By Vanessa Bristow
Anybody who has ridden the Nedbank Tour de Tuli’s Mapungubwe route will remember the stop-over at Sentinel Ranch with profound fondness. Vanessa and Digby Bristow are consummate hosts, and on their extraordinary property lies a wealth of fossilised treasure. Vanessa elaborates…
Sentinel Ranch is rich with dinosaur fossil sites that date back to the late Triassic Period of 250-208 million years ago, when the continents still were joined together in the super-continent Pangaea, with Gondwana in the south. A vast trans-continental desert extended over the entire Gondwana region, its massive dunes networked by streams and rivers that flooded periodically, sometimes in raging torrents, much as the seasonal Limpopo River does today.
A precursor to today’s crocodile, the extremely large Erythrosuchus africanus, lived in the area 240 million years ago. He was a flesh-eating archosaur that hunted the floodplains of that time. Its head alone reached a length of 700 cm and the size of its teeth is ample testimony to the ferocity and effectiveness with which it attacked its prey. In a river bed near Sandstone Camp one can see numerous large serrated fossilised teeth, and trace fossils (casts of teeth), embedded in the base sandstone.
Archosaurs were ancestors to the crocodilians, dinosaurs and birds. The most ubiquitous of the fossilised dinosaur species found on Sentinel is the prosauropod, Massospondylus carinatus owen, a long-necked, herbivorous (but possibly omnivorous) species that lived 210-190 million years ago (at the cusp of the Triassic/Jurassic Periods). Adults reached approximately 6 m in length, were bi-pedal, with small upper limbs, long necks, and relatively small heads with uniform serrated, blade-shaped teeth. They swallowed stones (gastroliths) to aid digestion. Massospondylus were gregarious and moved in herds. At one celebrated Sentinel fossil site there is a well-articulated bottom half of a Massospondylus skeleton preserved in a fine sandstone bed.
Numerous fossils of another primitive dinosaur from the same period, Euskelosaurus, were discovered on the mountain directly across from the Sandstone Camp. Remarkably, three left femurs of different sizes were found, indicating that at least three specimens died at this site. The herbivorous Euskelosaurus walked on all fours, had a long neck and reached a height of approximately 3 m, and a length of over 6 m.
Palaeontologists have made frequent trips to Sentinel, to preserve existing sites and to record sites which may merit excavation in the future. A very small segment of mammalian jaw bone and teeth was discovered in 2010 near a ledge containing a Massospondylus pelvis. There is no doubt a wealth of fossilised material remains to be discovered within the hills and valleys of this remarkable landscape.