Claim: Sauropod and ornithopod dinosaurs possessed no weapon-like appendages. Their only physical defenses were sheer size, assuming the taxon in question even had this to begin with.
Rebuttal:1.) One component of sauropod anatomy that has been brought up as a potential weapon is the tail
[1]. Even the most generic sauropods would have had (absolutely) long, heavy, and supple tails
[1]. How much force, and therefore how damaging a blunt trauma blow from a plain tail would be would depend on the speed and mass of the tail in question. While speed may be unknown (to my knowledge), the aforementioned suppleness of the tails suggests that they could be swung at reasonably high speeds.
So how massive were sauropod tails? Bates et al. (2015)
[2] provides volumetric models for three different sauropod species:
Dreadnoughtus schrani,
Apatosaurus louisae, and
Giraffatitan brancai. The minimum models (there were larger models, but this would not change the relative proportions of each animal) suggest that:
- A 22,117.98 kg
Dreadnoughtus has a tail weighing 1,011.35 kg. This makes the tail ~4.57% of total body mass.
- A 21,803.21 kg
Apatosaurus has a tail weighing 1,861.2 kg. This makes the tail ~8.54% of total body mass.
- A 19,946.35 kg
Giraffatitan has a tail weighing 774.76 kg. This makes the tail ~3.88% of total body mass.
How could a tail that doesn’t have any special weapons attached to them really damage another large animal? To find out, let’s put on our AvA game-faces (as silly and unprofessional as this may sound).
I found information regarding the total mass of the head of adult male African bush elephants
[3]. This included data on four adult male African bush elephants that had their total body mass and individual body parts weighed. One caveat: not all elephants had literally all their individual body parts weighed; some had their hearts discarded before they could be weighed, all but one had the brain discarded, one had tusk nerves missing, and one individual had its stomach and intestines weighed
with contents, as opposed to the rest having them weighed
without them. So total body masses reported may be a little incomplete, but the vast majority of their body masses have already been accounted for, considering how every elephant's total recorded mass was in excess of 5,000 kg or even around 6,000 kg for one individual. And if anything, this would artificially make these elephants have slightly
larger heads for their size than they'd have in real life.
And so this is what I did: I plotted total head mass against total body mass for all four elephant specimens. For missing brains I assumed a mass of 4 kg, based off of the one specimen that had its brain weighed. For the specimen missing tusk nerves, I assumed a mass of 12.1 kg, as this is the weight of the most massive tusk nerves out of the ones that had their tusk nerves weighed (as a means of being generous to the elephants).
So with our graph of elephant head mass vs total body mass (containing admittedly only four samples) and a corresponding equation for the linear line of best fit, we can get an idea of how an elephant's head would scale relative to total body mass.
At this point the reader is probably wondering where I'm going with all this data regarding sauropod tail and elephant head mass. Imagine an elephant fighting a sauropod at parity. More than likely, a sauropod using its tail as a weapon will have to cope with the elephant's head, considering that is the elephant's primary (actually sole) weapon, bearing tusks and all. Because the head obviously takes up comparatively small minority of the elephant's total body mass, it would obviously be easier to cause fatal injury if a sauropod used its tail to bludgeon the head as opposed to say, the torso (which of course does take up the great majority of an elephant's body mass). The question is,
is the sauropod's tail massive enough to deal serious, if not fatal damage to the elephant's head?Using our equation for elephant head mass above, we can get an idea for how massive the entire head would be when hypothetically scaled up to sauropod size.
- A
Dreadnoughtus-sized elephant would have a head weighing ~1,451.77 kg (0.0612(22,117.98)+98.145). The sauropod's tail is ~70% of the mass of the elephant's head.
- An
Apatosaurus-sized elephant would have a head weighing ~1,432.50 kg (0.0612(21,803.21)+98.145). The sauropod's tail is ~130% of the mass of the elephant's head.
- A
Giraffatitan-sized elephant would have a head weighing ~1,318.86 kg (0.0612(19,946.35)+98.145). The sauropod's tail is ~59% of the mass of the elephant's head.
We can see that some sauropods are in a better position than others (to the surprise of no one, given that sauropods are a diverse group that lived within a timespan of 144 million years). Could
Giraffatitan viably kill the elephant by fervently bashing its head with its tail, making sure to add more power to the blow by incorporating movements of its hips and hindlimbs? Not sure; certainly it would take more serious blows than the other sauropods would need to have a serious effect. But
Dreadnoughtus may seem like it would have a reasonable shot at this. Certainly
Apatosaurus, with a tail weighing 30%
more than the elephant's entire head, could seriously injure or kill the proboscidean in this manner.
