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NEW EVIDENCE FOR CANNIBALISM IN TYRANNOSAURID DINOSAURS FROM THE UPPER CRETACEOUS (CAMPANIAN/MAASTRICHTIAN) SAN JUAN BASIN OF NEW MEXICO

Authors:
  • New Mexico Museum of Natural History and Science

Abstract and Figures

An isolated anterior left dentary, proximal caudal centrum and an isolated right femur pertaining to adult, subadult and juvenile tyrannosaurid dinosaurs from the Upper Cretaceous deposits of the San Juan Basin in New Mexico preserve several bite marks and other feeding traces made by another tyrannosaurid. The dentary was recovered from the Ne-nah-ne-zad Member of the Fruitland Formation (Campanian); whereas, the femur was recovered from De-na-zin Member of the Kirtland Formation (Campanian), and the isolated caudal centrum was recovered from the Naashoibito Member of the Ojo Alamo Formation (Maastrichtian). The presence of bone surface healing around the bite marks in the dentary indicate that the biting occurred pre-mortem; whereas, the absence of bone surface healing around the bite marks in the caudal centrum and the right femur indicates the biting most likely took place post-mortem. Intensely tooth-marked bones clearly show that the San Juan Basin tyrannosaurids attacked and fed upon the remains of not only their most common prey such as ceratopsians, hadrosaurs, and sauropods, but also conspecifics. The bite marks described here represent four categories: bite-and-drag, drag-and-scrape, puncture, and puncture-and-collapse. The specimens provide new evidence for cannibalism among tyrannosaurids. Although extensively tooth marked, these bones do not support the previous assumptions of selective feeding behavior of these iconic predators based on inferred bite marks.
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Lucas, S. G., Hunt, A. P. & Lichtig, A. J., 2021, Fossil Record 7. New Mexico Museum of Natural History and Science Bulletin 82.
NEW EVIDENCE FOR CANNIBALISM IN TYRANNOSAURID DINOSAURS
FROM THE UPPER CRETACEOUS (CAMPANIAN/MAASTRICHTIAN)
SAN JUAN BASIN OF NEW MEXICO
SEBASTIAN G. DALMAN and SPENCER G. LUCAS
New Mexico Museum of Natural History, 1801 Mountain Road N. W. Albuquerque, NM 87104; -email: sebastiandalman@yahoo.com
Abstract—An isolated anterior left dentary, proximal caudal centrum and an isolated right femur
pertaining to adult, subadult and juvenile tyrannosaurid dinosaurs from the Upper Cretaceous deposits
of the San Juan Basin in New Mexico preserve several bite marks and other feeding traces made by
another tyrannosaurid. The dentary was recovered from the Ne-nah-ne-zad Member of the Fruitland
Formation (Campanian); whereas, the femur was recovered from De-na-zin Member of the Kirtland
Formation (Campanian), and the isolated caudal centrum was recovered from the Naashoibito
Member of the Ojo Alamo Formation (Maastrichtian). The presence of bone surface healing around
the bite marks in the dentary indicate that the biting occurred pre-mortem; whereas, the absence of
bone surface healing around the bite marks in the caudal centrum and the right femur indicates the
biting most likely took place post-mortem. Intensely tooth-marked bones clearly show that the San
Juan Basin tyrannosaurids attacked and fed upon the remains of not only their most common prey
such as ceratopsians, hadrosaurs, and sauropods, but also conspecics. The bite marks described here
represent four categories: bite-and-drag, drag-and-scrape, puncture, and puncture-and-collapse. The
specimens provide new evidence for cannibalism among tyrannosaurids. Although extensively tooth
marked, these bones do not support the previous assumptions of selective feeding behavior of these
iconic predators based on inferred bite marks.
INTRODUCTION
Tyrannosaurid dinosaurs represent one of the most
recognizable major groups of theropods that include some
of the iconic species such as Albertosaurus sarcophagus,
Daspletosaurus torosus, Gorgosaurus libratus, Tarbosaurus
bataar and Tyrannosaurus rex (Brochu, 2003; Carr et al., 2017;
Currie, 2003; Loewen et al., 2013; Fiorillo and Tykoski, 2014).
During most of the Late Cretaceous, tyrannosaurids, were the
apex predators in terrestrial environments of Asia and the coastal
plains of the Western Interior Basin of North America (Maleev,
1955a, 1955b; 1974; Russell, 1970; Currie, 2003a; Hurum
and Sabath, 2003; Holtz, 2004; Hone et al., 2011; Brusatte et
al., 2012; Loewen et al., 2013; Fiorillo and Tykoski, 2014; Lü
et al., 2014; Dalman et al., 2017; Dalman and Lucas, 2018a,
2018b; Dalman et al., 2018; McDonald et al., 2018). This highly
specialized group of carnivorous dinosaurs is characterized by
massive skulls with jaws that were able to deliver a powerful
bite that would crush the bones of their prey (Osborn, 1905;
Horner and Lessem, 1993; Erickson et al., 1996; Meers, 2002;
Therrien et al., 2005; Snively et al., 2006; Sakamoto, 2010).
Since the discovery over a century ago of the rst skeletal
remains of the most common North American tyrannosaurids
(e.g., Albertosaurus, Gorgosaurus, and Tyrannosaurus), the
feeding behavior of these iconic predators has been the subject of
extensive studies, including whether these predators were active
hunters, scavengers, or both (e.g., Horner and Lessem, 1993;
Farlow, 1994; Horner, 1994; Erickson et al., 1996; Carpenter,
1998; Ruxton and Houston, 2003; Happ, 2008; Holtz, 2008;
Horner et al., 2011). The scavenger argument is largely based on
the signicantly reduced forelimbs that all derived tyrannosaurids
exhibit (e.g., Albertosaurus, Daspletosaurus, Gorgosaurus,
Tarbosaurus, Tyrannosaurus). However, lever arm mechanics
suggest that the diminutive forelimbs of Tyrannosaurus rex had
a high mechanical advantage (Barrett and Rayeld, 2006). A
robust and columnar humerus of T. rex shows that the arms were
designed for force generation, and thus, capable of handling
prey (Carpenter and Smith, 2001).
The modication of the skull for prey handling in
tyrannosaurids most likely took place before the forelimb
reduction and is best reected in less derived forms such as
Dilong paradoxus (Xu et al., 2004), Eotyrannus lengi (Hutt et
al., 2001), Guanlong wucaii (Xu et al., 2006) and Yutyrannus
huali (Xu et al., 2012). D. paradoxus and G. wucaii are estimated
at 2 m and 3 m body length; whereas E. lengi is estimated at 4
m body length. In comparison with more derived, large-bodied
tyrannosaurids, the small body size of these less derived forms
is consistent with the trend of body size increase reported for
this group. They share numerous derived cranial similarities
with other tyrannosaurids; however, both have less robust skulls
(e.g., Xu et al., 2004, 2006). Some of these features are most
likely size related, but progressively larger size in Y. huali (9
m long) represents a phylogenetic trend in tyrannosaurids.
These less derived forms exhibit more derived modications
in the cranial skeleton than in the postcranial skeleton. They
possess 80% cranial diagnostic features relative to 25%
postcranial synapomorphies of tyrannosaurids, which supports
the hypothesis that cranial modication occurred earlier than
appendicular modication in tyrannosaurid evolution (e.g., Xu
et al., 2004, 2006).
