When someone studies migration patterns of different organisms, one may consider many lines of evidence. For modern organisms, that is easy: visual and audio cues, tracks, feces, etc. In the fossil record, it can be a bit trickier to establish what may be a possible migration behavior in a landscape and habitat that is much different today, with a limited set of data preserved in the fossil record. The best a paleontologist can hope for is some kind of pattern or link that unites fauna across different spatial zones.
A recent study published in PeerJ has found one such line of evidence for a charismatic group of organisms: Cretaceous sauropods. The study, lead by Femke Holwerda from the Faculty of Geosciences at Utrecht University in The Netherlands, has provided possible evidence for faunal connections through an unlikely source of information—their teeth. I asked Femke a few questions relating to this exciting study.
How did this study come about?
I was supervising a bachelors student from Utrecht University while he undertook a short research project in the collections of the Palaeontological Museum of Munich, Germany, on a sauropod tooth sample from the Kem Kem beds, Morocco. Verónica Díez Díaz [co-author of the study] and I decided to expand on these results, using an additional tooth sample from the same beds from the Palaeontological Museum in Zurich, Switzerland. Verónica realized the tooth sample morphologically matched some Cretaceous tooth morphotypes of Spain and France from her previous research. Finally, we got a colleague from Munich, Alejandro Blanco, on board to help with the statistical analysis. So the project has been quite an international one, with Spanish and Dutch researchers working on material from German and Swiss collections!
It seems like sauropod material should be fairly conspicuous (i.e., large and obvious!), but your paper points out that the sauropod material preserved in this region is almost exclusively teeth. Why aren’t large sauropod bones recovered in these regions? Why just teeth?
We are not entirely sure why there are so many more theropod skeletal remains from this area, and relatively few sauropod ones. As the major herbivorous components of most Mesozoic vertebrate ecosystems, you’d expect many more sauropods! One explanation is that the arid, riverine ecosystem of the Cretaceous of Northwest Africa supported a food web consisting of many predators and not so many herbivores (Läng et al., 2013). Still, sauropods were around, as their teeth got preserved. The handy thing about sauropod teeth is that they are relatively abundant in the fossil record, as sauropods shed their teeth continuously (unlike us humans, for example, who only shed teeth once in our lives). These teeth are covered in enamel, a hard substance which survives fossilization pretty well, and therefore can be used in species diversity studies.
You suggest that this region of study represents migratory routes for sauropods, but the deposits suggest and area somewhat devoid of vegetation. What would the environment have been like for these large animals? How would they have survived?
Our idea is that these large sauropods were able to migrate distances, which were quite far, in order to get enough food in. Sauropods were massive feeding machines and would have needed quite a bit of plant food, and perhaps they had to travel a distance to get enough sustenance in an arid region. A previous study (Fricke et al., 2011) demonstrates this for Jurassic sauropods, and we see no reason that these Cretaceous ones couldn’t do the same. Besides, the Mediterranean area in the Cretaceous was far more of a shallow sea with sand banks, which would provide coastal routes from one continent to the other. Europe was also a collection of island back then, and still similar sauropods have been found across, for example, Spain and France (Díez Díaz et al., 2018).
You are able to compare morphological similarity of teeth to various genera of sauropods. How would you say your study possibly changes or improves what we know regarding sauropod diversity and geographical distribution?
Several previous studies (e.g. Dal Sasso et al., 2016; Díez Díaz et al., 2018; Sallam et al., 2018) showed skeletal morphological similarities between North African and Southern European vertebrates, amongst others crocodylomorphs, theropods, sauropods and other smaller vertebrates. However, to our knowledge, no larger sauropod tooth morphological study has been done. We think this study confirms and builds upon the theory of faunal connections and possible landbridges between North Africa and Southern Europe.
Were there any surprises in your study?
I think this research started out as a small morphological study; but neither of us could anticipate that it would become a far broader study into possible migration routes, faunal connections or even landbridges! This was definitely very exciting to dig into, and to build on previous research on this (see for instance Csiki-Sava et al., 2015; Rabi 2015).
Can you explain the importance of enamel wrinkling? Does it have any functional significance?
Heavy wrinkling on enamel surface seems to be a special development for herbivory, although it is found not just in sauropods, but also in ornithopods (Chen et al., 2018) for instance. The specific functional significance is not entirely understood, but probably it has to do with the mechanical endurance of the enamel for heavy use (i.e., not munching on tender pieces of meat, but on heavy fiberous plants and stalks). As sauropods did not chew their food, but rather used a grip-and-pull motion to shear off vegetation, their teeth had to be pretty tough! In sauropods, so far, it seems that enamel wrinkling is species specific, and thus very useful in diversity studies (see e.g. Holwerda et al., 2015; Carballido et al., 2017).
