Dinosaur corner

Many adjectives have been applied to dinosaurs: terrifying; lumbering; long-dead; fierce; huge; nimble, carnivorous; herbivorous and so on. But exquisite and tiny do not immediately spring to mind. The mineral amber – strictly speaking a mineraloid because it isn’t crystalline – having formed from resins exuded by trees, preserves materials, including animals, that became trapped in the resin. The shores of the Baltic Sea used to be the main source of this semi-precious gemstone, but it has been overtaken by high-quality supplies from Kachin State in Myanmar. Most specimens contain small invertebrates, including spiders and insects, in varying states of preservation. Once in a while truly spectacular amber pebbles turn up. In early March 2020 the world’s media splashed a unique find: a miniature dinosaur (Xing, L. et al. 2020. Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature v. 579, p. 245–249; DOI: 10.1038/s41586-020-2068-4).

Amber pebble from Myanmar containing a tiny vertebrate’s skull (credit: Lida Xing, China University of Geosciences)

The amber specimen, from Middle Cretaceous (99 Ma) sediments, contains a perfectly preserved skull less than 2 cm long. At first glance it appears to be that of a tiny bird. The authors used micro-CT scanning to reconstruct the entire skull in 3-D. Although superficially resembling that of a bird, with eye sockets ringed by scleral ossicles that modern birds also have. These suggest that the animal was active during the daytime. Its beak-like jaws have many small teeth, as do many ancient fossil birds but not modern ones. These features led to its name: Oculudentavis khaungraaeI, translated as ‘eye-tooth bird’. So, is it a bird? A number of features shown by the skull suggest that, strictly speaking, it is not. Anatomically, it is a dinosaur, possibly descended from earlier types, such as the Jurassic winged and feathered dinosaur Archaeopterix, which evolved to early, true birds with which Oculudentavis coexisted during the Cretaceous Period. Having teeth, it was probably carnivorous and preyed on invertebrates: it may have been fatally attracted to tree resin in which insects had been trapped.

Micro-CT image of Oculudentavis khaungraaeI skull (top); artist’s impression of it in life (bottom) (credits: Xing, L. et al. 2020; Jingmai O’Connor, China University of Geosciences)

Even if it was a bird , it is smaller than the smallest living example, the bee hummingbird (Mellisuga helenae) and, weighing an estimated 2 grams,  Oculudentavis is about one-sixth the size of the smallest known fossil bird. As a dinosaur, it is two orders of magnitude smaller than the most diminutive example of those found as fossils, the chicken-sized Compsognathus. Rather than being just an oddity, Oculudentavis demonstrates that extreme miniaturisation among avian dinosaurs held out evolutionary advantages.

Watch a video about the discovery and analysis of the tiny dinosaur

See also: Benson, R.B.J. 2020. Tiny bird fossil might be the world’s smallest dinosaur. Nature, v. 579, p. 199-200; DOI: 10.1038/d41586-020-00576-6.

Artist’s rendering of a Middle Jurassic coastal plain in what is now the Isle of Skye across which a mixed dinosaur megafauna is migrating (credit: De Polo et al. 2020; Fig. 24; artist Jon Hoad)

And now for the lumbering and sometimes scary kinds of dinosaur. Since discovery of Middle Jurassic sauropod and theropod trackways with up to 0.5 m wide footprints at Brothers’ Point on the Trotternish Peninsula of Skye, the Inner Hebridean island has become a magnet for those wishing to commune with big beasts. Now the same team from the University of Edinburgh report more from the same locality (De Polo, P.E. and 9 others 2020. Novel track morphotypes from new tracksites indicate increased Middle Jurassic dinosaur diversity on the Isle of Skye, Scotland. PLoS ONE, v. 15, article e0229640; DOI: 10.1371/journal.pone.0229640). One set, referred to as Deltapodus was probably made by a species of stegosaur: the one with vertical plates on its back and a tail armed with large spikes, animated caricatures of which figure in inane YouTube clips, especially beating off Tyrannosaurs. The new locality preserves 50 dinosaur tracks that suggest a rich community of species. The most prominent suggest bipedal ornithopod herbivores and small, possible carnivorous theropods, both with three-toed feet, large quadripedal sauropods whose prints resemble those of elephants, as well as those with larger back feet than front attributed to stegosaurs. The sediment sequence displaying the tracks contains structures typical of deposition on a wide coastal plain.

Life with the Neanderthals

From Robinson Crusoe’s discovery of Friday’s footprint on his desert island to Mary Leakey’s unearthing of a 3.6 Ma old trackway left by two adults and a juvenile of the hominin species Australopithecus afarensis at Laetoli in Tanzania, such tangible signs of another related creature have fostered an eerie thrill in whoever witnesses them. Other ancient examples have turned up, such as the signs of mud trampled by 800 ka humans (H. antecessor?) at Happisburgh, Norfolk, UK (see Traces of the most ancient Britons, February 2014). From a purely scientific standpoint, footprints provide key evidence of foot anatomy, gait, travel speed, height, weight, and the number of individuals who contributed to a trackway. At Le Rozel on the Cherbourg Peninsula in Normandy, France – about 30 km west of the D-Day landing site at Utah beach – Yves Roupin, an amateur archaeologist, discovered a footprint on the foreshore in the 1960s close to the base of a thick sequence of late-Pleistocene dune sediments exposed below a rocky cliff. Fifty years later, rapid onset of wind and tidal erosion threatened to destroy the site, so excavations and scientific analysis began. This involved excavation of thick overburden on an annual basis to expose as much of five footprint-bearing horizons as possible (about 90 m2).

Le Rozel
The Le Rozel excavation, with weighted plastic sheets to protect the site from erosion between visits (credit: Dominique Cliquet)

More and more prints emerged, each photographed and modelled in 3-D, with the best being preserved as casts using a flexible material, similar to that used by dentists (Duveau, J. eyt al. 2019. The composition of a Neandertal social group revealed by the hominin footprints at Le Rozel (Normandy, France). Proceedings of the National Academy of Sciences. 9 September 2019; DOI: 10.1073/pnas.1901789116). At the end of the excavation hundreds of prints had been found and recorded. They had been preserved in wet sand, probably deposited in an interdune pond. Luminescence dating of sand grains revealed that the footprints were produced around 80 ka ago, 35 ka before Europe was occupied by anatomically modern humans. Scattered around the site are numerous fossils of butchered prey animals, together with stone tools typical of Neanderthal technology.

Such a large number of footprints presented a unique opportunity to analyse the social structure of the Neanderthal group that produced them, for they came in many different sizes. During the very short period in which they were produced and buried by wind-blown sand, an estimated 10 to 13 individuals had crossed and re-crossed the site – there may have been more individuals who didn’t happen to cross the wet patch But the evidence suggests that children and adolescents, one of whom may have been as young as 2 years, predominated. Two or three with the biggest feet were probably adults as tall as 1.9 metres – about 20 cm taller that the average for modern human males. That is surprising for Neanderthals who are widely believed to have been more stocky. The fact that footprints occur in 5 horizons suggests that the band, or perhaps family, found the site to be good for occupation. Wider hypotheses are a little shaky. Did Neanderthals have large families? Does the predominance of children and adolescents indicate that they died young? But perhaps children stayed close to habitations with just a few ‘minders’, while other adults went off hunting and foraging. Were the kids playing?