December 5, 2012
For the past twenty years, Eoraptor has represented the beginning of the Age of Dinosaurs. This controversial little creature–found in the roughly 231-million-year-old rock of Argentina–has often been cited as the earliest known dinosaur. But Eoraptor has either just been stripped of that title, or soon will be. A newly-described fossil found decades ago in Tanzania extends the dawn of the dinosaurs more than 10 million years further back in time.
Named Nyasasaurus parringtoni, the roughly 243-million-year-old fossils represent either the oldest known dinosaur or the closest known relative to the earliest dinosaurs. The find was announced by University of Washington paleontologist Sterling Nesbitt and colleagues in Biology Letters, and I wrote a short news item about the discovery for Nature News. The paper presents a significant find that is also a tribute to the work of Alan Charig–who studied and named the animal, but never formally published a description–but it isn’t just that. The recognition of Nyasasaurus right near the base of the dinosaur family tree adds to a growing body of evidence that the ancestors of dinosaurs proliferated in the wake of a catastrophic mass extinction.
In March of 2010, Nesbitt and a team of collaborators named a leggy, long-necked creature from the same Triassic rock unit in Tanzania they named Asilisaurus kongwe. This creature was a dinosauriform–a member of the group from which the first true dinosaurs emerged–and, even better, appeared to to be the closest known relative to the Dinosauria as a whole. The find hinted that the dinosaur lineage had probably split off from a common ancestor by this time, meaning that the most archaic dinosaurs may have already existed by 243 million years ago. Roughly 249-million-year-old footprints of dinosauriforms found among Poland’s Holy Cross Mountains, described by different researchers later the same year, added evidence that the dinosauriforms were diversifying right from the beginning of the Triassic–not long after the catastrophe that decimated life on earth at the end of the Permian, around 252 million years ago.
Nyasasaurus is another step closer to the first true dinosaurs, and is just as old as Asilisaurus. To find an animal with such distinctive, dinosaur-like traits in the Middle Triassic indicates that dinosaurs already existed, or their ancestral stem was already established. Either way, Eoraptor and kin from South America can no longer be considered as the first dinosaurs, but rather a later radiation of forms. Even though our knowledge of Nyasasaurus is only fragmentary–the dinosaur is represented by a right humerus and a collection of vertebrae from two specimens–the dinosauriform nonetheless marks an additional 12 million years of dinosaur time that paleontologists are only just starting to explore.
Whether or not we ever achieve a more complete view of Nyasasaurus depends on the luck and the caprices of the fossil record. In the new paper, Nesbitt and coauthors point out that the rare, fragmentary nature of the remains found so far reflects that dinosauriforms–and early dinosaurs–were marginal parts of the ecosystems they inhabited. Dinosaurs did not dominate from the very start. They were relatively meek, small animals that lived in a world ruled by archosaurs more closely related to crocodiles. It was only in the Late Triassic and Early Jurassic, when their archosaurian competition was diminished, that dinosaurs became dominant. That means the earliest dinosaurs and their ancestors are few and far between in the Triassic record.
Still, when I asked Nesbitt what Nyasasaurus might have looked like, he cited other dinosauriforms and early dinosaurs as templates to constrain our expectations. Nyasasaurus may have looked quite like Asilisaurus–a leggy animal with an elongated neck–although Nyasasaurus may have been bipedal. Future finds will test this idea, but the fact remains that paleontologists are closing in on what the very first dinosaurs were like. As paleontologists uncover more early dinosaurs and dinosauriforms, the dividing line between the two disappears–scientists are starting to smooth out the evolutionary transition between the first dinosaurs and their ancestors. What role Nyasasaurus played in that transformation isn’t yet clear, but the creature is a signal that over 10 million years more of uncharted dinosaur history remains in the rock.
