Post by Infinity Blade on Jul 31, 2023 22:47:29 GMT 5
Art by Joschua Knüppe->
Paleontologists generally accept that many non-avian theropods during the Mesozoic were capable of hunting prey as large as, or larger than, themselves. This view is reflected in popular culture and media. In this post, I will compile as many pieces of fossil evidence of attempted theropod predation on animals that were probably at least comparable in size (read: body mass) to themselves as I can. The point here is to demonstrate that the idea that theropods took prey comparable in size to themselves or larger is not merely a theoretical inference: there is actually some fossil evidence supporting this behavior. These cases will be sectioned by taxa, and will include instances of both successful and failed predation (as both prove the predator was willing to take on such prey). Less conclusive evidence will also be included, although I will warn the reader when it is such.
Tyrannosaurus rex:
The tooth crown of a Tyrannosaurus rex has been found embedded in the caudal vertebra of an Edmontosaurus.
The embedded theropod tooth crown is perfectly consistent with teeth from subadult T. rex in size, shape, and denticle morphology, and only T. rex (DePalma et al., 2013).
The theropod tooth crown is well preserved, with the broken basal portion of the tooth partially exposed (Fig. 1). Computerized tomographic (CT) scans revealed the crown height to be 3.75 cm, and visual inspection revealed the crown base length to be 2.35 cm and the crown base width 1.65 cm. Denticles are well preserved on the mesial and distal carinae (Fig. 3), and the distal basal denticle (DB) and mesial basal denticle (MB) densities are 16 per cm and 13 per cm, respectively. Comparison of the embedded tooth’s dimensions and morphometric relationships with the data from the Smith et al. (46) study reveals a strong alliance with T. rex (Fig. 4). The tooth is indistinguishable in morphology, size, and denticle character from known T. rex subadults (e.g., Los Angeles County Museum–23845 and Black Hills Institute–6439). An independent comparison of the ratio of the distance from crown tip (DCT) to the incremental crown length (ICL) for T. rex and Nanotyrannus, the only two contemporaneous large-bodied and large-toothed theropods (46–49), with that of the embedded tooth places it firmly within the T. rex range (Fig. 3). For this study, Albertosaurus was added as a control. In addition, study of the embedded tooth’s denticle density indicates that its DB and MB values overlap those of only one animal studied, T. rex (Fig. 3). Morphologic and morphometric characters of Nanotyrannus are sufficiently dissimilar from the embedded tooth to exclude it from candidacy for the tooth-producing taxon. Only one animal studied—T. rex—bears close resemblance to the tooth in question.
The bone growth associated with the injury is indicative of healing, and therefore that the Edmontosaurus was alive during the attack.
The rugose structures observed on the hadrosaur vertebrae are consistent in morphology with bone growth associated with healing injuries, as observed in modern and extinct animals (Fig. 1). In modern endothermic animals, trauma to bone is followed by signs of insipient bone healing within the first several weeks. The first macroscopic evidence of bone healing in mammals can be recognized 7–10 d after the injury (50). Healing of reptilian bone is much slower (50) and takes longer in reptiles (50–53), significantly delaying opportunity for its recognition on macroscopic examination. The massive bone reaction in this report suggests survival of the injury for a significant period, perhaps even years. The injury does not appear to have contributed to the demise of this hadrosaur.
There is also a specimen of Triceratops with healed bite marks from Tyrannosaurus rex. This specimen (an adult) had a severed left horn core with depression marks consistent with impact from large theropod teeth, as well as surface lacerations on its squamosal (frill). The presence of rugose growth and new bone disfigurement is indicative of osteomyelitis, and the rough edges of tooth marks being rounded out are consistent with healing bone growth (Happ, 2008).
A less ambiguous instance involves a second adult Edmontosaurus specimen with healed pathologies to its neural spines. The distribution of pathology is in an arc-like pattern, with one neural spine partially sheared off, and puncture marks on adjacent neural spines (Carpenter, 1998).
Although their attribution to a bite from T. rex has been disputed (Tanke & Rothschild, 2014), actual T. rex bite marks on Edmontosaurus caudal elements are not unprecedented, as is evident from the first example mentioned here.
Tyrannosauroidea indet.:
The holotype of Bisticeratops (Dalman et al., 2022) bears bite marks made by a tyrannosaurid. Some of these were healed, and others unhealed. Although the individual was not fully grown (as indicated by the contact surfaces between the premaxilla and maxilla being unfused), the complete skull was estimated to have been 2 meters long or slightly more. The specimen also had prominent orbital horn cores (one of which had a cast made of it before being lost) (Dalman & Lucas, 2018). Therefore, this individual was still a large, formidable prey item.
