Rattlesnakes: a Post-Flood Diversification in the new world

A fascinating adaptation to the New World after the flood

Chad Arment (2021)

Rattlesnakes are among the most recognizable of snakes. Most species acquire the notable tail rattle that when shaken serves to warn off predators and traipsing hoofstock. There are 32+ species of Crotalus and Sistrurus, the former being the typical rattlesnakes while Sistrurus is comprised of a few pygmy rattlesnakes. New species continue to be described (and subspecies occasionally rise to species status). For a creationist, there are a number of fascinating aspects to rattlesnake biology, but here I’ll focus on the rattlesnake (and its rattle) within the context of post-Flood adaptation and novel trait development.

How do we know rattlesnakes are post-Flood?

There were no rattlesnakes as such before the Flood. (Perhaps there were snakes with rattles before the Flood, among the many species that didn’t leave a fossil trace, but they weren’t the same genera we have today.) There were no rattlesnakes on the Ark. Rattlesnakes are part of a larger group of pit vipers known as the crotalines. Besides the subfamily Crotalinae, the viper family includes the subfamilies Viperinae (the true pitless vipers) and the subfamily Azemiopinae (containing only the genus Azemiops).

Creationists recognize groupings known as kinds. A kind comprises an original created pair or group of organisms (from the Creation week), and all subsequent offspring. All modern-day representatives of a single kind are related to each other through descent from that original created pair or group. Each kind is unrelated to other kinds, though kinds may share some morphological traits. (Dogs and whales are in separate kinds, though they share mammalian traits.) Kinds don’t hybridize with other kinds. (There is some controversial discussion regarding certain ‘distant hybridization’ in fish and amphibians, but there is no detailed published research in the creationist literature as of yet.)

Baraminic studies focus on the technical research that attempts to define kinds (or baramin). Creationists recognize the holobaramin as comprising the entirety of the original created organisms and their descendants up to the present day (some of which we may as yet be unaware). A monobaramin is any group within a baramin that can be reliably considered as such, but may not include the entirety of the holobaramin.

There is evidence that the two rattlesnake genera Crotalus and Sistrurus have hybridized in the wild (Bailey 1942; Rokyta et al. 2015), so are recognized as being within the same kind. Hennigan (2005; 2020) suggested that the rattlesnake kind could be a holobaramin, principally on the unique nature of the rattle. However, hybridization between a timber rattlesnake (Crotalus) and a copperhead (Agkistrodon) in a zoological facility (Arment 2020a) shows that rattlesnakes are simply a monobaramin, not a holobaramin.

The family Viperidae as a whole could be a single holobaramin, or each of the recognized subfamilies could be separate holobaramin. Could a higher clade, the Colubroides, be a holobaramin? That seems a stretch, but this would be a good area for future statistical baraminological studies. Regardless of where the holobaramin is situated, CrotalusSistrurusAgkistrodon is certainly a monobaramin, which suggests that the Crotalinae as a whole is a monobaramin. (Further baraminological analysis should be made regarding the latter point, of course, but the genetic and morphological evidence points in this direction.)

Accordingly, only one pair (whether of crotalines or their ancestral viperids) would have been on the Ark. Within the twenty-two genera of crotalines in the Old and New Worlds, only Crotalus and Sistrurus have rattles. Paleontological evidence shows that fossil rattlesnakes are found in post-Flood deposits (Arment 2020b). So, it is highly improbable that the Ark pair were rattlesnakes. Instead, rattlesnakes are a post-Flood diversification within the crotaline monobaramin after it reached the New World.

From left to right, Agkistrodon, Sistrurus, and Crotalus
(Sketches for the U.S. Railway Surveys)

Why are they called ‘pit vipers’?

The Crotalinae are characterized by a deep pit between the eye and nostril on each side of the head. These loreal pits lead to infrared-sensitive organs that allow them to hunt warm-blooded prey at night. Could loreal pits be a defining character of the holobaramin? They are certainly highly-specialized organs, not shared by the rest of the Viperidae. An alternative would be that the loreal pits were part of the ‘hidden’ code within the genome of an ancestral viperid pair on the Ark that expressed itself in the Old World, paving the way for increased diversification within the kind. Bolivar-G et al. (2014) reported finding a unique accessory structure, papillae on the infrared receptor organ, in seven Neotropical pit viper genera, that aren’t found in other crotalines. This might point towards the organ’s genetic foundation being variable enough to have been a post-Flood genomic expression.

Loreal pits can be seen more prominently on the timber rattlesnake (above) than the copperhead (below).
​Both snakes photographed in northern Pennsylvania.

