Tyrannosaur feeding behavior

Tyrannosaur feeding behavior evinced from hadrosaurian dinosaur remains in the Aguja Formation (Upper Cretaceous), Big Bend National Park, Texas, USA

Bryce M. McElvogue and Thomas M. Lehman

Article number: 29.3.a36
https://doi.org/10.26879/1657
Copyright Society of Vertebrate Paleontology, September 2026

Author biographies
Plain-language and multi-lingual abstracts
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Submission: 24 January 2026. Acceptance: 26 August 2026.

ABSTRACT

Bones of a large hadrosaur from the Aguja Formation bear numerous tooth marks. Aside from hind limb elements of the hadrosaur, only a broken tyrannosaur tooth crown was found at the collection site. The broken tooth, as well as the width and depth of the tooth marks indicate that the marks were made by one or more tyrannosaurs. Preservation of the hind limb elements in isolation suggests that they were removed from the carcass and brought to a separate site for feeding. The bones have bite marks on multiple sides, and their pattern indicates that these were made during the process of dismembering a dead animal, not while subduing a prey animal. Bite marks on the shafts of the bones consist mostly of long, curvilinear gouges at varied angles that do not fully penetrate the cortical tissue. The gouges are not in parallel series and are compatible with raking of large lateral teeth across the bone surfaces multiple times. Bite marks on the articular surfaces of the bones are instead punctures that penetrate more deeply and are consistent with pulling the bones from their distal ends using the premaxillary teeth. The ankles and feet of hadrosaurs likely had little muscle mass, and so the thorough effort to remove all flesh from these elements may record unusual behavior, perhaps brought about by food scarcity. However, the relatively common occurrence elsewhere of bite marks on distal hind limb elements of hadrosaurs could indicate that this was instead more typical tyrannosaur feeding behavior.

Bryce M. McElvogue. Department of Geosciences, Texas Tech University, Lubbock, Texas 79409, USA. [email protected]
Thomas M. Lehman. Department of Geosciences, Texas Tech University, Lubbock, Texas 79409, USA. (corresponding author) [email protected]

Keywords: Tyrannosauridae; tooth marks; feeding behavior; insect damage

Final citation: McElvogue, Bryce M. and Lehman, Thomas M. 2026. Tyrannosaur feeding behavior evinced from hadrosaurian dinosaur remains in the Aguja Formation (Upper Cretaceous), Big Bend National Park, Texas, USA. Palaeontologia Electronica, 29(3):a36.
https://doi.org/10.26879/1657
palaeo-electronica.org/content/2026/5962-tyrannosaur-feeding-behavior

Copyright: September 2026 Society of Vertebrate Paleontology.
This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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INTRODUCTION

Bite marks on fossil vertebrate bones have long been of interest in providing information about the feeding behavior of extinct predators and scavengers and their preferred prey - information that might otherwise be unobtainable (Erickson and Olson, 1996; Carpenter, 1998; Farlow and Holtz, 2002; Pobiner, 2008). The likely feeding behaviors of large theropod dinosaurs such as tyrannosaurs have been of particular interest because these were the largest terrestrial carnivores, and there has been debate as to whether these animals were primarily scavengers or active predators. Tooth marks on bones of herbivorous dinosaurs have provided a primary source of fodder for this debate (e.g., Farlow and Holtz, 2002; Paul, 2008; Holtz, 2008; Longrich, et al., 2010; Bell et al., 2012; DePalma et al., 2013).

Based on examples of hadrosaur and ceratopsian specimens with healed bite-marked wounds, and those with imbedded tyrannosaur teeth, it seems clear that tyrannosaurs were active predators - if not routinely at least occasionally (e.g., Farlow and Holtz, 2002; Happ, 2008; DePalma et al., 2013; Dalman and Lucas, 2018). Examples of some tooth marks, such as those described herein, are instead compatible with subsequent feeding activities or with scavenging, regardless of whether the animals had been brought down as prey (e.g., Fowler and Sullivan, 2006; Rivera-Sylva et al., 2012; Gignac and Erickson, 2017; Peterson and Daus, 2019). The notion that tyrannosaurs were obligate scavengers has been largely discounted (e.g., Paul, 2008; Holtz, 2008) although it remains possible or even likely that tyrannosaurs could have displaced smaller predators from a carcass or scavenged when carcasses were available (Hone and Watabe, 2010). Bite marks on tyrannosaur crania and mandibles show that tyrannosaurs also engaged in intraspecific combat and cannibalism (e.g., Bell and Currie, 2010; Longrich et al., 2010; Hone and Tanke, 2015).

