Earlier than they thought…

Figure 1. The Middle Devonian tetrapod tracks from 395 mya are 35 million years older than Ichthyostega, which could not walk like this on land.

Figure 1. The Middle Devonian tetrapod tracks from 395 mya are 30 million years older than Ichthyostega, which could not walk like this on land.

The discovery of early Middle Devonian (395 mya) tetrapod tracks (elevated belly and not dragging a tail, Fig. 1) prompts today’s post. More on this discovery online here and below.

New discoveries keep pushing prior time envelopes in palaeontology. In this case, these tracks predate Ichthyostega and kin by 30 million years. They also provide at least 55 million years for evolution to produce the first amniotes in the Viséan, 340 mya. At that time amniotes (reptiles) were already a diverse clade including Eldeceeon, Westlothiana and Casineria. That means the very first amniotes might have been contemporaries of Ichthyostega 25 million years earlier at 365 mya…or even earlier if those tracks at 395 mya are considered. Those numbers appear to break all the current paradigms.

So much so that I wonder about the validity of the strata dating.
Niedźwiedzki et al. 2010 reported the dates were secure. Even so, they are unexpected, to say the least (Fig. 2). Added later on pub day: This year (Narkiewicz and Narkiewicz 2015), the age of the Zachełmie Quarry sediment (determined by conondonts) was modified only slightly (4-5 my younger).

On a similar note
Bird tracks purported to be created in Triassic sediments were later identified as Eocene sediments. So such mistakes do happen. It’s a hard call…

Figure 2. The Devonian and events within it. Here the new tetrapod trackways from 395 mya is the lower blue bar.

Figure 2. The Devonian and events within it. Here the new tetrapod trackways from 395 mya is the lower blue bar.

Other time bumps
Earlier we looked at an erroneous (way too late) estimate for the origin and radiation of burrowing skinks (amphisbaenids). The traditional date for the origin of lizards (Wiki reports: Middle Jurassic) also fails to take into account Lacertulus (Late Permian) and the TA1045 varanid specimen (early Permian).

Earlier the origin of snakes was pushed back several millions years.

Turtles had their origins long before the late Triassic, where their earliest known and already diverse fossils are found. Stephanospondylus lived during the Early Permian. We don’t know if it lived alongside turtles of more modern aspect (perhaps, though still retaining teeth) or shortly preceded them. From what we know about turtles, they don’t do anything quickly.

The persistence of basal taxa into the Cretaceous or to the present should come as no surprise when Sphenodon, the extant sphenodontid, is considered.

To make matters worse,
as you already know, the first appearance of any fossil or ichnite in rocks probably does not the first appearance of the morphotype, but instead probably represents the height of that form’s  radiation — by which time other undiscovered forms had also probably radiated.

On the other hand…
The origin of some groups, like pterosaurs, hominids, whales, bats, birds and dinosaurs appear to be more tightly constrained, based on more extensive fossil records.

References
Niedźwiedzki G, Szrek P,  Narkiewicz K, Narkiewicz M and Ahlberg PE 2010. Tetrapod trackways from the early Middle Devonian period of Poland. Nature 463, 43-48. doi:10.1038/nature08623
Narkiewicz, K and Narkiewicz, M 2015, The age of the oldest tetrapod tracks from Zachełmie, Poland. Lethaia, 48: 10–12. doi: 10.1111/let.12083

http://onlinelibrary.wiley.com/enhanced/doi/10.1111/let.12083

 

 

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2 thoughts on “Earlier than they thought…

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