Dunkleosteus terrelli

[Life]

Dunkleosteus terrelli

Dunkleosteus terrelli boasted a 20-foot-long body covered with bony plates of armor. Fossil records indicate that this huge fish, one of the first large jawed vertebrates in the ocean, was an aggressive predator.

The razor-sharp edges of bones in this animal's jaws served as cutters. As they rubbed against each other, the opposing jaw blades acted like self-sharpening shears. These bones continued to grow as they were worn down by use.

Source: www.amnh.org/exhibitions/permanent-exhibitions/fossil-halls/hall-of-vertebrate-origins/dunkleosteus

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The Cleveland Museum of Natural History has some of the world's best fossil specimens of Dunkleosteus terrelli, including a giant armored skull on display in the Kirtland Hall of Prehistoric Life and a realistic reconstruction hanging overhead.

Dunkleosteus was possibly the fiercest and most terrifying creature alive in the Devonian "Age of Fishes," about 360 million years ago. Up to 30 feet in length and possibly weighing as much as four tons in weight, Dunkleosteus was larger than most other creatures alive at the time. Its huge jaws opened so quickly they created a suction force that pulled prey into its mouth. The closing of its jaws was just as fearsome; its bite was so powerful it could snap a prehistoric shark in two with its razor-sharp jawbones. And yet Dunkleosteus did not have teeth. Instead, the edges of their jawbones kept sharp by rubbing against each other like self-sharpening scissors.

Dunkleosteus is a member of Placodermi (placoderms), the only extinct class of vertebrates that ever evolved. Their heads and upper body were typically shielded by bony armor, leaving the rest of the body able to move freely, powering and steering the creature through water. These armored fishes died out by the early Carboniferous period, which followed the Devonian.

The Cleveland Connection

These long-extinct armored fish lived in the Cleveland area, which at the time—well before humans or dinosaurs existed—was covered by a shallow sea. The sea is gone but the sediments (sandstones and shales) that were laid down during its presence remain. As these rocks erode through the action of water and wind, a rich variety of fossil fish from the Late Devonian have been uncovered and collected. These finds have made Cleveland famous in the world of paleontology.

The largest species of placoderm ever found in the Cleveland Shale is Dunkleosteus terrelli. It was first discovered in 1867 on the shores of Sheffield Lake by local amateur fossil hunter named Jay Terrell, who was one of a group of fossil hunters in the Cleveland area in the late 19th and early 20th century. The early collections of Devonian fossils amassed by this group were passed on to the British Museum, the American Museum of Natural History in New York, and other institutions, because there was not an official natural history museum in Cleveland until 1920.

While the fish fossils are still relatively plentiful, collecting specimens from the Cleveland shale is notoriously difficult. It requires the ability to recognize significant fossils in the rocks, along with the patience to painstakingly extract and reconstruct them, often from fragments.

Today, The Cleveland Museum of Natural History is recognized as a leading resource center for the study of these armored fish. The Museum continues to prepare new specimens collected each year from throughout Cleveland and Ohio.

Fossil Hunting Pioneers

The original fossil-hunting group is credited with many successes. In addition to Dunkleosteus (then called Dinichthys) the group found many specimens of the primitive shark Cladoselache, also plentiful during the Devonian Period in this area but rarely found elsewhere.

Along with Jay Terrell, the group included: Rev. Herman Herzer, a minister and professor in natural science at German Wallace College, credited with first discovering the rich deposits of fossil fishes in the Cleveland area; Rev. William Kepler, a minister and professor of natural science at Baldwin University; two geology professors from Oberlin College, A.A. Wright and E.B. Branson; and many other professional men from around the region.

An honorary member of the group was Dr. John Strong Newberry. Born and educated in the Cleveland area, Newberry went on to join the faculty of Columbia University in New York. It was Newberry who first recognized the significance of the local amateurs' collections, described them scientifically, and ensured that they were passed on to appropriate museums.

Thanks to the work of these early fossil hunters, former Vertebrate Paleontology curator Dr. David Dunkle, and countless experts and enthusiasts over the years, the mighty Dunkleosteus terrelli continues be a source of wonder and study within the permanent collection of The Cleveland Museum of Natural History.

Source: www.cmnh.org/site/AtTheMuseum/OnExhibit/PermanentExhibits/Dunk.aspx

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STRANGEST BEASTS TO EVER DIE

by Ann M. Cairns

More than 99 percent of all species that have lived on Earth are now extinct. Sometimes extinctions actually accelerate the evolution of life on Earth. As some forms of life weaken and die off, they create opportunity for other species to grow and flourish. Take a look at these creatures and imagine what life would be like if they had survived!

