jeholornis are currently
recognized, J. prima and J. palmapenis (the holo-
type of “J. curvipes” is thought to be tampered)
(O’Connor et al., 2012). e Sapeornithiformes
is currently monospecic with all reported speci-
mens purportedly ontogimorphs of Sapeornis
chaoyangensis (Pu et al., 2013). Jeholornis and
Sapeornis clades occur predominantly in the Jiu-
fotang Formation with a few specimens also col-
lected in the Yixian. e Confuciusornithiformes
is much more diverse (Eoconfuciusornis, Confu-
ciusornis, Changchengornis, and Ya ngav i s : Wang
and Zhou, 2018; Wang et al., 2019b). e early-
diverging Eoconfuciusornis zhengi and another
indeterminate confuciusornithiform have been
reported from the Huajiying Formation (Zhang
et al., 2008b; Navalón et al., 2018). Most confu-
ciusornithiform specimens are referable to Con-
fuciusornis sanctus and are found in the Yixian
Formation with a few specimens from the Jiufo-
tang. C. dui (Hou et al., 1999), Changchengornis
hengdaoziensis (Chiappe et al., 1999), and Yanga-
vis confucii (Wang and Zhou, 2018) are known
only from single specimens. Enantiornithines
and ornithuromorphs are found throughout the
entirety of the Jehol Biota, with diversity increas-
ing through time, peaking in the Jiufotang For-
mation. Currently, approximately 41 valid species
of enantiornithines are recognized compared to
approximately 19 species of ornithuromorphs.
Diverse subclades are also recognized, such as
the enantiornithine Pengornithidae (e.g., Eopen-
gornis, Chiappeavis: O’Connor et al., 2016a),
Bohaiornithidae (e.g., Sulcavis, Longusunguis:
Wang et al., 2014b), and Longipterygidae (e.g.,
Boluochia, Longipteryx: O’Connor et al., 2011b),
and the ornithuromorph lineage, the Hongsha-
nornithidae (e.g., Archaeornithura, Longicrusa-
vis: O’Connor et al., 2010). e Pengornithidae
and Hongshanornithidae lineages persisted for
the entire duration of the Jehol Biota (Wang et
al., 2014a, 2015). Jehol equivalent deposits in
nearby basins also preserve enantiornithines
(e.g., Qiaotou, Dabeigou, and Yijinhuoluo
formations).
e slightly younger Aptian Xiagou Forma-
tion in Gansu, northwestern China, has also pro-
duced a small diversity of enantiornithines (e.g.,
Feitianius, Qiliania: Ji et al., 2011; O’Connor et
al., 2016b) and ornithuromorphs (Jiuquanornis,
Changmaornis: Wang et al., 2013b) with a major-
ity of the collected specimens assigned to the
ornithuromorph Gansus yumenensis (You et al.,
2006). e Late Cretaceous record consists of
only two isolated specimens referable to the
Enantiornithes: Parvavis from the Turonian-San-
tonian Jiangdihe Formation (Wang et al., 2014c)
and an unnamed taxon from the upper Upper
Cretaceous Qiupa Formation.
Fukuipteryx prima is the rst nonornithotho-
racine pygostylian to be found outside of the
Jehol Biota basins (Imai et al., 2019). Its partial
skeleton as well as a single enantiornithine
humerus have been reported from the Lower
Cretaceous Tetori Group in Japan (Matsuoka et
al., 2002; Imai et al., 2019) from the Barremian
Kuwajima Formation and Aptian Kitadani For-
mation respectively. Confuciusornithiforms and
enantiornithines have been reported in the
North Korean Lower Cretaceous Sinuiju series
(Gao et al., 2009). In southeastern Asia, Ceno-
manian (~99 Ma) age amber from Myanmar has
recently become an unlikely major source of
Cretaceous birds, recording a fauna of very small
precocial enantiornithines including the taxon
Elektorornis (Xing et al., 2016, 2017, 2019a,b,c).
