I’m surprised and grateful for your response here. I really do consider it a pleasure to be interacting with a creation.com author and talking about data and not just mudslinging (as both sides so often do, including occasionally me, despite my better ideals).
Did you read my earlier post? In it, I talk about your statement that
The stratum in question has yielded many hundreds of bones, including those of a rhinoceros (Hyrachyrus),3 a lizard,4 a crocodile (Charactosuchus kugleri),5 a turtle,5 sea cows (‘abundant remains of sirenians’1), and possibly a primate,6 along with lots of invertebrate marine fossils (mollusks, etc.).7
I pointed out that the Domning article actually describes the presence of all those bones at Seven Rivers, which is not a “stratum.” If you said, “the wider site” it would be better, and true, but still misleading. As I noted, sites are divided into groups, groups into formations, formations into members, and members into beds (strata). Just because two things are at the same site together doesn’t mean that all these animals fell into the same tar pit together or something.
Would you also correct this wording?
By the way, since you chimed in, I took the liberty of tracking down an email address for Dr. Downing and jotting off an email to him to see if he’d be willing to clarify some aspects of this discovery for us. Turns out, he’s also interested in the faith-science dialogue, having written a book called Original Selfishness: Original sin and evil in the light of evolution. So you never know! Maybe we’ll hear from him about his own discovery!
I’m hoping Dr. Domning himself may clarify some of your questions better than I, but I do think I have something worth considering to say here.
This is not question-begging.
The evolutionary model says all mammals started on land.
We know that several branches of modern mammals are now obligate aquatic mammals. This is observable.
This suggests (a deduction!) that they must have gone through a transition from land- to water-dwelling.
With other such transitions, we have already found species between terrestrial and obligate aquatic where they lived on land and hunted in the water. (I realize you don’t grant this, but understand it’s part of the model, provisionally…)
This, in other words, is a hypothesis that can be tested. Will this hold true for sirenians, too?
If so, the transitional form would probably be found around the early- to mid- Paleogene — not too far into the Age of Mammals.
In other words, the age of the rocks in which the Pezosiren was found is an independent criterion that wound up fitting the model when it didn’t have to. The model predicts that a Pezosiren in rocks dated to 500 million years ago would be utterly impossible (no land animals yet) and that a Pezosiren in rocks dated to 10 million years ago would be unlikely (outcompeted by more aquatically adapted sirenians). There’s actually a fairly narrow geological range in which the Pezosiren could be found… and that’s just where it was found!
None of the papers I consulted when writing my article mentioned the exposure at the Seven Rivers site of any strata other than the Guys Hill Formation, and you have produced no evidence to the contrary.
I was unable to confirm that the primate fossil also came from the Seven Rivers site, so I erred on the side of caution and merely identified all those different types of creatures as being found in the Guys Hill Member, rather than in the one specific spot (Seven Rivers quarry) within the Guys Hill Member.
Well, it seems you may have dug a bit deeper into this than I presumed. I think to be fair I owe you an apology. And I appreciate your measured tone.
Would you be willing to share a couple of these papers with me here? This is less my doubting you this time and more my wanting to catch up to what you’ve read.
Since I’m a bit late to this discussion, I won’t presume that the discussion has missed some key points. But let me run my list of confirmations that I seek (from either side of the discussion), just to know exactly where we are:
We’ve read the YEC article about the discovery quite a while ago of the 4 legged sirenian (Pezosiren portelli): Ancient mutant Jamaican sea cows?
The significance of the find is not that it looks like a Sea Cow, but that it was the much awaited fossil with clear anatomical references to Sea Cows … but with four legs. In other words, in order to establish a credible evolutionary path from land mammal to marine mammal, researchers had been looking for the convincing “missing link” between land mammal (with many anatomical commonalities with non-four-legged Sea Cow fossils).