Nesbitt, S., Sidor, C., Irmis, R., Angielczyk, K., Smith, R., Tsuji, L. 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464, 7285: 95–98. doi:10.1038/nature08718
Nesbitt, N., Barrett, P., Werning, S., Sidor, C., Charig, A. 2012. The oldest dinosaur? A middle Triassic dinosauriform from Tanzania. Biology Letters. http://dx.doi.org/10.1098/rsbl.2012/0949
April 30, 2012
There’s a lot we don’t know about spinosaurs. Even though a few of these croc-snouted animals are known from mostly complete skeletons—including Baryonyx and Suchomimus—many spinosaurs are known from only sparse bits and pieces. The large spinosaur Oxalaia from the Cretaceous rock of Brazil is known from two skull fragments, and only a few elements have been found from the newly announced Ichthyovenator. We know even less about another recently proposed spinosaur. Called Ostafrikasaurus, this dinosaur is represented by a pair of teeth.
Paleontologist Eric Buffetaut described the dinosaur teeth in the journal Oryctos. They were found a century ago by the German fossil expeditions to Tanzania. During that time, the field team collected more than 230 teeth attributable to Late Jurassic theropod dinosaurs, predators that lived among sauropods and stegosaurs around 150 million years ago. Determining exactly which dinosaurs these dental tidbits belonged to has been a persistent problem. Mammal teeth, with their various cusps and troughs, are often distinctive enough to identify genera and species, but isolated dinosaur teeth are not usually so informative. Many dinosaur species named from teeth alone have turned out to be synonyms of dinosaurs known from better material. Unless you have a detailed knowledge of the dinosaurs that lived in a particular area at a given time, attributing isolated teeth to particular dinosaurs is a risky proposition. Anatomical context is extremely important in these situations.
No surprise, then, that the teeth Buffetaut described have had a complicated history. German paleontologist Werner Janensch, who did much of the initial descriptive work on the Jurassic dinosaurs of Tanzania, thought that the serrated, ridged and slightly curved teeth probably belonged to a dinosaur O.C. Marsh named from the Jurassic of North America, “Labrosaurus.” (“Labrosaurus” is now considered a synonym of Allosaurus.) More recently, in 2000, paleontologists James Madsen and Samuel Welles suggested that the teeth belonged to a form of Ceratosaurus, a highly ornamented theropod typically found in the Late Jurassic rock of western North America. And in 2008, paleontologist Denver Fowler mentioned that these peculiar teeth from Tanzania might hint at a connection between ceratosaurs and spinosaurs. With this in mind, Buffetaut reexamined the strange teeth and concluded that they represent a hitherto unknown form of early spinosaur.
Buffetaut singled out two possible spinosaur teeth—specimens designated MB.R.1084 and MB.R.1091. Both of these teeth have relatively coarse serrations and a number of prominent vertical ridges along both sides of the teeth, with more on the tongue side than the cheek side. Overall, they look similar to the teeth of Baryonyx, and so Buffetaut created a new genus and species of dinosaur for the two teeth: Ostafrikasaurus crassiserratus.
If Ostafrikasaurus is a spinosaur, it would be the earliest known and could help elucidate what these dinosaurs were like before they became fish-catching specialists. But there’s too little material to be sure. The Ostrafrikasaurus teeth look similar to spinosaur teeth, but as previously recognized by other paleontologists, they also resemble ceratosaur teeth. We need a nice skull set with Ostrafrikasaurus-like teeth to determine what this dinosaur actually was. The same is true of a large claw found in the Late Jurassic strata of North America, currently attributed to Torvosaurus, that has been highlighted as possible evidence of a spinosaur. There may have been spinosaurs in North America, and their history might have stretched back 150 million years to the time of Apatosaurus, but definitive proof remains elusive. Until adequate fossil evidence turns up, the idea of Late Jurassic spinosaurs will be left hanging.
Buffetaut, E. 2011. An early spinosaurid dinosaur from the Late Jurassic of Tendaguru (Tanzania) and the evolution of the spinosaurid dentition. Oryctos. 10, 1-8
July 28, 2011
In North America, the Morrison Formation is a famous and fossil-rich slice of time; its rock contains the bones of some of the quintessential dinosaurs. Apatosaurus, Allosaurus, Stegosaurus and more—the Morrison represents the heyday of Jurassic dinosaurs. A less similar but less famous site represents the Late Jurassic world. The fossil sites of Tendaguru, in Africa, preserve dinosaurs similar to, yet distinct from, their North American counterparts.