Another factor that has been used to argue against the
predatory life style for Tyrannosaurus rex is that it was not a high-
speed runner, but instead a slow moving giant (e.g., Farlow et al.,
1995, 2000; Hutchinson and Garcia, 2002; Brusatte et al., 2010;
Kane et al., 2016; Sellers et al., 2017). The scavenger argument
has been met with skepticism by other workers (e.g., Holtz,
2008; Carpenter, 2013; Krauss and Robinson, 2013; Nesteruk,
2019). It has been demonstrated that the jaws of tyrannosaurids
and, in particular, T. rex are reinforced vertically, which helped
to create exceptional biting power (e.g., Thomson, 1966; Molnar
and Farlow, 1990; Molnar, 1998; Kemp, 1999; Hurum and
Currie, 2000; Hurum and Sabath, 2003; Rayeld, 2004; Therrien
et al., 2005; Snively et al., 2006). Tyrannosaurid teeth and the
skull, particularly of Tyrannosaurus rex are more robust than
that of other large theropods (Farlow et al., 1991; Abler, 1992;
Brochu, 2003; Hutchinson and Padian, 1997; Henderson, 2002;
Therrien et al., 2005; Reichel, 2010). The skulls have large areas
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for attachment and expansion of upper and lower jaw muscles
that allowed for a powerful bite deep into bone (Carpenter,
1998; Erickson et al., 1996; Molnar, 1998; Meers, 2002). The
dentaries of large tyrannosaurids have high section moduli that
could withstand high force during feeding than in equivalently
sized non-avian theropods (e.g., Therrien et al., 2005), and also
have anterodorsally inclined intermandibular symphysis, which
are enhanced dorsally by the anterior step of the dorsal lingual
lamina (=anterior step of the lingual bar of Dalman and Lucas,
2015, 2017a). The biomechanical analyses of the skull and neck
of T. rex (Currie et al., 2003; Hurum and Sabath, 2003; Snively
and Russell, 2007a, 2007b) reveal bite mechanics that allow
for puncture and pull/shake feeding behavior. New discoveries
and new research, especially of the potential tyrannosaurid prey
items, most of which are hadrosaurids found with healed bite
traces, suggest failed attacks that demonstrate conclusively that
this iconic theropod was not only capable of active predation,
but that tyrannosaurids likely engaged in this behavior on a
regular basis (e.g., Carpenter, 1998, 2013; Varricchio, 2001;
Happ, 2008; DePalma et al., 2013; Murphy et al., 2013; Dalman
and Lucas, 2018c, 2018d).
Some of the bones of ceratopsians and hadrosaurs,
commonly recovered from the Upper Cretaceous deposits in
the Western Interior Basin of North America, contain numerous
elongate and puncture marks, which have been identied as bite
marks made by tyrannosaurids (e.g., Fiorillo, 1991; Erickson et
al., 1996; Carpenter, 1998; Farlow and Holtz, 2002; Fowler and
Sullivan, 2006; Happ, 2008; Hone and Rauhut, 2010; Fowler et
al., 2012; Rivera-Sylva et al., 2012; DePalma et al., 2013; Dalman
and Lucas, 2018c, 2018d). In addition to the tooth-marked
bones of herbivorous dinosaurs, are tooth-marked bones of
tyrannosaurids, in particular of Albertosaurus, Daspletosaurus,
Gorgosaurus, Nanotyrannus, and Tyrannosaurus (e.g., Tanke
and Currie, 1998; Peterson et al., 2009; Bell, 2010; Bell and
Currie, 2010; Hone and Tanke, 2015). The documented tooth
marks preserved on tyrannosaurid bones appear to have been
made by another tyrannosaurid, suggesting agonistic behavior,
especially among the juveniles, and antagonistic behavior
and cannibalism among juveniles and adults (Peterson et al.,
2009; Bell and Currie, 2010). Evidence for intraspecic and
intrafamilial antagonistic behavior in large theropods has been
previously described from bite marks on bones (e.g., Petersen et
al., 1972; Tanke and Currie, 1995, 1998) and teeth (Tanke and
Currie, 1995, 1998). Although cannibalism has been previously
suggested in tyrannosaurids (e.g., Jacobsen, 1998), this behavior
was conclusively documented a decade ago in Tyrannosaurus
(e.g., Longrich et al., 2010) and in recent years in Daspletosaurus
sp. (e.g., Hone and Tanke, 2015). Among other theropod groups,
cannibalism has been documented in Coelophysis bauri (e.g.,
Rinehart et al., 2009) and in Majungasaurus crenatissimus
(Rogers et al., 2003).
Here, we document an isolated proximal end of the left
dentary, proximal caudal centrum and an isolated right femur
pertaining to tyrannosaurid dinosaurs from the San Juan Basin in
northwestern New Mexico. The skeletal elements are extensively
tooth marked. Additionally, the tooth marks preserved on the
bones match the teeth of tyrannosaurids. The lack of bone
surface healing around the tooth marks on the proximal caudal
centrum and the right femur indicates that the biting most likely
occurred at the time of death (postmortem); whereas, partially
healed bone surface around the tooth marks on the left dentary
indicates that the biting occurred when the animal was still alive
(premortem). The bones provide new evidence for cannibalistic
behavior among tyrannosaurids and question the previously
proposed idea by Hone and Watabe (2010) of selective feeding
behavior in these iconic predators, based on inferred bite marks.
Additionally, new types of biting marks are identied on the
bones, including puncture-and-collapse, drag-and-scrape and
drag-and-puncture.
MATERIALS AND METHODS
Preparation of the specimens at NMMNH was
accomplished by the senior author, with air scribes and dental
tools. The specimens were examined and photographed at
NMMNH; whereas others at KU. The bite marks described
here were compared with other previously described specimens
that exhibit similar traces. These include Albertosaurus
sarcophagus (TMP 2003.45.64), ‘Daspletosaurus sp. (TMP
1994.143.0001); Gorgosaurus libratus (TMP 91.36.500);
Nanotyrannus lancensis (BMR P-2002.4.1); Saurornitholestes
langstoni (TMP 88.121.39); Sinraptor dongi (IVPP 10600),
Theropoda indeterminate (SMP VP-2407, SMP VP-3375); and
Tyrannosaurus rex (BHI 3033, FMNH PR2081, MOR 902, MOR
1126, UCMP 137538). Further comparisons of the bite traces
include tooth-marked bones of herbivorous dinosaurs such as
Alamosaurus sanjuanensis (SSM 5428), Hypacrosaurus (MOR
549), the Farmington Sandstone Member new chasmosaurine
species (NMMNH P-50000), Hadrosaurinae indeterminate
(NMMNH P-70319); Hadrosaurinae indeterminate (SMP VP-
2206); Pentaceratops sternbergi (SMP VP-1900); Saurolophus
(MPC-D 100/764); and Triceratops horridus (MOR 799).
Institutional Abbreviations: BHI, Black Hills Institut of
Geological Research, Black Hills, South Dakota, USA; BMR,
Burpee Museum of Natural History, Rockford, Illinois; CM,
Carnegie Museum of Natural History, Pittsburgh, Pennsylvania;
FMNH, Field Museum of Natural History, Chicago,
Illinois; IVVP, Institute of Vertebrate Palaeontology and
Palaeoanthropology, Beijing, China; KU, University of Kansas
Museum of Natural History, Kansas City, Missouri; MOR,
Museum of the Rockies, Bozeman, Montana; MPC, Mongolian
Palaeontological Center, Mongolian Academy of Sciences,
Ulaanbaatar, Mongolia; NMMNH, New Mexico Museum of
Natural History and Science, Albuquerque, New Mexico; SMP,
The State Museum of Pennsylvania, Harrisburg; TMP, Royal
Tyrrell Museum of Palaeontology, Drumheller, Alberta, Canada;
UCMP, University of California, Museum of Paleontology,
Berkeley, California; YPM, Yale Peabody Museum of Natural
History, New Haven, Connecticut.
GEOLOGICAL SETTING
The isolated bones of tyrannosaurid dinosaurs described
here were recovered from the upper Campanian deposits of
the Ne-nah-ne-zad Member of the Fruitland Formation, De-
na-zin Member of the Kirtland Formation and from the upper
Maastrichtian deposits of the Naashoibito Member of the Ojo
Alamo Formation, which are exposed in the San Juan Basin,
located in northwestern New Mexico (Hunt and Lucas, 1992)
(Fig. 1).
The Fruitland Formation is underlain by the Pictured
Clis Sandstone, and overlain by the Kirtland Formation.
The formation has been 40Ar/Ar39 dated at 75.56 ± 0.41 Ma
(Sullivan and Lucas, 2006). The formation is divided into two
sub-units: the lower Ne-nah-ne-zad Member, which has been
dated to 75.5-75 Ma and the upper Fossil Forrest Member, which
has been dated 75-74.5 Ma (Sullivan and Lucas, 2006). The
Fossil Forrest Member is considered a part of the Hunter Wash
Member of the Kirtland Formation, based on shared vertebrate
fauna (Sullivan and Lucas, 2006).
