An Unbearable Rush -- Antarctic Whale Fossil Poses a Challenge to Evolution that Won't Go Away
Evolution News &Views
As many readers are aware, the standard whale evolution scheme suggests that a fully terrestrial land mammal evolved into a fully aquatic whale in less than 10 million years. Richard Sternberg (see Part 1 and Part 2), Casey Luskin (see here and here), Jonathan M, and others have explained that this is not enough time for neo-Darwinian mechanisms to produce the many complex adaptations found in whales that allow for a fully aquatic lifestyle. (For another great discussion of this challenge to neo-Darwinism, see the film Living Waters.)
The situation changed in 2011, making things worse for neo-Darwinism. Casey Luskin wrote about the discovery that year of an Antarctic whale jawbone fossil that was dated to 49 million years ago (Ma).
Previously, the supposed transition was from fully terrestrial ancestors of whales at about 50 Ma to fully aquatic whales called "basilosaurids" at 40 Ma. That left about 10 million years for the transition. But the new jawbone find seemed to make whale evolution even more rapid than previously thought, compressing the time available to as little as a million years -- an unbearable rush.
That is "far too little time to allow the origin and fixation of all the multitude of traits necessary to convert a land-mammal into a whale," Luskin wrote. He observed, "The problem that Richard Sternberg has identified for whale evolution just got even worse."
But that was just based on a news report. We were curious to see what would happen when the discoverers published their find in a scientific journal. Earlier this year they did so, formally giving a date on these Antarctic whale fossils.
Well, in their paper, the authors assert a probable date for this fossil of 49 Ma. Instead of 10 million years for the transition from terrestrial to aquatic, this leaves only 1 million years.
The key question is where the whale fossil specimen MLP 11-II-21-3 was found, because it was stratigraphically lowest (i.e., oldest). Here's what they say in the paper (some internal references omitted):
Age control within the La Meseta Formation has been based primarily on biostratigraphy and suggests that its deposition spanned during much of the Eocene, but there is uncertainty about the precise age of particular units within this formation. In particular, the age of the lower part of the La Meseta Formation (TELMs 2-5), where MLP 11-II-21-3 was collected, is still disputed. Based on the low overall 87Sr/86Sr ratios derived from bivalve carbonate, Dutton et al. (2002) suggested the deposition of TELMs 2-5 took place during the early-middle Eocene (Ypresian and Lutetian in the chronostratigraphic scheme of Cohen et al., 2013). In contrast, Ivany et al. (2008) suggested an early Eocene age (54-48.8 Ma; Ypresian) for these units. TELM 4 includes a significant number of reworked shells, which could have biased the strontium-isotope data. The uncertainty is heightened by the small degree of variance in the global seawater curve for the early to the middle Eocene. However, overlying shells from TELM 5 produce ratios that suggest an age for the base of the unit of ca. 51 Ma. Finally, an early Eocene age of the lower part of the La Meseta Formation is consistent with estimates derived from dinoflagellate and diatom biostratigraphy.
A younger age for TELM 4 and TELM 5 has been discussed as a feasible alternative to an early Eocene age in a number of publications. The most recent comprehensive analysis of the La Meseta Formation is a magnetostratigraphically calibrated dinocyst biostratigraphic framework for the early Paleogene of the Southern Ocean, which support a middle Eocene age for TELM 4. Samples from La Meseta basal stratigraphic units are characterized by an abundance of Antarctic endemic dinocyst taxa (Enneadocysta diktyostila, Vozzhennikovia apertura, Spinidinium macmurdoense, Deflandrea antarctica, and Octodinium askiniae; Douglas et al., 2014). The first occurrence of Enneadocysta diktyostila (earlier assigned to Enneadocysta partridgei), which is dominant in these sediments, has been calibrated to Chron C20r (~45 Ma; Brinkhuis et al., 2003; Williams et al., 2004). Essentially, all dinocyst taxa present in these sediments (E. diktyostila, Vozzhennikovia aperture) belong to the so-called transantarctic fauna, whose dominance reflects an age near the early-middle Eocene boundary (49 Ma or younger; Bijl et al., 2011).
In summary, considering that 87Sr/86Sr ratios provided for TELM 4 might be biased (because of potential reworking and oscillation of the marine Sr isotope curve during the Eocene), we interpret the age of the horizon that produced MLP 11-II-21-3 (i.e., TELM 4) as early middle Eocene (~46- 40 Ma; middle Lutetian to early Bartonian based on ICS International Chronostratigraphic Chart 2015; Cohen et al., 2013) and follow the most recent chronostratigraphic interpretation for the La Meseta Formation. This age is also more consistent with the published stratigraphic record of basilosaurids elsewhere.
Previous reports of basilosaurids in the Southern Hemisphere come from approximately coeval deposits from New Zealand (39.5-34 Ma, late Bartonian-Priabonian based on recent interpretation of the lower Greensand Member; Marx and Fordyce, 2015) and Peru (41-37 Ma, Bartonian; Uhen et al., 2011). With a middle Lutetian-early Bartonian age, MLP11-II-21-3 predates other basilosaurid records and provides the oldest Pelagiceti record known worldwide, documenting an early global dispersal of basilosaurids.