The Shark Eater: Dunkleosteus

During Earth's "Age of Fishes" 400 million years ago, Dunkleosteus was a genuine sea monster. This aggressive predator, more than 11 feet in length with a skull two feet long, was armor-plated. Instead of mere teeth, it had two long bony blades that snapped and crushed its prey. Dunkleosteus dined on all kinds of seafood including early sharks, which didn't have a chance to diversify and grow to great sizes until Dunkleosteus went extinct about 360 million years ago.

Source: dsc.discovery.com/earth/slideshows/10-extinct-beasts/top-10-extinct-beasts.html

[Life]

Feeding mechanics and bite force modelling of the skull of Dunkleosteus terrelli, an ancient apex predator

Abstract

Placoderms are a diverse group of armoured fishes that dominated the aquatic ecosystems of the Devonian Period, 415–360 million years ago. The bladed jaws of predators such as Dunkleosteus suggest that these animals were the first vertebrates to use rapid mouth opening and a powerful bite to capture and fragment evasive prey items prior to ingestion. Here, we develop a biomechanical model of force and motion during feeding in Dunkleosteus terrelli that reveals a highly kinetic skull driven by a unique four-bar linkage mechanism. The linkage system has a high-speed transmission for jaw opening, producing a rapid expansion phase similar to modern fishes that use suction during prey capture. Jaw closing muscles power an extraordinarily strong bite, with an estimated maximal bite force of over 4400 N at the jaw tip and more than 5300 N at the rear dental plates, for a large individual (6 m in total length). This bite force capability is the greatest of all living or fossil fishes and is among the most powerful bites in animals.

1. Introduction

The structure and function of placoderm skulls are important aspects of the evolutionary history of vertebrate feeding, because these ancient predators are considered to be the sister group to the rest of jawed vertebrates (Goujet & Young 2004). This phylogenetic placement, coupled with remarkable morphological variation in the feeding system, makes placoderms one of the earliest examples of jaw diversification among vertebrates (Carr 1995). The largest of the placoderms were voracious predators, such as the arthrodire Dunkleosteus terrelli (figure 1), that were equipped with powerful, bladed jaws that conferred the novel ability to fragment prey items prior to ingestion (Miles 1969). Modern sharks possess a set of well-known jaw mechanisms which also accomplish this task (Dean et al. 2005; Wilga 2005). However, the earliest definitive examples of shearing, bladed teeth in elasmobranchs did not develop until the Mesozoic, 100 Myr after Dunkleosteus was a top predator of the Devonian seas (Janvier 1996).

Figure 1

Anatomy and biomechanical model of the skull and thoracic region of Dunkleosteus terrelli. (a) Anatomy of Dunkleosteus terrelli, highlighting the cranio-thoracic joint and quadrato-mandibular joints involved in skull mechanics. (b) Drawing showing the four rotational joints (green) forming the four-bar linkage that mediates skull and mandibular rotation. The lines of action of four muscles are shown, including epaxialis and coracomandibularis in blue and cranial depressor and adductor mandibulae in red. (c) Four-bar linkage motion during opening. Scale bar, 20 cm. Specimen no. CM6090, Cleveland Museum of Natural History.

Biomechanical models based on engineering theory are often used to test ideas regarding fish skull function (reviewed by Westneat 2006). Models of living fishes can accurately represent the mechanics of skull function, and studies have shown that skull mechanisms are correlated with natural diet. Biomechanical models have also been employed in surveys of fossil forms to examine jaw mechanics in extinct herbivores (Bellwood 2003) and predatory gars (Kammerer et al. 2006). Here, we take advantage of the exquisite three-dimensional preservation of placoderms to conduct a biomechanical analysis of cranial kinesis in one of the largest aquatic predators ever to have lived. Our goals are to develop a biomechanical model of D. terrelli that involves a novel four-bar linkage mechanism, and to use reconstructions of the mass, volume and force trajectories of the jaw muscles to simulate the speed, angular rotations and bite forces of Dunkleosteus.

2. Material and methods

The feeding mechanism of D. terrelli was modelled as a four-bar linkage, using techniques similar to previous skull modelling (Westneat 2006). Five specimens of D. terrelli from the Cleveland Museum of Natural History (CM5768, CM6090, CM7054, CM7424 and CM6194) were used to develop this model. For the largest specimen (CM5768), muscle casts were made to fit muscle cavities, from which we measured muscle length, volume and cross-sectional area. For muscle simulations, a range of average muscle contraction speeds from 2.3 to 5.0 muscle lengths s−1 (Josephson 1993) and a peak muscle stress of 200 kPa were used.