The healed bite marks are evidence of a failed attack by a tyrannosaurid. Although the abstract states that the unhealed bite marks were made postmortem, the article text also says that there is no evidence of scavenging on the skull, lacking extensive crushing that would likely be made by a scavenging carnivore (Dalman & Lucas, 2018). I have personally emailed the authors of this publication, and have been told that the ceratopsian would have been attacked once and survived, but then attacked again, killed, and eaten this time. Therefore, the Bisticeratops holotype shows evidence of both failed and successful predation by tyrannosaurids.
Something of note is that at least some of the bite marks are labiolingually compressed in shape, not incrassate like those of adult tyrannosaurids. The bite pattern on the skull also only exhibits a single row of teeth on both sides of the skull, indicating the attacker(s) in question had a narrow snout. Originally, this was attributed to a tyrannosaurid with a skull similar to that of Gorgosaurus (supposedly having a narrow snout compared to say, Daspletosaurus) (Dalman & Lucas, 2018). However, as can be seen in the figure below (from Voris et al., 2022), adult albertosaurines possessed narrow snouts as juveniles, which widened as they grew into adulthood. Likewise, their dentition changed in morphology from ziphodont to incrassate (Therrien et al., 2021).
Teeth of Bistahieversor sealeyi, a basal tyrannosauroid, are labiolingually compressed (Dalman & Lucas, 2016), suggesting it or a similar predator could have killed this ceratopsian.
Allosaurus sp.:
Direct evidence of Allosaurus interacting with Stegosaurus, likely in predation events, is known from the fossil record. One such piece of evidence comes in the form of an Allosaurus caudal vertebra with a punctured left transverse process. The spike of a Stegosaurus fits inside the puncture wound. Because the bone was extensively remodeled, the Allosaurus survived this injury, although it must have died before full remodeling could occur (given how little bone deposition occurred within the puncture) (Carpenter et al., 2005).
A second piece of evidence comes in the form of a bitten Stegosaurus cervical plate. The U-shaped notch present on this plate fits with the snout of Allosaurus, suggesting that one bit off a piece of this cervical plate. It is unlikely that this is a product of scavenging for a few reasons. First, the plate would have had little nutritional value, with no muscle or viscera overlaying the plate. Second, it would have been geometrically difficult for the Allosaurus to bite the plate when the Stegosaurus was lying dead, probably on its side with the plates drooping downward. Third, this was a cervical plate, and the neck is a common target for predators. Given this, and because no evidence of healing is mentioned, this suggests the Stegosaurus was attacked by an Allosaurus while it was still alive, but did not survive the attack (Carpenter et al., 2005).
Lastly, there is an Allosaurus pubic boot with a puncture would that penetrated it completely. Evidence of infection is present on the pubis, and the lack of healing indicates that the theropod died of this wound. The size and shape of this wound match a Stegosaurus spike (Bakker et al., 2014).
Velociraptor mongoliensis:
Unambiguous evidence of conflict between Velociraptor mongoliensis and Protoceratops andrewsi exists in the form of the famous Fighting Dinosaurs specimens. The left hand of the Velociraptor was clutching the head of Protoceratops, while its left hypertrophied digit II pedal claw was in the area of its neck, suggesting an attack to the ceratopsian’s neck. On the other hand, the Protoceratops retaliated by biting the right forelimb of the Velociraptor. The right hindlimb of Velociraptor has been variously proposed being trapped underneath the Protoceratops (Carpenter, 1998) or attacking its stomach (Barsbold, 2016).
Deinonychus antirrhopus:
The following is not direct evidence of predation by Deinonychus antirrhopus. However, an examination of the Tenontosaurus individuals associated with Deinonychus (typically in the form of shed teeth) revealed that the majority of the individuals were half-grown. This may indicate a prey size preference by Deinonychus (Roach & Brinkman, 2007).
Forster (1984:162) noted that an examination of the sizes of the tenontosaurs found associated with D. antirrhopus (their presence typically indicated by the occurrence of diagnostic shed teeth) revealed that “the majority [of the tenontosaurs] were in the half-grown range” possibly indicating a prey size-class preference by D. antirrhopus. In concurrence with this observation, the unpublished results of morphometric analyses conducted by the junior author on 10 different pedal phalanges commonly preserved for T. tilletti indicate that specimen YPM 5466, the tenontosaur remains found at the YPM 64-75 site was, in fact, an approximately half-grown, subadult individual at the time of its death.