Entering the New World

The secular model, using molecular phylogenetics and the fossil record, argues that vipers evolved between the late Palaeocene and middle Eocene, and that crotalines invaded the New World somewhere near the Oligocene-Miocene boundary (Alencar et al., 2016). The earliest identifiable Crotalus comes from Late Arikareean (Early Miocene) deposits, Sistrurus from Clarendonian (Miocene) deposits, and Agkistrodon from Middle Hemphillian (Late Miocene) deposits (Holman 2000; Parmley and Holman 2007). Interpreting this for a creationist model, this simply means that the appearance of vipers in the fossil record occurs in post-Flood deposits. After departure from the Ark, whether viperid or crotaline, rapid diversification in the Old World preceded one lineage of crotalines making it to the New World.

Genetically, all New World crotalines are closer to each other than to Old World crotalines (Alencar et al., 2016; Wüster et al., 2008), which suggests that one primary cross-over event was responsible for the starting population in the New World. Interestingly, Crotalus—Sistrurus—Agkistrodon are closer together than to other New World crotalines. The molecular evidence suggests that a founding pit viper population ended up rafting on Flood debris from Asia to the New World (or possibly crossing on the Beringian Land Bridge), then continued to diverge and adapt in several directions: a) the Crotalus—Sistrurus—Agkistrodon group, b) the South American Lachesis (bushmaster) group, and c) the other South American pit vipers (Bothrops, etc.). The progression into South America would have occurred via the Isthmus of Panama.

I should note that the bulk of herpetological dispersion events from Asia to North America are theorized by mainstream biologists to have occurred via the Beringian Land Bridge (e.g., Burbrink and Lawson 2007; Guo et al. 2012). Guo et al. (2012) notes, regarding several migrations postulated from Asia to North America in the late Oligocene: “It thus appears that the natricines, along with the ratsnakes, crotalines, and Plestiodon skinks share similar areas of origin, routes, and times of dispersal, suggesting a more common mechanism is at play rather [than] random oceanic dispersal.” Of course, creationists aren’t positing random oceanic dispersal, but evolutionary models have nothing to compare to the massive, widescale, post-Flood debris rafts postulated by creationists to aid trans-oceanic dispersal of small organisms. (And, significantly, Holman (2000) notes that the earliest viperid fossils in North America are smaller than average.) This is an area that creation biologists need to examine more closely.

Crotalus rattle

Development of the Rattle

When we talk about the rattle, we’re not simply discussing the keratinous segments that buzz when shaken. The rattle organ system includes those segments, along with a modified terminal bone, scales, connective tissues, and specialized musculature. Meik and Schuett (2016) note that the segmented rattle grows as keratinized lobed rings accumulate and interlock, one each time the snake sheds its skin. Rattlesnakes are born with a pre-button on the end of their tail, lost with the first shed. The second segment, which is bi-lobed, becomes the button that starts the rattle chain. Osteologically, the rattlesnake’s skeletal tail ends in a bony club (called the style). This bony style serves as an attachment point for specialized tailshaker muscles (for sustained and faster rattling, far more so than is seen in other snakes that vibrate their tails). The style, scales, and connective tissues of this specialized organ, are collectively termed the matrix. With each shed, the lobes and prongs at the terminal end of the matrix create a mold that forms the next rattle segment. The new segment grows beneath, and is separate from, the tail’s outer body scales—segments are not simply part of the old skin. Segments are formed from a much more durable material than is found in the body scales. Between sheds, a separate process shifts the latest segment back so that it disengages from the matrix, allowing a new segment to form adjoining it (for interlocking) rather than nesting into it directly.

Reiserer and Schuett (2016) pointed out that, “As an integrative system, the rattle combines complex morphological . . ., physiological . . ., and behavioral . . . characteristics that appear highly unlikely to have evolved in a single evolutionary step. . . .” In other words they argue against a ‘hopeful monster’ approach to the appearance of the rattle organ system. They suggest that it “evolved in an Agkistrodon-like New World pitviper that very likely displayed . . . (a) defensive tail thrashing and vibration . . ., (b) presence of caudal luring with contrasting tail coloration . . ., (c) heavy reliance on ambush predation . . ., and (d) a broad diet with ectothermic prey, including invertebrates, important to neonates. . . .” This is foundational for their Caudal Luring Hypothesis to the origin of rattles. (There are other evolutionary proposals, but these authors do a good job of pointing out problems with theories that focus on the end-result, such as the aposematic display hypothesis, rather than the initial selective pressures on a pre-button or small-button snake.) Caudal luring is the movement of a tail to attract smaller prey. The Caudal Luring Hypothesis argues that “early evolution of the terminal scute of proto-rattlesnakes resulted from selection for tails that better mimicked a cephalized region of a moth or beetle larva.”