What did we just read?
The authors say there is "uncertainty" about the age, an observation they will exploit to justify going with the youngest age possible. (As we'll see below, they prefer an age of "~46-40 Ma".)
Dutton et al. (2002) found 87Sr/86Sr dating methods suggest the early-middle Eocene (Ypresian and Lutetian), which means between 56-41.3 Ma.
Ivany et al. (2008) suggested an early Eocene age (54-48.8 Ma; Ypresian), and found the base of the unit dates to 51 Ma.
Dinoflagellate and diatom biostratigraphy date it to early Eocene (54-48.8 Ma).
Based upon the above, there are good reasons to think this fossil of a fully aquatic whale is no younger than 48.8 Ma. We'll call it 49 Ma.
However, that is much too early for the standard whale evolution scheme. Fully aquatic whales should not have lived so early. So the authors say they want "a younger age" which they claim is "a feasible alternative to an early Eocene age" based upon dinocyst biostratigraphy. Yet even then they admit that under dinocyst biostratigraphy it could be as old as 49 Ma:
Essentially, all dinocyst taxa present in these sediments (E. diktyostila, Vozzhennikovia aperture) belong to the so-called transantarctic fauna, whose dominance reflects an age near the early-middle Eocene boundary (49 Ma or younger; Bijl et al., 2011).
Geological dating is all about using multiple methods that, together, constrain the age of a rock unit to something ever more precise. In this case, there is an age that fits all the different methods used: about 49 Ma.
That's the same age that was originally reported, and that age makes the most sense for this fossil. But the authors don't want that age, for the reasons already stated. In the end, they claim the age of the earliest basilosaurid fossil they found is "~46-40 Ma" because that is "more consistent with the published stratigraphic record of basilosaurids elsewhere." In other words, that age makes their evolutionary timeline a bit more bearable. Still, that contradicts a lot of the other data discussed.
Even then, having settled on a 46-40 Ma age range, they admit this still means that basilosaurids had a "rapid radiation":
In addition, one of these records is among the oldest occurrences of basilosaurids worldwide, indicating a rapid radiation and dispersal of this group since at least the early middle Eocene. ... These findings suggest a rapid radiation and dispersal of protocetids and basilosaurids into the Southern Hemisphere at least since the early middle Eocene (Lutetian).
Yet an age of about 49 Ma remains the most likely conclusion for these true whale fossils.
Obviously, the authors want to reject that age and prefer their basilosaurid fossils to be younger. Evolutionary considerations are plainly pushing the interpretation of data here. The story is not an unfamiliar one.
Evolution News &Views
As many readers are aware, the standard whale evolution scheme suggests that a fully terrestrial land mammal evolved into a fully aquatic whale in less than 10 million years. Richard Sternberg (see Part 1 and Part 2), Casey Luskin (see here and here), Jonathan M, and others have explained that this is not enough time for neo-Darwinian mechanisms to produce the many complex adaptations found in whales that allow for a fully aquatic lifestyle. (For another great discussion of this challenge to neo-Darwinism, see the film Living Waters.)
The situation changed in 2011, making things worse for neo-Darwinism. Casey Luskin wrote about the discovery that year of an Antarctic whale jawbone fossil that was dated to 49 million years ago (Ma).
Previously, the supposed transition was from fully terrestrial ancestors of whales at about 50 Ma to fully aquatic whales called "basilosaurids" at 40 Ma. That left about 10 million years for the transition. But the new jawbone find seemed to make whale evolution even more rapid than previously thought, compressing the time available to as little as a million years -- an unbearable rush.
That is "far too little time to allow the origin and fixation of all the multitude of traits necessary to convert a land-mammal into a whale," Luskin wrote. He observed, "The problem that Richard Sternberg has identified for whale evolution just got even worse."
But that was just based on a news report. We were curious to see what would happen when the discoverers published their find in a scientific journal. Earlier this year they did so, formally giving a date on these Antarctic whale fossils.
Well, in their paper, the authors assert a probable date for this fossil of 49 Ma. Instead of 10 million years for the transition from terrestrial to aquatic, this leaves only 1 million years.
The key question is where the whale fossil specimen MLP 11-II-21-3 was found, because it was stratigraphically lowest (i.e., oldest). Here's what they say in the paper (some internal references omitted):
Age control within the La Meseta Formation has been based primarily on biostratigraphy and suggests that its deposition spanned during much of the Eocene, but there is uncertainty about the precise age of particular units within this formation. In particular, the age of the lower part of the La Meseta Formation (TELMs 2-5), where MLP 11-II-21-3 was collected, is still disputed. Based on the low overall 87Sr/86Sr ratios derived from bivalve carbonate, Dutton et al. (2002) suggested the deposition of TELMs 2-5 took place during the early-middle Eocene (Ypresian and Lutetian in the chronostratigraphic scheme of Cohen et al., 2013). In contrast, Ivany et al. (2008) suggested an early Eocene age (54-48.8 Ma; Ypresian) for these units. TELM 4 includes a significant number of reworked shells, which could have biased the strontium-isotope data. The uncertainty is heightened by the small degree of variance in the global seawater curve for the early to the middle Eocene. However, overlying shells from TELM 5 produce ratios that suggest an age for the base of the unit of ca. 51 Ma. Finally, an early Eocene age of the lower part of the La Meseta Formation is consistent with estimates derived from dinoflagellate and diatom biostratigraphy.
