PYTHONIDAE — The Pythons
“In my town, we [believe] that this particular specie of Snakes - Pythons (The big, long and black snakes) are our ancestors. They don’t attack us and we NEVER kill them. I remember one time when I was really young, we found one of those snakes ‘sunbathing’ right in the middle of our compound. While everyone of us ran for cover, my Granny gently walked up to the Snake and entered into a conversation with it. As if that was not enough, the Snake lazily crawled away after their ‘conversation’! When we asked her what she said, she claimed to have pleaded with it to go somewhere else[,] that we were all scared!” — a contemporary python myth from Nigeria, found on an internet discussion thread from 2010.
Papuan olive python (Apodora papuana) by Guido Mocafico © 2003. This species has the ability to change color, though how it does this and why are not completely understood.
My interest in pythons wasn’t borne of myth. More than likely, Mutual of Omaha’s “Wild Kingdom” 1960s television series, Tarzan movies and the St. Louis Zoo had something to do with it. No, there were no wild pythons roaming about in North America (err, back then I mean!), or even in Central and South America, or Europe for that matter (more about that shortly). So for many (of those so inclined) there was no choice but to rely on popular culture or zoos to get our fix of gorgeous python. One of the most memorable appearances by a python on the silver screen was in a fight with a tiger in Malaya (both survived) in the 1932 jungle adventure documentary classic “Bring ‘Em Back Alive”. However the absurd treatment of these marvelous creatures in the “Python” franchise at the turn of this century did nothing to inspire the wonder engendered in earlier works.
“Python” has its etymological roots in Greek mythology. Python was the dragon (depicted in art of the period as a serpent) guarding the “navel” or center of the earth at what was later to become the shrine of the Oracle at Delphi. In myth, the site Delphi had previously been called “Pythia”, the site where the god Apollo had slain Python.
Beautiful iridescence displayed by a southern white-lipped python (Leiopython hoserae) photographed near Muting, in southern Papua, Indonesia © Burhan Tjaturadi. Until recently this species (as well as four other species) was considered as a form of D’Albertisi’s water python (Leiopython albertisii).
In terms of evolutionary roots, snakes made their appearance on the vertebrate tree of life some 150 million years ago. See a simplified figure. This is guesswork because of the “delicate skeletal structure” of snakes does (did) not lend itself to fossilization. Initially snakes were small too, compounding the “unlikelihood” of surviving early fossils. And when fossils did survive that material was usually fragmented, mostly vertebrae which, and in such a state, are difficult to definitively ascribe to snakes over other close relatives. Pythons (Family Pythonidae) are one of the most primitive snake families and are more closely related to boas (Family Boidae) than any other extant family. Pythons are thought to have branched out about 100 million years ago (see previous figure link).
Pythons are most closely related to boas (Family Boidae). This Pacific boa (Candoia carinata) was photographed near Sarmi, in northern Papua, Indonesia © Burhan Tjaturadi.
There are two competing theories about the evolution of snakes, and they have jockeyed for prominence back and forth over the years, often in response to new fossil discoveries. One theory sees snakes evolving from a marine reptile lineage. This is based on morphological similarities to an extinct marine group, the mosasaurs. Similar skull structure, reduced or absent limbs, and other anatomical features found in both mosasaurs and snakes suggests a relationship. Snake adaptations such as fused, transparent eyelids and loss of external ears could be advantageous in an aquatic environment. But these same adaptations would also support a burrowing existence, in line with the alternative theory that snakes evolved from a terrestrial burrowing lizard. The fossil record shows that both terrestrial and aquatic snakes were in existence by about 95 million years ago thus leaving the question of which form evolved first unresolved at this point. So whilst it is not known if the ancestor that led to snakes was aquatic, terrestrial or burrowing, or some combination, it is agreed that snakes evolved from lizards. This is evidenced in pythons by their “spurs”, remnant hind legs that reflect evolutionary history: “pythons evolved from animals that walked”. Today, these spurs have evolved for use in mating.
Pythons are generally large, muscular snakes. In fact, Asia’s reticulated python (Broghammerus reticulatus, formerly Python reticulatus) is the world’s longest snake (the world’s heaviest snake is the related Boidae family species, the green anaconda (Eunectes murinus)). B. reticulatus can probably reach a maximum length of slightly more than 10 meters. In other places pythons also hold the longest or largest records in their region: the African rock python (Python sebae) is Africa’s largest snake; the Southern African python (Python natalensis) is southern Africa’s largest snake; and Australia’s longest snake is the scrub python (Morelia kinghorni).
Pythons possess solid teeth that curve backwards. This keeps the prey moving in the “right direction”. Most pythons have special infrared-sensitive organs called heat sensory or “labial” pits in the middle of scales along the jaw line which help them track prey. Only the black-headed python (Aspidites melanocephalus) and the Woma (Aspidites ramsayi) lack these. Boas have these pits too for the same reason, but they are positioned between scales. Pythons have a large number of mid-body scale rows, as well as the above-mentioned vestigial limbs or spurs. All python species are oviparous (lay eggs) and this is a major difference with boas, most of which give live birth; only 3 species of boa lay eggs. Pythons incubate their eggs, and are among the very few species of snakes which must do so. They “shiver”, i.e. use muscular contractions to generate heat while coiled around their clutches. This constant vigilance to maintain a steady temperature of the eggs takes a toll on the female which does not eat during nesting. She may lose half her body weight during the incubation period.