In Central Asia, a large number of fragments
have been collected from the Turonian Bissekty
Formation in Uzbekistan (Panteleev, 2018).
ese are apparently referable to enantiorni-
thines and ornithuromorphs, including forms
related to Ichthyornis (Kurochkin, 2000). e
controversial and fragmentary enantiornithine
taxon Horezmavis comes from Albian deposits of
the Khodzhakul Formation, also in Uzbekistan
(Kurochkin, 2000). A hesperornithiform, Asia-
hesperornis, has been described from numerous
fragments collected from Maastrichtian deposits
66 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
in Kazakhstan (Dyke et al., 2006). A few speci-
mens have been collected in Russia including
Evgenavis and Mystiornis from the Barremian
Ilek Formation, both of uncertain phylogenetic
anity (Kurochkin et al., 2011; O’Connor et al.,
2014), and Hesperornis rossicus from the Campa-
nian Rybuskha Formation (Kurochkin, 2000). In
western Asia, a single enantiornithine specimen
(Enantiophoenix) has been collected from Ceno-
manian marine limestones in Lebanon (Dalla
Vecchia and Chiappe, 2002).
Several early-diverging avialan skeletons as
well as nests have been discovered in Mongolia.
e enantiornithine Holbotia and the ornithu-
romorph Ambiortus were collected from the
Hauterivian-Barremian Andaikhudag Forma-
tion in the Central Mongolian Altai, both pre-
serving so tissue (O’Connor and Zelenkov,
2013; Zelenkov and Averianov, 2016). All other
specimens are from Late Cretaceous deposits.
e early Late Cretaceous Javkhlant Formation
has yielded enantiornithine embryos (Varric-
chio et al., 2015). e Campanian-Maastrich-
tian Barun Goyot Formation has produced
several specimens of the enantiornithine Gobi-
pteryx (Elzanowski, 1977) and the only known
specimen of the ornithuromorph Hollanda (Bell
et al., 2010). e Ukhaa Tolgod locality, which
is attributed to the Campanian Djadokhta For-
mation, has produced a skull of the enantiorni-
thine Gobipteryx (Chiappe et al., 2001) and the
only known specimen of the ornithuromorph
Apsaravis (Norell and Clarke, 2001; Clarke and
Norell, 2002). e Tögrögiin Shiree locality of
the Campanian Djadokhta Formation has
yielded the enantiornithine Elsornis, which is
represented by a partial articulated skeleton
(Chiappe et al., 2007). Both the Barun Goyot
and Djadokhta formations have also produced
nests probably belonging to enantiornithines
(Varricchio and Barta, 2015). Fragmentary hes-
perornithiforms including Brodavis mongolien-
sis and Judinornis and the enantiornithine
Gurilynia were collected in the Maastrichtian
Nemegt Formation (Kurochkin, 2000; Clarke
and Norell, 2004).
e Oxfordian-aged anchiornithines were
rst described as early birds and this phyloge-
netic placement has been recovered by several
independent studies (Xu et al., 2008, 2011a;
Agnolín and Novas, 2013; Godefroit et al., 2013a;
2013b). However, until consensus is reached (see
Pittman, et al., chapter 1), Archaeopteryx of Ger-
many remains the oldest unequivocal bird (see
Europe section below).
A: Fragmentary enantiornithines
are reported from the Barremian-Aptian Wont-
haggi Formation (Close et al., 2009) and the
Albian Toolebuc and Griman Creek formations
(Molnar, 1986; Kurochkin and Molnar, 1997;
Molnar, 1998; 1999). Contra Molnar (1999),
reports of ornithuromorphs are likely misidenti-
ed enantiornithines (J. O’C., personal obs.).
E: Outside China, the greatest concen-
tration of exceptionally well-preserved speci-
mens of nonavian avialans occurs in the Early
Cretaceous (Barremian) Las Hoyas lagerstätte
(La Huerguina Formation) near Cuenca, Spain.
