Tetrapod Zoology

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In the previous post we looked at the diversity of the rhinogradentians (aka rhinogrades or snouters) belonging to the so-called monorrhinan or uni-snouter division, and we also started to go through the asclerorrhinan or soft-nosed snouter division. Here, in the second post on this much-discussed and highly popular subject, we finish our tour of asclerorrhinans before going on to look at the last and most anatomically complex group, the polyrrhinans or multi-snouters. We finish by looking at the modern-day renaissance in rhinogradentian research: an endeavour which has resulting in the scarcely believable discovery of living relict species. Needless to say, the previous post is required reading before you tackle this one…

Conventionally regarded as the most recently evolved of the soft-nosed snouters were the snout leapers, and in the previous post we looked at the diverse arboreal and terrestrial members of this clade. Primitively quadrupedal, and with a jointed nasarium that functioned as a spring-action pseudo-limb, they also included the short-bodied true snout leapers or hopsorrhinids, a group where hindlimbs were absent.

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The best known and most studied snout leaper – and indeed one of the best known and most studied of all rhinogradentians – was the Earwing Otopteryx volitans [skeleton shown above: sketch of live animal shown in adjacent image]. While conventionally awarded its own ‘family’ it was more likely a derived hopsorrhinid as it certainly possessed all the derived peculiarities of this group. When terrestrial hopsorrhinids leapt, they were sometimes observed using their large ears to help steer their progression. This perhaps gives us a clue as to how the flight ability of Otopteryx evolved, as this remarkable rhinogradentian used its enormous wing-like ears to fly with. The enormous aural cartilages and their hypertrophied muscles – particularly the m. aeroplano-jugalauris – allowed Otopteryx to flap its ears in rapid, skillfull flight and it was even able to avoid avian predators on the archipelago (Stumpke 1967). Jurassic specimens of Otopteryx were reported from France in 1995 [see image below: from here] and are so similar to the Hi-yi-yi population that they were initially referred to the same species. This is possible of course but would be unprecedented for a mammal, and the possibility remains that the fossil should be named as a distinct taxon.

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Finally among the snout leapers, there were the specialised orchidiopsids or orchidsnouters. Indeed these rhinogradentians are so unusual that their classification among the snout leapers was initially not suspected. Entirely arboreal, they lacked hindlimbs and hence probably descended from hopsorrhinids (in fact, it is probably accurate to regard them as part of Hopsorrhinidae, rather than as a separate ‘family’), but unlike hopsorrhinids, they possessed a large, flattened rhinarium that resembled a leaf or petal. The large ears were also petal-like. Standing vertically on their powerful tail, and climbing slowly with their prehensile hands, they mimicked leaves and flowers and preyed on insects. At least one species, the Glowing lily snouter Liliopsis thaumatonasus, was bioluminescent: this apparently being due to symbiotic bacteria.

Polyrhiny – the condition in which the nasarium is divided into several or multiple snouts – was unique among rhinogradentians to the polyrrhinans, or multi-snouters. These are the most familiar of rhinogradentians, but they are also the most mysterious, as their origins remain obscure and they so differed from other rhinogradentians in so many details that they are generally thought to have diverged as early as the Cretaceous (Stumpke 1967). This has been validated by the discovery of hopsorrhinids in the Jurassic as just mentioned.

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Polyrrhinans were divided by Stumpke into the tetrarrhinidans (four-snouters), hexarrhinidans (six-snouters) and dolichoproatans (tasselsnouters). Tetrarrhinidans include the well-studied snout walkers or nasobemes and the amazing Predacious snouter Tyrannonasus imperator [in adjacent image, a Predacious snouter is attacking a Nasobema. Image originally from Stumpke 1967 but taken from reproduction here]. The frugivorous nasobemes were able to walk on their four long snouts thanks to an internal skeleton of corpora spongiosa and a hydraulic system that provided turgidity when needed. The tail of these animals was equally unusual: it was distally hollow and boneless and connected to the caecum. By forcing intestinal gas into the tail, nasobemes were able to shoot out the ribbon-like tail for a distance of up to 3 m (this in a rhinogradentian with a rhinarium and body length of about 1 m: they were among the largest members of the group). Tyrannonasus preyed upon nasobemes, capturing them following pursuit on-nose and killing them with a poisonous tail spike. Various characters of the digestive tract indicate that Tyrannonasus evolved from frugivorous species and it has even been proposed that its predatory lifestyle developed from an original habit of stealing fruit from nasobemes, this piracy developing over time into predation.