The specimen described herein (TxVP 43679-1) consists of parts of the hind limbs of a large hadrosaurian dinosaur that exhibit numerous tyrannosaur bite marks. The bite marks are unusually concentrated on the distal hind limb elements and feet and differ from many described elsewhere that are attributed to tyrannosaurs. This curious distribution may record feeding behavior that differed from that typical of tyrannosaurs. The purpose of the present report is to document the types and distribution of tooth marks on this specimen, compare these marks with others ascribed to tyrannosaurs, and interpret the likely feeding behavior evinced by the pattern of tooth marks in this case. Herein we generally follow the descriptive terminology for tooth marks established by Hone and Watabe (2010).

Abbreviations. In the following account, we use the informal abbreviated term “tyrannosaur” to refer to all members of Tyrannosauroidea (e.g., Carr and Williamson, 2010). Although we recognize that the specimens discussed herein likely pertain to family Tyrannosauridae (e.g., Currie et al., 2003), it is possible that they might represent less derived taxa. TxVP = Vertebrate Paleontology Laboratory at the Jackson School Museum of Earth History at The University of Texas in Austin, Texas (formerly TMM = Texas Memorial Museum).

BACKGROUND

Upper Cretaceous non-marine strata in the Big Bend region of Texas are divided into the Aguja Formation (Campanian) and overlying Javelina Formation (Maastrichtian; Figure 1A). The Aguja Formation has two non-marine intervals - the Abajo Shale Member and the Alto Shale Member (Lehman et al., 2024). The specimen discussed herein (TxVP 43679-1) was collected from the uppermost part of the Alto Shale Member, just below its contact with the overlying Javelina Formation. The collection site is in the southern part of Big Bend National Park, just north of the Rio Grande in Brewster County, Texas (Figure 1B). Exact locality information is on file with the Jackson School Museum of Earth History Vertebrate Paleontology Laboratory at the University of Texas in Austin, Texas.

The uppermost part of the Alto Shale Member (biozone IV of Lehman et al., 2024) consists of fluvial channel and floodplain deposits and is of late Campanian age - ca. 77 to 72 Ma. This part of the Alto Shale is locally interbedded with pyroclastic deposits that resulted from intermittent phreatomagmatic eruptions at nearby maar craters (e.g., Wick, 2023). The collection site considered here is within a thick interval of dark green mudstone interpreted as fluvial overbank floodplain facies (Figure 1C; Lehman et al., 2024). Buried paleosols and fossil woods within this interval are indicative of deposition under a warm and subhumid to humid climate (Nordt et al., 2011; Wheeler and Lehman, 2000).

Aguja Hadrosaurs

Hadrosaur skeletal elements are among the most common dinosaur remains found in the Aguja Formation (Davies, 1983; Wagner, 2001). Several taxa are recognized - Angulomasticator daviesi Wagner and Lehman (2009), Aquilarhinus palimentus Prieto-Márquez et al. (2019) and Malefica deckerti Prieto-Márquez and Wagner (2023). All three of these hadrosaurs are known only from the Aguja Formation; and as is presently known represent much smaller animals than TxVP 43679-1. Moreover, all three are known only from the lower part of the formation (Aguja biozones I, II, and III of Lehman et al., 2024).

The skeletal elements preserved in TxVP 43679-1 are not sufficiently diagnostic to recognize specifically which hadrosaur they may represent; however, given the great size of the individual, and the stratigraphic level of the collection site, it most likely represents a taxon yet to be identified in the Aguja Formation (e.g., Wagner, 2001 assigned the specimen only to Hadrosauria incertae sedis). Davies (1983) and Wagner (2001) reviewed most specimens known from these strata, and both suggested that Kritosaurus or a very similar taxon was likely present in the Aguja Formation. Kritosaurus sp. has been reported from the lowermost part of the overlying Javelina Formation (Lehman et al., 2016). Based on its large size and stratigraphic position, it is possible that TxVP 43679-1 could pertain to Kritosaurus. Regardless, the specimen represents a very large animal, given the length of MT III (47 cm) and distal width of the tibia (36 cm), they pertain to a hadrosaur about 9 to 11 m in length and weighing 2 to 4 metric tons (Figure 1D; estimates based on those given for K. navajovius; e.g., Prieto-Márquez, 2014).

