Dinosauria ├─Ornithischia └─┬─Theropoda │ └─Sauropodomorpha ├─Prosauropoda └─Sauropoda ├─Cetiosauridae └─Neosauropoda ├─Diplodocomorpha │ ├─Rebbachisauridae │ └─Diplodocidae └─Macronaria ├─Brachiosauridae └─Somphospondylii ├─Chubutisaurus ├─Aegyptosaurus ├─Paralititan ├─Venenosaurus ├─Euhelopodidae └─Titanosauria ├─Andesaurus ├─Argentinasaurus └─Titanosauridae ├─Nemegtosauridae └─Saltasaurinae
What can we say about the largest animals ever to walk the Earth? It seems almost disrespectful to devote the essay to technical trivia about anatomy or cladistics. It would be trite to list their statistics, as if they were football players or potential investments. All of this is important, but the truth is that we really don't understand much about what it means. These are creatures who may have pushed the possible limits of the tetrapod design -- whose mass might exceeded ours in the same proportion that we outmass a hamster. Hamsters on the order of 100 kg are somewhat thin on the ground. We cannot simply scale up animals by three orders of magnitude and expect them to work.  It may be worth reviewing some of the problems involved, since these are precisely the critical issues of sauropod biology.
One of the chief problems is simply breathing. The trachea is very long, and presumably as wide as it can be to minimize turbulence and frictional resistance to air flow against the walls of the trachea. This means that the trachea itself represents a rather large volume of "dead space." Significant gas exchange cannot occur in this volume for two reasons. First, this space is filled with deoxygenated air from the animal's last exhalation. Second, the surface area per unit volume of air is low, so that physiologically significant gas exchange cannot occur. Sucking this deoxygenated air back into the lungs on inhalation reduces the oxygen available for absorbtion. Yet, because of the length of the neck, the total lung volume may not be much bigger than the dead space. How can we get fresh air into the lungs without creating huge and impractical lungs? How do we pump that much air through the trachea in the first place? As Paladino et al. (1997: 498-98) state, "The allometrically predicted tidal volume [the volume of air in a breath] for an Apatosaurus ... would only be about 19 liters ... . This amount would be totally insufficient and would not even move enough air to replace the dead space volumes ... ." Giraffes have a similar problem. See Re: How do girraffes breathe?? However, unlike a giraffe, a sauropod has no diaphragm. Breathing in reptiles is generally accomplished either by sloshing the liver back and forth to force air in and out of the lung, or by squeezing the ribs to accomplish the same result. I am told by Usually Reliable Sources that sauropods probably lacked the equipment to do either of these things well.
Second, assuming that the sauropods had engineered around this problem, how did they deliver the oxygenated blood to the brain? The act of raising the head would very likely cause a catastrophic loss of blood pressure to the brain. Worse, pumping blood against gravity to the brain would require very considerable pressure. Not only does this demand a massive heart, but the pressure would be high enough to cause serious loss of fluid across permeable capillary beds, especially in the lungs. Reid (1997).
Third, how did they move around? The traditional view of sauropods was that they were barely able to sustain their own weight and therefore lived in swamps. Bakker 1986) and others pointed out that this was very unlikely for any number of reasons. Not the least of these was that sauropods were heavy, with relatively small feet for their size. Accordingly, they would have stuck fast in a swamp. Bakker argues that, in fact, sauropods probably avoided marshy areas as much as possible. The reasoning seems impeccable. Unfortunately, sauropods keep turning up in places whch appear suspiciously swamp-like. Generally, the paleoecology of fossil sites is vague enough that the precise context is unclear. Recently, however, Smith et al. (2001) dug up one of the largest sauropods of all, Paralititan, from what they carefully determined were the fine-grained sediments of a very low energy tidal flat facies covered with mangroves -- in other words, a mangrove swamp.  As anyone who has spent significant time in mangrove swamps can attest, it is rather easy for human beings to get mired in this environment, much less an 80 ton Paralititan. Yet, the animal seems to have walked out there on its own. Perhaps this was simply a mistake which caused its death. The senior author of the paper seems to think otherwise. Re: Paralititan (mangrove swamps).
Finally, how did titanosaurs protect themselves from predation? As much as we like to imagine sauropods stamping their feet and lashing their tails to drive off the vicious theropod predators, the scenario is unlikely for a simple reason. The conduction velocity of ordinary motor neurons, even in mammals, is on the order of 20 m/sec. By the time a 30m titanosaur perceived the threat, determined its probable intentions, and began to lash out in the proper direction, 2-3 seconds might have passed. Although few predators would want to take on a rampaging sauropod, however uncoordinated, it is difficult to see how this would discourage an agile predator from taking a quick snack and departing -- leaving the trampling titanosaur to its tantrum.
