09 gennaio 2012

Amphicoelias fragillimus è un Rebbachisauridae?

Amphicoelias fragillimus è uno dei dinosauri più enigmatici e controversi della storia.
Questo taxon, basato su un singolo arco neurale di una dorsale di un enorme sauropode (Cope 1878) andato perduto, viene citato sovente come il potenziale dinosauro massimo. Io stesso non ho resistito in passato a tentare di stimare le dimensioni di questo sauropode, che secondo Carpenter (2006) avrebbe potuto raggiungere quasi 60 metri di lunghezza. 
Sia la mia che quella di Carpenter, che altre, stime sulle dimensioni del fantomatico gigantesco animale partono dall'assunzione di base che esso sia un Diplodocidae. Tuttavia, tale assunzione deve essere dimostrata su basi filogenetiche e non solo meramente su somiglianze la cui polaritù nell'albero dei sauropodi non è chiarita.
In breve, è necessario immettere A. fragillimus in una filogenesi per poter dire che è un diplodocide (e di conseguenza dire che è un super-diplodocide).
La mia affermazione non è peregrina: già Cope e Mook (1921), gli ultimi a menzionare la vertebra del supergigante ed i primi a notare che essa fosse scomparsa dalle collezioni di Cope, notarono che le caratteristiche dell'arco di A. fragillimus erano differenti dalla specie-tipo di Amphicoelias, A. altus (di dimensioni "normali" per un diplodocide). Tali differenze potrebbero essere ben più significative di una mera differenziazione di specie dentro lo stesso genere? 
Per tentare di dare una risposta, ho immesso quel poco che si sa di A. fragillimus nell'analisi filogenetica dei diplodocoidi di Withlock (2011).
Il risultato, data la frammentarietà di A. fragillimus, è poco risoluto. L'animale risulta sì un diplodocoide, ma in un'ampia politomia che comprende Haplocanthosaurus, Amphicoelias altus ed i rebbachisauridi basali. Notare che A. fragillimus non risulta in Diplodocoidae (idem Amphicoelias altus già dall'analisi originale)! Quindi, usare Diplodocus come base per le stime di A. fragillimus perde di giustificazione, e varrebbe né più né meno che Nigersaurus. Il fatto che anche A. altus sia in questa politomia indica che per ora non si può scartare l'ipotesi che A. fragillimus sia effettivamente un Amphicoelias. Tuttavia, tale ipotesi, come mostra l'albero, non è l'unica possibile per spiegare la morfologia del misteriorso sauropode. In particolare è molto interessante il fatto che tra le altrernative ugualmente parsimoniose, ci sia un possibile status da Rebbachisauridae basale. In effetti, A. fragillimus ed i Rebbachisauridae condividono un grado estremo di laminazione dell'arco neurale. Possibile, quindi che A. fragillimus non fosse un grande diplodocide, bensì un grande rebbachisauride?
Ammettiamo per un attimo che ciò sia corretto, ciò potrebbe spiegare una delle caratteristiche più strane dei rebbachisauridi, proprio la loro marcata laminazione vertebrale. In generale, il grado di laminazione aumenta con l'aumento delle dimensioni del sauropode (ed infatti A. fragillimus prende il suo nome "fragilissimo" dal grado estremo di laminazione coerenti con le sue grandi dimensioni). I rebbachisauridi violano questa "legge" dato che hanno dimensioni medio-piccole per essere sauropodi. Quindi, ci si è domandati quale meccanismo alternativo all'aumento delle dimensioni generò le ampie laminazioni dei Rebbachisauridae. Tuttavia, se i rebbachisauridi discendenssero da sauropodi giganti, le loro laminazioni sarebbero solamente un'eredità dei loro antenati giganti, un carattere evolutosi durante la fase di gigantismo e poi conservato quando divennero "nani".

Ovviamente, questo post è solo una provocazione. A. fragillimus è un enigma anche solo per stabilire se sia davvero esistito e quali dimensioni abbia avuto. Tuttavia, se non fu un diplodocidae ma una forma più basale, forse sarà necessario rivedere al ribasso le sue enormi stime.

Bibliografia:

Carpenter, 2006. Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus Cope, 1878. In Foster, J.R. and Lucas, S. G., eds., Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36.
Cope, E.D., 1878. A new species of Amphicoelias: American Naturalist, v.12, p. 563-565.
Osborn, H.F. and Mook, C. C., 1921. Camarasaurus, Amphicoelias and other sauropods of Cope: Memoirs of the American Museum of Natural History NS, v. 3 (3), p. 249-387.
 Whitlock, J. (2011). A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). Zoological Journal of the Linnean Society 161: 872–915.