Aguja Tyrannosaurs

Other than the hadrosaur hind limb elements described herein, a broken tyrannosaur tooth crown is the only fossil recovered at the site (Figure 2; TxVP 43679-2). The base of the crown is preserved but is missing both the root and tip (crown basal length = 13.5 mm, width = 9 mm), and is part of a lateral tooth. The mesial carina is deflected lingually, with fine denticles at the base and coarser beyond that (from 17 to 15 per 5 mm). The distal carina has coarser denticles along its entire preserved length (13 to 12 per 5 mm); these have the chisel-shaped form and blood grooves typical of tyrannosaurs (e.g., Samman et al., 2005). The tooth size, crown base ratio, denticle count, and denticle form correspond with those found among the smaller tyrannosaurs (e.g., DePalma et al., 2013; Figure 2). The size and serration count are compatible with other isolated tyrannosaur teeth found in the Aguja Formation (Lehman and Wick, 2013; Rivera-Sylva et al., 2009a).

Remains of tyrannosaurs are not common in the Aguja Formation. Specimens known thus far are too fragmentary to identify specifically; however, it seems clear from these remains that the known Aguja tyrannosaurs were relatively small compared to many other tyrannosaurs (c.a. 5 m length, 700 kg weight; see Lehman and Wick, 2013). Most of these specimens have, however, been recovered from the lower part of the Alto Shale Member (Aguja biozone II of Lehman et al., 2024). The present specimen is from the uppermost part of this unit (Aguja biozone IV) and likely represents a different taxon. Nevertheless, even the fragmentary remains of tyrannosaurs thus far recovered from the upper part of the formation represent relatively small individuals (Figure 1D). Mature individuals of the local taxon were certainly not “giant” tyrannosaurids comparable in size to Tyrannosaurus rex.

Hadrosaurs as Prey

In a survey of tooth-marked dinosaur bones in the Dinosaur Park Formation of Alberta, Jacobsen (1998) found that compared to ceratopsid and theropod bones, a relatively high number of hadrosaur bones (14% of the hadrosaur specimens examined) had tooth marks. This suggests that hadrosaurs may have been among the preferred prey of tyrannosaurs. Moreover, among the documented examples of hadrosaurs that survived failed predation attempts by tyrannosaurs, many exhibit wounds inflicted on the tail (e.g., DePalma et al., 2013; Murphy et al., 2013; Peterson and Daus, 2019; Rivera-Sylva et al., 2019). This may simply indicate that an attack to the tail could have been more readily escaped or more survivable than a wound to the neck or torso. However, hadrosaur tail vertebrae are also where many examples of crocodylian bite marks are found (e.g., Rivera-Sylva et al., 2009b). Paul (2008) suggested that the base of the tail would have been a likely point of attack for a pursuing tyrannosaur. The tail may have just been a part of the body more readily grasped by a predator (e.g., modern squamates evolved detachable tails to evade predators; Baban et al., 2022). Regardless, it seems clear that hadrosaurs were, if not preferred, at least typical prey of tyrannosaurs. Given the abundance of their remains, they were certainly the most common large herbivore in environments recorded by the Aguja Formation.

DESCRIPTION

TMM 43679-1 consists of the distal end of a very large hadrosaur right tibia, the right astragalus, parts of the right fibula, several metatarsals from both right and left pes, and parts of several pedal phalanges (Figure 3). All the elements were disarticulated, but scattered within a small area of about 10 m². Most had completely weathered out at the time of collection and were reassembled from fragments. Although it was not possible to reunite some of the fragments with the larger parts preserved, all of these parts belong to the distal hind limb elements, and, given their compatible sizes, pertain to a single large individual. Given the nature of the outcrop at the site, it is also apparent that no other parts of the skeleton were preserved nearby, and apart from the broken tyrannosaur tooth crown (TxVP 43679-2), no other fossils were found at the site. The great size of the hadrosaur remains, together with their preservation and close association in fine-grained fluvial floodplain mudstone, makes it unlikely that they had been transported hydraulically from where they had originally lain post-mortem. All bone fragments were collected, and even those which could not later be reunited with the identified elements appear to pertain to them. So, we consider it unlikely that collecting bias resulted in failure to recognize skeletal elements that were originally present at the site.