One of the early articles discussing the importance of Pezosiren portelli:
GEOTIMES, December 2001 Paleontology: Macro-evolution at its finest
"In the evolutionary history of aquatic mammals, sea cows, the group that includes manatees and dugongs, once walked into the sea. It was all the rage during the early Tertiary as intermediate forms of mammals adapted to a marine life. But something was missing in the history of sea cows. None of the fossil evidence till now has shown a sea cow ancestor with four legs strong enough to support its weight on land. When did they make that critical transition from land to sea and what did the animal look like? . . . "
"The find is “most significant,” says William Clemens of the Museum of Paleontology in Berkeley, Calif. “It gives us new insight into the origin of the sirenians.” The creature Pezosiren portelli . . . stands on four legs and is a little more than 2 meters (7 feet) long. It is the first skeleton of the order Sirenia with legs and pelvic structure that would have been strong enough to support its massive rib cage and body on land. Today’s manatees and dugongs have foregone hind limbs for a muscled tail and use flippers instead of front feet or hooves. But they still consume sea grasses, the niche that supposedly lured sirenians to the sea. "
"The closest living land relative of the modern sea cow is the elephant. And unlike the great whale debate — where fossil evidence has only recently supported biological determinations that hippos are whales’ nearest living relative (see Geotimes, November 2001) — morphological and molecular evidence agreed about the sea cows’ shared ancestral history with elephants years ago. But none of the sea cow fossils found has had legs strong enough for land, until now. "
One of the more recent articles (2010) showing that this specimen is still important to understanding the evolution (“macro-evolution”?) of the Sea Cow lineages:
“Evolution of Sirenian Pachyosteosclerosis, a Model-case for the Study of Bone Structure in Aquatic Tetrapods”
Authors: Vivian de Buffrénil, Aurore Canoville, Ruggero D’Anastasio, Daryl P. Domning
Original Paper: First Online: 26 February 2010
Abstract
"Osteosclerosis, or inner bone compaction, and pachyostosis, or outer hyperplasy of bone cortices (swollen bones), are typical features of tetrapods secondarily adapted to life in water. These peculiarities are spectacularly exemplified by the ribs of extant and extinct Sirenia. Sea cows are thus the best model for studying this kind of bone structural specializations. In order to document how these features differentiated during sirenian evolution, the ribs of 15 species, from the most basal form (Pezosiren portelli) up to extant taxa, were studied, and compared to those of other mammalian species from both morphometric and histological points of view. "
A fairly dry article on a Sea Cow related find in the Pisco formation in Peru (2014/2015):
Bone histology as a clue for resolving the puzzle of a dugong rib in the Pisco Formation, Peru
By: Eli Amson, Christian de Muizon, Daryl P. Domning, Christine Argot & Vivian de Buffrénil
And lastly, a 2017 article that cites the brief article in (5) above:
Preliminary Report of Pachyosteosclerotic Bones in Seals
Irina Koretsky and Sulman J Rahmat
Sulman J Rahmat, Laboratory of Evolutionary Biology, Department of Anatomy, College of Medicine, Howard University, Submission: August 08, 2017; Published: September 06, 2017
I guess the first question I would have is how a scientist can be mocked for finding a “missing link” by actually accusing him of putting a four-legged fossil into the discussion … when that was exactly what he was looking for to show the continuity from four-legged land mammal to a flipper-equipped marine mammal lineage with obvious similarities in anatomy right down to the molecular level of its bones?
@Lambinator, could you re-state your objection regarding this study, or the original author, or of the fossil?
Descriptions of all the geologic units and formations can be found in this paper. The Guys Hill formation and the Seven Rivers formation are two different things, or at least that is how I read it. The paper describes rhino fossils in the Seven Rivers formation but not in the Guys Hill formation. The fossils associated with the Guys Hill formation are crocodiles, turtles, and sea cows along with larger foraminiferal fauna.
From my reading, it is incorrect to associate the ungulate fossils found in the Seven Rivers site with the transitional sea cow fossils found at the Guys Hill site because they are two different sites and two different formations. All we really have is @Lambinator unevidenced accusation that Domning can not tell the difference between ungulate and early sirenian limbs. Until such an accusation is backed by some evidence, I don’t see why it should even be considered.
In reading the Creation.com article on the transitional sea cow, one has to laugh a bit. The inset on “mosaic creatures” really makes you wonder what YEC/OEC’s think a transitional fossil is. A transitional fossil is a mosaic creature, by definition. Here is the definition of transitional fossil from Wiki:
“A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group.[1] This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. Therefore, it cannot be assumed that transitional fossils are direct ancestors of more recent groups, though they are frequently used as models for such ancestors.[2]” Wiki
A sea cow with legs is a mosaic creature, and it is also a transitional fossil. It really makes you wonder what YEC/OEC’s mean when they talk about transitional fossils. What would a fossil need in order for them to accept it as being transitional? It is also rather strange that they think arbitrary human groupings prevent a fossil from being transitional. If we are talking about the fish to tetrapod transition we only have two groups to choose from: fish or tetrapod. All fossils will be put in one of those two bins INCLUDING THE TRANSITIONALS. Just because a fossil is classified as a fish or tetrapod does not exclude it from being transitional.
It’s a bit like dividing humans into two groups: short and tall. Does this mean that one person can not be in between the height of two other people? NO. The very act of dividing humans into two groups means that intermediates will have to be put in one of two groups, and the line between short and tall is going to be an arbitrary one. The same applies to evolutionary transitions.
As the author of the article under discussion, I’ve been asked to weigh in on all of this. Most of the disputed points seem to have been clarified already by others, but I’ll try to clear up some of the remaining areas of doubt.
• The “Seven Rivers site” is a single, artificially-dug drainage ditch in the vicinity of the village of that name. The strata exposed there (in total, about 7 meters of section) are part of what is now called the Litchfield Formation (formerly Guys Hill or Chapelton Formation). This is part of the Yellow Limestone Group, which is widely exposed in Jamaica. The strata in the Seven Rivers site are estimated to be Middle Eocene in age (circa 41-43 million years old). This is close to being as old as any other fossil sirenians in the world, except for Prorastomus sirenoides, which came from another site in western Jamaica that is slightly older (in the early Middle Eocene Stettin Formation, circa 47 mya); it is also more primitive than Pezosiren.