You mention that some of this material is scarce. Any intention to follow up with more collections-based research or fieldwork to increase sample size?
Yes, definitely! It seems these type of sauropod teeth are quite common in collections, as they are usually found in batches and then distributed from Morocco to museums all over the world. We are expecting to follow up on this study, and perhaps go into an in-depth morphological study on Cretaceous sauropod teeth, perhaps using geometric morphometrics to better quantify similarities and differences in tooth shapes better. Stay tuned for this!
What is your favorite part of your research on sauropods?
Sauropods are the largest vertebrates to ever have walked the earth. No terrestrial animal ever got that big again. This is fascinating to us, because it’s still not entirely clear how they could get so big! Also, they were immensely successful; we find their remains in every continent throughout the Mesozoic. There is still plenty left to learn about them, which is why they are my favorite type of dinosaur.
Anything else you’d like to share?
This is only the tip of the iceberg! Several studies are currently being developed; redescribing and analyzing the Cretaceous sauropod faunas from Africa and Europe from a systematic and palaeobiogeographic point of view. So, in the next few years, we probably will have more information about the migratory patterns of this huge animals.
Thanks, Femke and colleagues for this great work! Find the paper online at PeerJ.
Carballido JL, Holwerda FM, Pol D, Rauhut OW. 2017. An Early Jurassic sauropod tooth from Patagonia (Cañadón Asfalto Formation): implications for sauropod diversity. Publicación Electrónica de la Asociación Paleontológica Argentina 17:50-57
Chen, J., LeBlanc, ARH, Jin, L., Huang, T, Reisz, RR. 2018. Tooth development, histology, and enamel microstructure in Changchunsaurus parvus: Implications for dental evolution in ornithopod dinosaurs. PLoS ONE 13(11):e0205206
Csiki-Sava Z, Buffetaut E, Ősi A, Pereda-Suberbiola X, Brusatte SL. 2015. Island life in the Cretaceous – faunal composition, biogeography, evolution, and extinction of land-living vertebrates on the Late Cretaceous European archipelago. ZooKeys 469:1-161
Dal Sasso C, Pierangelini G, Famiani F, Cau A, Nicosia U. 2016. First sauropod bones from Italy offer new insights on the radiation of Titanosauria between Africa and Europe. Cretaceous Research 64:88-109
Díez Díaz V, Garcia G, Pereda Suberbiola X, Jentgen B, Stein K, Godefroit P,Valentin X. 2018. The ttitanosaurian dinosaur Atsinganosaurus velauciensis (Sauropoda) from the Upper Cretaceous of southern France: new material. Phylogenetic affinities, and palaeobiogeographical implications. Cretaceous Research 91:429-456
Fricke HC, Hencecroth J, Hoerner ME. 2011. Lowland-upland migration of sauropod dinosaurs during the Late Jurassic epoch. Nature 480:513-515
Holwerda FM, Pol D, Rauhut OWM. 2015. Using dental enamel wrinkling to define sauropod tooth morphotypes from the Cañadón Asfalto Formation, Patagonia, Argentina. PLOS ONE 10:e011810
Holwerda FM, Díez Díaz V, Blanco A, Montie R, Reumer JWF. 2018 Late Cretaceous sauropod tooth morphotypes may provide supporting evidence for faunal connections between North Africa and Southern Europe. PeerJ 6:e5925 https://doi.org/10.7717/peerj.5925
Läng E, Boudad L, Maio L, Samankassou E, Tabouelle J, Tong H, Cavin L. 2013.Unbalanced food web in a Late Cretaceous dinosaur assemblage. Palaeogeography, Palaeoclimatology, Palaeoecology 381–382:26-32
Rabi M, Sebök N. 2015. A revised Eurogondwana model: Late Cretaceous notosuchian crocodyliforms and other vertebrate taxa suggest the retention of episodic faunal links between Europe and Gondwana during most of the Cretaceous.Gondwana Research 28:1197-1211
Sallam HM, Gorscak E, O’Connor PM, El-Dawoudi IA, El-Sayed S, Saber S, KoraMA, Sertich JJ, Seiffert ER, Lamanna MC. 2018. New Egyptian sauropod reveals Late Cretaceous dinosaur dispersal between Europe and Africa. Nature Ecology & Evolution 2:445-451