The hadrosaur bones show little pre-burial breakage or weathering; cortical bone surfaces are generally well preserved, but the cancellous articulation surfaces had partly decomposed prior to fossilization. The distal end of the right tibia is well preserved, but the shaft of the tibia appears to have been broken prior to burial; only fragments of the remaining lateral side of the shaft are preserved, but no other parts of the shaft or proximal end of the tibia were recovered at the site. The right astragalus is complete and well preserved. Both right and left metatarsal III are nearly complete, and although it was not possible to reassemble some parts of the shafts both bones were originally unbroken when buried. Only parts of the distal end and shaft of the right fibula were recovered; the remainder of the shaft and proximal end had been entirely fragmented. Left metatarsal IV was also complete at the time of burial but it was not possible to reassemble some parts of the shaft. Only the proximal end of left metatarsal II was recovered. Although parts of right metatarsals II and IV are also recognizable among the fragments preserved, neither could be reassembled. All the pedal phalanges except right phalanx II-1 are fragmented, and only proximal and distal ends of a few others can be identified (Figure 3). Apart from pre-burial breakage of the shaft of the tibia, few other pre-burial breaks are evident on the preserved parts. Some bone breakage intimately associated with tooth marks likely resulted directly from biting (see below). Otherwise, the broken surfaces remaining on the preserved elements reflect breakage due to modern exposure and a failure to reunite fragments with those larger parts preserved.

The cortical surfaces on several of the bones have very shallow, sinuous, channels with minute striations that appear to record insect damage (Figure 4). These faintly striated channels are only apparent when viewed under markedly oblique lighting. The marks differ somewhat from the borings in bone due to feeding by dermestid beetles (e.g., ichnogenus Cubiculum; El Hedeny et al., 2023) but may be attributable to similar necrophagous insects (e.g., ichnogenus Osteocallis; Roberts et al., 2007).

Form and Distribution of the Tooth Marks

Bones with crocodylian tooth marks are common in the Aguja Formation - particularly in the coastal and deltaic facies in the lower part of the formation (Aguja biozones I and II; Figure 5). Most of these tooth marks have been attributed to the giant crocodilian Deinosuchus (e.g., Rivera-Sylva et al., 2009a; Schwimmer, 2002, 2010; Lehman and Wick, 2010). Crocodylian bite marks are distinctive and consist primarily of depressed conical punctures with nearly circular outlines, typically arrayed in linear series (e.g., Njau and Blumenschine, 2005; Figure 5). Stout conical crocodylian teeth tend also to produce linear gouges that are broad and U-shaped. In contrast, the narrow, tapering, V-shaped tooth marks on TxVP 43679-1 differ from those made by crocodylians and are instead compatible with those made by theropod dinosaurs (Longrich et al., 2010).

The width, depth, and spacing of the bite marks on TxVP 43679-1 are too great for the marks to have been made by smaller carnivorous theropods, such as the dromaeosaurs known from the Aguja Formation (e.g., Wick et al., 2015), and instead are like those of larger theropods. The compact lateral dentition of smaller theropods results in shallower, serrated, and closely spaced tooth marks than those produced by tyrannosaurs (Erickson and Olson, 1996; Brown et al., 2021). The size and morphology of the bite marks on TxVP 43679-1, along with the recovery of a broken tyrannosaur tooth at the site, are compelling evidence that the tooth marks in this case are those made by one or more adult tyrannosaurs.

Bite marks attributed to tyrannosaurs fall into two basic types with variation along a spectrum between the two end-members (e.g., Hone and Watabe, 2010). At one extreme are “punctures” - deep oval depressions that may penetrate the entire bone cortex (“pits” of authors; e.g., Binford, 1981); and at the other extreme are “drag marks” - curvilinear grooves cut to varied length and depth along the bone surface (“scrapes”, “scratches”, “scores”, or “scoring marks” of various authors; e.g., see Binford, 1981). In between are “bite-and-drag marks” - punctures or partial punctures that extend into curvilinear grooves (e.g., those attributed to the “puncture-and-pull” feeding behavior described by Erickson and Olson, 1996; Hone and Watabe, 2010). Among the bite marks described herein are some that might be described instead as “drag-and-bite marks” with the opposite relationship - curvilinear grooves that end in punctures. All varieties of bite marks may occur either in isolation or in semi-parallel series. Punctures vary from semi-circular to oval to U-shaped in outline, and drag marks from narrow V-shaped to broader U-shaped in cross-section

The bone surfaces in TxVP 43679-1 were examined under low magnification with oblique lighting to identify the tooth marks, and corresponding photographs were used to delineate the form and distribution of marks on each bone. Most of the bones have at least a few definitive tooth marks, as well as other marks that are only lightly indented, vague, or because of weathering of the bone surface regarded herein as only doubtfully identifiable as tooth marks. The marks of less certain origin are distinguished with question marks in the accompanying diagrams (Figure 6).