The De-na-zin Member of the Kirtland Formation overlies
the Hunter Wash and Farmington members and underlies the
Naashoibito Member of the Ojo Alamo Formation (Lucas and
Sullivan, 2000; Jasinski et al., 2011). The lowest sub-unit of the
Kirtland Formation, the Hunter Wash Member, has been 40Ar/
Ar39 dated at 74.55 ± 0.2Ma (Fassett and Steiner, 1997; Sullivan
and Lucas, 2006). The boundary between the Farmington
and De-na-zin members has been 40Ar/Ar39 dated at 73.37
41
FIGURE 1. Index map (A), showing location of the De-na-zin Member of the Kirtland Formation and the Naashoibito Member of
the Ojo Alamo Formation in northwestern New Mexico. Geologic map (B), showing the exposure of the Upper Cretaceous of the
Kirtland Formation, De-na-zin and Farmington members Kk(undi) and the Ojo Alamo Formation, Naashoibito Member [Ko(n)].
Intermittent outcrops of the Naashoibito and Kimbeto [To(k)] members have been mapped to the southeast (Schneider et al., 1979;
Lucas and Sullivan, 2000), and Tn = Tertiary (Paleocene) Nacimiento Formation. Map modied after Lehman (1985).
± 0.28Ma (Lucas and Sullivan, 2000; Sullivan et al., 2005;
Sullivan and Lucas, 2006). The top of the De-na-zin Member,
which contains the Willow Wash local fauna, has been 40Ar/
Ar39 dated at 73.04 ± 0.2Ma, which is a late Campanian age
(Sullivan and Lucas, 2006).
The Ojo Alamo Formation is divided into two members,
the Kimbeto Member (upper) and the Naashoibito Member
(lower), both separated by a substantial unconformity (Baltz et
al., 1966). Outcrops of the Naashoibito Member are located in
the southwestern part of the San Juan Basin; from Hunter Wash
in the northwest to Betonnie Tsosie Wash in the southeast (Baltz
et al., 1966; Lucas and Sullivan, 2000; Fowler and Sullivan,
2011). The maximum thickness of the unit is approximately
25.9 m at Barrell Springs, De-na-zin Wash; minimum 1.5 m, on
the western branch of Ojo Alamo Arroyo, Alamo Wash (Baltz
et al., 1966). The Naashoibito Member was deposited during
the late Maastrichtian at approximately 67 Ma and represents a
very short amount of geologic time, on the order of 1Ma or less
(Lucas and Sullivan, 2000; Fowler and Sullivan, 2011).
TOOTH MARKS
Tanke and Currie (1998) described several examples of
tooth marks in large theropods that include healed and unhealed
marks on the cranial bones. They categorized these marks
into the following types: punctures, serrations, scores or tooth
drags, and embedded and broken teeth. Similarly, Hone and
Watabe (2010) identied three types of tooth marks made by a
tyrannosaurid (Tarbosaurus bataar) on an isolated left humerus
(MPC−D100/764) of the hadrosaur Saurolophus from the Bugin
Tsav locality in Mongolia. They identied the following types
of tooth marks: bite-and-drag, drag, and punctures. The tooth
marks or feeding traces preserved on the isolated proximal
end of the left dentary (KU VP-96888), the caudal centrum
(NMMNH P-40953) and the right femur (NMMNH P-25083)
described here fall into the following types: drag-and-puncture,
bite-and-drag, drag-and-scrape, punctures, and puncture-and-
collapse. Three types of tyrannosaurid tooth marks described
here have not been identied before, including drag-and-
puncture, drag-and-scrape and puncture-and-collapse. We also
add new information to the denition of bite-and-drag marks
based on the specimens described here.
Bite-and-drag. The teeth partially penetrate the surface of
the bone and are pulled, leaving elongate traces in the bone that
are gently curved with ragged or healed margins. This type of
biting represents the most common form of large theropod tooth
trace found on dinosaur bones (e.g., Erickson and Olson, 1996).
Bone grain is redirected as the tooth is pulled across the bone
(Currie and Jacobsen, 1995). Deep marks penetrate the cortex,
and, occasionally, bone fragments have been removed. Bite-
and-drag marks can occur singly when only one tooth contacts
the bone surface. This type of tooth mark also occurs in parallel
series when more than one tooth contacts the bone surface at
a low angle, causing a divot of bone to be partially expelled
(Tanke and Currie, 1998).
Drag-and-puncture. These traces start as shallow elongate
marks, extending across the bone surfaces and in their posterior
region are deep punctures that penetrate the bone. The result of
drag-and-puncture is the removal of the outer bone surface, but
also biting through bone cortex. The tooth traces are usually
extensive, elongated single lines made by either the maxillary or
dentary teeth pulled across the bone in unison during biting and
a portion of bone is removed.
Drag-and-scrape. These traces are shallow, made by
repeated dragging movements of the maxillary or dentary teeth
across the bone surface (Dalman and Lucas, 2017b). The result
of drag-and-scrape is the removal of the outer bone surface,
including a portion of the bone cortex. The tooth traces are
usually densely packed together.
Punctures. These are circular to oval in outline, and some
can be elongate. In unhealed examples, the outer surface of the
bone is folded inwards into the puncture hole or forms a small
mound directly around it (Tanke and Currie, 1998). The circular
puncture traces partially or fully penetrate the surface of the
bone. They can be found within the bite-and-drag marks and
42
also within the drag-and-scrape marks. Their position within
the bite-and-drag marks and within the drag-and-scrape marks
indicates the direction of movement of the teeth across the bone
during feeding. The tooth or teeth of the predator make contact
with the bone of its prey. First the teeth puncture the bone, and
then they are being dragged across the bone.
The punctures are characterized by deep and shallow traces.
In deep punctures the teeth penetrate the bone cortex and may
cause the bone to break o or fracture (Tanke and Currie, 1998;
Hone and Watabe, 2010).
Puncture-and-collapse. This type of biting is identied
here in tyrannosaurids for the rst time. The tooth that contacts
the bone surface makes a puncture trace. The tooth does not
penetrate deeply into the bone cortex, but the applied force
collapses a large portion of the bone, forming an extensive
ovoid-shaped concavity (compression fractures). The collapsed
bone surface is only slightly fractured around its margins.
However, some fracturing can occur within the collapsed bone
surface in close proximity to the puncture mark.
SYSTEMATIC PALEONTOLOGY
SAURISCHIA Seeley, 1888
THEROPODA Marsh, 1881
COELUROSAURIA von Huene, 1914
TYRANNOSAURIDAE Osborn, 1906
Tyrannosauridae indet.
Figs. 2, 3
Material: KU VP-96888, anterior left dentary
Locality, horizon and age: Ne-nah-ne-zad Member,
Fruitland Formation, San Juan Basin, northwestern New
Mexico. The age is late Campanian, ~ 75.5 Ma.
Description
KUVP-96888, an isolated anterior end of the left dentary, is
referred to a tyrannosaurid dinosaur (Figs. 2, 3). The specimen is
being described by us in detail in another paper as belonging to a
new genus and a new species; therefore, its morphology is only
briey described here. KUVP-96888 is 36.5 cm long and 14
cm dorsoventrally deep. The dentary is missing the tooth row;
however, remnants of anteriormost alveoli are faintly preserved.
Some of the tyrannosaurid morphological features that KUVP-
96888 has include four principal rows of vascular foramina: the
alveolar row and lateroventral row located on the lateral side,
the anterior row located on the anterior side, and the ventral
row on the ventral side. Furthermore, the other tyrannosaurid
morphological features that KUVP-96888 has include the
FIGURE 2. KU VP-96888, a left anterior dentary of a
tyrannosaurid from the Campanian of the Ne-nah-ne-zad
Member, Fruitland Formation, New Mexico, in lateral view (A),
close up of drag-and-puncture (B), close up of full penetration
punctures (C), close up full penetration puncture (D).
FIGURE 3. KU VP-96888, a left anterior dentary of a
tyrannosaurid from the Campanian of the Ne-nah-ne-zad
Member, Fruitland Formation, New Mexico, USA, in medial
view (A), close up of full penetration puncture (B), close up of
full penetration punctures (C), close up of full penetration of
puncture, which is a part of the drag-and-puncture.
convex inection point an area where the anterior and ventral
margins of the dentary meet and the medially convex lingual
articular brace (=convex articular brace of Brusatte et al., 2012).