Pythons are ambush predators that kill their vertebrate prey by constriction which causes suffocation; the prey are not “crushed” to death. Due to general snake evolutionary adaptations of the jaws, and elongation of the trunk and organs, pythons can sometimes consume prey that is very large in relation to the snake itself. Click here and here. And while there are sensational reports of pythons, particularly reticulated pythons killing and swallowing humans, this must be extremely rare. Such events would have been somewhat more common when (if) hunter-gatherer cultures still existed. In 1976 a study of anecdotal python attacks among the Agta people of the Philippines found that “a traumatic python incident—leading either to a fatality or an injury—occurred every 2 to 3 years from the 1940s to the 1970s”. But the relationship was more complicated than that. The interviews revealed that the Agta also hunted pythons for food. Additionally the Agta and pythons were competitors for other prey species. (By the 1990s the hunter-gather culture of the Agta became extinct.) Other studies reveal that this hunter-hunted relationship can also be seen between species of primates and snakes.
Pythons have always been regarded and characterized as non-venomous snakes. Employing constriction as their method of killing prey helps reinforce this view. But curiously, from time to time venom detection kits in Australia have registered what have been considered “false positives” for envenomation of victims bitten by pythons. It turns out that pythons and boas (and iguanids, in the same study), do still produce “relic amounts” of venom (because in the evolutionary past they were probably potently venomous). An unforeseen consequence stemming from this evolutionary holdover is that the detection kits can be wasted on effectively non-venomous bites.
Pythons as a family inhabit a broad range of habitats from arid scrublands to rainforests and exhibit the full spectrum of niche usage and adaptations: terrestrial, arboreal and semi-aquatic.
The extant pythons count 40 species. (Less than a decade ago this was about 30 species, indicating increased taxonomic understanding today, let’s hope, and not too much taxonomic glory seeking…See Schleip WD, O’Shea M (2010) in the references). Pythons used to be present in Europe as recently as 23-5 million years ago. They are now found only in the warmer regions of the Old World. As mentioned previously, they’re not found in the New World. There are eight genera (number of species in parentheses): Antaresia (4), Apodora (1), Aspidites (2), Bothrochilus (1), Leiopython (6), Liasis (3), Morelia (11), Python (10). A large majority–more than two-thirds of species–are found in the “Australo-Papuan” region. Indonesia, sprawling across at least four faunal zones has the most pythons of any nation at 18 species. Australia has 14 species and Papua New Guinea, 12. Meanwhile the island of New Guinea proper hosts 11 species of python, more if satellites are included. Asia (South, Southeast and China) follows as the region with the next most python species, and the African region has the fewest number of species (4).
A green tree python (Morelia viridis) from Australia in a tree, spotted by ScottHarte. This species shares a remarkable amount of similarities to its distant Neotropical cousin, the emerald tree boa (Corallus caninus) due to convergent evolution.
Pythons are actively exploited for specialist leather products like belts and boots, wallets and watchbands. At a local level the skin operations can be shockingly inhumane. At the national level, theoretically trade in pythons (skins and live animals) by the major exporting countries is controlled under the CITES treaty, but this is heavily dependent on an honor system, for example in regard to setting and administering annual export quotas which are mostly effected by the countries themselves. All pythons fall under Appendix II of the treaty (except Python molurus, Appendix I, no trade allowed) which means species that are “not necessarily threatened with extinction, but in which trade must be controlled in order to avoid utilization incompatible with their survival”, can be traded. Most pythons in trade come out of Southeast Asia (Indonesia and Malaysia… and Viet Nam) but West Africa is also a significant contributor. Species in trade with the recent highest CITES export quotas are, in descending order, Broghammerus (Python) reticulatus, P. breitensteini, P. regius and P. brongersmai. Of the 40 python species only 12 have been assessed for the IUCN Red List of Threatened Species. Four species fall into some (elevated) threat category: Aspidites ramsayi (Endangered), Python bivittatus (Vulnerable; ironic given the invasive species problem), P. kyaiktiyo (Vulnerable; not surprising given its tiny range) and P. molurus (Near Threatened).
Pythons, as their prominent place in the global pet trade indicates, capture the imagination of many people. See what some python owners have to say about their passion. But often passion can prove ephemeral for some. And this has contributed to a massive problem of an invasive takeover of the Florida Everglades by the Burmese python (Python bivittatus) and other pythons and boas. A large amount of these snakes have been dumped there, presumably because they grew too big for the passion of the owner to handle them. And then they started breeding…After an initial lag, at least one researcher noted a shocking decline in observations of mammals in the areas since the 1990s. He noted the following decreases in observations (percentage decrease in parentheses): raccoons (99.3), possums (98.9), white-tailed deer (94), bobcats (87.5). He blames these alien serpents. Read about this here. Now of course correlation doesn’t have to be causation, but there is no doubt that these foreign invaders are having a detrimental effect on the ecology of the region. For one thing this apex predator role already had an occupant, the American alligator (Alligator missssippiensis). “No one knows precisely how many pythons inhabit South Florida, but reliable estimates run to 30,000 or more”.
So as Project Noah enters in celebration of Snake Week, I end this post with this ironic cautionary tale of Eat Prey and Love, of the marvelous pythons!
References and Further Reading
American Museum of Natural History “A World of Snakes – Burmese Python”
Sequencing the genome of the Burmese python (Python molurus bivittatus) as a model for studying extreme adaptations in snakes.
Schleip WD, O’Shea M (2010) Annotated checklist of the recent and extinct pythons (Serpentes, Pythonidae), with notes on nomenclature, taxonomy, and distribution. ZooKeys 66 : 29 – 79 . doi: 10.3897/zookeys.66.683 [On-line]
May 20, 2013