Paleontologists Wolf-Dieter Heinrich, Robert Bussert and Martin Aberhan just reviewed the history and significance of Tendaguru in Geology Today. In 1906, a German mining engineer made the fortuitous discovery of dinosaur bones near Tendaguru Hill in Tanzania. News made it back to Germany, and after an initial expedition in 1907, Berlin’s Museum of Natural History launched a major effort to uncover the area’s dinosaurs between 1909 and 1913. The result? Over 225 tons of dinosaur bones from one of the most productive fossil sites in all of Africa.
The Jurassic dinosaurs of the Tendaguru sites have often been seen as a rough equivalent to those of the Morrison. Big, long-necked sauropods, such as Dicraeosaurus, Tornieria and Giraffatitan (formerly Brachiosaurus), were numerous and a prominent part of the dinosaur fauna. There was also the spiky stegosaur Kentrosaurus, the ornithopod Dysalotosaurus and a host of poorly known predatory dinosaurs, including Elaphrosaurus and an Allosaurus-like theropod.
Frustratingly, no complete, articulated dinosaur skeletons were ever found at Tendaguru, but the sites preserve some intriguing fossil features. For one thing, the early 20th century expeditions found bonebeds of Kentrosaurus and Dysalotosaurus. They were once thought to represent mass deaths when herds of dinosaurs were killed en masse by local flooding, though, as Heinrich and co-authors point out, the bonebeds could have been created by dinosaurs becoming stuck in the mud and dying over a relatively longer period of time. The fact that the articulated feet of big sauropod dinosaurs have been found in an upright position hints that some of these huge dinosaurs also became mired and died—life alongside the Jurassic lagoon could be dangerous.
But one of the most curious aspects of the Tendaguru dinosaurs is that they are so similar to those found in North America’s Morrison Formation. After all, Giraffatitan was previously described as a species of Brachiosaurus—a dinosaur found in Jurassic North America—and problematic big theropod remains from Tendaguru have been attributed to Allosaurus, not to mention the presence of stegosaurs and other dinosaurs on both continents. Whereas the Tendaguru dinosaurs were once thought to be nearly equivalent to those of North America, a different picture has emerged in which the dinosaurs of Tanzania were similar to those found in the Morrison Formation, but actually belonged to different genera. Nevertheless, the close correspondence between the two raises the question of why very similar dinosaur communities independently came to exist on two different continents. Paleontologists will have to dig deeper to find out.
Heinrich, W., Bussert, R., & Aberhan, M. (2011). A blast from the past: the lost world of dinosaurs at Tendaguru, East Africa Geology Today, 27 (3), 101-106 DOI: 10.1111/j.1365-2451.2011.00795.x
July 8, 2011
Kentrosaurus was a dinosaur you wouldn’t want to mess with. This smaller cousin of Stegosaurus, found in the Late Jurassic deposits of Tanzania, was armed with a formidable array of paired spikes along its tail. (And, in one of my favorite bits of fossil terminology, the spiked tails of stegosaurs are known as “thagomizers.”) Get hit with a tail like that and you’d be turned into an instant shish kebab. But just how much damage was the tail of Kentrosaurus capable of inflicting?
Late last year paleontologist Heinrich Mallison presented a revised look at the mechanics of Kentrosaurus. Among other findings, Mallison reported that Kentrosaurus was a fairly flexible dinosaur. When under attack, for example, Kentrosaurus may have thrown its head back to keep an attacker in its sights, and this armored dinosaur may have also bowed its forelimbs to better support itself while swinging its tail about. Now, in a follow-up to last year’s paper, Mallison has published the results of an investigation into how flexible and powerful Kentrosaurus‘ spiked tail itself may have been.