• Of the 20 lithologically-distinct beds or strata that are identified in the Seven Rivers site, several have produced bones, but the vast majority of the bones have come from just 5 layers, as others have stated. Of these 5 major bonebeds, the rhinoceros Hyrachyus has only been identified in the lowest; it and other land-dwelling vertebrates are vanishingly rare throughout the section, whereas sirenians are represented by hundreds of bones. (Turtles and crocodiles are also common.)
• The sirenian Pezosiren portelli is the only sirenian found in the bottom 3 major bonebeds and makes up the vast majority of the sirenian fossils found, including associated and semi-associated partial skeletons. In the upper 2 major bonebeds, the sirenians all seem to belong to a different genus and species that has not yet been named. (I apologize to the human race for the long delay in publishing this new animal, along with an exhaustive description of the remains of P. portelli. These contributions are to form the main part of a multi-authored volume describing the entire Seven Rivers fossil fauna; most of the chapters have been completed, but several important ones are still in preparation. If you’ve ever been an editor of a similar multi-authored book, I know you can sympathize!)
• The key difference between Pezosiren and the later, more derived genus is that the former has a sacrum comprising 3 or 4 tightly-jointed vertebrae that together connect the rest of the backbone to the pelvis and hindlimbs, as in a normal land mammal. The later seacow has a sacrum consisting of only a single vertebra, also attached to the pelvis; the other sacral vertebrae had become loosened from each other, making the vertebral column as a whole more flexible in the hip region. This was a necessary evolutionary step toward the degree of flexibility of the backbone seen in all later sirenians, as well as in whales and dolphins, which all swim by undulation of the tail rather than kicking with hind limbs.
• Several sacra of Pezosiren have been collected from the lower bonebeds, but never from the two higher ones; and no sacrum like the one from the 2 higher bonebeds has been found among the scores of vertebrae in the lower beds. This supports the idea that the later species had either evolved or moved into the area – and Pezosiren had departed – by the time those higher beds were deposited.
• Concentrations of numerous animal carcasses of the same species (or mixed species) are not at all uncommon in the fossil record. As can be seen happening today, this can result from mass mortality from natural disasters, as well as from gradual accumulation of dead animals in a spot where the bones become buried by sediments with little or no disturbance. The Seven Rivers bone accumulations seem to have occurred in a brackish coastal lagoon, likely near a river delta that was supplying sediment. This is exactly the sort of place where one expects to find both land-dwelling, semiaquatic, and fully marine organisms buried together. Carcasses of the herd-dwelling seacows were mostly dismembered; no skeleton was preserved complete, but a few partial ones remained more or less associated (which helps to confirm that, e.g., pelvic bones of a certain type were associated with sirenian ribs or other bones and not some other kind of mammal). When the time comes to analyze accumulations like these, it’s usually not hard to tell whether a given isolated bone is from a seacow, a rhino, a crocodile, etc. – bones of different animals really look different, so it’s generally not a matter of guesswork!
• As stated in my Nature paper, the skeleton illustrated is a composite of bones from different bonebeds but representative of the same species, with a few parts restored that were not found at all – e.g., foot bones, which were logically among the first to fall off a rotting carcass or be nibbled off by the numerous crocodiles. (We only found 3 foot bones, as I recall, but these suffice to show that the feet were built for land and were not manatee-like flippers.)
• Also, no widespread catastrophe needs to be postulated to explain a pile of bones only a few meters across. Dozens of African wildebeests, for example, might drown when a huge herd of them crosses a single river, and the bodies could end up piled and eventually buried on the next point bar downstream. And this could happen over and over again in the same place, years apart or centuries apart.
• Finally, a personal note: As a lifelong practicing Christian, I am always dismayed to see evolution being a stumbling block that divides my fellow Christians against one another. It’s not necessary! I can testify that in my own career, not only have I personally dug plenty of “transitional fossils” out of the ground, but also found that Christian theology makes a lot more sense in the light of old-Earth, Darwinian evolution (with modern updates, of course) than otherwise. Let’s keep it respectful, sisters and brothers – and a merry and blessed Christmas to all!
What a treasure to have you weigh in here. Thank you for taking the time!
I thought perhaps this was the case, but not being a paleontologist, I didn’t have the life experience to assert this for sure, so I’m glad you said this! Comments like this help us non-specialists to get a “feel” for what it’s like to make a discovery like this when we’ll never get out to a dig ourselves. Thank you!
This too is very helpful for informing how we think about these sites. Thank you.
Let me just take the opportunity to apologize to everyone, especially @Lambinator, for my acrimonious, and mistaken, attacks on this point. The grace shown by both Andrew Lamb & Dr. Domning is humbling to me — hopefully I’ll learn something from it, and my face will be more egg-free in future.
I find it helpful even to know that there are a “vast” number of sirenian fossils in this area. That again helps us to envision this discovery — that it’s not just a bunch of patchwork guesses strung together to make some goofy chimera.
Again, I’m very grateful for your comments — so helpful to us all. Have a merry & blessed Christmas!
P.S. @BradKramer, I’d love to flag this one for some sort of highlight of some sort. Yes, it’s embedded in a meandering conversation that’s not always gracious, but there are great insights in Dr. Domning’s reply that could be really helpful for wider BioLogos’s readership!
