In case you go to a specific stretch of South Africa’s Cape South coast, about 400km east of Cape City, you’re stepping again in time – in additional methods than one. That’s as a result of a whole bunch of fossil tracksites dot the world. These websites date again to between 400,000 and 35,000 years in the past, in the course of the Pleistocene Epoch. They happen in aeolianites (cemented dunes) and cemented foreshore deposits, the stays of dune and seashore surfaces on which animals left their tracks.
Since 2007 our analysis staff has recognized greater than 250 fossil tracksites on the Cape south coast, revealing sudden findings that weren’t obvious within the conventional physique fossil file. For instance, giraffe, hatchling sea turtles and crocodiles as soon as inhabited this shoreline.
First fossil trails of child sea turtles present in South Africa
Our newest work has centred on avian tracksites, revealing proof for the primary time from this era of a number of the chicken species that when roamed the Cape south coast. In an article just lately revealed within the journal Ostrich, we summarised our findings from 29 websites on that coast.
One avian observe, most likely made by a big gull or a small goose, was present in sediments which have been dated to about 400,000 years. That makes it the oldest avian observe reported from southern Africa.
Six of the tracksites we recognized confirmed proof of enormous avian trackmakers. For instance, tracks at one web site that seem to have been made by a crane have been bigger than any extant crane species in Africa, and a trackway at one other web site carefully resembled that of a flamingo – besides that the tracks have been bigger than these of the extant Higher Flamingo.
At this web site, which was remarkably effectively preserved, we additionally documented flamingo feeding traces for the primary time within the world fossil file. The creation of those traces may be readily noticed in flamingo behaviour at present: the birds fire up their meals provide by “rhythmic stomping” or “marking time” whereas shifting slowly backwards, leading to “tramline traces”.
These tracksites have the potential to enrich the normal physique fossil file and supply extra insights into what natural world occurred within the area in the course of the Pleistocene, largely within the 130,000 to 80,000 yr age vary. They will additionally assist us perceive which of those species could have develop into extinct, maybe pushed by climatic shifts. This discovering was sudden, as there was no earlier proof of Pleistocene avian extinctions in Southern Africa.
Tracing the tracks
Avian tracks are typically much less frequent and fewer apparent than mammal and reptile tracks. That is partly as a result of birds fly and perch, so many species left few tracks to be interpreted at present. Our findings of chicken tracks on what have been seashores and dunes is extraordinarily uncommon – globally, most fossil chicken tracks are discovered on the margins of lakes and lagoons.
A few of our websites have been robust to achieve. For instance, one web site was amongst excessive, brittle cliffs on the under-surface of the ceiling of a tiny overhang.
Initially solely two tracks have been seen. However, following some excavation we recognized a complete of 5 tracks and created sufficient house to take images for photogrammetric research that enabled us to create a 3D digital mannequin of the trackway which in any other case couldn’t be adequately studied.
What do these massive tracks inform us? Their outer digits confirmed some curvature, strongly suggesting that the trackmaker had webbed ft. However the tracks couldn’t be definitively linked to these of any member of southern Africa’s present avifauna.
These findings increase two potentialities. The primary, in step with proof from elsewhere on the earth, is that some Pleistocene chicken species have been bigger than their trendy counterparts – they bought smaller over time.
The second chance is of beforehand unsuspected Pleistocene avian extinctions. We might postulate, for instance, that a big freshwater chicken species could have been pushed to extinction by a change in local weather that we all know inundated the considerable wetland habitat that beforehand existed on the adjoining Palaeo-Agulhas Plain.
The Pleistocene physique file fossil doesn’t present any such proof. It extends again to about 80,000 years in the past and many of the tracksites we now have documented look like from the 130,000 to 90,000 yr vary. So it’s believable that Pleistocene avian extinctions predated any proof which may be out there by way of the skeletal file.
Although the websites we’re exploring are historical, they’re additionally ephemeral. Tracks are made on a dune, coated by one other layer of sand, after which buried by 100,000 years or extra. As soon as uncovered by way of the forces of abrasion they’re destined to vanish inside a really brief time frame, additionally by way of erosion or different pure forces – and typically, regrettably, by way of graffiti on the rocks.
The sumptuous fossil flamingo tracksite is an unlucky instance of this. It was obliterated by a robust storm surge within the winter of 2020. Nonetheless, the photogrammetric file that we obtained ensures that this distinctive floor has not been misplaced to science, and it might be possible to create a precise reproduction.
Nonetheless, the message is obvious: we must be vigilant, and to maintain on looking, exploring, and documenting – as a result of like their mammal and reptile counterparts, fossil chicken tracks have so much to show us.