When compared to the dentaries of other tyrannosaurids such as
Albertosaurus, Bistahieversor, Daspletosaurus, Gorgosaurus,
Lythronax, Tarbosaurus, Teratophoneus and Tyrannosaurus, the
body length of KUVP-96888 was close to 10 m.
Lateral side: The lateral side/surface of the dentary
contains several large bite marks (Fig. 2). The bite marks are
situated in the anteriormost end of the dentary and along the
alveolar margin (Fig. 2C-D). The anteriormost bite marks
are large, elongated and nearly parallel each other and the
anterolateral margin of the dentary. The more dorsally oriented
bite mark starts as a narrow and shallow groove, which extends
and deviate anterodorsally. The length of the entire bite mark
is 7.5 cm, the minimum width of the bite mark at the place of
origin is 0.3 cm, and the maximum width at the alveolar margin
is ~ 5 cm. In lateral view, the dorsal margin of the bite mark is
strongly curved dorsally towards the alveolar margin; whereas,
the ventral margin of the bite mark is straight. The bone surface
within the narrower part of the bite mark is slightly rugose;
whereas, towards the alveolar margin as the bite marks begin
to deviate the bone surface is irregular and rugose. The terminal
end of the bite mark is marked by a large and deep puncture that
is ~ 2.5 cm in diameter. The puncture mark penetrates the bone
cortex and exits on the medial side of the dentary (Fig. 3C). This
type of bite mark is a combination of drag-and-puncture and is
characterized by a partial bone penetration and ending with full
bone penetration and eventual bone removal.
Directly ventral to-and parallel to the drag-and-puncture
mark is an elongated drag mark, which is nearly straight. The
tooth mark is ~ 1.5 cm apart from the drag-and-puncture mark.
The length of the tooth mark is 8 cm. The minimum width of the
tooth mark at the place of origin is 0.6 cm; whereas, the maximum
width at the terminal end of the tooth mark (anterolateral dentary
margin) is 1.2 cm.
Posterior to the drag-and-puncture mark and the drag mark
are two large full bone penetration punctures. These punctures
are extensive, aligned together, approximately 1.2 cm apart from
each other and are visible on the medial side of the dentary. In
lateral view the punctures nearly parallel the other two more
anterior tooth marks.
The length (along the long axis) of the more complete
43
contains a large bite mark, which is approximately 8.5 cm
long dorsoventrally (Fig. 4). The bite mark is 3 cm wide at its
dorsal end and 2.5 cm wide along its ventral end. It is deeper
dorsally than ventrally. The anterior surface of the bite mark
for an approximately 2.5 cm portion of the dorsoventral length
is vertical and nearly parallels the femoral head. As the bite
mark continues dorsally, its surface becomes slightly convex.
The convex surface is 6 cm long. The opposing surface of the
bite mark is angled laterally at an angle of 32°. This surface is
nearly 5 cm long and is at and slightly rugged. As it progresses
dorsally, it deviates laterally at a 37° angle. The bite mark then
extends onto the dorsal surface of the femoral head and nearly
wraps around it.
The dorsal surface of the femoral head is heavily damaged
and covered by numerous elongate bite marks with rugged
margins that extend across its entire surface (Fig. 5).
There is a large bite mark consisting of two elliptical-shaped
tooth traces cutting through the dorsal surface of the greater
trochanter (Fig. 5A). These tooth marks are perfectly aligned
and have rugged margins. The tooth mark that is closer to the
lesser trochanter is 3 cm long, 1.5 cm wide; whereas the tooth
mark posterior to it is 1.7 cm long and, 1 cm wide. It appears that
the dorsal surface of the greater trochanter was bitten hard and
as a result the teeth penetrated the bone and gouged out these
large marks and at the same time a large portion of the bone
surface may have been broken o as a result.
The anterior and dorsolateral surfaces of the lesser trochanter
are heavily damaged, and several distinctive puncture marks can
be seen across its surface (Figs. 4A-B, 5A, 6A-B). The puncture
marks are largely concentrated on the dorsolateral surface of the
lesser trochanter.
The posterior surface of the proximal end of the femur
contains several bite marks, which are concentrated on the
posterolateral margin of the bone (Fig. 7). The bite traces are
elliptical-shaped and slightly elongated. The elliptical-shaped
bite marks are precisely aligned in a “U”-shape. Each bite trace
is approximately 1 cm long and, 1.5 cm wide and closely spaced
together. Within the more laterally oriented bite mark a single
puncture mark is preserved (Fig. 7B). The puncture mark is
situated at the anterior end of the more laterally oriented bite
mark and directly on its long axis.
Femoral shaft: The shaft of the femur appears almost
intact, and the bone surface is smooth. However, two sets of
distinct bite marks are located on the posterior surface at the mid
height of the shaft (Fig. 8). The rst set consists of three elongate
tooth marks that are between 3 cm and 4.5 cm long, and each is
puncture is 2 cm and the width is 1.4 cm. The overall shape
of the puncture matches a tyrannosaurid tooth. The plates of
bone (outer bone surface) are folded down and inwards into the
puncture hole. This type of bite mark corresponds to TYPE 1
bite mark of Tanke and Currie (1998).
Posterior to the puncture marks approximately 7 cm is
another large bite mark. However, in this region the dentary is
broken; therefore, it is unclear how large was the tooth mark.
Judging from the preserved outline of the bite mark it appears
that it is also a puncture, and thus, a TYPE 1 of Tanke and Currie
(1998). The bone surface directly below the bite mark is strongly
folded and irregular.
Medial side: The medial side of the dentary preserves full
penetrations of TYPE 1 puncture marks (Fig. 3). However, these
are small punctures, which correspond to the puncture marks on
the lateral side and are here interpreted as the exit sites of TYPE
1 full penetration.
Material: NMMNH P-25083, right femur.
Locality, horizon and age: NMMNH L-3342, De-na-zin
Member, Kirtland Formation, San Juan Basin, northwestern
New Mexico. The age is late Campanian, ~ 74 Ma.
Description
NMMNH P-25083, an isolated complete right femur,
is referred to a tyrannosaurid dinosaur. This specimen is
being described by us in detail in another paper; therefore, its
morphology is only briey described here. NMMNH P-25083 is
81 cm long, and the shaft circumference is 33.2 cm. In contrast, the
femur of Tyrannosaurus rex (FMNH PR2081) is approximately
132 cm long. By applying the equation y = 1.0276x + 0.8437
(Currie, 2003b) to compare formulae that relate femoral lengths
(x) with body lengths (y) in a variety of theropods, the body
length of NMMNH P-25083 can be estimated at nearly 7 m.
Based on this estimate, NMMNH P-25083 was not a fully
grown individual.
Proximal femur: The anterior surface of the femoral head
FIGURE 4. NMMNH P-25083, a right femur of a tyrannosaurid
from the Campanian of the De-na-zin Member, Kirtland
Formation, New Mexico, USA, in anterior view (A), close up
of the anterior surface of the femoral head showing a large bite
mark cutting through the bone (B).
FIGURE 5. NMMNH P-25083, femoral head of the right femur
in dorsal view of a tyrannosaurid from the Campanian of the De-
na-zin Member, Kirtland Formation, New Mexico, USA, bite
mark on the dorsal surface of the greater trochanter (A), multiple
bite marks on the dorsal surface of the femoral head (B).
44
approximately 1.2 cm wide. The tooth marks are not perfectly
aligned and are separated from each other. The dorsalmost tooth
mark is approximately 2.5 cm from the second consecutive
tooth mark, whereas the second tooth mark is 4 cm from the
third tooth mark. The second set consists of eight tooth marks
that are nearly perfectly aligned. The dorsalmost tooth mark is
approximately 3 cm ventral to the base of the 4th trochanter. The
tooth mark is 2 cm long and 1.2 cm wide. Ventral to it are two
tooth marks in close proximity to each other. The tooth marks
are 3 cm long and 1.6 cm wide. Approximately 0.8 cm ventral
to these tooth marks there are two elongate tooth marks in close
proximity to each other. The dorsal tooth mark is 4.6 cm long
and nearly 1 cm wide, whereas the ventral tooth mark is 4.2
cm long and 1.2 cm wide. Ventral to these tooth marks (~1 cm)
are three consecutive tooth marks. Two of these tooth marks are
nearly 3 cm long, whereas the other tooth mark is 2.5 cm long.
