The Xenarthrans include the armadillos, anteaters and sloths. What makes these animals different from other mammals? They all have a unique projections on their vertebral (back) bones; the ischium and sacrum bones of the hip are fused, unlike all other mammals; the males have internal testicles (no external scrotum) located near the bladder and they experience much lower metabolic rates—just think of the characterization of sloths as slow moving—than other mammalian groups.
They have one other thing in common: all 31 living species of Xenarthrans are found exclusively in the New World (North and South America). If we include fossils species the Xenarthrans we must include extinct groups of animals such as the Glyptodonts (see: Glyptodonts Armadillos and Ken Ham’s Hyper-speciation Model) and giant sloths as well as additional relatives of the more familiar taxa alive today. This accounts for an additional 200+ species of Xenarthrans that have walked the face of the Earth. All of these lived only in the New World.
Where did all this diversity come from why are these amazing creatures restricted to the New World?
Xenarthrans: another failed test of the creationist post-flood dispersal and speciation model.
Here on Naturalis Historia I have written numerous times about the increasingly strong stance that literal six-day creationists have taken with respect to the recent and rapid diversification of life (eg. Ken Ham’s Darwinism: on the Origin of Species by Means of Hyper-Evolution). Their “Biblical” evolutionary model includes the special creation of “kinds” or types of ancestral animals which were endowed with the capacity to diversify into a multitude of species. Most of this diversification, or speciation, is said to have occurred after representatives of each “kind” of animal departed from Noah’s ark just 4350 years ago, although the word translated “kind” usually refers to species-level populations when used elsewhere in the Bible.
This rapid speciation proposal has become a widely accepted among literal six-day creationists. They seem to think that species can be created from a common ancestor via blink-of-an-eye naturalistic mechanisms. More and more I see followers of Young Earth Creationist (YEC) literature saying that a lion and panther coming from a common ancestor is no different than two breeds of domesticated dogs being derived from a wolf. This is a woefully uninformed view of genetics but one that AiG has been promoting with great vigor in recent years.
Setting the enormous genetic obstacles to this view aside for a moment, what can Xenarthrans tell us about the YEC hyper-evolution model?
Consider the fact that in addition to the restricted range of living Xenarthrans, no fossil species of a Xenarthran has ever been found outside the New World (South and North America) except a single location in Antarctica near the tip of South America.* Furthermore, the majority of xenarthrans—living and extinct—are found only in South America.
This raises several challenging—though by no means uncommon—questions for the young-earth paradigm:
- If there were armadillos before Noah’s Flood why are no fossils of them found anywhere except in South America?
- Where fossils do exist they are found only in “recent” rocks, thought by most YECs to have been formed after Noah’s Flood. In other words, there is NO record of Xenarthrans living before the Flood. Why, if they were part of the original “created kinds,” were none preserved in Noah’s Flood?
- If there is a single common ancestor of all of the Xenarthrans (>200 species) on Noah’s Ark, how did they make it all the way from the Middle East to South America without leaving any evidence of their existence on other continents? If more than one, why did all of them move to the same place?
- How did all of these living and extinct species of Xenarthrans diversify within a few hundred years just 4350 years ago? Nearly all the fossilized extinct species disappeared by the end of the last Ice Age (a few survived until as recently as the building of the pyramids). Most YECs believe there was just a single Ice Age that occurred no more than a few hundred years after Noah’s Flood. If this is true, Xenarthrans had to migrate all the way from the Middle East to South America, speciate into hundreds of species, including many massive ones (which tend to have longer generation times), and then most had to go extinct soon after being created, while still being populous enough to leave behind much evidence of their life and lifestyle.
What about the giant armadillos and giant sloths? Ken Ham loves to talk about how natural selection just sorts genetic information and always leads to a “loss of information.” This is why he doesn’t refer to speciation from a common ancestor as evolution but think of it as de-evolution. So where did these huge armadillos come from? To grow to such an enormous size, these animals must have had many specialized physiological and anatomical functions compared to their smaller relatives. Some sloths even adapted to foraging for food in the ocean. How does that constitute de-evolution?
We have addressed some of these questions before (Cacti Biogeography: A Prickly Problem for Young Life Creationism, An Armadillos Test Case of Post-Flood Dispersal Speed, Glytodonts Armadillos and Ken Ham’s Hyper-speciation Model) The same problems arise again and again each time we examine a new group of organisms.
First we need to examine what YECs think these animals are. Does the fact they all share many unique morphological traits mean that they are derived from a common ancestor? YECs can’t agree. There are a few that believe that all Xenarthrans may, in fact, be related by a single common ancestor. Dr. Kurt Wise, a paleontologist recently featured in the YEC film Is Genesis History has suggested (Wise, 2009) that the living and extinct Xenarthrans all are derived from a single pair of animals preserved on Noah’s Ark.
However, I expect the majority of YEC will take their cue from an article published by Answers in Genesis, Mammalian Ark Kinds, by Jean Lightner. Dr. Lightner proposed that the Xenarthrans are not evolved from a common ancestor but are rather the product of three independently created kinds, or baramins. These would be the armadillos, anteaters and sloths. The 200+ extinct species presumably all fall into one of these three “kinds.”