The four-bar linkage mechanism in D. terrelli is unique due to the connections of the skull, thoracic shield, jaw depressor muscle and inferognathal (lower jaw), which are joined by kinetic joints (figure 1). The cranio-thoracic articulation (nuchal joint) connects the back of the skull to the thoracic shield, allowing the skull to rotate dorsally during contraction of epaxial (EP) muscles. The jaw depressor muscle (coracomandibularis, CM) originates on the scapulocoracoid and inserts on the anteroventral portion of the inferognathal (Johanson 2003). The thoracic shield forms a framework for three movable elements: the skull, the inferognathal, and the depressor muscle. This structure is a classical four-bar linkage from mechanical engineering (figure 1c), involving a fixed link (thoracic shield) and three rotational links. As the skull is rotated dorsally by the action of the EP, the jaw joint is pulled forward and the inferognathal rotates due to its connection with the thoracic shield (figure 1b,c).

A computer model was developed to simulate skull motions and bite forces by shortening four cranial muscles (figure 1b). These include the EP muscles that rotate the skull dorsally (figure 2a, EPv2), and open the four-bar linkage at the jaw joint (figure 2a, Epv3), and the CM muscle which rotates the inferognathal ventrally. Owing to tension in the CM, EP force is transmitted to the jaw (figure 2a, Epv4). For jaw closing, the cranial depressor (CD) muscle rotates the skull downward and pushes the jaw joint rearward (figure 2b, CDv2). The adductor mandibulae (AM) jaw muscle rotates the jaw and forces the jaw joint rearward (figure 2b, AMv2). Thus, the bite force from the upper jaw (figure 2b, BF1 and BF3) comprises CD force exerted by the skull lever and AMv2 force that is transmitted by the four-bar linkage. Lower jaw bite force (figure 2b, BF2 and BF4) is generated by the powerful lever advantage of the AM muscles.

Figure 2

Biomechanics of feeding in Dunkleosteus terrelli, under a muscle contraction speed of 5 muscle lengths s−1. (a) During jaw opening, epaxialis vector 1 (EPv1) and coracomandibularis vector 1 (CMv1) cause cranial elevation (EPv2) and jaw depression (EPv3 and EPv4). (b) Jaw closing mechanics is driven by force vectors of the cranial depressor (CDv1) and adductor mandibulae, reconstructed in two configurations (AM1v1 and AM2v1). Bite force is exerted by both lever and linkage force vectors (BF1 and BF2) or between the rear dental blades (BF3 and BF4). Simulated kinematics in five specimens of Dunkleosteus terrelli include (c) skull rotation, (d) mandibular rotation and (e) change in gape during feeding. The simulated positions of skeletal elements are shown in (f) closed, (g) intermediate and (h) open positions, with their corresponding points shown (black arrows) on the kinematic plots.

We simulated a 10% contraction of the opening muscles in increments of 0.5%, then reversed this pattern, closing the system with the CD and jaw closers. These simulations focused on linkage motion, assuming that the skull closes without encountering a prey item. Important variables include mechanical advantages of muscles on rotational levers (computed as inlever distance divided by outlever distance) and the kinematic transmission coefficient (KT) of the linkage, calculated as output rotation of the mandible divided by the input rotation of the skull (see electronic supplementary material for specific variables). Bite forces were calculated in a separate set of simulations at each stage of jaw closing by assuming that a prey item was caught between the jaws at that position (figure 2). We used the physiological cross-sectional area of the CD and AM to calculate the force that was transmitted through the four-bar linkage as bite force.

3. Results and discussion

The anatomical configuration of the skull, thoracic shield, mandible and jaw depressor muscle in placoderms may be accurately modelled as a four-bar linkage mechanism. The cranio-thoracic articulation, which is a key component of this linkage design, is found only in the placoderms (Janvier 1996). The central result of this study is that D. terrelli used this unique four-bar linkage in the skull to achieve high speeds during jaw opening and transmit extremely high bite forces to its prey during jaw closing. Dunkleosteus appears to have had a rapid gape expansion, going from closed jaws to peak gape in as little as 20 ms and completing the feeding cycle in 50–60 ms, using an average muscle speed estimate of 5 muscle lengths s−1 (figure 2c–e). This rapid gape expansion is comparable to that of modern fishes, which use suction feeding to assist in prey capture (Westneat 2006). Simulations using slower muscle velocities (such as shark muscle at 2.3 or 3.8  muscle lengths s−1) resulted in longer duration feeding strikes of up to 130 ms, slower than teleost suction feeding but similar to the duration of suction feeding in nurse sharks (Motta et al. 2002). Previous research (Miles 1969) had speculated that Dunkleosteus had a powerful but slow jaw system; however, the average opening KT for Dunkleosteus is 3.0 (see table 1 of electronic supplementary material), indicating that the lower jaw rotates at three times the speed of the cranial rotation that drives it. This KT is twice as high as the highest values calculated for a different type of oral jaw linkage in modern groups (Wainwright et al. 2004). This high KT is augmented by CM contraction that pulls the lower jaw downward, providing Dunkleosteus with a two-muscle opening system that had the ability to rapidly achieve high gape. We conclude that the Dunkleosteus skull is an early example of a complex, kinetic feeding mechanism that may have utilized an early form of suction feeding.