The tooth marks are narrow. The dorsalmost is 1.2 cm wide, the
second is 0.7 cm wide, and the third or the ventral tooth mark
is 0.6 cm wide. The third tooth mark slightly deviates laterally
from the long axis of the second tooth mark. It is 3.5 cm long
and 1.2 cm wide. All the tooth marks are slightly sinuous, but
are not deep.
Distal femur: The distal end of the femur is extensively
covered by numerous tooth marks (Fig. 9). Most of the tooth
marks are located on the lateral condyle. Here, the outer bone
surface is removed, and the tooth traces are closely spaced
together. The tooth marks are short drag-and-puncture marks.
Dorsal to this extensively damaged bone surface are two
distinctive tooth marks that are in close proximity to each other.
One of the tooth marks is a characteristic puncture trace with a
diameter of 2 cm, whereas the other is a reversed “L”-shaped
mark. The “L”-shaped tooth mark is 3 cm long and 1.3 cm wide
FIGURE 6. NMMNH P-25083, a right femur of a tyrannosaurid
from the Campanian of the De-na-zin Member, Kirtland
Formation, New Mexico, USA, in lateral view (A), close up of
the lesser trochanter showing extensive trauma on the lateral and
dorsal surfaces of the trochanter (B).
FIGURE 7. NMMNH P-25083, a right femur of a tyrannosaurid
from the Campanian of the De-na-zin Member, Kirtland
Formation, New Mexico, USA, in posterior view (A), close up
of the posterior surface of the proximal femur showing several
bite marks (B).
at its dorsal end. The bone surface around the tooth marks is
rugged and does not exhibit any sign of healing/remodeling.
The distal end of the lateral condyle, precisely its distal end,
has a puncture mark with a diameter of 1 cm (Fig. 10A-D). A
similar puncture trace with a diameter of 1 cm is located on the
lateral surface of the crista tibiobularis (Fig. 10). Both puncture
marks are precisely aligned and approximately 5 cm apart from
each other.
The medial condyle is also extensively tooth-marked (Fig.
11). A part of the outer bone surface of the medial condyle is
removed, especially in the medioventral and posteromedial
areas. Some of the best preserved tooth marks are elongate
and some are puncture marks, whereas others are not clearly
distinguishable, as the bone surface looks as it has been scraped
o. The bone surface around the tooth mark is rugged and lacks
any signs of healing/remodeling.
Tyrannosauridae indeterminate
Material: NMMNH P-40953, isolated proximal caudal
centrum.
Locality, horizon and age: NMMNH L-5439, Naashoibito
Member, Ojo Alamo Formation, San Juan Basin in northwestern
New Mexico. The age is late Maastrichtian, 68 Ma.
Description
The isolated proximal caudal centrum NMMNH P-40953
is nearly complete, missing a part of the right lateral surface,
including the right anterior and the right posterior neural
arches. The left lateral surface is complete. The overall length
of NMMNH P-40953 is 10 cm, and the height of the anterior
and posterior articular surfaces is 9 cm. Large pneumatopores
are absent in NMMNH P-40953, but small foramina are present
on the lateral surfaces. In general, the rst nine vertebrae in the
45
caudal series in tyrannosaurids, and, in particular, Tyrannosaurus
rex, have small foramina located on the lateral sides of the
centrum (e.g., Brochu, 2003). Thus, based on the presence of
these foramina NMMNH P-40953 is one of the rst centra in
the caudal series. Multiple perforations are mainly located on
the dorsolateral surface of the centrum, which further indicates
that NMMNH P-40953 is one of the anteriormost caudal centra
(e.g., Brochu, 2003). The relatively small size of the centrum
indicates that NMMNH P-40953 is from a juvenile individual.
When compared to other known tyrannosaurid specimens the
body of the animal to which NMMNH P-40953 belongs was
approximately 5 m long from the tip of the snout to the end of
the tail.
Right lateral side: The right lateral side of NMMNH
P-40953 contains ve bite marks (Figs. 12, 13). The largest bite
mark occupies the anteroposterior length of the centrum (Fig.
12A). It is ovoid-shaped and approximately 5.7 cm long and
3.3 cm wide dorsoventrally at its mid-section. The depth of the
bite mark is 0.8 cm. A small, circular, puncture-like depression
located within the bite mark approximately 2 cm from its
posterior margin most likely represents the mark of the tip of the
tooth that produced the bite mark. The applied pressure of the
bite force caused part of the lateral bone surface of the centrum
to collapse.
FIGURE 8. NMMNH P-25083, a right femur of a tyrannosaurid
from the Campanian of the De-na-zin Member, Kirtland
Formation, New Mexico, USA, close up of the femoral shaft
showing the better preserved set of bite marks consisting of
eight nearly perfectly aligned lesions.
FIGURE 9. NMMNH P-25083, a right femur of a tyrannosaurid
from the Campanian of the De-na-zin Member, Kirtland
Formation, New Mexico, USA, in lateral view (A), close up of
the distal lateral condyle showing extensively damaged bone
surface with multiple bite marks (B).
FIGURE 10. NMMNH P-25083, a right femur of a tyrannosaurid
from the Campanian of the De-na-zin Member, Kirtland
Formation, New Mexico, USA, in distal view (A), close up of
the distal lateral condyle showing a puncture mark (B), posterior
view (C), close up of crista tibiobularis in posterior view
showing a puncture mark that aligns with the puncture mark on
the distal surface of the lateral condyle (D).
46
FIGURE 11. NMMNH P-25083, a right femur of a tyrannosaurid from the Campanian of the De-na-zin Member, Kirtland Formation,
New Mexico; in medial view (A), close up of the distal medial condyle showing extensively damaged bone surface with multiple
bite marks (B).
Ventrolateral side: Directly ventral to this extensive bite
mark and located mostly in the posterolateral region of the
centrum are four smaller bite marks (Fig. 13A-D). The largest
one of these bite marks has an elliptical or V-shape with rugged
margins and is situated 3 cm from the posterolateral margin of
the centrum and nearly parallels it. The characteristic shape of
this bite mark indicates that the tooth that made it would have
possessed prominent mesial and distal carinae (sensu D’Amore
and Blumensehine, 2009). The bite mark is 3 cm long and 1
cm wide at its mid-section and has a single small puncture
mark in the middle. Cutting through this bite mark is another
smaller elliptically-shaped bite trace with rugged margins. This
bite mark is at a 40° angle to the larger bite mark. Posterior to
these bite marks, approximately 0.2 cm from them, is another
bite mark that is 1.5 cm long, has an elliptical shape and is 0.5
cm at its mid-section. Approximately 2.5 cm posteroventrally
from it is another much smaller bite mark, which is 0.4 cm long
and 0.2 cm wide. However, this bite mark is shallow and not as
pronounced as the other bite marks on the centrum. The margins
of this particular bite mark are rugged.
Left lateroposterior side: The left lateral side of the
centrum has only one bite mark situated in the posterolateral
47
FIGURE 12. NMMNH P-40953, proximal caudal centrum of a tyrannosaurid from the Maastrichtian of the Naashoibito Member,
Ojo Alamo Formation, New Mexico; in right lateral view (A), close up of puncture mark within large elliptical-shaped puncture-
and-collapse bite mark (B).
end (Fig. 14). The bite mark has an elliptical shape, rugged
margins, and is 4.5 cm long and 1 cm wide at its mid-section.
It originates as a lower depression 0.2 cm wide that is situated
along the long axis of the centrum and approximately 3.5 cm
from the lateroposterior margin of the centrum. The bite mark
continues posteroventrally at a 60° angle and cuts through the
lateroposterior margin of the centrum and terminates on the
posterior surface for the articulation with the respective centrum.
Here, the bite mark is nearly 2 cm deep, whereas at its point of
origin it is approximately 0.2 cm deep.
IDENTITY OF THE BITE MAKER
It is unlikely that the bite marks could have been produced
by other predators such as crocodiles, or small theropods such
as dromaeosaurids or troodontids and mammals. Crocodiles
would not have produced the tooth marks described here. The
unserrated conical teeth of crocodylians produce shallower
to deep puncture marks (Njau and Blumenschine, 2005).