22 commenti:

  1. Tu cosa ne pensi riguardo alle ipotetiche dimensioni di certi sauropodi colossali (come appunto Amphicoelias, ma anche Bruhathkayosaurus e Seismosaurus)? Voglio dire, pensi sia possibile che avessero dimensioni così monumentali (40-60 metri per 100 e più tonnellate) oppure pensi che possano essere in qualche modo esagerate?
    Grazie in anticipo
    Simone

    RispondiElimina
  2. Le dimensioni da ossa singole sono sempre degli azzardi. Recentemente, "Seismosaurus" è stato ridimensionato a 33 metri. I pesi poi spesso sono eccessivi perché ci si dimentica che i sauropodi avevano i sacchi aerei e quindi erano relativamente "vuoti" e quindi più leggeri di quanto si pensi.

    RispondiElimina
  3. Concordo. Bisogna tener presente però che le dimensioni comunque sono stimate sulla base di uno standard (_Diplodocus_) usato in generale per tutti i diplodocoidi, in particolari per quelli di dubbia posizione, come in questo caso.
    Già il blog SVPOW comunque considerava le dimensioni di Carpenter scorrette e sopravvalutate già partendo dal fatto che la ricostruzione delle dimensioni totali della vertebra (basandosi sul disegno di cope) erano state sovrastimate. Quindi credo che, anche a fini scientifici, il problema delle dimensioni sia secondario.

    Nel caso fosse un Rebbachisauridae, bisognerebbe però chiedersi come mai è l'unico di questo clade ad essere del Giurasssico e ad essere del Nordamerica. Cose credo non di poco conto.

    Credo che, al momento, ogni analisi sia insufficiente per mancanza di dati, e che quindi ogni posizione sia talmente poco robusta da doversi astenere dal trarre conclusioni.

    Marco Castiello

    RispondiElimina
  4. Interesting! I struggled to make my way through Goodgle's lumpen translation, but what you're saying seems sound. If you were to want to translate and re-post it, we would certainly link from SV-POW!.

    RispondiElimina
  5. Mike, I can give a short version:
    A. fragillimus is often assumed to be a diplodocid, but based on what we know of it, entering in Whitlock (2011) analysis it turns out as a non-flagellicaudatan diplodocoid.
    Given that among the alternative placements of A.fragillimus there is as a basal rebbachisaurid, and given that A.fragillimus shares extensive lamination of the neural arch with rebbachisaurids, I speculated (as a mere hypothesis) that rebbachisaurids are dwarf descendant of a giant highly laminated sauropod like A. fragillimus. Extensive lamination of rebbachisaurids, under that hypothesis, would be a feature inherited from their giant ancestors.

    RispondiElimina
  6. Scusa la domanda OT, ma volevo chiederti se sono mai state trovate evidenze di piumaggio negli ornithomimosauri. Grazie in anticipo
    Simone

    RispondiElimina
    Risposte
    1. Finora non è stato pubblicato nulla.

      Elimina
  7. Non so se l'hai già visto, ma credo potrebbe essere utile nella tua indagine riguardo alla struttura delle lamine.

    Alejandro Haluza, Juan I. Canale, Alejandro Otero, Leandro M. Pérez &
    Carlos A. Scanferla (2012)
    Changes in vertebral laminae across the cervicodorsal transition of a
    well-preserved rebbachisaurid (Dinosauria, Sauropoda) from the
    Cenomanian of Patagonia, Argentina.
    Journal of Vertebrate Paleontology 32 (1) 219-224.
    DOI:10.1080/02724634.2012.620674

    RispondiElimina
  8. Fragillimus3353/2/13 20:45

    In his paper Carpenter says he simply scaled up Diplodocus c.’s vertebra to 2.7 meters. The only problem is that he used the dimensions from Seismosaurus for diplodocus’s vert, but said the length of Diplodocus was only 26.25 meters. This small mistake of recording diplodocus’s vert as 1.22 meters instead of .946 meters has lead to the widespread belief that Amphicoelias was 60 meters long and 120 tons in weight. In reality using carpenter’s method with the correct numbers we get, 2.7/.946=2.864. 2.854×26.25 meters=75 meters long. Also 2.856^3=23.2. 23.2×12 tons=278 tons.

    A quote from Zach Armstrong on the subject. (note, he uses a 11.5 ton Diplodocus)

    I’m not sure where Carpenter got his mass and length estimates–since he says he basically says he just scaled it up isometrically. A 2.7 meter tall vertebra is 2.79 (270 cm/96.6 cm=2.79)times as tall as the D10 in D. carnegii which means a length of 69.75 meters if D. carnegii was 25 meters long or 73.23 meters if it was 26.25 meters like Carpenter assumes. A resulting mass estimate should then be 247.38 tonnes (2.79^3=21.7; 21.7*11.4 tonnes=247.38 tonnes)!