The marks in this specimen show both of the two basic forms described above as well as variations in between - narrow, linear drag marks with V- or U-shaped profiles, and oval or U-shaped punctures. Several of the linear slashes are terminated in punctures. Most of the drag marks occur on the shafts of the bones, and do not fully penetrate the thick cortical tissue - which is quite thick in this case, up to 3 cm on the metatarsals. The punctures are instead primarily on or near the articulation surfaces and penetrate more deeply into the cancellous spongiosa tissue. Some of both types of marks occur in linear or semi-parallel series, but most are instead at slightly varied angles, lengths, and depths. None of the marks have preserved serrated edges, but smooth continuous margins. For clarity, each set of closely associated tooth marks is identified and illustrated with a consecutive bite number in the following description.

The tibia has one set of sub-parallel, deeply gouged, drag marks on the postero-lateral margin with several matching lightly indented marks on the antero-lateral margin that likely resulted from the same bite (bite 1a, 1b; Figure 6A-B, Figure 7A). Several fragments of the lateral margin of the shaft also have drag marks, but their locations along the shaft are imprecise (bite 2a, 2b; Figure 6A-B). The medial margin has only a few sub-parallel lightly indented drag marks (bite 3). The posterior face of the lateral malleolus has multiple punctures, although these are partially weathered and indistinct (?bites 4, 5; Figure 6B). The astragalus has no obvious bite marks. The calcaneum was either not preserved or reassembled from the preserved fragments.

The distal end of the fibula has two sets of well-defined drag marks at differing angles on both lateral and medial surfaces that must have resulted from multiple bites (bites 6, 7; Figure 6E, Figure 7F). Only fragments of the fibular shaft and proximal end are recognizable, and of these only a few have lightly indented and somewhat dubious drag marks (?bite 8; Figure 6C-D, Figure 7H).

The metatarsals have the most markedly defined and deeply gouged tooth marks preserved on the specimen. Left metatarsal III has several punctures on the anterolateral surface of the distal end, and a matching set of punctures with associated drag marks on the posterolateral surface that were likely a result of the same bite (bites 9a, 9b; Figure 6J-K, Figure 7G). The posterior surface also has at least three sets of deeply gouged sub-parallel drag marks - one set along its medial articulation surface for metatarsal II, another set along the lateral side of its shaft, and a third near the proximal end (bites 10, 11, 12; Figure 6K, Figure 7B). Left metatarsal II is only partly preserved but has several lightly indented punctures adjacent to its articulation surface for MT III, and another on the postero-medial edge (?bite 13, 14; Figure 6H-I). Left metatarsal IV has a set of sub-parallel punctures with associated drag marks on the anterior side of its distal condyle, and a set of similar matching punctures on the posterior side that probably resulted from the same bite (bite 15a, 15b; Figure 6L-M, Figure 7C). There is also a set of subparallel drag marks on the anterolateral side of the shaft that, given their different angle, probably records a separate bite (bite 16; Figure 6L). The posterior side of the shaft has three sets of drag marks with differing angles also recording as many as three separate bites (bites 17, 18; Figure 6M, Figure 7E). Of the right metatarsals, only MT III is preserved; it has two widely separated deeply gouged drag marks on its posterior surface adjacent to the articulation for MT II that must record two separate bites (bites 19, 20; Figure 6G). The distal condyle has two lightly indented punctures on the posterior side of the distal condyle, with two matching drag marks on the anterior side that are likely due to the same bite (?bite 21a, 21b; Figure 6F-G).

Of the pedal phalanges that are partly preserved or identifiable, right phalanx II-1 has at least two sets of subparallel drag marks on its anterior face - one on the lateral side, and one on the medial side at a different angle, recording two separate bites (bites 22, 23a; Figure 6N-O). A set of four corresponding drag marks on the posterior face could record the same bite as the one on the medial side, although their angles also differ (bite 23b; Figure 6O). The proximal end of right phalanx IV-1 has a set of subparallel drag marks on the anterior face (bite 24; Figure 6Q), and the proximal end of right IV-5 also has a deep drag mark on its anterior face (bite 25; Figure 6S, Figure 7D). The remaining identifiable parts of phalanges (left II-2 and left III-4) have no obvious tooth marks (Figure 6P-R).