ese deposits have produced half a dozen enan-
tiornithines, several of which represent distinct
taxa (Concornis, Eoalulavis, and Iberomesornis),
with most preserving at least some so tissue
(Sanz et al., 2002; Navalón et al., 2015). A pellet
containing several juveniles and a perinate has
also been collected (Sanz et al., 2001; Knoll et al.,
2018). Two enantiornithine specimens (includ-
ing the holotype of Noguerornis) have also been
collected from the lithographic limestones of the
Hauterivian-Barremian La Pedrera de Rúbies
Formation near Montsec, Spain (Lacasa-Ruiz,
1988; Sanz et al., 1997; Szwedo and Ansorge,
2015). Fragmentary enantiornithines including
the holotype of Martinavis cruzyensis and the
ornithothoracine Gargantuavis have been col-
lected from late Campanian–early Maastrichtian
deposits in southern France (Buetaut et al.,
1995; Buetaut, 1998; Walker et al., 2007). In
Romania, an enantiornithine nesting colony that
also preserved bones has been found in the
Maastrichtian Sebeş Formation (Dyke et al.,
2012), and an enantiornithine humerus has been
described from Upper Cretaceous deposits in the
2020 PITTMAN ET AL.: THE FOSSIL RECORD 67
Hateg Basin (Wang et al., 2011). Several enan-
tiornithine elements have been described from
the Santonian Csehbánya Formation in Hungary,
including a tarsometatarsus used to erect the
taxon Bauxitornis (Dyke and Ösi, 2010). A cra-
nial endocast inferred to be avialan (Cerebavis)
was collected from Cenomanian deposits in
European Russia (Kurochkin et al., 2007). Frag-
mentary remains of Hesperornithiformes are
known from Campanian marine deposits of
southern Sweden (Rees and Lindgren, 2005). A
historically important specimen is Enaliornis
from the Cambridge Greensand member of the
West Melbury Marly Chalk Formation of south-
east England. is specimen was one of the rst
Mesozoic avialans ever collected and is now con-
sidered a hesperornithomorph (Elzanowski and
Galton, 1991).
S A: In 1981 the Enantiornithes
was named from a large collection of isolated ele-
ments found in the Maastrichtian Lecho Forma-
tion of northwestern Argentina (Walker, 1981).
Several taxa have been named, consisting of a few
elements or less (e.g., Enantiornis, Elbretornis, and
Yungavolucris) (Chiappe, 1993; Walker and Dyke,
2010). e partial skeletons of the avisaurid enan-
tiornithine Neuquenornis (Chiappe and Calvo,
1994) and the early-diverging ornithuromorph
Patagopteryx (Alvarenga and Bonaparte, 1992)
were found soon aer in the Santonian Bajo de la
Carpa Formation of central Argentina, which has
also yielded nests with embryonic remains (Sch-
weitzer et al., 2002; Fernández et al., 2013). Frag-
mentary enantiornithines have been reported in
the Campanian Las Curtiembres Formation of
northwestern Argentina (Intiornis) (Novas et al.,
2010) and the Upper Cretaceous La Colonia For-
mation of southern Argentina (Lawver et al.,
2011). Fragmentary ornithuromorph taxa have
also been published from the Campanian-Maas-
trichtian Allen Formation (Limenavis) (Clarke
and Chiappe, 2001) and the similarly aged Los
Alamitos Formation (Alamitornis) (Agnolín and
Martinelli, 2009), both located in central Argen-
tina. A partial ornithuromorph coracoid was
described from the Turonian-Coniacian Portezu-
elo Formation, also in central Argentina (Agnolín
et al., 2006). In Brazil several important enantior-
nithines have been described from the Lower Cre-
taceous Crato Formation (Naish et al., 2007; de
Souza Carvalho et al., 2015). More recently a
diverse but as yet undescribed enantiornithine
avifauna is being excavated in the Campanian-
Maastrichtian Bauru Group (Nava et al., 2015).
Neogaeornis, from the Campanian-Maastrichtian
Quiriquina Formation of Chile (Lambrecht,
1929), was identied as an early representative of
Gaviiformes (loons) (Olson, 1992); however, it is
based on a single tarsometatarsus and its identi-
cation as a crown bird is highly uncertain (Mayr,
2009, 2016).