Among the most specialised rhinogradentians, the hexarrhinidans (six-snouters) include the ribbon snouters, six-flowered snouters and flower-faced snouters. Ribbon snouters (Eledonopsis) lived in burrows and were shrew-like, but for the ribbon-like snouts that extended along the ground, some distance (up to c. 30 cm) away from the burrow. A ciliated epithelium extended along the entire dorsal surface of each snout, and small insects that became stuck here were carried by the cilia toward the mouth. Six-flowered snouters (Hexanthus) presumably descended from Eledonopsis-like forms but, instead of long ribbons, their proboscides took the form of long tubes, each sprouting a flower-like tip that the animal would wind about the stems of adjacent plants. Flying insects, deceived by these flower-like structures, would settle on them and be caught, and then moved by peristalsis along the tubes.

An apparent deviation from the cryptic lifestyle of other hexarrhinidans was adopted by flower-faced snouters (Cephalanthus). Equipped with petal-like fleshy growths surrounding the mouth, the best known members of this group remained sessile as remarkable flower-mimics. While young Cephalanthus had a ‘normal’ mammalian tail, in adults it was a long, stiff structure rooted in the ground. After birth, a young Cephalanthus would climb to the top of a tall flower, bite off the flower head, and then take up life as a flower-mimic, an exudate from the mouth attracting flying insects. The sessile attraction of insects, aided by oral exudates, may not be unique to rhinogradentians among tetrapods, as it has been suggested that frogmouths may also employ this technique (Diamond 1985). As discussed in my previous article on flightless future bats, Cephalanthus is also strikingly similar to the sedentary Flooer Florifacies mirabila of the Batavian forests (Dixon 1981).

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While some of the polyrrhinans, such as the nasobemes and Predacious snouter, were quite large, they are dwarfed by the Bearlike shaggyfaced snouter Mamontops ursulus [shown in adjacent image], a herbivorous six-snouted species that attained a vertical height of 1.2 m in the males. Equipped with a thick woolly coat and short limbs that were well tucked-in to the pelage, it was a highland specialist that lived in small herds. Tasselsnouters, the dolichoproatans, were also large and possessed the most elaborate nasarial morphology of any rhinogradentian, with a ridiculous 18 snout pairs.

When Stumpke 1967 was published, rhinogradentians were regarded as unique to the Hi-yi-yi archipelago. As discussed earlier however, Jurassic fossils show that snout leapers – members of an apparently derived (and thus comparatively young) rhinogradentian clade – were formerly present in what is now continental Europe, suggesting that rhinogradentians were originally of very wide distribution. Several even more exciting recent discoveries have shown, amazingly, that relict rhinogradentians have survived to the present in various Old World locations. In 1999 a live rhinogradentian was discovered in Slovenia. Representing a new taxon, Acrorrhinos, it appears to be particularly archaic and closely related to Haeckel’s primitive snouter [image below from here: this site also provides an account of this taxon's discovery].

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In 2004, a new, extant colonial rhinogradentian was discovered (Kashkina 2004), and later in the same year it was realised that various hermit crab parasites were also highly modified, tiny parasitic rhinogradentians (Bukashkina 2004). As discussed in the previous post, it was remarkable enough that the tiny turbellarian-like allsnouters were originally mistaken for invertebrates but, as ridiculous as it sounds, we now know of two rhinogradentian lineages that diverged from the mammalian body plan to such an unprecedented degree. It’s well known that a parasitic or infaunal lifestyle can lead to an overall simplification in form and function, and these incredible tiny boneless mammals provide what might be the best example of this in the whole of zoology.

Given that very little rhinogradentian material exists in collections, many species are only known from field sketches. Several workers have attempted in recent years to reconstruct some of the species three-dimensionally: Japanese model-maker Takeshi Tokiwa has produced models of many species (viewable here), as has Michaela Fortuber of the Naturhistorisches Museum at Braunschweig, Germany. Naturally, rhinogradentians have made many apperances in the technical literature and their affinities and origins continue to be debated. It remains tragic that the vast majority of species are now extinct, especially when they were such unique, remarkable creatures.

I’d like to thank everyone who has supported my academic interest in rhinogradentians over the years (particularly Dr Vector), and to all my readers for being so patient in waiting for these articles to appear. Rhinogradentians have been mentioned here at Tetrapod Zoology for some considerable time now (check the archives) and, despite requests that I should keep making the promises but perpetually fail to publish the promised articles, I always planned to deliver. At last, my work is done.

Refs – -

Bukashkina, V. V. 2004. New parasitic species of colonial Rhinogradentia. Russian Journal of Marine Biology 30, 150.

Diamond, J. 1985. Filter-feeding on a grand scale. Nature 316, 679-680.

Dixon, D. 1981. After Man: A Zoology of the Future. Granada, London.

Kashkina, M. I. 2004. Dendronasus sp. – a new member of the order nose-walkers (Rhinogradentia). Biol. Morya 30 (2).

Stumpke, H. 1967. The Snouters: Form and Life of the Rhinogrades. The Natural History Press, Garden City, New York.