INTERPRETATION

Because the bite marks on TxVP 43679-1 show no evidence for bone healing, and are on multiple lateral, medial, and articular surfaces of the bones (requiring that the bones were disarticulated before or during the time the marks were produced), the bites were evidently inflicted post-mortem and were not a result of the struggle to subdue a living prey animal. The ankles and feet could hardly have been disjointed while living, and these are unlikely to have been targets of a predator’s attack in the first place. Instead, these tooth marks record the process of dismembering and removing the flesh from a dead animal. The hind limb bones were preserved in isolation from any other parts of the skeleton, suggesting that the hind limbs had been removed from the carcass and brought to a separate location. The tooth marks in this instance, therefore, most likely record the actual process of feeding. Given the abundance of tooth marks on most of the hind limb elements, and on those only partly preserved, as well as on both identifiable and unidentifiable bone fragments, it seems likely that most or all the elements, even those that were not fully preserved, were probably tooth-marked. The specimen therefore records quite a thorough effort on the part of one or more tyrannosaurs to dismember and deflesh parts of a carcass.

The tooth marks appear at first glance to be randomly arrayed along the shafts and articular surfaces; however, the puncture and “drag-and-puncture” marks tend to be concentrated along the distal articular condyles of the metatarsals (e.g., bites 9, 15, 21; Figure 6). The orientation of these marks is indicative of biting motion that resulted in pulling each bone lengthwise from its distal end. This would imply that the biter had previously dismembered the pedal phalanges or had them in its mouth while biting. Punctures on the distal end of the lateral malleolus of the tibia are indicative of the same sort of lengthwise pulling motion (?bites 4, 5; Figure 6) and similarly would have required that the metatarsals (at least MT IV) had been freed prior to biting. Altogether these puncture and “drag-and-puncture” marks suggest primarily efforts to pull and dismember the metatarsals from the ankle, or from one another, or perhaps pull away the connective tissue between them. The relatively close spacing in linear series, with opposing punctures on both sides of the bone, suggest that the incisiform premaxillary teeth at the tips of the jaws were used to grip and pull these bones (Figure 8).

Drag marks instead are concentrated on the posterior sides of the metatarsals, particularly adjacent to their mutual articulation surfaces (e.g., bites 10, 11, 17, 18, 19; Figure 6). These tooth marks are instead primarily indicative of sideways (i.e., medio-lateral) raking motions and suggest that the soft tissues in these areas were of particular interest to the feeding tyrannosaur. Drag marks along the shaft of the tibia, fibula, and those on the phalanges have similar orientations also indicative of sideways raking, not lengthwise pulling (e.g., bites 2, 8, 22; Figure 6). The slightly differing angles and depths of individual marks within a sub-parallel set may reflect the staggered arrangement of teeth along the jaws and varied intersection points of those teeth along the curved surfaces of the bones. This pattern could have been produced by raking large lateral dentary or maxillary teeth across the bone surfaces multiple times during the same ‘bite’, but at slightly varied angles, or by nipping with the incisiform premaxillary teeth at the tissues covering the bone surfaces. The narrow, V-shaped drag marks in this case were most likely made by lateral teeth, given that tyrannosaur premaxillary teeth typically have a blunt, D-shaped cross-section.

Numerous shallow V-shaped drag marks made by teeth raked across bone surfaces without piercing through the cortical tissue, such as are most common in the present case, have been attributed to scavenging behavior (Pobiner, 2008). Moreover, the tooth marks in this case differ somewhat from those thought to result from “puncture and pull” feeding, a behavior generally attributed to tyrannosaurs, which lacked specialized dentition, and relied on their great body mass, bite force, and powerful neck musculature to dismember and remove flesh from a carcass (Erickson and Olson, 1996; Erickson et al., 1996). The tooth marks also bear no resemblance to those attributed to bone gnawing and osteophagy recorded by some tyrannosaur bite marks (Gignac and Erickson, 2017). The numerous shallow tooth marks evident in TxVP 43679-1 record at least 25 separate bites and are in keeping with a more delicate and thorough feeding behavior that entailed nipping and trimming of flesh from parts of a carcass, whether or not the animal had succumbed to predation. Therefore, these marks might record actions more typically employed by tyrannosaurs of relatively small stature compared to their prey, or methods engaged particularly on hind limb elements, or perhaps behavior induced under unusual circumstances. Regardless, the basic feeding process implied by the bite marks here is one in which the tyrannosaur might have stood erect, using the premaxillary teeth at the tips of the jaws primarily to drag the hadrosaur hind quarters, or to pull it apart, but would likely have required being down “on its haunches” in order to deflesh the smaller individual parts (Figure 8).