N A: Only Late Cretaceous birds
have been collected in North America. Alexornis
(Enantiornithes) from the Campanian Roja (La
Bocana Roja) Formation in Baja California is the
only specimen known from Mexico (Brodkorb,
1976). In the United States, fragmentary remains
of enantiornithines have been collected in the
Campanian Kaiparowits (Mirarce) and Two Medi-
cine (Gettyia) formations (Atterholt et al., 2018),
the Campanian Mooreville Chalk (Halimornis)
(Chiappe et al., 2002), and the Cenomanian
Woodbine Formation (Flexomornis) (Tykoski and
Fiorillo, 2010). e Maastrichtian Hell Creek For-
mation has yielded fragmentary remains of enan-
tiornithines (Avisaurus), indeterminate
(non-hesperornithiform or ichthyornithiform)
ornithurines, and hesperornithiforms (Longrich
et al., 2011). Hesperornithiforms have also been
collected from the late Coniacian–early Campan-
ian Smoky Hill Chalk Member of the Niobrara
Formation and the Campanian-Maastrichtian
Pierre Shale (Bell and Chiappe, 2015). Numerous
specimens of the ornithurine Ichthyornis have
been collected from the Smoky Hill Chalk Mem-
ber of the Niobrara Formation, with additional
remains found in Turonian and Campanian
deposits belonging to the Mancos Shale, Moorev-
ille Chalk, and other formations (Clarke, 2004).
The fragmentary ornithurines Apatornis and
Iaceornis are also known from the Smoky Hill
Chalk Member (Clarke, 2004). e Maastrichtian
68 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
Lance Formation has also yielded indeterminate
ornithurine fragments (Longrich et al., 2011).
Fragmentary specimens of enantiornithines
and ornithuromorphs have been collected across
Canada, reported in the Campanian Northum-
berland Formation (Nanaimo Group, from
which the Ornithurine Maaqwi is reported)
(Morrison et al., 2005; McLachlan et al., 2017)
and Cenomanian Ashville Formation (Tokaryk
et al., 1997), the latter including the hesperor-
nithiform Pasquiaornis. An enantiornithine frag-
ment has been reported from the Campanian
Dinosaur Park Formation (Buetaut, 2010), and
the Campanian Belly River Group has produced
a fragmentary fauna consisting primarily of
ornithurine birds (Longrich, 2009). Enantiorni-
thines, indeterminate ornithurines, and hesper-
ornithiform fragments are reported from the
Maastrichtian Frenchman Formation (Longrich
et al., 2011; Martin et al., 2012). Fragmentary
Ichthyornis-like material has been reported from
the Turonian Kaskapau Formation and Cenoma-
nian Belle Fourche Formation (Clarke, 2004).
From within the Canadian Arctic circle two spe-
cies have been named: Tingmiatornis, a large
ornithurine from Turonian age deposits (Bono et
al., 2016) and Canadaga, a Maastrichtian hesper-
ornithiform (Hou, 1999).
A: Avialan remains are yet to be discov-
ered on the African continent although a large
number of avialan bones have been collected
from the Maastrichtian Maevarano Formation in
nearby Madagascar, consisting of a diversity of
enantiornithines (O’Connor and Forster, 2010)
as well as the ornithuromorph, Vorona (Forster
et al., 1996). Rahonavis was also described as an
avialan from this formation, but although this
was supported by some subsequent analyses
(Agnolín and Novas, 2013; Cau, 2018; Novas et
al., 2018), Rahonavis has also recognized as a
dromaeosaurid by several studies (Makovicky et
al., 2005; Turner et al., 2012; Pei et al., in press).
A: Latest Cretaceous deposits in
Antarctica have produced some avialan remains,
including the ornithurines Vegavis (Noriega and
Tambussi 1995; Clarke et al. 2005), Polarornis
(Chatterjee, 2002) and Antarcticavis (probable
ornithurine; Cordes-Person et al., 2020). Prelimi-
nary descriptions have placed Veg avis in the
Anatoidea (Clarke et al., 2005) and some cladis-
tic analyses suggest this taxon may be an early
stem-group anseriform (Agnolín et al., 2017;
Worthy et al., 2017). However, others have
argued that Veg avis falls outside the avian crown
clade (Wang et al., 2014b; Mayr et al., 2018), so
its status as a crown bird is contentious. Polaror-
nis was described as a stem loon (Chatterjee,
2002), but the only available images of this speci-
men appear to be heavily reconstructed making
any interpretations equivocal. Antarcticavis was
described as an ornithuromorph that probably
belongs to the Ornithurae (Cordes-Person,
2020). Some undescribed Ichthyornis-like mate-
rial is also known (Zinsmeister, 1985).