The puncture marks described here do not resemble those of
crocodilians, but those made by laterally compressed serrated
teeth of theropods. Dromaeosaurids and troodontids are known
from the San Juan Basin (Evans et al., 2014; Jasinski, 2015);
however, the bite marks described here and the spacing between
them are larger than the bite marks described for dromaeosaurids
and troodontids (e.g., Currie and Jacobsen, 1995). There is no
evidence for the occurrence of a large-bodied dromaeosaurid in
the San Juan Basin (Sullivan and Lucas, 2015) that rivaled the
size of Dakotaraptor steini (DePalma et al., 2015), a species
that reached 5.5 m in length, known from the late Maastrichtian
in the Hell Creek Formation of South Dakota. Dinosaur bones
tooth-marked by dromaeosaurids are rare (Gignac et al., 2010).
Dromaeosaurid teeth do not exhibit extensive wear, which
suggests, that during feeding they avoided biting into the bone
(Longrich, 2008). In contrast, tyrannosaurid teeth have extensive
wears and spalling surfaces largely located at the tips and along
the mesial carina (Farlow and Brinkman, 1994; Schubert and
Ungar, 2005; Dalman, 2013; Dalman and Lucas, 2015, 2016a;
Dalman et al., 2018). The presence of bone and bone fragments
in a tyrannosaur coprolite suggest the consumption of hard
tissue by these iconic theropods (Chin et al., 1998).
Mammals are known to gnaw on dinosaur bones; however,
mammalian gnaw traces are much smaller than those of
theropods, consisting of closely spaced, paired tooth marks
(Longrich and Ryan, 2010).
The tooth marks described here were not made by insects.
However, insects can modify bones of large vertebrates, but their
traces are typically small, meandering tunnel-like structures
(Britt et al., 2008).
Therefore, as described here a large tyrannosaurid made the
bite marks on the left anterior dentary (KU VP-96888), the right
femur (NMMNH P-25083) and the proximal caudal centrum
(NMMNH P-40953). The identication of the bite makers as
tyrannosaurids is supported by the overall morphology, pattern,
and size of these traces, including the spacing between some of the
tooth marks, which is similar to that of described tyrannosaurid
bite marks (e.g., Erickson and Olson, 1996; Erickson et al., 1996;
Hone and Watabe, 2010; Dalman and Lucas, 2018c, 2018d;
Peterson and Daus, 2019). Furthermore, the spacing between
the tooth marks of individual teeth, especially those preserved
on the left anterior dentary (KUVP-96888) and the right femoral
shaft (NMMNH P-25083), equal 1 cm and represent a single bite
mark made by a large predator. At present, there is no evidence
48
FIGURE 13. NMMNH P-40953, proximal caudal centrum of a tyrannosaurid from the Maastrichtian of the Naashoibito Member,
Ojo Alamo Formation, New Mexico; in right lateral view (A), close up of the anteroventral portion of the centrum showing several
distinct bite-and-drag marks (B), ventral view (C) close up of the ventral portion of the centrum showing the same bite-and-drag
marks from a dierent angle (D).
for the occurrence of two tyrannosaurid species in the Ne-nah-
ne-zad, De-na-zin and in the Naashoibito members (Dalman
and Lucas, 2017b, 2018b). The tyrannosaurid Bistahieversor
sealeyi (Carr and Williamson, 2010) is known exclusively from
the Hunter Wash Member of the Kirtland Formation, and is
approximately 1.5 million years younger than the Ne-nah-ne-
zad Member tyrannosaurid, and 1.55 million years older than
the De-na-zin Member tyrannosaurid and approximately 5.84
million years older than the Naashoibito Member tyrannosaurid.
Over the years several axial and appendicular skeletal elements
pertaining to large tyrannosaurids were recovered from the
Upper Cretaceous deposits of the Ne-nah-ne-zad, De-na-zin and
the Naashoibito members (Gilmore, 1916, 1935; Jasinski et al.,
2011; Dalman and Lucas, 2016b, 2016c, 2018b). However, some
of these fossils were referred by other workers (e.g., Lehman and
Carpenter, 1990) to the invalid species Aublysodon mirandus
and to the known genera Albertosaurus, Daspletosaurus,
Gorgosaurus and Tyrannosaurus (e.g., Gilmore, 1916, 1935;
Lucas et al., 1987; Hunt and Lucas, 1992; Carr and Williamson,
2000). The study by Dalman and Lucas (2016b, 2016c, 2017b,
2018b) suggests that the De-na-zin and the Naashoibito member
tyrannosaurids represent new species. The Ne-nah-ne-zad
Member tyrannosaurid also represents a new species. Notably,
the Naashoibito Member tyrannosaurid lived at the same time
as Tyrannosaurus rex. Contrary to previous claims by Carr and
Williamson (2004), Longrich et al. (2010), Brusatte and Carr
(2016) and Carr et al. (2017), this supports the hypothesis that
T. rex was not the last or the only member of Tyrannosauridae
during the nal stage of the Maastrichtian in North America
(Dalman and Lucas, 2017b, 2018b).
COMPARISON TO OTHER TYRANNOSAURID
BITE MARKS
The overall morphology of the bite marks described here is
similar to the feeding traces described for other tyrannosaurids
from Asia and North America (e.g., Fowler and Sullivan, 2006;
Peterson et al., 2009; Bell, 2010; Bell et al., 2012; Hone and
Tanke, 2015; Hone et al., 2018; Peterson and Daus, 2019).
However, the bite marks can be dierentiated especially from
those attributed to Tyrannosaurus rex. A single large bite-and-
drag mark preserved on the isolated proximal caudal centrum
(NMMNH P-40953) from the Naashoibito Member of the Ojo
Alamo Formation is deep and narrow, which suggests that the
tooth that made this trace was strongly labiolingually compressed
and blade-like. Indeed, isolated tyrannosaurid teeth recovered
from the San Juan Basin are all blade-like, whereas the teeth
49
FIGURE 14. NMMNH P-40953, proximal caudal centrum of a tyrannosaurid from the Maastrichtian of the Naashoibito Member,
Ojo Alamo Formation, New Mexico; in left lateral view (A), close up of a large bite-and-drag mark (B), distal view (C), close up
of the bite-and-drag mark (D).
of T. rex are thicker (e.g., Smith, 2005; Dalman, 2013; Dalman
and Lucas, 2016b, 2016c, 2017b, 2018b, 2018c, 2018d). This
provides further support for the presence of a distinct southern
Maastrichtian tyrannosaurid in North America during the nal
stage of the Cretaceous (Dalman and Lucas, 2017b).
Some of the bite marks on the isolated right femur
(NMMNH P-25083) closely resemble the bite marks preserved
on a ceratopsian pelvis from the De-na-zin Member described
by Fowler and Sullivan (2006), who attributed the bite marks
to Daspletosaurus. However, the skeletal material recovered
from the De-na-zin Member does not belong to Daspletosaurus
(Dalman and Lucas, 2016b, 2016c, 2017b, 2018b).
The bite marks preserved on the left anterior dentary
(KUVP-96888) also suggest that the teeth that made them were
labiolingually compressed. The teeth of the late Campanian
genera Albertosaurus, Daspletosaurus and Gorgosaurus
are labiolingually compressed more so than the teeth of
Tyrannosaurus rex (e.g., Buckley et al., 2010). However,
currently there is no evidence for the occurrence of these genera
in the San Juan Basin (Dalman and Lucas, 2017b).
The best examples of Tyrannosaurus rex bite marks
described by Erickson and Olson (1996), Happ (2008), and
Longrich et al. (2010) come from a hadrosaurid pubis (CM
105), metatarsal (UCMP uncatalogued), ceratopsid frill element
(TMP 1998.102.2), Triceratops left supraorbital horncore
and left squamosal (SUP 9713), Triceratops right squamosal
(YPM VP-53263), and Triceratops pelvis (MOR 799), but also
several isolated bones pertaining to T. rex: humerus (MOR 902),
metatarsal III (MOR 1602), pes phalanges (MOR 1126 and
UCMP 137538). These specimens show numerous deep bite
marks, including punctures. However, drag-and-scrape marks
are not identied on these specimens. Therefore, this may reect
dierent feeding behaviors due to bones with dierent shapes and
how the soft tissue that surrounded these bones was accessed by
the De-na-zin Member tyrannosaurid, the Naashoibito Member
tyrannosaurid, and Tyrannosaurus.