This is by no means an exhaustive list of sauropod problems. However, it is not necessary to rely on gravitational anomalies or similar nonsense to resolve these particular issues. In fact, they may all have have been handled with a single adaptation -- the generous application of air sacs. The presence of numerous pleurocoels in sauropod bones is well documented and uncontroversial. Large, avian-style respiratory air sacs are speculative, but entirely reasonable. At least, they are frequently invoked. In addition, a third type of air sac is known from a group of modern dinosaurs, the Anhimidae or Screamers. These rather weird, primitive South American birds are ducks of a sort. In addition to other odd characteristics, the anhimids have a layer of air-filled tissue between the skin and the body wall -- something like the plastic bubble wrap used to ship glassware.
We may imagine a large sauropod with all three types of pneumatization. If respiratory air sacs were present, the respiration problem is solvable because the animal could adopt one-way breathing as in birds. Birds do not take air directly into their lungs. Rather, fresh air is shunted off to the air sacs, then fed into the lung from the back as the stale air exits via the trachea. The dead space issue evaporates because air flow is only one way. The blood pressure problem remains significant, but could at least be simplified by a system of pneumatic locks preventing rapid changes in blood pressure. Some have suggested active pneumatic pumping of blood. This requires an unprecedented evolutionary novelty, but cannot be eliminated as a possibility. Mobility and mechanical problems are much easier to address if titanosaurs were lighter than their size would suggest. By way of example, if we model a sauropod body as something between a cylinder and a sphere with (in either case) a diameter of 200 cm, then a very low density, air-filled layer of about 25 cm under the skin would reduce mass by as much as 40-50% over the equivalent volume of normal tissue, even without accounting for respiratory air sac volume. This same layer would provide protection against any serious wound from the "one free bite" which the sauropod's slow reaction might give a fast-moving predator.
All this, of course, is simply speculation; but something was clearly rather special about sauropod anatomy. Not only has no other group of terrestrial tetrapods come close to their size, but the uniformity of the sauropod body plan over 120 My suggests that there was not much room for variation on some special basic theme. Perhaps our 100 ton hamster was not so far off after all, if they were active, but puffed up like scaly zepplins. So much for the dignity of the titanosaurs ... (ATW 010911)
 In the image, Alamosaurus meets a 100,000 kg hamster. The location is, of course, Tokyo -- the traditional venue for such encounters.
 Part of the quarry lies in a tidal channel, raising the possibility that the animal followed the presumably firmer footing in the channel to reach the flat. But this simply revives the idea of a semi-aquatic habit which appeared to have been discredited. In the image, a fairly small specimen of Argentinasaurus is placed in a (modern) mangrove swamp. Back to the swamps -- again?
Somphospondylii: Euhelopus + Saltasaurus, Rogers & Forster (2001). But used here as the stem group Saltasaurus > Brachiosaurus, i.e., to include Titanosauria and Macronarians incertae sedis other than brachiosaurids. This latter use be more appropriate if Macronaria is treated as a node, the crown group Brachiosaurus + Saltasaurus; but the Rogers & Forster usage is more appropriate if Macronaria is the stem group Saltasaurus > Diplodocus.
Range: Middle Jurassic to Late Cretaceous.
Phylogeny: Macronaria: Brachiosauridae + * : Chubutisaurus + Aegyptosaurus + Paralititan + Venenosaurus + Euhelopodidae + Titanosauria
References: Rogers & Forster 2001). (ATW 020325).
Chubutisaurus: C. insignis delCoro, 1974.
Range: middle Cretaceous of South America southern Argentina)
Phylogeny: Somphospondylii : Aegyptosaurus + Paralititan + Venenosaurus + Euhelopodidae + Titanosauria + *.
Characters: 20+ m; vertebrae with large pneumatic spaces; tail short; forelimbs shorter than the hindlimbs.
Chubutisaurus insignis Corro, 1974
Place: West Gondwana Argentina)
Remains: two partial skeletons
Length: 23 meters
Weight: 30 tonnes?
Comments: A number of middle Cretacous forms previously considered to be brachiosaurs now seem to be titanosaurs. Although they do not have the distinct characteristics of the family Titanosauridae, they are certainly representative uncles and aunts; earlier forms continuing to exist alongside their more recent relatives. Chubutisaurus is typical of this group. Previously considered among the brachiosaurs, this huge animal seems to be a representative basal (ancestral) type, closely related to the Titanosauridae. (MAK 011115)
Links: DinoData CHUBUTISAURUS; CHUBUTISAURUS; Yahooligans! Science- Dinosaurs; Paleontology and Geology Glossary- Ch; Argentina On View - News and Press; Chubutese dinosaurs. ATW040207.