E F R C B
(A)
Much of our contemporary understanding of
crown-bird macroevolution has come from
large-scale molecular phylogenies, which are
ever improving in light of the development of
new sequencing technologies and analytical
methods (Hackett et al., 2008; McCormack et
al., 2013; Jarvis et al., 2014; Prum et al., 2015;
Reddy et al., 2017; Kimball et al., 2019; see also
Pittman, et al., chapter 1). However, the only
direct evidence of crown-bird evolutionary his-
tory comes from the fossil record, placing a pre-
mium on the discovery of early fossil
representatives of crown birds that can shed
light on when (see Field et al.’s divergence time
section in chapter 5) and where (see Ding et al.’s
biogeography section, chapter 4) the major
groups of crown birds originated.
Unfortunately, the earliest fossil record of
crown birds is extremely sparse, as is the Late
Cretaceous fossil record of the crownwardmost
portion of the avialan stem group (g. 1; table 5)
(Mayr, 2016). e crownwardmost stem avialans
known include classic Mesozoic taxa such as Ich-
thyornithiformes and Hesperornithiformes
2020 PITTMAN ET AL.: THE FOSSIL RECORD 69
(Marsh, 1880), both of which persisted into the
terminal Maastrichtian (Dyke et al., 2002; Lon-
grich et al., 2011; Dumont et al., 2016), as well as
more poorly known marine taxa such as Iaceor-
nis (Clarke, 2004), and the single specimen of the
Campanian Apsaravis (Clarke and Norell, 2002),
whose phylogenetic position is controversial and
oen unstable in recent analyses (Field et al.,
2018a). Recent work on the anatomy and phylog-
eny of this portion of the avialan tree has revealed
a multitude of anatomical plesiomorphies exhib-
ited by these closest Mesozoic relatives of crown
birds (e.g., in Ichthyornis, a strongly anteriorly
projecting squamosal, primitive beak lacking a
palatal shelf, extensive dentition throughout the
upper and lower jaws; Field et al., 2018b). Clearly,
our current knowledge of the closest-known
stem-group relatives of crown birds must be
incomplete: a range of hierarchically internested
taxa crownward of Hesperornithiformes and Ich-
thyornithiformes must have existed, and their
discovery will be necessary to document the
acquisition of a fully crownlike avian skeleton. It
is hoped that the coming years will reveal such
fossils and clarify how, when, and where crown
birds themselves originated.
e latest Cretaceous fossil record of crown
birds is even more sparse. Total-clade loons
(Gaviiformes) were long regarded as present in
the latest Cretaceous on the basis of Neogaeornis
(Olson, 1992) and Polarornis (Chatterjee, 2002),
although the status of these taxa as gaviiforms is
dubious (Mayr, 2016) and at least Polarornis may
be closely related to, if not synonymous with,
Vegavis (Clarke et al., 2016). Until recently, only
one comparatively well-supported crown-bird
fossil has emerged from the entirety of the Meso-
zoic and, even then, from within approximately
one million years of the end-Cretaceous mass-
extinction event (Noriega and Tambussi, 1995;
Clarke et al., 2005). e phylogenetic position
of this taxon, Vegavis iaai, is debated (Agnolín et
al., 2017; Mayr et al., 2018), with recent analyses
recovering it as an early stem-group anseriform
(Worthy et al., 2017) and others questioning
its validity as a crown bird (Mayr et al., 2018).