I've also recently come across
this GDI estimate-> of
Barosaurus lentus specimen AMNH 6341. It is not from a scientific paper, but the GDI model was created using skeletal reconstructions made by scientists, or by people who, in turn, used scientific publications for reference. The tail weighed a total of ~2,910 kg, or nearly 3 tonnes (making this tail ~19.33% of the total body mass of this sauropod, which was ~15,052 kg). Once again, using our elephant head mass equation above, we can estimate a hypothetical
Barosaurus-sized scaled up elephant to have a head weighing a total of 1,032.8742 kg (0.0612(15,052)+98.145). This makes the sauropod's tail
almost 3 times more massive than the elephant's whole head. The effects of a tail blow should be obvious.
2.) All sauropods possessed three large curved claws on each pes. Many sauropods (with the supposed exception of titanosaurs) possessed a single inward-facing manual claw on each manus
[4]. Both manual and pedal claws could be used as weapons via raking/stabbing motions with a forelimb and kicking motions with a hindlimb, respectively. In fact, because the manual claw is often not preserved in sauropod forefoot prints, it is believed that this claw was cocked upwards off the ground (while still being capable of being rotated downward), keeping it relatively sharp and even more effective as a weapon
[1]. Additionally, vertical scores found within sauropod manus prints show that at least some taxa had tough semi-conical tubercles projecting from the front and sides of the forefoot
[5]. Darren Naish believes that these spiky projections could have been useful for multiple functions, defense among them
[4].
3.) This is something no one could have known until relatively recently, but work in 2015 analyzed the morphology of apatosaurine cervical vertebrae. Several characteristics of apatosaurine cervical morphology are suggestive of the neck for use in combat. These are:
“
1. Ventral displacement of cervical ribs improved the lever arms of the hypaxial muscles, strengthening ventral neck movements.
2. Ventrolaterally directed parapophyseal rami were oriented to resist ventral impacts.
3. The ventral trough between the cervical ribs provided soft-tissue protection for the trachea, oesophagus, and major blood vessels.
4. The ventrolateral processes on the cervical ribs may have been bony clubs, bearing thickened pads of connective tissue or keratinous knobs or spikes.”
These suggest that apatosaurines used their necks in combat, crashing them downwards or sideways, possibly having keratinous knobs or spikes to aid in damage
[7].
4.) Ornithopods had their own physical defenses as well. Greg Paul has suggested that hadrosaurs would have kicked out at predators with their powerful, heavy-footed hindlimbs, possibly fleeing from their predators while landing as many kicks as possible
[7]. Like all dinosaurs (barring “protodinosaurs”, the first theropods, and “prosauropods”
[8]), hadrosaurs had large pelves/hips, allowing for powerful thigh musculature. Furthermore, a backwards-directed kick would be powered not only by the extensor muscles on the hips and legs, but also additionally by the massive
Musculus caudofemoralis longus muscle (which pulls the femur back). In hadrosaurs, this muscle was indeed increased in size
[9]. Although these leg muscles primarily played a role in pulling the leg back during locomotion, these same muscles would, logically, pull the leg back during a posteriorly-directed blow with the limb. Some pathologies examined in Late Cretaceous hadrosaurs from Alberta, Canada have been speculated to be from kicks from the hind feet of conspecifics
[10]. And if hadrosaurids were capable of this action, it does not require a leap of faith to see other large-bodied quadrupedal ornithopods doing the same.
Some ornithopods possessed rather trenchant pedal unguals on their feet (see
Tenontosaurus-> or
Parksosaurus->;
here-> is an additional pic of
Tenontosaurus' foot claws). Pointed, sharp claws would be even more damaging than the blunt, hoof-like nails seen on the feet of other ornithopods.
5.) The last source mentioned in point #4 also suggests that the heavy tails of hadrosaurs could have been used as weapons
[10]. As with sauropods, the amount of force, and therefore how damaging a blunt trauma blow from the tail would be depends on the speed and mass of the tail in question.
How massive were these tails? A
Lambeosaurus lambei specimen that would have weighed a total of 2,500 kg was estimated to have had the totality of its tail muscle mass to amass 290 kg
[10]. This is already 11.6% of total body mass (and proportionately more impressively sized than the whole tails of any of the sauropods mentioned above). The caudal vertebrae would, of course, add onto the mass of the tail. A graphic double integration of
Edmontosaurus annectens specimen
MOR 003-> suggests that the tail would have comprised ~15.7% of its total body mass. The tail itself weighs 1,585.7 kilograms.