To experiment with Kentrosaurus, Mallison created virtual models of the dinosaur’s skeleton. This provided the framework on which muscles could be reconstructed and the forces generated by the tail could be estimated. Of particular importance was Mallison’s reconstruction of the dinosaur’s tail muscles. Rather than give Kentrosaurus a thin tail typical of many dinosaur illustrations, Mallison reconstructed the creature with a deep, thick tail that would have generated more power but would have also been quite heavy.
As it turns out, Kentrosaurus was a heavy hitter. According to Mallison’s models, the spikes at the tip of the dinosaur’s tail could have hit their target at a top speed of over 40 meters per second, and Kentrosaurus could have swung its tail at a speed in excess of 10 meters per second in a 75 degree arc. “At this speed,” Mallison writes, “the spikes could penetrate deeply into soft tissues or between ribs and were able to shatter bones.” He adds: “Penetrating impacts at 10 m/s created forces greater than those sufficient to fracture a human skull.” Ouch.
For more on Kentrosaurus defense, check out Mallison’s own post on the subject at the Palaeontologia Electronica blog.
Mallison, H. (2011). Defense capabilities of Kentrosaurus aethiopicus Hennig, 1915 Palaeontogia Electronica
September 16, 2010
Since the early days of paleontology, the posture of dinosaurs and the range of motion they were capable of have been contentious subjects for paleontologists. During the 19th century, especially, the general view of what dinosaurs would have looked like changed no less than three times, and investigations into how these animals moved continue to this day. Among the spate of recent studies on dinosaur flexibility, posture and motion is a new paper by Heinrich Mallison which used the Jurassic stegosaur Kentrosaurus to investigate some of the hypotheses surrounding this armored dinosaur.
Most of what we know about Kentrosaurus comes from the approximately 153-million-year-old Tendaguru Formation in Tanzania. It was there that the German paleontologist Edwin Hennig found numerous isolated bones and elements of disarticulated Kentrosaurus skeletons—in addition to the bones of many other dinosaurs—during the early 20th century; he was also lucky enough to find one partial skeleton of the stegosaur that was suitable for mounting. This specimen, reconstructed with sprawling limbs and a dragging tail, was on display at the Museum für Naturkunde in Berlin for decades. When it was taken apart to restore it in a more accurate posture in 2005, scientists made laser scans of each bone in order to create a digital restoration. It is this digital Kentrosaurus that formed the basis of Mallison’s new study—the closest thing a paleontologist has to a living dinosaur to examine.
In addition to its normal posture and range of motion, Mallison’s study looks at several controversial, little-studied ideas about this dinosaur and its kin. According to Hennig, Kentrosaurus had a squished, lizard-like posture and could not use its spiky tail for defense. In the 1980s, however, paleontologist Robert Bakker went to the opposite extreme, restoring stegosaurs with an erect posture that would have allowed them to pivot and swing their formidable tails at attacking predators. Additionally, Bakker proposed that Stegosaurus and its kin could have adopted a “tripodal” posture in which they reared back to rest on their tails, too, and were much more dynamic animals than envisioned by Hennig and other early 20th-century paleontologists.
Although Mallison stresses that the findings based upon his model are provisional, Kentrosaurus appears to have used different postures for different reasons. While walking, it would have held its limbs erect, but when threatened it was capable of flexing its forelimbs out into a sprawling position to help support itself as it swung its tail at an offending predator. In the latter circumstance, Kentrosaurus would have also been able to extend its neck to look backwards at an attacking dinosaur, though shifting position to keep a predator in view may have created blind spots that would have left this armored dinosaur vulnerable to multiple predators. As far as feeding was concerned, Kentrosaurus was indeed capable of rearing back to rest on its tail, though how often it would have done so—and what sort of food it would have been able to reach by doing so—is unknown. Overall, Kentrosaurus was not as stiff as Hennig proposed. Quite the contrary—this stegosaur was capable of altering its posture to suit a variety of circumstances, and it is likely that at least some of its relatives had similar abilities.
Mallison, H. (2010). CAD assessment of the posture and range of motion of Kentrosaurus aethiopicus Hennig 1915 Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0024-2