    And this is assuming it was the 10th dorsal! What if it was the 9th? Scaling the vertebrae, we get 270/94.6=2.85; 2.85^3=23.14; 23.14*11.4
    tonnes=263.79 tonnes!

    Adding intravetebral cartilage, which accounts for ~10% of the body lengths of most birds and reptiles, increases the dimensions even more.

    These estimates are backed by scientific methods, and are the best way we have of guessing Amphicoelias’s dimensions.

    Spread the word!

    Measurement for Diplodocus’s vert is from: Osborn, H.F., and Mook, C. C. (1921). “Camarasaurus, Amphicoelias and other sauropods of Cope.”

    RispondiElimina
  9. "These estimates are backed by scientific methods, and are the best way we have of guessing Amphicoelias’s dimensions."
    False. The best way would be using a regression curve derived from a large sample of measurements, and not just a linear proportion.
    Thus, the exact size of A. fragillimus (assuming its vertebra was truly that big) remains unknown.

    RispondiElimina
  10. Fragillimus33510/2/13 13:35

    Dude it’s actually a simple mistake, just read the paper. And the guys at SV-POW have talked about the problem in the comments for the post about Amphicoelias. Paleontologists are not immune from mistakes, and guys behind laptops are not incapable of correcting them.

    The sizes are not fully improbable! They are the most accurate estimate we have, are you paying attention? Every professional that has worked on Amphicoelias has agreed it’s basically a scaled up diplodocus, so Amphicoelias was most likely ~2.85 times as long as a 26.25 meter diplodocus.

    RispondiElimina
    Risposte
    1. In absence of a real specimen, all about A. fragillimus is merely a series of speculative opinions: nobody can falsify Cope's publication, so A. fragillimus is currently beyond science.
      Pending new bones, I don't care much about discussing again about it.

      Elimina
  11. Fragillimus33510/2/13 16:26

    Sadly, I am not able to chat with a professional Paleontologist. But the fact is, I don't need to, the problem is as simple as a typo, just fix it and move on. Please read the paper yourself, and come to your conclusion

    RispondiElimina
    Risposte
    1. My conclusion is what I wrote above: a single page written in the XIX century does not represent a robust evidence for the existence a super-giant sauropod. As a paleontologist, I need more robust evidence. I'm not saying "it never existed", just: I need more evidence, and in absence of more evidence, I'm not interested in discussing more on this (boring) topic.

      Elimina
  12. Fragillimus33510/2/13 16:34

    Sadly, I am not able to chat with a professional Paleontologist. But the fact is, I don't need to, the problem is as simple as a typo, just fix it and move on. Please read the paper yourself, and come to your conclusion. Here's my new scale, with an 85 meter Amphicoelias.

    RispondiElimina
  13. brolyeuphyfusion10/2/13 16:56

    First, we must fill in missing info and estimate the length of Amphicoelias altus.

    If we were to scale up using Diplodocus, we would get:
    ~28.5 meters based on femur length, and,
    ~25.4 meters based on LTV height.

    If we were to scale up based on Barosaurus, we would get:
    33.04 meters based on femur length, and,
    ~27.36 meters based on LTV height.


    Amphicoelias fragillimus vertebra has been estimate to be 2.7 meters tall. Also, Greg Paul estimated it to be 2.4-2.6 meters tall.

    To be as unbiased as possible, all three measurements will be used. That vertebra has been thought to be the last to second to last trunk vertebra.

    We will assume it to be the last trunk vertebra for now.

    Since the last trunk vertebra height of A. altus is 1.075 meters, A. fragillimus would have dimensions ~2.512 times that of A. altus based on a 2.7-meter LTV height, ~2.42 times based on 2.6-meter LTV height, and ~2.23 times based on 2.4-meter LTV height.

    So we have come to estimate the size of Amphicoelias fragillimus:

    First, the Diplodocus-based estimates:

    Based on the ~28.5-meter length for A. altus, which was based on femur length and scaled from Diplodocus, we get:
    71.592 meters based on a LTV height of 2.7 meters for A. fragillimus,
    68.97 meters based on a LTV height of 2.6 meters, and,
    63.555 meters based on a LTV height of 2.4 meters.

    Based on the ~25.4-meter length for A. altus, which was based on last trunk vertebra height and scaled from Diplodocus, we get:
    63.8048 meters based on a LTV height of 2.7 meters for A. fragillimus,
    61.468 meters based on a LTV height of 2.6 meters, and,
    56.642 meters based on a LTV height of 2.4 meters.