A mapping of Reiserer and Schuett’s (2016) hypothetical developmental process starts with selective pressures towards mimicry and shifts to selective pressures towards aposematism (exaptation being the term used for a trait used for one purpose that later shifts in function):

1. The precursor to the rattlesnake had a cone-shaped tail tip that could be used for caudal luring, as can be seen in modern juvenile Agkistrodon.

2. Selective pressures led to the development of an enlarged tail tip, so that the terminal vertebrae could enlarge and fuse, forming an enlarged matrix.

3. Selection for a constriction at the enlarged tail tip reconfigured the matrix into a more ‘larva’-like shape.

4. Development of interlocking rattle segments from a reconfigured matrix that allows segments to clasp. At the same time, a segment-shifting mechanism must be in place to allow production of a rattle-chain. Once a short rattle is produced, there would be selective pressure on (a) producing at least a low-volume sound, (b) sustained rattling, and (c) morphology of the style to boost muscle attachment.

5. Selection for increased sound, leading to growth of fully formed rattles. This is accompanied by a fully developed style and robust musculature.

6. Selective pressures lead to hyper-aposematism in body/rattle size, rattle coloration, and defensive behavior. This hyper-aposematism involves multi-modal signaling towards potential predators, including rattling, hissing, posture display, tail banding, and mock strikes.

Reiserer and Schuett (2016) suggest that this hyper-aposematism may be due to a behavioral strategy (prey luring) that can end up developing out-of-equilibrium within a natural system, producing a ‘spectacular morphology,’ that goes beyond simple adaptation. (See Enquist et al. (2002) for a discussion of this process.)

From a creationist perspective, this looks like a completely reasonable hypothesis with a few caveats. Obviously, biblical creationists work with a much shorter timeline. I think Jeanson’s (2017) approach works well for understanding rapid speciation, and there may be other creationist approaches worth considering. Selective pressures (resulting in differential trait selection) and adaptation certainly play a role in how organisms have changed since Creation (and the Flood) (Jeanson 2013), but they do so with a genetic framework that was designed to adapt. We don’t have to rely on random mutations to provide the necessary genetic resources.

This leads to obvious issues within this step-wise process where fundamental changes occur (e.g., the development of specialized musculature, or the development of the segment-shifting process that allows the segments to form an interlocking chain) that are far beyond what blind natural processes can create. This can’t be glossed over without an absurd amount of evolutionary bias.

The creation model offers a mechanism for such trait appearance, however. A designed genome offers a hidden reserve of genetic answers to environmental problems. (This appears to have particularly been the case in the period between the Flood and the Ice Age.) I think it is very possible that natural selective pressures set the stage for, or possibly triggered, more extreme morphological changes.

It is interesting to note that the only other venomous snake with a tail appendage is the Iranian spider-tailed viper (Pseudocerastes urarachnoides). This is a small desert viper with an enlarged bulb at the tip of its tail from which sprout numerous long scales that give it an ‘arachnid’-like appearance. The viper uses this appendage to lure in insectivorous birds (Bostanchi et al. 2006; del Marmol, Mozaffari, and Gállego 2016). It is the only species within its genus that has this appendage (Fathinia and Rastegar-Pouyani 2010), indicating that it is another post-Flood adaptation.

Timber rattlesnake with its rather lengthy rattle prominently raised, from Pennsylvania.

Is the loss of a rattle ‘evolution’?

Occasionally, creationists will see another aspect of rattlesnake biology promoted as ‘evolution in action.’ This is due to the reduction or loss of the physical rattles within certain (usually island) populations. In the Santa Catalina Island rattlesnakes (Crotalus catalinensis), the distal lobes of the matrix and the distal prongs on the style are both reduced, so newly-formed rattle segments cannot be retained and attached in a chain (Meik and Schuett 2016). Exactly why these rattlesnakes have lost their rattles is still being debated by biologists. It doesn’t appear to be a function of stealthier predation activity (Martins, Arnaud, and Murillo-Querro 2008), but other suggestions include lack of predators on the island (though they still vibrate their tails when harassed) or perhaps a genetic glitch that has not been selected against on the island (Arnaud and Martins 2019).

Whatever the reason, morphological or functional loss is well-recognized within creation models as a natural result of genetic entropy. That it hasn’t been selected against is no argument for Neo-Darwinian common universal descent.


Rattlesnakes are among the many organisms that deserve more attention by creation biologists who have the means to do both baraminological and organismal research. There are a number of intriguing aspects to their morphology, physiology, and behavior worth exploring. Several species are of conservation concern, also.

The rattle's development is a post-Flood adaptation that likely started out functionally as a prey lure, but through an as yet unrecognized genomic trigger emerged as a complex aposematic display system.


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