Moreover, the stem lineages of the deepest
clades within crown birds—Palaeognathae and
Neognathae—are entirely unknown. is lack of
stem palaeognaths and stem neognaths, which
must have been present in the latest Cretaceous,
has contributed to ongoing uncertainty regard-
ing the antiquity of the avian crown group
(Cracra et al., 2015; Ksepka and Phillips, 2015;
Mitchell et al., 2015; Prum et al., 2015; Berv
and Field, 2018; see also Field et al.’s molecular
rate variation section in chapter 5), precluding
the application of a hard-minimum age for the
avian root in node-dating analyses. Recently, the
oldest clear evidence of a crown neognath was
described from the Maastrichtian of Belgium
(Field et al., 2020), and appears to represent an
early galloanseran. is taxon, Asteriornis maas-
trichtensis, suggests that even earlier crown bird
fossils are likely to be discovered from sediments
in the Northern Hemisphere.
Although denitive representatives of Aves
are exceedingly rare in Mesozoic sediments, iso-
lated, oen fragmentary remains from the latest
Maastrichtian of North America (Hope, 2002;
Longrich et al., 2011) may derive from crown-
group birds. e only phylogenetic analysis to
test the position of these specimens recovered
several of them in a large polytomy with Aves
and Iaceornis, crownward of Ichthyornithiformes
and Hesperornithiformes. However, given the
substantial presumed phylogenetic distance
between these stem birds and Aves as discussed
above, these isolated remains may instead be
more likely to derive from the crownwardmost
portion of the avian stem. With luck, continued
exploration in the Late Cretaceous of North
America may reveal more complete remains of
these fragmentary avialans, and help clarify their
phylogenetic anities.
Beyond the Mesozoic, the earliest Paleocene
fossil record of crown birds is also extremely
sparse. Bird-producing lagerstätten comparable
to the famous Eocene localities of Messel, Green
River, and Fur have not been discovered in
Paleocene sediments. Considering that a major
diversication of crown birds, including Neoaves
70 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
(which comprises >95% of extant avialan diver-
sity) may have taken place within a narrow tem-
poral window during the Paleocene (see Field et
al.’s molecular rate variation section in chapter
5), avian fossils from this interval have strong
potential to reveal important insights into the
pattern and timing of the extant avian radiation,
and will help shed light on the ancestral mor-
phologies and biogeography of major avian lin-
eages. With the exception of a handful of
important fossil discoveries providing divergence
time constraints across the bird tree of life (e.g.,
the earliest stem penguin Waimanu, the possible
stem tropicbird Australornis, the earliest pelago-
rnithid Protodontopteryx from New Zealand, as
well as the stem mousebird Tsidiiyazhi from the
southwestern United States (Slack et al., 2006;
Mayr and Scoeld, 2016; Ksepka et al., 2017;
Mayr et al., 2019)), the early Paleocene avialan
fossil record remains greatly undersampled with
respect to subsequent epochs.
Importantly, the oldest of these discoveries,
the stem-lineage mousebird Tsidiiyazhi abini
from New Mexico (Ksepka et al., 2017) is
approximately 62.5 million years old—dating to
more than three million years aer the end-Cre-
taceous mass extinction. Where are the diagnos-
able bird fossils closer in age to the K–Pg
boundary? e Chicxulub asteroid impact 66.02
million years ago is hypothesized to have devas-
tated avialan population sizes (Robertson et al.,
2004; Field, 2017; Field et al., 2018a), which may
help explain the rarity of birds in the lowermost
Paleocene. Additionally, avialan body sizes are
hypothesized to have been reduced in the wake
of the K–Pg mass extinction event (Berv and
Field, 2018), potentially adding a taphonomic
bias against the preservation and discovery of
birds from this time interval.
Furthermore, the early Cenozoic crown-bird
fossil record is strongly biased towards remains
from the northern hemisphere. Although con-
siderable dissent regarding the biogeographic
origins of crown birds and the major avian sub-
clades is ongoing (Mayr, 2009; Claramunt and
Cracra, 2015; Cracra and Claramunt, 2017;
Mayr, 2017; Field and Hsiang, 2018; Saupe et
al., 2019; see also Ding et al.’s biogeography
section in chapter 4), analytical reconstructions
have supported a scenario in which many lin-
eages of crown birds originated in the southern
hemisphere—specically, South America and
west Antarctica—and expanded northward fol-
lowing the end-Cretaceous mass extinction
(Claramunt and Cracra, 2015). If this sce-
nario is accurate, then the scarcity of crown-
bird fossils from the latest Cretaceous and
earliest Paleocene may be at least partly
explained by sparse sampling from relevant
geographic regions (Claramunt and Cracra,
2015).