Both opinions about the ancestry of the Xenarthrans pose steep challenges to the YEC. If they are three unique ark kinds then the questions about how they all migrated only to South America, leaving no evidence of ancestry or migration behind, are intensified. In addition, either proposal leads to speculation that massive speciation has occurred in a very short period of time. Since more than 85% of the diversity of Xenarthrans is extinct and nearly all that extinct diversity disappeared before the last Ice Age (according to the YEC understanding of an Ice Age), YECs must account for both the formation of all that diversity (and population) and its extinction within the very narrow timeframe of 200 years or less.
Natural selection or supernatural hyper-evolution?
Either way, whether there were three ancestral pairs or a single ancestral Ark pair, this would require the evolution of some highly divergent traits. Taking just armadillos as an example, the 21 living species vary in tooth number, placentation type, construction of their keratinous armor shells and many physiological and behavioral traits. How could all of these traits—not to mention traits in fossil species of glyptodont armadillos such as the huge size, massive bony tails and bony armored shells (including a bony shell on their heads) which no living armadillo species displays—have evolved in just a few hundred years? Natural selection, though a powerful mechanism used by God for adapting organisms to their environment, has not been observed to have the capacity to make such fundamental changes in such a short period of time.
Ken Ham’s Darwinism or natural selection is not really Darwinism at all but an appeal to unobserved forces of change which he has clothed in what he calls observational science—the mechanisms of natural selection. But his “observational” science provides no support for his view of rapid evolution, since there are no observations of genetic change over generations at the rate required to produce the observed amount of species diversity from the proposed number of “kinds.” Molecular and fossil data suggest that it has taken as much as 30 million years just for the extinct glyptodonts to achieve their amazing size and features compared to their armadillo relatives. YECs have only a few hundred years available in their timeline to achieve the observed amount of genetic and morphological diversification. We do not observe natural selection acting at this pace. Natural selection does not provide an explanatory mechanism for the YEC view of species formation.
Even if it was possible that all the genetic information for making a 200+ separate species could be contained at one time in an ancestral pair of parents, natural selection as a mechanism for segregating that variation into defined species would take hundreds of thousands of generations to produce the complex combinations of genomes observed in species that we see today. Genetic sorting takes a lot of time. There is no observed mechanism for generating new species at the pace that creationists are proposing. The options left to them are supernatural intervention or hypothesizing that there is an entirely novel mechanism of species formation that scientists have yet to discover (though they continue to assert that “observational science” supports such claims).
The Ark Encounter, that “life-size” replica of Noah’s Ark, preaches to those that visit that natural selection acting on as-yet-unexplained super-charged genetic ancestors can produce hundreds of species in a short period of time, but this has never been observed nor is there any biblical evidence to support such an assertion. Rather than observational science, Ken Ham is relying on the unseen and hypothetical events. Ironically these events and actions are what he berates evolutionists for having faith in.
The biogeographic dilemma that YECs continue to struggle to resolve
Remember that all Xenarthrans, past and present, are restricted to the New World and most only to South America. Why? Is there anything about the YEC’s flood geology model that would led them to predict or expect to find animals displaying such a restrictive biogeographic distribution after dispersing from Noah’s Ark? If there is, I have yet to hear it. YECs have proposed various ad-hoc explanations for how some animals might have dispersed from the Ark to their current homes, but none of them are supported by evidence. For example, massive rafts of rotting flood debris have been proposed to explain how kangaroos may have hitched a ride across the ocean to populate Australia. Of course this is not predicted by Flood geology nor is it likely. It is just “possible.” It may be possible that is how they got to Australia but it doesn’t explain why no kangaroo (or any marsupial besides possums) remained in any other part of the world but hardly any placental animals were able to hitch a ride on plant debris rafts heading for Australia.
The distribution of Xenarthrans poses the same problems. We have also looked at how these problems are not restricted to animals but are also found when plant biogeographic patterns are observed (see: Cacti Biogeography: A Prickly Problem for Young Life Creationists, also The Lost World of South American Ungulates). As slow-moving, warm-temperature loving animals, why would any of them have chosen to migrate from the Middle East or the tropics of Africa and Asia—which has ideal habitat for many of these animals—all the way to South America. That trip would have taken them across the very cold Bering land bridge between Alaska and Russia or across the Atlantic by some unevidenced means such as the aforementioned vegetation mats. Not only that, but it would have had to have happened three times if armadillos, anteaters and sloths were on the ark or they would have had to travel together for no apparent reason.
Xenarthrans are an enigma to the young earth paradigm
- There is no evidence that any of them existed before the Flood (as YECs reckon it) and thus no evidence they existed in the “original” creation.
- There is no evidence that they originated in the Middle East and migrated to South America.
- There is no eyewitness testimony in the Bible of the existence of any Xenarthran.
- There is no eyewitness testimony or physical evidence that they speciated into many species in the space of a few hundred years.
- There is no viable scientific theory for how they could have evolved and multiplied so rapidly and so recently.
The alternative is fairly simple and does not require multiple ad-hoc hypotheses to provide only slightly plausible explanations. The biogeographic pattern is no surprise at all for those that accept the evidence that the earth is old and groups of organism developed on isolated continents over time.
* There is an Eocene fossil of a possible Xenarthran from Seymour Island in West Antarctica. This still fits with the western hemisphere distribution since in the early Eocene the tip of South America and this island were very close to each other before continental drift has pulled them to their present positions.
Wise, K. 2009. Mammal Kinds: How many where on the Ark? Center for Origins Research Issues in Creation No.5 pp. 129-162.
Cover image: Brown Throated 3-toe Sloth By Christian Mehlführer, User:Chmehl – Own work, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=4481336
Editing providing by LC