If so, consider that an adult Tenontosaurus tilletti is estimated to weigh ~600 kg (Paul, 2016). A half-grown subadult Tenontosaurus would thus weigh ~300 kg. Body mass estimates for Deinonychus antirrhopus range from ~60 kg (Paul, 2016) to ~100 kg (Campione et al., 2014). This would suggest that Deinonychus hunted subadult Tenontosaurus at least three times more massive than itself, if not more.
Theropoda indet.:
This example is obscure, but intriguing. There is an uppermost Maastrichtian site in Arén (Huesco, Spain) known as Blasi 3. Among the fossils found there are several hadrosaurid caudal vertebrae belonging to the same individual. One mid caudal vertebra exhibits a pathology with unusual bone swelling and an oval hole (Canudo et al., 2005).
The general shape of the centre, a high neurapophysis and an incipient transverse process, allow this vertebrate to be mid-positioned within the caudal series. There are at least thirty caudal vertebrates which are associated at Blasi 3, and, although they are not all articulated, we can suppose that they belong to the same specimen. The neurapophysis of Blasi3|140 is clearly pathological, presenting asymmetry in antero-posterior view with a curved shape, an anomalous bone swelling, a hole and anomalous bone growth with regards to fractures. The simplest explanation is that all pathologies are the result of the same circumstance and the same illness. In the Blasi3 collection there are two fragments of neurapophysis of two caudal vertebrae (not prepared) of an anatomical position near to Blasi3|140. Both present a similar pathological curvature, which allows us to state that the pathology is located exclusively in the mid-part of the caudal series.
This pathology was interpreted as the bite mark of a theropod.
In order to interpret the fractures and swelling of the bone in the same position, which we presume are the result of the same process, we have based our study on a practically complete hadrosaurid specimen (DMNH 1493) recovered at the Hell Creek Formation in Montana (USA). It is identified as Edmontosaurus annectens Marsh, 1872 and is currently exhibited at Denver Museum. Carpenter (1998) offers an exhaustive description of this fossil, indicating the unusual shape of the caudal vertebrae 13 to 17, which can only be explained by a trauma. Vertebra 15 is lacking the third part of its superior end, and also finishes with a distinctive coarse surface. The remaining neuropophyses 13, 14, 16 and 17 are curved, which gives it an anomalous appearance in dorsoposterior view. This pathology is correctly located in a part of the tail, since the remaining dorsal and caudal neurapophyses lack the same. Carpenter (1998) interprets the coarse surface as a result of osteomyelitis resulting from an infection of a wound due to the introduction of pathogen micro-organisms present in the saliva of an attacker. Hence the pathology presented in DMNH 1493 can be explained by the bite of a large carnivore, which, given the geological context, Carpenter (1998) believes could have been a Tyrannosaurus rex Osborn, 1905. His interpretation is based on four observations: the trauma is located exclusively in the dorsal part of a small section of the tail. In addition to the absence of part of a neurapophysis, there are four more deformations, which are those closer to the absence. The neurapophyses present holes interpreted as teeth marks. These marks are aligned in the traumatised area. The hadrosaur undoubtedly survived the attack, as evidenced by the formation of callus, for which reason we have a model similar to that of Blasi3|140.
However, large theropods, especially those that can deliver a bite from a tall standing height, are not known from Blasi. Therefore, it is believed that one or more smaller theropods may have jumped on top of this hadrosaur and delivered bites that eventually became infected and killed the hadrosaur. Theropod material from Blast consists of isolated teeth from a medium-sized neoceratosaurian and small-medium sized dromaeosaurids.
The fossil association of Blasi (López-Martínez et al., 2001, Torices et al., 2004) lacks a large theropod which could produce a bite from top to bottom as suggested by Carpenter (1998), which would have been produced by a T. rex in an attack on the Edmontosaurus, as we saw previously. Hence, one possibility is that one or a series of smaller theropods would have jumped on top of the Arén hadrosaur, producing bites which would not have been lethal in themselves, but which would have caused death through infection.
Also recovered from Blasi 3, we have isolated theropod teeth, including some of a Neoceratosauria indet, of medium size, and several kinds of small and medium-size dromaeosaur ( TORICES et al. , 2004).