DISCUSSION
The pennaraptoran fossil record has
expanded phenomenally since they were rst
discovered in the mid 19th century, bringing
about huge leaps in our understanding of the
group. Archaeopterygiformes, anchiornithines,
and scansoriopterygids tell us that the clade had
originated by the Late Jurassic, with other pen-
naraptoran groups either unknown at that time
as in oviraptorosaurians (Osmólska et al., 2004)
or based on fragmentary specimens as in drom-
aeosaurids (Heckert and Foster, 2011). e
anchiornithines are the best represented group
of Jurassic paravians after Archaeopterygi-
formes, but their status as birds, troodontids,
early-diverging deinonychosaurs, or sister to
Paraves remains controversial, even though
consensus for their near-avialan status is emerg-
ing (Pei et al., in press). e search for Jurassic-
aged pennaraptorans should therefore remain a
priority moving forward, both from lagerstätten
that have recovered them already, like the Soln-
hofen Limestone of southern Germany and the
Tiaojishan Formation of northern China, and
from new localities. Although Konservat Lager-
stätten are few and far between, it is heartening
to note that new exposures containing Jehol and
Yanliao biota fossils are cropping up across
northern China with increasing collection
2020 PITTMAN ET AL.: THE FOSSIL RECORD 71
eorts. ey are also present, but undersampled
in Mongolia, where only a few feathers have
been excavated (Kurochkin, 2000). In general,
the uneven nature of the pennaraptoran record,
which is biased toward key formations like the
Yixian and Djadokhta, needs to be better coun-
terbalanced to ensure our understanding of this
group is not being biased by potential local or
regional factors. is is easier said than done,
but a healthy awareness of this issue will at least
help to minimize any chance of conating sepa-
rate evolutionary signals.
O: Tooth-bearing early-
diverging oviraptorosaurians like Incisivosaurus
and Caudipteryx remain rare and oviraptorosau-
rians with more ancestral theropod body plans
are expected in the Late Jurassic, but have not
been found. is is potentially the most impor-
tant priority for future work because it should
shed more light on the evolution of the beak and
the changes involved in skull specialization.
Future nds of later-diverging taxa that could
better characterize the caenagnathid and ovirap-
torid split would also be very useful, especially as
early-diverging caenagnathids are not known
from complete cranial material and include
giant, evidently specialized forms like Gigan-
toraptor (Ma et al., 2017). Oviraptorosaurians
and Scansoriopterygidae are currently exclu-
sively Laurasian groups, but experience in other
pennaraptoran groups, including those with a
longer collection history, suggests that future
Gondwanan nds are possible. us, eorts to
seek such material whether in the eld or in
existing collections could be fruitful.
S: Scansoriopterygids
are among the least known early-diverging pen-
naraptorans because of their representation by a
small pool of specimens. More specimens, par-
ticularly from adult growth stages, will be critical
in solidifying the taxonomic status of the group
and uncovering key events in their evolutionary
history as well as their correct phylogenetic posi-
tion. Yi preserves feathered, membranous wings
that appear to be an alternative dinosaurian
volant strategy to feathered, muscular wings (Xu
et al., 2015a; Wang et al., 2019a). is astonish-
ing discovery warrants extensive further study
that will require additional so-tissue-preserving
specimens. Further discoveries are also needed
to determine whether scansoriopterygids were a
short-lived experiment or they persisted to the
terminal Cretaceous like oviraptorosaurians.
D: Dromaeosaurids are
among the most widely distributed pennarap-
torans aer birds. is, coupled with their gener-
ally more ground-based lifestyle compared with
early birds (early birds could probably cross bar-
riers more easily), provides the best opportunity
to understand the impact of Mesozoic biogeog-
raphy on pennaraptoran evolution. is is exam-
ined in the next chapter on coelurosaurian
biogeography. Encouraging potential for further
nds in underrepresented parts of Gondwana,
e.g., the Wadi Milk Formation of Sudan and
James Ross Island, Antarctica, underscores the
importance of Dromaeosauridae in understand-
ing pennaraptoran biogeography more generally.