It is perhaps not surprising that, as in the present example, tyrannosaurs may have routinely employed their incisiform premaxillary teeth in dismembering a carcass (e.g., Hone and Watabe, 2010). Even though mammalian carnivores possess more specialized dentition (carnassial premolars and molars) for processing skin and bone, their relatively small, simple incisors are unexpectedly important in feeding. For example, among large African carnivores (lion, hyena, cheetah, wild dog) the incisors are frequently used with the canines to cut muscle and pull it away from bones (Van Valkenburgh, 1996).

DISCUSSION

The extensive tooth marks on TxVP 43679-1 document a thorough process of tyrannosaur feeding on the lower hind limbs of a hadrosaur. Given the anatomical similarity to birds, it seems likely that the lower hind limbs of hadrosaurs had little flesh. Therefore, one possible interpretation of the thorough feeding effort in this case may be that this specimen records an unusual occasion where prey animals were very scarce such that this tyrannosaur was under stress and consumed all the available flesh on the carcass. Another possibility is that hadrosaur lower hind limbs were ‘meatier’ than imagined, and that this was a relatively routine feeding pattern for tyrannosaurs.

Observations of modern large mammalian carnivores may support the first of these two possibilities. For example, in carcasses consumed by African lions, while the intermediate limb elements (radius, ulna, tibia) are mostly defleshed and tooth-marked, tooth marks are rarely found on bones of the distal limb elements, and the metapodials are left unmodified with little or no flesh removed (based on a sample consisting mostly of wildebeest and zebra; Dominguez-Rodrigo, 1999). The lower legs are also left behind at most tiger feeding sites (prey animals in this case were warthog, springbok, and larger antelope; Fábregas et al., 2017). This likely reflects the fact that there is very little flesh even available on the metapodials of most large ungulates. Given sufficient time, large mammalian carnivores will typically consume all edible parts of a carcass, regardless of whether they are social feeders (e.g., wolves, lions) or solitary predators (e.g., tigers; Fábregas et al., 2017), so abandoning the lower limb elements of a carcass is likely normal behavior for large carnivores. Even among large mammalian carnivores that engage in osteophagy (wolves, bears, hyenas, lions), while the proximal end and shaft of the tibia are often thoroughly gnawed, the distal end typically remains little modified (based on bovid tibiae studied by Haynes, 1983). Jacobsen (1998) also noted that particularly where prey animals are abundant, modern large mammalian carnivores do not bother to consume meat from the lower legs. He suggested therefore that the case of frequently bitten hind limb bones of hadrosaurs found in the Dinosaur Park Formation might indicate that prey availability was low in those environments. If so, tyrannosaur tooth marks on lower hind limb elements of hadrosaurs might record behavior induced by scarcity of prey.

However, several observations instead support the latter of the two possible interpretations. Tooth marks on hadrosaur lower hind limb elements are unexpectedly common (Figure 9). For example, among the relatively high number of tooth-marked hadrosaur bones that Jacobsen (1998) documented in the Dinosaur Park Formation, nearly half were bones from the lower hind limbs (tibiae, fibulae, and metapodials). Moreover, tooth-marked hadrosaur lower hind limb elements have been widely reported elsewhere. For example, Hone and Rauhut (2010) illustrated a hadrosaur fibula (attributed to Hypacrosaurus sp.) with an embedded tyrannosaur tooth. Longrich et al. (2010) illustrated a hadrosaur metatarsal, and Pobiner (2008) described a hadrosaur proximal pedal phalanx (referred to Edmontosaurus sp.); both specimens exhibit multiple deep tooth marks attributed to bites from Tyrannosaurus. Brown et al. (2021) also described several hadrosaur pedal ungual phalanges with tooth marks. Although Gangloff and Fiorillo (2010) noted that tooth marks are more extensive on skull elements, vertebrae, and ribs in an Edmontosaurus bone-bed, they also illustrated two proximal pedal phalanges with shallow punctures and drag marks (on phalanges II-1 and III-1).