Comments

  1. #1 Kevin W. Parker
    April 1, 2007

    I’d be interested in any comments you might have regarding how mome raths* are related to the snouters. While they are clearly not themselves snouters, the similarity is striking.

    *Carroll, L. 1872. Through the Looking Glass, Macmillan, London.

  2. #2 sparc
    April 1, 2007

    Next year reproduction of Ascentus lateralis?

  3. #3 Jeb, FCD
    April 1, 2007

    This is one of the most elaborate April Fool’s jokes I’ve ever seen.

    Well done!

  4. #4 Jonathan Vos Post
    April 1, 2007

    The “Spinal Tap” of Zoology!

  5. #5 natural cynic
    April 1, 2007

    It should be noted that the greater tragedy that resulted from the destruction of the Hi-Iay archipelago was the release of one rather destructive specimen of Megamegamegalosaurus godzillae. Rare and historically accurate films have been made of that tragic event, but have been supressed by Japanese censors. Only the fictionalized versions have been released to the public.

  6. #6 David Marjanovi?
    April 1, 2007

    Great. Temnospondyls next! :o)

  7. #7 RM1(SS) (ret)
    April 2, 2007

    In 1999 a live rhinogradentian was discovered in Slovenia.

    Damn. I didn’t get to Slovenia until 2003….

  8. #8 Allen Hazen
    April 2, 2007

    Is it certain that the Rhinogradentia are a monophyletic group? Due to the sketchy nature of the available descriptions, it seems possible that their classification has been based on superficial resemblances. This can be hazardous, even when the animals display highly unusual morphologies: convergence is all over the place. Consider the American species Condylura cristata: if known only from a description and depiction similar to those in Stumke’s monograph, it might well be taken for a Rhinogradentian (perhaps a basal Tassel-snouter?). But Condylura is a well-attested member of a Boreoeutherrian clade, the crown group of the Eulipotyphla. And surely the monophyly of the Eulipotyphla is beyond all POSSIBLE… oh, never mind!

  9. #9 Mike
    April 2, 2007

    I hope you’ll keep us updated on future developments in our knowledge of the remarkable Rhinogradentians.

    It seems, though, that some of the less well-informed have seized on the coincidence of your posting this on April 1 and seem to think this is a joke, while the discovery of the diverse fauna (and flora) of the Hi-yi-yi Archipelago and their subsequent demise at man’s hand (or finger) is one of the triumphs and tragedies of 20th Century zoology.

  10. #10 Mickey Mortimer
    April 2, 2007

    What a cool skelet… wait a second… mammals don’t have ossified external ears! It’s a fake! ;)

  11. #11 Dr Vector
    April 2, 2007

    It seems, though, that some of the less well-informed have seized on the coincidence of your posting this on April 1 and seem to think this is a joke

    Agreed. I’d like to direct the doubters to Amazon, where reprints of Stumpke’s monograph are still available for as little as 7.21 USD. Don’t miss the chance to own this piece of zoological history!

  12. #12 Dr Beano Grosswanger
    April 2, 2007

    What a cool skelet… wait a second… mammals don’t have ossified external ears! It’s a fake! ;)

    Sigh, you obviously haven’t read Stumpke 1967, have you? Those are the auricular cartilages, a well known autapomorphy of Otopteryx. Read the technical literature before making such ill-informed comments, pleeeeeeeeeeease!

  13. #13 John H
    April 2, 2007

    Any level 23 ubergeeks may recollect that Tyrannonasus imperator has been published on in the fantasy as well as the scientific literature– at least I recall that the greatest roleplaying game ever, Runequest, had a “nasobeme” monster that had the latin name of T. imperator, and fit the description of said beastie. It was kinda wimpy.
    /ubergeek powers, deactivated… temporarily/

  14. #14 dinogami
    April 2, 2007

    I’d like to direct the doubters to Amazon, where reprints of Stumpke’s monograph are still available for as little as 7.21 USD.

    …or, if you’re willing to spend twice as much, there are lots of used copies out there in various conditions — check out the listing at abebooks.com, for example.

  15. #15 Joe Cain
    July 5, 2007

    Don’t forget the case of “Eoornis pterovelox gobiensis” by Augustus C. Fortheringham. Along the same lines, published in 1928. This is a parody of the AMNH’s Gobi expeditions. The authors used a car hood ornament as the subject. A facsimile of original edition is back in print from Euston Grove Press, at my request.

  16. #16 Johannnes
    November 26, 2008

    I just want to say thanks 4 the great pictures.
    I searched very long for some kind of real pictures (i just have the old book).

    greatings from germany.
    Ps.: sorry 4 the bad english i am just a puple in the 12th class.