Range: Early Cretaceous of Africa
Phylogeny: Somphospondylii: Chubutisaurus + Paralititan + Venenosaurus + Euhelopodidae + Titanosauria + *.
Aegyptosaurus baharijensis Stromer, 1932
Horizon: Continental Intercalaire
Place: north-central Gondwana Egypt)
Remains: Remains: leg bones, fragmentary vertebrae (destroyed in WW2)
Comments: An early representative of the Titanosaur group. Its relationship to later members is not known. (MAK 011115)
Range: Early Cretaceous of Africa
Paralititan stromeri J. B. Smith, Lamanna, Lacovara, Dodson, J. R. Smith, Poole, Giegengack, and Attia, 2001
Horizon: Baharija Formation of Egypt
Age: early Cenomanian
Place: north-central Gondwana Egypt)
Remains: postcranial material including a humerus, shoulder girdle, and tail vertebrae
Length: 30 meters
Weight: upto 70 tonnes
Comments: A huge animal, Paralititan apparently lived in a swampy mangrove environment. It is not clear how it avoided becoming mired. (MAK 011115)
Range: middle Cretaceous of North America
Phylogeny: Somphospondylii: Chubutisaurus + Aegyptosaurus + Paralititan + Euhelopodidae + Titanosauria + *.
Venenosaurus dicrocei Tidwell, Carpenter & Meyer, 2001
Horizon: Poison Strip member of the Cedar Mountain Formation, Utah
Place: Western Laurasia Utah); Cashenranchian Fauna
Remains: adult: partial skeleton, including limb elements and tail vertebrae. Juvenile material probably of the same species.
Comments: May be closely related to Cedarosaurus, if so, the latter is not a brachiosaur, but a titanosaur. (MAK 011115).
Euhelopodidae: Euhelopus, Klamelisaurus. As with Mamenchisaurids, unclear whether this group should include more than Euhelopus.
Range: Middle Jurassic to Early Cretaceous(?) of China, and perhaps Australia & South America.
Phylogeny: Somphospondylii : Chubutisaurus + Aegyptosaurus + Paralititan + Venenosaurus+ Titanosauria + *.
Characters: Short steep-snouted squarish skull; peg-like (or "spoon-like"?) teeth similar to diplodocids, but larger and not restricted to anterior jaw; nares on top of skull; long neck with 19? (17?) vertebrae; skid-like chevrons; forelegs as long as hindlimbs.
Links: DinoData: Euhelopus; Dann's Dinosaur Info: Rhoetosaurus; Dinobase, DINOSAUR CARDS; Dinosaur Families - Enchanted Learning Software; Euhelopus; euhelopodidae Best on the Web); Untitled Document; Euhelopodidae.
Note: Probably only Euhelopus belongs here. Other Euhelopidids, if that's applicable any more, are probably closer to Mamenchisaurus. 010904.
Titanosauria: To be consistent, Titanosauria really ought to be Saltasaurus + Nemegtosaurus or something of that sort. However, the Nemegtosauridae are not sufficiently well known or well-defined, so the term is used in a non-cladistic way to include all "traditional" titanosaurs.
Range: Late Jurassic to Late Cretaceous of South America, Europe, Africa, North America & Australia?
Phylogeny: Somphospondylii : Chubutisaurus + Aegyptosaurus + Paralititan + Venenosaurus+ Euhelopodidae + *:
Introduction: While other sauropod groups died out during the late Jurassic or Middle Cretaceous, the titanosaurs continued roight until the end of the period. And not only continued, but flourished. They have been found almost worldwide; only central to northern North America western "Asiamerica" was probably free of them (I wouldnt be surprised if - on the weight of purely biogeographical reasons - the strangely primitive Australian Austrosaurs turn out to be abberent titanosaurs; after all, titanosaurs were common everywhere else in Gondwana)
All titanosaurs were rather primitive and unspecialised sauropods, for a long time considered on the basis of their peglike teeth and badly reconstructed skulls, to be cousins of the diplodocids. It is now known that they are related rather to brachiosaurs and camarosaurs, being grouped with them in the clade Macronaria. They ranged in size from realtively small sauropods to some the hugest animals that ever walked on land. (MAK 011115).