A younger age for TELM 4 and TELM 5 has been discussed as a feasible alternative to an early Eocene age in a number of publications. The most recent comprehensive analysis of the La Meseta Formation is a magnetostratigraphically calibrated dinocyst biostratigraphic framework for the early Paleogene of the Southern Ocean, which support a middle Eocene age for TELM 4. Samples from La Meseta basal stratigraphic units are characterized by an abundance of Antarctic endemic dinocyst taxa (Enneadocysta diktyostila, Vozzhennikovia apertura, Spinidinium macmurdoense, Deflandrea antarctica, and Octodinium askiniae; Douglas et al., 2014). The first occurrence of Enneadocysta diktyostila (earlier assigned to Enneadocysta partridgei), which is dominant in these sediments, has been calibrated to Chron C20r (~45 Ma; Brinkhuis et al., 2003; Williams et al., 2004). Essentially, all dinocyst taxa present in these sediments (E. diktyostila, Vozzhennikovia aperture) belong to the so-called transantarctic fauna, whose dominance reflects an age near the early-middle Eocene boundary (49 Ma or younger; Bijl et al., 2011).
In summary, considering that 87Sr/86Sr ratios provided for TELM 4 might be biased (because of potential reworking and oscillation of the marine Sr isotope curve during the Eocene), we interpret the age of the horizon that produced MLP 11-II-21-3 (i.e., TELM 4) as early middle Eocene (~46- 40 Ma; middle Lutetian to early Bartonian based on ICS International Chronostratigraphic Chart 2015; Cohen et al., 2013) and follow the most recent chronostratigraphic interpretation for the La Meseta Formation. This age is also more consistent with the published stratigraphic record of basilosaurids elsewhere.
Previous reports of basilosaurids in the Southern Hemisphere come from approximately coeval deposits from New Zealand (39.5-34 Ma, late Bartonian-Priabonian based on recent interpretation of the lower Greensand Member; Marx and Fordyce, 2015) and Peru (41-37 Ma, Bartonian; Uhen et al., 2011). With a middle Lutetian-early Bartonian age, MLP11-II-21-3 predates other basilosaurid records and provides the oldest Pelagiceti record known worldwide, documenting an early global dispersal of basilosaurids.
What did we just read?
The authors say there is "uncertainty" about the age, an observation they will exploit to justify going with the youngest age possible. (As we'll see below, they prefer an age of "~46-40 Ma".)
Dutton et al. (2002) found 87Sr/86Sr dating methods suggest the early-middle Eocene (Ypresian and Lutetian), which means between 56-41.3 Ma.
Ivany et al. (2008) suggested an early Eocene age (54-48.8 Ma; Ypresian), and found the base of the unit dates to 51 Ma.
Dinoflagellate and diatom biostratigraphy date it to early Eocene (54-48.8 Ma).
Based upon the above, there are good reasons to think this fossil of a fully aquatic whale is no younger than 48.8 Ma. We'll call it 49 Ma.
However, that is much too early for the standard whale evolution scheme. Fully aquatic whales should not have lived so early. So the authors say they want "a younger age" which they claim is "a feasible alternative to an early Eocene age" based upon dinocyst biostratigraphy. Yet even then they admit that under dinocyst biostratigraphy it could be as old as 49 Ma:
Essentially, all dinocyst taxa present in these sediments (E. diktyostila, Vozzhennikovia aperture) belong to the so-called transantarctic fauna, whose dominance reflects an age near the early-middle Eocene boundary (49 Ma or younger; Bijl et al., 2011).
Geological dating is all about using multiple methods that, together, constrain the age of a rock unit to something ever more precise. In this case, there is an age that fits all the different methods used: about 49 Ma.
That's the same age that was originally reported, and that age makes the most sense for this fossil. But the authors don't want that age, for the reasons already stated. In the end, they claim the age of the earliest basilosaurid fossil they found is "~46-40 Ma" because that is "more consistent with the published stratigraphic record of basilosaurids elsewhere." In other words, that age makes their evolutionary timeline a bit more bearable. Still, that contradicts a lot of the other data discussed.
Even then, having settled on a 46-40 Ma age range, they admit this still means that basilosaurids had a "rapid radiation":
In addition, one of these records is among the oldest occurrences of basilosaurids worldwide, indicating a rapid radiation and dispersal of this group since at least the early middle Eocene. ... These findings suggest a rapid radiation and dispersal of protocetids and basilosaurids into the Southern Hemisphere at least since the early middle Eocene (Lutetian).
Yet an age of about 49 Ma remains the most likely conclusion for these true whale fossils.
Obviously, the authors want to reject that age and prefer their basilosaurid fossils to be younger. Evolutionary considerations are plainly pushing the interpretation of data here. The story is not an unfamiliar one.
No comments:
Post a Comment