  17. #17 Bolko
    December 17, 2010

    From the start it seemed somewhat fake. When I was reading it, I thought: are these things real aliens, or products of imagination?
    Seriously, are there any land sessile animals?

  18. #18 David Marjanović
    December 18, 2010

    It’s all completely made up. It’s a sort of long-standing inside joke that spans decades so far. It’s speculative zoology.

    And no, there aren’t any terrestrial sessile animals.

  19. #19 Allen Hazen
    December 18, 2010

    “All completely made up”? Next you’ll be revealing the secret handshake, David!

    So, how close to sessility do terrestrial animals come? There are lots of ambush predators, and some move around more than others. Nearest I can think off hand to a sessile land animal is the ant lion: larval form of some insect which, as I understand it, stays at the bottom of a hole with only its head exposed and eats ants that fall into the hole. Can someone do better?

    There is, of course, H. sapiens, var. couch-potato.

  20. #20 Cameron
    December 19, 2010

    And no, there aren’t any terrestrial sessile animals.

    Female scale insects.

  21. #21 Bolko
    December 19, 2010

    And captive reptiles, too.

    I have made up some quite interesting speculative stories.
    1. If, theoretically, sea turtles somehow escape extinction somewhere, or less probable, humans go extinct, there is the possibility of a future group of small, light-shelled sea turtles to evolve flight. They could fly using their front flippers and might replace some seabird species, at least in warm areas.
    2. Due to chemical pollution witch we cause constantly and the climate change, many, maybe all of the amphibian species will go extinct. Mudskippers could hypothetically re-evolve into tetrapods.
    3. Snakes might re-evolve fleshy appendages through the length of their bellies.
    4. Couldn’t terrestrial animals evolve sessility if they live in a environment of constant sprinkling of nutrient-rich water, such as in caves behind waterfalls?
    5. Something neither tetrapod, nor animal but witch will affect much the terrestrial landscape and ecosystem: If nearly most of the modern plants go extinct, the strange and fast evolving podostemaceae
    http://coo.fieldofscience.com/2010/07/simple-stream-life.html
    may replace them. Then, we will have no forests, but amorphous piles of thin branches and pseudo-leaves. However, this is very unlikely.
    These were my speculative thoughts.

    Finally, a question somewhat out of context. Does the abscence of ribs limit the size of terrestrial frogs?

  22. #22 Allen Hazen
    December 19, 2010

    Bolko–
    Re your final question, about what limits the size of terrestrial frogs (post 21):
    Back in 2008, Darren discussed a large Cretaceous frog (Beelzebufo):
    http://scienceblogs.com/tetrapodzoology/2008/03/tiny_pterosaurs_pacman_frogs.php

    THAT Tetrapodzoology post contains a link back to a 2006 (“version 1″) post that also discusses big frogs. In it, Darren suggests the hypothesis that what limits the size of frogs (there are fossils that may be somewhat bigger than the extant African Goliath frog, but not REALLY BIG frogs) is their dependence on cutaneous respiration. The ratio of surface area to body volume or body mass goes down as you get bigger, so if you depend on absorbing oxygen through your skin you are in trouble, even if your metabolic rate is as low as a frog’s, by the time you’re the size of a large dog.

    I don’t know if Darren would want to be committed to this hypothesis, but if you are interested in the question I’d recommend his old posts as a starting place.

  23. #23 David Marjanović
    December 20, 2010

    If, theoretically, sea turtles somehow escape extinction somewhere, or less probable, humans go extinct, there is the possibility of a future group of small, light-shelled sea turtles to evolve flight.

    Where would they take the necessary metabolism from?

    maybe all of the amphibian species will go extinct

    Highly unlikely. Keyword: cane toad.

    Mudskippers could hypothetically re-evolve into tetrapods.

    If they evolve a way to breathe air. Currently they don’t do that. They hold their breath.

    Snakes might re-evolve fleshy appendages through the length of their bellies.

    How? Their development genetics makes that… difficult at best.

    Couldn’t terrestrial animals evolve sessility if they live in a environment of constant sprinkling of nutrient-rich water, such as in caves behind waterfalls?

    Nutrient-rich waterfalls? Caves behind waterfalls that stay stable for millions of years instead of being eroded away in a few thousand? Then yes…

  24. #24 Bolko
    December 20, 2010

    Turtles could obtain energy by their food normally.

    When I say of appendages, I don’t mean true legs, but fleshy ventral protuberances witch will aid the snake to grip tightly to surfaces, soil etc.
    In wikipedia
    http://en.wikipedia.org/wiki/Mudskipper
    it says that mudskippers are wel adapted to land. They can respire by their mouth and cutaneously, and even when they become submerged, they maintain an air pocket in their burrow. On land they walk with their pectoral fins. Good neo-tetrapod ancestors.