    Now, for the Barosaurus-based estimates:

    Based on the 33.04-meter length for A. altus, which was based on femur length and scaled from Barosaurus, we get:
    82.99648 meters based on a LTV height of 2.7 meters for A. fragillimus,
    79.9568 meters based on a LTV height of 2.6 meters, and,
    73.6792 meters based on a LTV height of 2.4 meters.

    Based on the ~27.36-meter length for A. altus, which was based on last trunk vertebra height and scaled from Barosaurus, we get:
    68.72832 meters based on a LTV height of 2.7 meters for A. fragillimus,
    66.2112 meters based on a LTV height of 2.6 meters, and,
    61.0128 meters based on a LTV height of 2.4 meters.

    Now, the real issue is which vertebra height is most likely, for that, we must see the quote by Zach:

    http://svpow.com/2010/02/19/how-big-was-amphicoelias-fragillimus-i-mean-really/#comment-10857

    It is the last paragraph.

    So it seems that the 2.7-meter figure for the LTV height, and thus the higher estimates, are more likely.

    The mass will be estimated later.

    RispondiElimina
  14. Fragillimus33510/2/13 17:04

    Thanks, and as Amphicoelias a. goes, its femur was measured at 1.77 meters, and supposedly had a total length of ~30 meters. According to Greg Paul. Running the numbers for Amphicoelias again, I seem to be getting numbers clustering in the 75-85 meter range. This is with an isometrically longer neck, but no additional intervertabral cartilage. Weights of 350 tons seem fully possible.

    RispondiElimina
  15. brolyeuphyfusion10/2/13 17:35

    First, estimate the size of A. altus...

    Amphicoelias altus has a 1.77-meter long femur, thus:

    Based on CMNH10380, it would be about ~16.174 meters long with a mass of ~13.22 tonnes.

    Based on CM572, it would be about ~16.88 meters long with a mass of ~13.93 tonnes.

    Amphicoelias altus has a last trunk vertebra height of 1.075 m, and Amphicoelias fragillimus about 2.7 m, so based on the CMNH10380-based estimate, it would be about:
    ~40.62 meters long, and ~209.46 tonnes in mass

    Based on the CM572-based estimate, the size would be:
    ~42.4 meters long, with a mass of ~220.71 tonnes

    RispondiElimina
  16. brolyeuphyfusion12/2/13 18:25

    This is why we need an Amphicoelias altus skeletal…it’s not just like a Diplodocus otherwise they would have been synonymized already…

    Actually I am just being open-minded towards the possibility of sauropods being larger than the blue whale.

    The fact that you called them “bullshits” instead of speculations proves that you’re a bit close-minded.

    They are based off of simple scaling.

    The upper limit for terrestrial animals is suggested to lie between 105 and 106 kilograms, or between 100 and 1000 tonnes…
    http://www.miketaylor.org.uk/dino/hokkanen/Size-Hokkanen.html

    RispondiElimina
  17. "Bullshits" is a word used only by you.
    Re-read my words, and please, stop such childish speculations in this blog.
    If you want to believe in super-giant sauropods based on nothing more than a problematic publication, it's your freedom. I don't care if you consider my conservative approach as "narrow-minded". You must provide more EVIDENCE of such animal, since this is how science works.

    RispondiElimina
  18. brolyeuphyfusion12/2/13 19:19

    This has nothing to do with this topic...

    The possibility is still open though, as the discovered fossil record is puny compared to those that are undiscovered.

    Not really, it's because if it had Brachytrachelopan's wimpy neck, it's feeding area would not be enough to sustain a massive body...

    If Amphicoelias fragillimus was a gigantic ~30-meter Brachytrachelopan, then it would have a mass of approximately 185.19-370.37 tonnes*...a wimpy Brachytrachelopan-type neck isn't going to sustain it...

    *I scaled from a 9-meter, 5-10 tonne Brachytrachelopan, from this: http://scienceray.com/biology/brachytrachelopan-the-short-necked-sauropod/

    That would make a 30-meter Brachytrachelopan about ~111 tonnes, but Brachytrachelopan isn't really that much related to Amphicoelias, so that still does not speak of it's size.

    That would make Amphicoelias fragillimus about ~81.14 meters long with a mass of ~364.72 tonnes...

    But I was looking for femur lengths for basal diplodocoideans, not flagellicaudatans, so I can make estimates to satisfy both sided.

    RispondiElimina
  19. Avrei un paio di domande:
    1. Se la posizione in Rebbacchisauridae venisse confermata, le stime dimensionali di Amphicoelias diminuirebbero? (mi ricordo di aver letto da più di una fonte che le neurospine di Rebbacchisauridae sono proporzionalmente più lunghe di quelle di Diplodocidae).
    2. Quali caratteri sostengono Suuwassea in Dicraeosauridae in questo cladogramma?

    RispondiElimina

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