Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
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Re: Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
#2This is the important bit:
> among the oldest tracks on Earth of shelled-egg-laying animals, such as reptiles, and the earliest evidence of vertebrate animals walking in sand dunes
Re: Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
#3An interesting note is, the footprints where formed on the supercontinent Pangea.
Re: Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
#4The paper Early adaptation to eolian sand dunes by basal amniotes is documented in two Pennsylvanian Grand Canyon trackways [1]:
> The narrow width of both trackways indicates that both trackmakers had relatively small femoral abduction angles and correspondingly relatively erect postures. They represent the earliest known occurrence of dunefield-dwelling amniotes―either basal reptiles or basal synapsids...
This geological formation was from the Moscovian age (315.2 to 307 Ma) or the Kasimovian age (307 to 303.7 Ma) in the Pennsylvanian period.
[1] https://journals.plos.org/plosone/article?id=10.1371/journal...
Re: Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
#5Can someone explain how these tracks were preserved on a sand dune?
As far as I know a sand dune moves constantly. I can't imagine tracks would last a day.
Looking at the tracks it looks more like they were made in mud and later covered by sand dunes?
Re: Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
#6Can someone explain how these tracks were preserved on a sand dune? As far as I know a sand dune moves constantly. I can't imagine tracks would last a day. Looking at the tracks it looks more like they were made in mud and later covered by sand dunes?
Maybe the low parts near water? It had to be wet to capture what appear to be claw marks.
Re: Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
#7Can someone explain how these tracks were preserved on a sand dune? As far as I know a sand dune moves constantly. I can't imagine tracks would last a day. Looking at the tracks it looks more like they were made in mud and later covered by sand dunes?
The authors of the paper actually describe their hypothesis for how it occurred [0]. Basically perfect conditions were required to preserve them.
In short the first tracks were made in dry sand, eroded a little, moistened by fog, dew, or light rain, and then covered by dry sand again. The second tracks were made through the dry sand into the moist layer which was then crusted over with calcite and covered. Only the toe markings from the second tracks were preserved.
[0] https://journals.plos.org/plosone/article?id=10.1371/journal...
Re: Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
#8Erroneous dating.
"The intelligent layman has long suspected circular reasoning in the use of rocks to date fossils and fossils to date rocks. The geologist has never bothered to think of a good reply, feeling the explanations are not worth the trouble as long as the work brings results (American Journal of Science 276:51)." –J. E. O’Rourke
Re: Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
#9Erroneous dating. "The intelligent layman has long suspected circular reasoning in the use of rocks to date fossils and fossils to date rocks. The geologist has never bothered to think of a good reply, feeling the explanations are not worth the trouble as long as the work brings results (American Journal of Science 276:51)." –J. E. O’Rourke
And the humble layman knows that this is resolved by radiological techniques being able to date things on the scale of billions of years.
Re: Fallen Boulder Reveals 313M-Year-Old Fossil Footprints at Grand Canyon
#10Erroneous dating. "The intelligent layman has long suspected circular reasoning in the use of rocks to date fossils and fossils to date rocks. The geologist has never bothered to think of a good reply, feeling the explanations are not worth the trouble as long as the work brings results (American Journal of Science 276:51)." –J. E. O’Rourke
For not circular methods, take a look at https://en.wikipedia.org/wiki/Radiometric_dating#Accuracy_of...