FACE BITING
50
FIGURE 15. Position of the maxilla and dentary with relation to
the proximal caudal centrum during the consumption; maxilla
(left reversed ) NMMNH P-27469 holotype of Bistahieversor
sealeyi in lateral view (A), right dentary NMMNH P-27469
holotype of Bistahieversor sealeyi (B) proximal caudal centrum
NMMNH P-40953 in posterior view (C, D) lateral tooth
NMMNH P-71331 (E) lateral tooth NMMNH P-64454 (F).
Tanke and Currie (1998) described several examples of face-
biting behaviors in large theropods, including tyrannosaurids
with unhealed and healed bite marks. Some of these examples
include the subadult Daspletosaurus sp. (TMP 94.143.1) from
the Dinosaur Park Formation, which skull and the elements of
the lower jaw exhibit at least 50 abnormalities that were later
described by Hone and Tanke (2015) as bite marks made by
another tyrannosaur. The bite marks on the skull are interpreted
as premortem injuries because they show evidence of healing
and are most likely the result of intraspecic combat; whereas,
the bite marks on the elements of the lower jaw were made
postmortem (Hone and Tanke, 2015).
Bell and Currie (2010) reported on a partial left dentary
(TMP 1996.05.13) of an adult tyrannosaurid with an embedded
tooth of another tyrannosaur. TMP 1996.05.13 provides evidence
for intraspecic and intrafamilial antagonistic behavior among
large theropods, which has been described before from bite
marks on dinosaur bones (e.g., Petersen et al., 1972; Tanke and
Currie, 1995, 1998; Bell and Currie, 2010) and teeth (Tanke and
Currie, 1995, 1998; Tanke and Rothschild, 1997). Furthermore,
two other tyrannosaur specimens with tooth-marked cranial
bones include the left maxilla and nasal of the controversial
Nanotyrannus lancensis (BMR P2002.4.1; Peterson et al.,
2009, g. 2) and the left dentary of Albertosaurus sarcophagus
(TMP 2003.45.64; Bell, 2010, g. 3). KUVP-96888 provides
another unequivocal evidence for face-biting behavior among
tyrannosaurids.
Tanke and Currie (1998) suggested that tooth marks
preserved on cranial bones in tyrannosaurids and in other large
theropods can be attributed to intra- and interspecic face-biting
behavior, which may reect establishment of group dominance,
mating, territoriality or play. However, it is unlikely that KUVP-
96888 died of some other unrelated causes long after the bite
marks were made. The tooth marks preserved in KUVP-96888,
suggest that the biting was violent and occurred post-mortem,
because the bone surface around the bite marks lacks remodeling,
indicating that KUVP-96888 was already dead and fed upon.
Alternatively, KUVP-96888 was killed rst and then most likely
was fed upon. However, the absence of other skeletal elements
may prove it dicult to determine with total certainty the fate
of the animal; however, if the bite indeed took place after the
death of KUVP-96888 then cannibalism is implied here and
interpreted as the feeding behavior.
The true predation and cannibalism usually involve a large
individual attacking a smaller one (Tanke and Currie, 1998).
However, in life KUVP-96888 was a relatively large individual.
The proportion of the bite marks also suggests that the bite
maker was also a large individual.
THE FEEDING BEHAVIOR OF THE BITE MAKER
The overall morphology of the bite marks described here
provides important information about the feeding behavior
employed by the predator, in this case a tyrannosaurid. Some of
the puncture marks, especially those on the proximal end of the
femur, are closely aligned D-shape traces, suggesting that these
were made by the use of the premaxillary teeth during biting and
the removal of the soft tissue from the bone. Similarly, the drag-
and-scrape marks preserved on the distal condyles were in part
made by the use of the premaxillary and the anterior teeth of the
maxilla. The puncture marks within the drag-and-scrape display
a pattern of closely aligned D-shape traces that correlate well
with the premaxillary dental arcade of derived tyrannosaurids.
The teeth of the premaxillary dental arcade in tyrannosaurids
and in theropods in general are more closely spaced than those
of the maxillary and dentary dental arcades (Brochu, 2003;
Smith, 2005, 2007; Buckley et al., 2010). Furthermore, the drag-
and-scrape marks on the lateral and medial surfaces of the distal
condyles are sub-parallel to each other, suggesting that they
were made by the action of the upper and lower jaws in unison.
The tooth marks occur on all sides of the femur, suggesting
that the bone was separated from the carcass during feeding
to provide better access to all sides. This assumption is
supported by a large and deep bite-and-drag mark located on
the anterodorsal surface of the femoral head. It is likely that this
trace was made by the repetitive action of one or two teeth, most
likely of the maxilla, and based on the depth of this trace the
intention of the predator was likely to cut o the bone in this
region. Although the bite marks are found on all sides of the
femur, they are largely concentrated on the proximal and distal
ends, which may suggest a deliberate or varying feeding strategy
of the tyrannosaurid that made them. However, this may have
been an attempt by the predator to remove the cartilage from the
proximal and distal ends of the femur or to separate it at the joints
in order to better access the soft tissue. Although both ends of the
femur are extensively tooth-marked, the proximal end exhibits
more severe damage. The proximal end of the femur contains
several muscle attachment scars, including the following: M.
iliofemoralis externus insertion, M. iliotrochantericus insertion
(lesser trochanter), M. ischiotrochantericus insertion, and M.
puboischiofemoralis externus insertion (greater trochanter)
(Carrano and Hutchinson, 2002), which would have been
the primary targets in the removal of the soft tissue from the
bone. Indeed, the lesser trochanter is nearly entirely removed,
including a dorsal portion of the accessory trochanter.
The isolated proximal caudal centrum provides further
information about the feeding behaviour employed by a
tyrannosaurid. The puncture marks preserved on the body of the
centrum are small and shallow. As described before, some of the
puncture marks are preserved within the bite-and-drag marks,
but also within the newly recognized puncture-and-collapse
mark. The punctures within the bite-and-drag marks occur on
both lateral sides of the centrum and on its ventrolateral side and
show where the tooth made contact with the bone. This suggests
that the maxillary and dentary teeth were used by the predator
during feeding (Fig. 15A-B).
The most extensive damage preserved on the NMMNH
P-40953 centrum is that of the puncture-and-collapse mark.
As described before, a single puncture is situated within the
collapsed surface of the bone. The collapsed surface is the result
of the force applied by a single tooth from the upper jaw and
teeth from the lower jaw in unison. The missing part of the
neural arch and the entire neural spine were most likely removed
51
by the predator and consumed. Tyrannosaur tails had substantial
muscles such as m. caudofemoralis brevis, M. caudofemoralis
longus, M. ilio-ischocaudalis, M. longissimus, and M. spinalis
(Persons and Currie, 2010) that might have been the target
of early stage consumption. The bite marks preserved on the
NMMNH P-40953 centrum suggest that the tyrannosaur was
feeding on the haemal complexes, and the supercial hypaxial
muscles and M. caudofemoralis longus had been removed; thus,
suggesting a later-stage carcass consumption and postmortem
feeding behaviors.
Tyrannosaurids, and, in particular Tyrannosaurus rex, are
known to have consumed hard tissue (Chin et al., 1998, 2003;
Gignac and Erickson, 2017). However, most of the feeding traces
described here, such as those that are represented by shallow
traces, appear to be unintentional rather than an active choice.
These include a pattern of three and eight elongate traces aligned
together in a single line on the femoral shaft (Fig. 8). This suggests
that the teeth (most likely maxillary) that were doing the action
were stripping away the soft tissue and accidently connected
with the bone. Alternatively, these traces can be related to the
removal of the femur from the body by the predator. We agree
with Hone and Watabe (2010) that consumption of bones by
tyrannosaurids was not a fundamental part of feeding by these
iconic predators. However, their powerful jaws were able to
crush and remove bones from the carcasses of other dinosaurs
(Gignac and Erickson, 2017).
Tyrannosaurids, therefore, seem to have been indiscriminate
and opportunistic feeders, which fed not only on herbivorous
dinosaurs such as ceratopsians and hadrosaurids, but also on
members of their own species. However, it is not clear if the traces
described here are the result of opportunistic feeding on decaying
carcasses or active killing by the predators. Alternatively,
we interpret these traces as the result of an individual slowly
consuming a kill. The proximal caudal centrum NMMNH
P-40953 and the right femur NMMNH P-25083 both belong to
juvenile individuals. Thus, it seems probable that tyrannosaurids
occasionally killed members of their own species, which may
have been inuenced by intrapack dominance or when food
was scarce (e.g., Tanke and Currie, 1998). The discovery of
monospecic bone beds of Albertosaurus sarcophagus in
the early Maastrichtian deposits in Alberta, Canada, and of
Daspletosaurus sp. in the late Campanian deposits in Montana,
USA, suggests gregarious behavior of these theropods (e.g.,
Currie, 1998; Currie et al., 2005; Currie and Eberth, 2010;
McCrea et al., 2014).