Furthermore, apart from the specimen described herein there are other examples from the Aguja Formation. A hadrosaur calcaneum from the lower part of the Aguja Formation has a series of semi-parallel tyrannosaur tooth marks on its distal articulation surface that are consistent with the style of feeding suggested here (TxVP 45921-39; Figure 10). An astragalus (TxVP 45921-22) likely from the same individual, also has a tooth mark - corresponding with those on the calcaneum when placed in articulation. Rivera-Sylva et al. (2012) documented tyrannosaur bite marks on the distal end of a hadrosaur tibia from the lower Aguja Formation in Coahuila, Mexico; these are likewise quite similar to those shown here. The widespread occurrence of tyrannosaur tooth marks on the distal hind limb elements of hadrosaurs suggests that feeding on tissues of the lower hind limbs may have been a common behavior for different tyrannosaur species, not simply one induced by low prey availability.

Although hadrosaur feet were anatomically similar to bird feet, and probably had little muscle mass, footprints and life restorations of hadrosaurs indicate that the feet had thick pads of soft-tissue beneath the ankles and surrounding the toes (e.g., Paul, 1987; Sereno et al., 2025). The pattern of bite marks on TxVP 43679-1 suggests that, in addition to the skin and muscle, the connective tissue and the cartilaginous pads on bone articulation surfaces may have been the tissue consumed by the tyrannosaur in this case. So, the lower hind limbs of hadrosaurs may have provided more flesh than is typical of large birds or mammalian ungulates (e.g., akin to the pig ‘trotters’ and ‘ham hocks’ consumed by human beings).

Contrariwise, the prevalence of tooth marks on hadrosaur hind limb elements might simply reflect a general observation that these bones tend to be sturdier, with thicker cortical tissue, and so a higher preservation potential (e.g., Fiorillo, 1991). This would make them more likely to be collected than the delicate ribs, dorsal and cervical vertebrae, that might have been similarly tooth-marked but less preservable and/or more readily destroyed during feeding. If so, the abundance of tooth marks on distal hind limb elements could be solely a taphonomic artifact. A broader survey of the sort conducted by Jacobsen (1998) that includes more numerous dinosaur bone collections from several stratigraphic units might determine whether this is the case.

CONCLUSIONS

An isolated set of associated, disarticulated, hadrosaur lower hind limb bones from the upper Aguja Formation bear numerous tooth marks attributable to tyrannosaurs. The tooth marks consist of punctures and drag-and-puncture marks primarily applied to the distal ends of the metatarsals, and drag marks primarily applied to the medial and lateral sides of the tibia, fibula, metatarsals, and pedal phalanges. The tooth marks are compatible with one or more tyrannosaurs feeding on hind limbs that had been removed from a hadrosaur carcass, either brought down elsewhere as prey, or by scavenging the carcass of an animal that succumbed from previous cause. The hadrosaur in this case was substantially larger (2-4 metric tons) than the local tyrannosaurs (c.a. 700 kg). The great size differential may have favored scavenging rather than predation on such large animals.

The tooth marks record at least 25 separate bites that imply the incisiform premaxillary teeth were used to grip and pull the tibia and metatarsals lengthwise from their distal ends, perhaps to drag the hind limb or dismember the ankle joint, while instead the lateral teeth were employed by sideways raking or scraping to remove flesh from the plantar sides and articulation surfaces of the metatarsals and phalanges. The tooth marks could have been produced by multiple feeding individuals or repeated biting by one individual. Clearly in this case, a substantial effort was expended in removing what would seem to be very little flesh from otherwise unappealing parts of a carcass. This could record unusual behavior brought about by food scarcity, and so may not be typical. However, the lower hind limbs, ankles, and feet of hadrosaurs may have been more ample than generally assumed, and the remarkably common occurrence of tyrannosaur tooth marks on hadrosaur distal hind limb elements instead suggests that this may have been typical feeding behavior.

ACKNOWLEDGMENTS

We thank M. Brown and J.C. Sagebiel of the Texas Vertebrate Paleontology Laboratory at Jackson School Museum of Earth Sciences at the University of Texas in Austin for their long-term support of our research and for assistance with curation of specimens. J. Wagner and C. Treat helped with collection, reassembly, and preparation of the specimens described herein. This paper resulted in part from an undergraduate research project conducted in and supported by the Department of Geosciences at Texas Tech University. As an ‘amateur’ paleontologist, the late K. Barnes labored diligently many years collecting and documenting Aguja dinosaur bones, among which are several with crocodylian bite marks described herein that were part of his collection donated to the Texas Vertebrate Paleontology Laboratory. The present report benefitted from the unpublished observations, notes, and photographs (several included herein) that he graciously provided, as well as from our multifarious and thoroughly entertaining conversations with him over many years regarding the specimens in his care and his geological notions of the Big Bend. His work serves as a great example of what may be accomplished by ‘amateur’ collectors.

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