Dunkleosteus also had one of the most powerful bites in vertebrate history. Simulations showed that a large specimen was able to generate maximum bite forces of 4414 N on the anterior fang and 5363 N on the posterior part of the blade. Simulation of an alternative muscle reconstruction (AM1, figure 2f) resulted in slightly lower bite forces, from 4004 N anteriorly to 4469 N posteriorly. These bite forces greatly exceed the bite forces collected for all other fish species that have been reported (Huber et al. 2005) and those for most modern mammalian predators, including the spotted hyaena (Binder & Van Valkenburgh 2000), which is known to crack bones with its jaws. The Dunkleosteus specimen on which these estimates are based is large (estimated to be 6 m long and 1000 kg) and the bite forces conform to a recently compiled scaling trend of increasing bite force with body mass (Huber et al. 2005). The only reports of higher bite forces are those found in some extremely large alligators and dinosaurs (Erickson et al. 2003). The biomechanical source of high bite forces in Dunkleosteus is a combination of large adductor muscles, the efficient force transmission characteristics of a four-bar linkage (figure 2), and high mechanical advantage of the jaw closing lever (see table 1 of electronic supplementary material).

The bladed dentition of Dunkleosteus provided for extremely high local bite stress (force/area) because the bite force was focused into a small area, the fang tip (147 million N m−2) or the blade edge (107 million N m−2). High bite stress enabled Dunkleosteus to puncture and fragment hard materials, such as cuticle or dermal bone. The Cleveland Shale is known primarily for its placoderms, but also contains selachian sharks, arthropods and ammonoids. These were all free-swimming organisms that shared the presence of a hard armour (cuticle, calcium carbonate or dermal bone), which must be punctured prior to consuming the flesh underneath. These mobile and often hard prey would require both high capture speed and high bite force to consume, for which the feeding system of Dunkleosteus, with its high forces and high KT values, appears well suited. The combination of power and speed seen in Dunkleosteus would have allowed it to consume virtually all other aquatic species in the fauna, making it one of the first true apex predators seen in the vertebrate fossil record.

Source: rsbl.royalsocietypublishing.org/content/3/1/77.full

[Deleted]

Dunkleosteus skeletal reconstruction by Scott Hartman.



If the skull is around ~72 centimeters, it seems to be roughly around ~6.5 meters long. I'm just eyeballing it though.

[blaze]

It's 5.6m assuming the skull stops at the posteriormost visible parts, less if it keeps on, that's about the same as my estimate.

[Infinity Blade]

Here's a new reconstruction of Dunkleosteus, both in morphology of the tail fin as well as body size. It's still smaller than the 10 meter monster it was often touted as, but it's actually substantially bigger than the ~6 meter estimate above. It's estimated as 8.79 meters here, and it looks like a tank of a placoderm.

peerj.com/articles/4081/

[moldovan0731]

[Infinity Blade]

Dunkleosteus was a chonker according to the recent paper downsizing its length. Although it was much shorter than previously estimated, it was still a literal metric ton.

That said, although Dunkleosteus appears to be much shorter than previously thought, it also appears to be extremely massive relative to its length. When estimating the body mass of arthrodires using a multivariate ellipsoid equation, arthrodires are found to be much more massive relative to their length than sharks (Figure 10). This is largely due to the fact that arthrodires have shorter, deeper, and wider bodies than sharks when scaled to the same body mass (Figure 12). For example, CMNH 5768 is estimated to weigh approximately 1008.4 kg and measure 341 cm in length. In order for a typical (i.e., non-lamnid) shark to reach similar weights, it would need to add another 161 cm of length (i.e., measure 502 cm in total length; Supplementary File S3: Section 17.6). Notably, this is only considering the flesh mass of arthrodires, and thus arthrodires may have been even heavier due to their dermal armor. However, as noted under Results the contribution of the armor to the total weight of Dunkleosteus may be smaller than previously believed.

The largest known specimen is estimated to have been ~410 cm in total body length. Isometrically scaling up you get an animal weighing ~1,700 kg.


www.mdpi.com/1424-2818/15/3/318

[moldovan0731]