Tracy (1976) and Naeye (1996) were the rst to suggest
that tyrannosaurs may have been cannibalistic. Among theropod
dinosaurs, cannibalistic behavior is well documented in
Coelophysis bauri (Rinehart et al., 2009) and in the abelisaurid
Majungasaurus crenatissimus (Rogers et al., 2003). Bones of
tyrannosaurids tooth-marked by other tyrannosaurids have
been reported and described from the Dinosaur Park Formation
(Jacobsen, 1998; Tanke and Currie, 1998; Bell and Currie,
2010; Hone and Tanke, 2015) and from the Horseshoe Canyon
Formation in Alberta, Canada (Bell, 2010). In the Dinosaur Park
Formation fauna two tyrannosaurid species are recognized:
Gorgosaurus libratus and Daspletosaurus sp. (Lambe, 1917;
Farlow and Pianka, 2002; Currie, 2003a, 2005). But, the co-
occurrence of these species can make it dicult to suggest that
the tooth-marked bones of tyrannosaurids represent cannibalism
(Nesbitt et al., 2006). However, according to Currie and Russell
(2005), in the Dinosaur Park Formation Gorgosaurus is more
commonly found than Daspletosaurus. Thus, the tooth-marked
bones of Gorgosaurus most likely represent feeding traces
of another Gorgosaurus and therefore represent cannibalism
(Longrich et al., 2010). Other examples of intraspecic biting
in tyrannosaurids have been recognized and described in
Albertosaurus sarcophagus (Molnar and Currie, 1995; Bell,
2010), Bistahieversor sealeyi (Williamson and Carr, 1999),
Gorgosaurus libratus (Molnar, 2001), and Tyrannosaurus rex
(Larson, 2001a, 2001b; Longrich et al., 2010; McLain et al.,
2018).
Cannibalism is common among large extant carnivores
(Fox, 1975). These include bears (Tietje et al., 1986; Mattson
et al., 1992; Amstrup et al., 2006), hyenas (Kruuk, 1972), felids
(Lesowski, 1963; Elo, 1984), Komodo dragons (Auenberg,
1981), and crocodylians (Pooley and Ross, 1989; Rootes and
Chabreck, 1993; Webb and Manolis, 1998). Documented
examples of cannibalism in large carnivores are largely due to
predation. This behavior has also been documented in birds,
especially in Red-tail Hawks (Clevenger et al., 1974), Great Grey
Owl (Fisher, 1975), Moorhens (Cawston, 1983), Tree Swallows
(Rendell, 1993), and Crows (Andersen, 2004). Therefore, it
is likely that cannibalistic behavior was widespread in large,
carnivorous dinosaurs, including tyrannosaurs (Longrich et al.,
2010).
CONCLUSIONS
These newly described trace fossils add new information
to tyrannosaurid feeding and cannibalistic behavior. The
examples of feeding traces described here are condently
referred to as tyrannosaurids cannibalizing the carcasses of other
tyrannosaurids. The pattern and distribution of the feeding traces
on the isolated proximal left dentary, proximal caudal centrum
and the right femur extend our knowledge of tyrannosaurid
behavior. However, no selective feeding has been detected on
either bone. The variation between feeding on the proximal and
distal ends of the femur and the femoral shaft demonstrates that
the predator used various techniques to strip o the soft tissue
from the bone. The feeding traces also show that the predator
used the teeth of the premaxillary, maxillary, and dentary dental
arcades, for extracting the soft tissues. Tyrannosaurid feeding
on another tyrannosaurid most likely suggests an opportunistic
behavior displayed by these iconic predators.
ACKNOWLEDGMENTS
We are grateful to Anna Whitaker for providing digital
pictures of KU VP-96888 specimen. We thank the reviewers,
Claudia Serrano-Brañas and D. Edward Malinzak for helpful
comments, which improved this study.
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This study provides a detailed osteological description of an isolated proximal caudal centrum and two nearly complete isolated metatarsals II and IV of the left foot of a gracile theropod dinosaur from the Lower Campanian of the Merchantville Formation in northern Delaware, USA. The caudal centrum and the metatarsals are referred to Tyrannosauroidea. The centrum is not well preserved, and thus not diagnostic; however, both metatarsals are diagnostic. The referral to Tyrannosauroidea is supported by several morphological features, including extensive surfaces on metatarsals II and IV for the articulation with metatarsal III, and a characteristic low, slightly convex muscle scar on metatarsal IV developed as a thin low ridge located on the posterior surface between the M. gastrocnemius pars lateralis insertion scar and the metatarsal III articular surface. This ridge has been previously interpreted as the plantar ridge, which is present in some derived Late Campanian tyrannosauroid taxa. Additionally, metatarsal IV has a deep medial notch for the accommodation of an “L”– shaped proximal articulation of metatarsal III, and a “U”– shaped proximal articular end. The Merchantville Formation tyrannosauroid exhibits arctometatarsalian metatarsals, as do tyrannosaurids. The Merchantville Formation tyrannosauroid is differentiated from other known basal and derived tyrannosaurids by having a characteristically shaped proximal articular surface of metatarsal II in which the proximal and posterior ends lie on the long axis of the proximal articular surface. However, the posterior proximal articular surface of metatarsal II is not as strongly angled laterally as in more derived tyrannosauroids. The Merchantville Formation tyrannosauroid adds to the record of Appalachian tyrannosauroid, evolution and paleostratigraphic position, and provides new morphological information about the metatarsal anatomy of these iconic theropods.
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A recently discovered tyrannosaurid metatarsal IV (SWAU HRS13997) from the uppermost Cretaceous (Maastrichtian) Lance Formation is heavily marked with several long grooves on its cortical surface, concentrated on the bone's distal end. At least 10 separate grooves of varying width are present, which we interpret to be scores made by theropod teeth. In addition, the tooth ichnospecies Knethichnus parallelum is present at the end of the distal-most groove. Knethichnus parallelum is caused by denticles of a serrated tooth dragging along the surface of the bone. Through comparing the groove widths in the Knethichnus parallelum to denticle widths on Lance Formation theropod teeth, we conclude that the bite was from a Tyrannosaurus rex. The shape, location, and orientation of the scores suggest that they are feeding traces. The osteohistology of SWAU HRS13997 suggests that it came from a young animal, based on evidence that it was still rapidly growing at time of death. The tooth traces on SWAU HRS13997 are strong evidence for tyrannosaurid cannibalism-a large Tyrannosaurus feeding on a young Tyrannosaurus.
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Background. The estimations of maximum speed of Tyrannosaurus Rex vary from 5 to 20 m/s and higher and still are the subject of scientific discussion. Some scientists consider T. Rex the largest terrestrial super-predator that needed speeds greater than 60 km/h (17 m/s) to capture its prey. Some recent publications indicate that it wasn't able to run at all due to its large mass and significant loads on the skeleton and limit its walking speed to 5-7.5 m/s. Objective. We will try to answer the question of whether large animal or robot sizes are an obstacle to rapid running and to evaluate the maximum possible speed of T. Rex. Methods. We will use: a) two energy efficiency indicators-the drag-to-weight ratio or the cost of motion and the recently developed capacity-efficiency (connected with the power-to-weight ratio or metabolic rate); b) the vertical acceleration estimations; c) the available data about the speed, the stride and the leg length of human and animals. Results. The drag-to-weight ratio and the capacity-efficiency were estimated for running of different animals and humans. It was shown that the maximal running speed of T. Rex may reach the values 21-29 m/s. The values of its vertical acceleration are typical for bipedal running. Conclusions. Large dimensions of Tyrannosaurus Rex couldn't be an obstacle to achieving rather high speeds during short intervals of fast running. Such conclusions allow us not to abandon the assertion that the dinosaur was a super-predator. Presented approach could be useful for studying locomotion in modern and fossil animals, human sport activity and for design of fast bipedal robots.
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