There have been suggestions that the ossified tendons of hadrosaurs would stiffen the tail and compromise their effectiveness as weapons
[7]. But computer models of the tails of
Tenontosaurus (a non-hadrosaurid iguanodont) and
Brachylophosaurus (a hadrosaurid) found no evidence that ossified tendons affected mediolateral movements on the tail significantly, if at all. This is because the network of tendons was primarily distributed across the parasagittal plane
[11].
Therefore, when making quick forceful lateral movements of the tail to strike other animals, the ossified tendons should not have compromised the flexibility of the tails of ornithopods much, if at all.
There are two final points to be made with regards to tail strikes, for both ornithopods and the aforementioned sauropods. Because of the square cube law - kinetic energy increases cubically as long as the animal doesn’t slow down (it begs the question as to why the tail alone would suddenly become drastically slower) while tissue resistance to rupture or fracture only increases quadratically - a strike from the tail would be more damaging at the gigantic (>1,000 kg) size scales giant ornithopods and most sauropods operated at. Also, everything noted above regarding tail strikes does not assume anything about movement of the hips and hindlimbs playing a role in tail swinging, thus underestimating total impact force of a sauropod or giant ornithopod tail. It has been noted that hip and hindlimb movements would probably have played an important role in tail swinging in ankylosaurids
[12], and so it would be reasonable to assume the same would hold true for ornithopods and sauropods.
6.) Some (but not all) ornithopods possessed a large spike on the pollex. Examples include
Iguanodon-> and
Lurdusaurus->. Certainly these animals could not be deemed weaponless.
Interestingly, the manual unguals of
Tenontosaurus tilletti have been described as "claw-like" in a character description and recoded data matrix from an osteological description of the species
[13]. The two bolded an underlined 0s correspond to the description of the 48th and 49th listed anatomical features, and indicate claw-like unguals.
What's more, the phalanges of
Tenontosaurus appear to have been flexible enough to clasp objects, and one of the proposed functions for this was the ability to clasp predators
[13].
References:[1] Hallett, M., Wedel, M.J. (2016).
The Sauropod Dinosaurs: Life in the Age of Giants. JHU Press. p. 69, 198-199, 201.
[2] Bates, K. T., Falkingham, P. L., Macaulay, S., Brassey, C., & Maidment, S. C. (2015).
Downsizing a giant: re-evaluating Dreadnoughtus body mass.
Biology letters, 11(6), 20150215.
[3] Byers, D.A.; Ugan, A. (2005).
Should we expect large game specialization in the Late Pleistocene? An optimal foraging perspective on early Paleoindian prey choice.
Journal of Archaeological Science, 32(11), 1624–1640. doi:10.1016/j.jas.2005.05.003
[4] tetzoo.com/blog/2019/1/18/the-life-appearance-of-sauropod-dinosaurs[5] Milàn, J., Christiansen, P., Mateus, O. (2005).
A three-dimensionally preserved sauropod manus impression from the Upper Jurassic of Portugal: Implications for sauropod manus shape and locomotor mechanics.
Kaupia, 14.
[6] Taylor, M. P., Wedel, M. J., Naish, D., & Engh, B. (2015).
Were the necks of Apatosaurus and Brontosaurus adapted for combat?.
[7] Larson, P. L., & Carpenter, K. (Eds.). (2008).
Tyrannosaurus rex, the tyrant king. Indiana University Press. p. 333
[8] Paul, G. S. (2016).
The Princeton field guide to dinosaurs (Vol. 110). Princeton University Press.
[9] Persons, W. S., & Currie, P. J. (2014).
Duckbills on the run: the cursorial abilities of hadrosaurs and implications for tyrannosaur-avoidance strategies.
Hadrosaurs, 449.
[10] Tanke, D. H., & Rothschild, B. M. (2014).
Paleopathology in Late Cretaceous Hadrosauridae from Alberta, Canada with comments on a putative Tyrannosaurus bite injury on an Edmontosaurus tail.
[11] Organ, C. L. (2006).
Biomechanics of ossified tendons in ornithopod dinosaurs.
Paleobiology, 32(4), 652-665.
[12] Arbour, V. M. (2009).
Estimating impact forces of tail club strikes by ankylosaurid dinosaurs. PLoS One, 4(8), e6738.
[13] Tennant, J. (2013).
Osteology of a near-complete skeleton of Tenontosaurus tilletti (Dinosauria: Ornithopoda) from the Cloverly Formation, Montana, USA.
arXiv preprint arXiv:1304.2616.