large to gigantic herbivores; very small, peg-like slender teeth; supratemporal fenestrae transversely oriented [R&F]; supratemporal fenestrae narrowed [VN]; quadrate hollow, with excavation posterior [R&F]; distal end of paroccipital process slender and elongated (reversed in Quaesitosaurus) [VN]; vertebrae with uncleft spines; cervical vertebrae elongate with shallow lateral pleurocoels [R&F]; cervical pleurocoels simple and undivided reversed in Saltasaurus) [VN]; cervical and anterior dorsal spines single and without median tubercle (several reversals) [VN]; at least 10 dorsal vertebrae [S+05]; pleurocoels usually eliptical, with well-developed system of internal divisions [S+05]; anterior and mid dorsal spines posteriorly inclined; [VN]; dorsal vertebrae with accessory posterior spinodiapophyseal laminae [S+05$]; dorsal vertebrae with posterior centroparapophyseal lamina [S+05$]; $ hyposphene-hypantrum articulation in posterior trunk vertebrae [R&F]; presacrals fiilled with spongy bone; 6 sacrals [S+05]; second sacral rib directed anterolaterally & distally expanded [S+05]; $ < 35 caudal vertebrae [R&F]; caudal vertebrae of spongy bone [R&F$]; $ anterior caudals strongly procoelous having "ball and socket" articular faces; chevrons simple; distal caudal vertebrae reduced in number and not elongated [VN]; caudal vertebrae, neural arches with well-developed prespinal laminae [S+05]; caudal vertebrae, neural spine vertically oriented [S+05]; scapular glenoid medially inclined; anterior limbs at least as long as posterior limbs; semilunar sternal plates; coracoid long compared to sternal articulation of coracoid [VN]; prominent deltopectoral crest on humerus [VN]; ulna stout [VN]; $ olecranon process of ulna projects above proximal articulation [R&F]; $ distal width of radius twice width at midshaft [R&F]; elongate metacarpals [R&F]; claw on manual digit I absent; expanded, sacrum tilted antero-dorsally; semicircular preacetabular process of ilium [R&F]; ilium, pre- and postacetabular processes expanded laterally [S+05]; ischium length/pubis length = 0.90 or less [R&F$]; elongate pubis [R&F]; femur usually anteroposteriorly compressed [S+05]; distal end of femur may be expanded transversely; tibia, distal portion expands transversely [S+05]; fibula outer surface convex & inner surface slightly concave [S+05]; astragalus tall & transversely thin [S+05]; diverse dermal armor with plates and small ossicles.
Note: The characters marked "[VN]" show as synapomorphies in an analysis I ran of essentially the [R&F] data set. ATW010907.
Links: DinoData: Titanosauridae; titanosaurid megatracksite; Terrestrial trans-Tethyan dispersals (only marginally relevant, but interesting); The Journal of Vertebrate Paleontology; Nature Science Update; Abstract; g00n3a3.pdf; paralititan.pdf; What groups of dinosaurs existed- brief paragraph);
Range: middle Cretaceous of South America.
Phylogeny: Titanosauria : Argentinasaurus+ Titanosauridae + *.
Andesaurus delgadoi Calvo and Bonaparte, 1991
Horizon: Rio Limay Formation of Neuquen Province, Argentina
Place: west Gondwana Argentina)
Length: 40 meters?
Weight: 80 tonnes?
Comments: This gigantic primitive titanosaur shows some resemblance to Argentinasaurus, and shares a similar vertebral structure. Andesaurus is the standard-bearer of paraphyletic, or maybe even polyphletic, group of mostly gigantic proto-titanosaurids sometimes referred to as "Andesauridae." The family was named by Jose Bonaparte, the great Argentine paleontologist, and includes the genera Phuwiangosaurus, Andesaurus, Argentinasaurus, Malawisaurus, and perhaps Iuticosaurus (formerly Titanosaurus valdensis Huene - DinoData page). Many workers now consider Andesauridae an invalid taxon and its representative forms as simply generic early/basal titanosaurids. In any case, these animals belong at the base of the titanosaurid tree, intermediate between contemporary forms like Chubutisaurus and more advanced titanosaurs. Inasmuch as true titanosaurids seem to have evolved as early as the Late Jurassic, that means that the "Andesauridae" also extend back equally as far, and continued alongside thier descendents for some 50 million years. (MAK 011115).
Characters: dorsal vertebrae with hyposphene- hypantrum articulation; caudal centra amphicoelous, with ?laminated spines.
Links: DinoData Andesaurus; ANDESAURUS (basic data and reference); Andesaurus Spanish: similar, with a bit more detail); Argentina On View. ATW030709.
Range: Early Cretaceous of South America.
Phylogeny: Titanosauria : Andesaurus+ Titanosauridae + *.
Argentinosaurus huinculensi Bonaparte & Coria, 1993
Horizon: Rio Limay Formation of Neuquen Province, Argentina
Place: west Gondwana Argentina)
Length: length around 35 to 45 meters
Weight: weight upto 80 tonnes
Comments: possibly the largest known dinosaur. It may be related to Andesaurus. In any case it lived in the same geographic region at much the same time. (MAK 011115).