The reconstruction of flight capabilities in
Microraptor makes microraptorines an obvious
subclade to focus more attention on (Pei et al., in
press). However, the unenlagiine Rahonavis also
has similar ight potential, and so this clade
should also be studied more intensively, espe-
cially given that it represents the only detection
of nonavialan ight potential in Gondwana (Pei
et al., in press).
T: Troodontids are thought
to be a Laurasian clade, but the discovery of a
possible troodontid tooth from the Kallamedu
Formation of India (Goswami et al., 2013) jus-
tifies further search efforts to confirm this
Gondwanan record and explore biogeographic
differences among troodontids in more detail
(see Ding et al., chapter 4). The taxonomic sta-
tus of Anchiornithinae should be another
study priority and will benefit from Jurassic
nonavialan paravian finds, particularly from
the Solnhofen and Tiaojishan as well as the
sparse Early Cretaceous of North America.
The discovery of more troodontid specimens
with transitional anatomical features between
72 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 440
longer-armed earlier-diverging forms and
shorter-armed later-diverging forms (e.g.
Sinusonasus and Jianianhualong (Xu et al.,
2017)) would also shed more light on troodon-
tid character evolution.
A: Despite the incredible number of
new specimens unearthed within the past four
decades, there remain numerous major gaps in
the fossil record of stem avialans. ere is a 20
million year gap in the record between the
155–150 Ma Archaeopteryx and the beginning
of the Jehol avifauna captured by the 131 Ma
Huajiying Formation. Specimens from this 20
Ma gap are critical to understanding early skel-
etal transitions such as the evolution of the
pygostyle and the evolution of the rst avialan
edentulous beak, let alone a host of other fea-
tures like solidication of the pectoral girdle
and plumage specialization. Notably, non-orni-
thothoracines are almost exclusively found in
the Solnhofen limestones (Archaeopterygi-
formes) and in the Early Cretaceous Jehol
lagerstätten, which may suggest early-diverging
lineages went extinct fairly early, being unable
to compete with ornithothoracines. No Meso-
zoic avialan has been collected from the Afri-
can continent, despite its great potential
(although remains are known from Madagas-
car). Globally, the Early Cretaceous record is
far stronger than the Late Cretaceous record
(mostly due to the Jehol Biota), but there are
currently no Early Cretaceous avialan fossils
known from North America. A major gap in
the avialan fossil record consists of the con-
spicuous absence of fossils documenting the
crownwardmost portion of the avian stem lin-
eage, i.e., crownward of the Late Cretaceous
ornithurine groups Hesperornithiformes, Ich-
thyornithiformes, and Iaceornis. Similarly, the
earliest stages of crown-bird evolution are
poorly known at present, and many of the
greatest questions regarding the early evolu-
tionary history of Aves will be resolved by new
discoveries of crown birds from the Late Creta-
ceous and early Paleogene, including questions
related to avialan survivorship, ecological selec-
tivity, and recovery across the end-Cretaceous
mass extinction. It is hoped that the coming
years will yield avialan fossils lling the critical
temporal and geographic gaps discussed
above—and in the process, shed important new
light on the Mesozoic and Cenozoic evolution-
ary history of avialan pennaraptorans.
ACKNOWLEDGMENTS
is paper arose from discussions at the Inter-
national Pennaraptoran Symposium, held at the
University of Hong Kong and supported by Ken-
neth H.C. Fung and First Initiative Foundation.
is study was supported by the Research Grant
Council of Hong Kong’s General Research Fund
(17103315 to M.P., X.X., and P.A.G.) and the
National Science Foundation of China (41688103,
41120124002, and 91514302 to X.X.). It was also
supported by Faculty of Science of the University
of Hong Kong (to M.P.). M.A.N.’s support came
from the American Museum of Natural History
(Division of Vertebrate Paleontology), the Macau-
lay Family Endowment, and NSF Earth Sciences.
D.J.F. is supported by UK Research and Innova-
tion Future Leaders Fellowship MR/S032177/1.
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