Episode 64 is all about Kentrosaurus, a stegosaur smaller than Stegosaurus and with shoulder spikes.
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In this episode, we discuss:
- The dinosaur of the day: Kentrosaurus
- Name means “prickle lizard”
- Close relative of Stegosaurus
- Described by Edwin Hennig in 1915
- Fossils found in the Tendaguru Formation (no complete skeletons found, but hundreds of bones found on German expeditions to German East Africa from 1909 to 1912
- First Kentrosaurus fossil found in 1909 (Werner Janensch said in 1910 it was a type of stegosaur)
- Over 1200 bones found from 50 individuals (many destroyed during WWII); 350 specimens at the Museum of Natural History in Berlin
- Though multiple specimens found, they did not die a mass death at the same time, so they don’t represent a single herd (so hard to guess about their behaviors)
- Type species is Kentrosaurus aethiopicus
- Species name aethiopicus comes from the provenance from Africa
- Hennig did not designate a holoytpe in his original description, but picked the most complete partial skeleton for his monography in 1925 (which is now part of the mounted skeleton in Berlin)
- Hennig published a monography in 1925, but by then only one tooth had been found (later more tooth fragments found and a tooth-bearing bone from the lower jaw); very similar to Stegosaurus, but smaller
- Controversy over the name (similar to the ceratopsian Centrosaurus); in 1916 Hennig renamed it Kentrurosaurus (pointed tail saurian) and Franz Nopcsa from Hungary renamed the ceratopsian Doryphosaurus (lance bearing saurian); but the renaming wasn’t necessary because the spellings and pronunciations are different, so Kentrosaurus is valid (and Kentrurosaurus is a junior synonym)
- In 1993, George Olshevsky classified fossils of Stegosaurus longispinus (named by Charles Gilmore in 1914) as Kentrosaurus longispinus, but paleontologists did not accept this, and it became its own genus, Natronsaurus (has longer tail spikes than Kentrosaurus and a slightly different pelvis and vertebrae structure)
- Kentrosaurus was similar to but smaller than Stegosaurus
- Adult Kentrosaurus was on average about half the length of an adult Stegosaurus
- Mallison in 2011 described the difference between Kentrosaurus and other dinosaurs in the Stegosauria group; included the neural spines in the tail being vertical in the middle of the tail and hook-shaped in the back of the tail
- Had elongated spikes (one specimen had a bone core length of 731 mm)
- Spikes and plates were probably covered
- Stegosaurus only had one row of plates and two rows of spikes on the tail end
- Kentrosaurus had thinner spikes than Stegosaurus (more likely to bend)
- Ragna Redelstorff said in a 2013 study that based on bone histology Kentrosaurus had a higher growth rate than Stegosaurus (though it was smaller, and contradicts the idea that larger dinosaurs grew more quickly than smaller dinosaurs)
- Kentrosaurus had shoulder spikes, which were originally thought to be on its hips (until Chinese stegosaurs)
- Similar shoulder spikes on Chinese stegosaurs Gigantspinosaurus and Huayangosaurus
- Kentrosaurus lived in the Late Jurassic, in Tanzania
- Lived in a subtropical to tropical area, with seasonal rains and dry periods
- Other dinosaurs included Dysalotosaurus, Giraffatitan, Barosaurus, Allosaurus, Ceratosaurus, Elaphrosaurus
- Kentrosaurus was about 15 ft (4.5 m) long, weighed one ton
- Had hoof-like claws on toes
- Small, elongated head
- Small brain, size of a walnut
- Had a good sense of smell
- Scientists found enough Kentrosaurus brain cavities to gather data on its intelligence and sense of smell
- Probably had two rows of small plats on its neck and back, and spikes on the hip and tail (longest ones were on the tail)
- Plates were not much protection, more for display
- Also had a long spine on each shoulder
- Used its spikes for defense (had a muscular tail)
- More than half its length is the tail
- Because of its center of mass, not much weight support by front legs, which means it had a tight turning radius
- Heinrich Mallison created a digital skeleton model of Kentrosaurus in 2005 to study its range of motion (and found it had a flexible neck)
- Mallison also made models of Kentrosaurus‘ tail
- Tail had at least 40 caudal vertebrae, which means it was very mobile (swing at 180 degree arc, at potentially up to 31 mph (50 kph); rapid swings could have slashed through skin or broken bones, and direct blows with the tail spies would fracture bones (would have really hurt small and medium theropods and potentially hurt large theropods)
- “At this speed,” Mallison wrote, “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.
- Based on recent CAD (computer) models of stegosaurs, probably had better posture than normally depicted (no horizontal neck or neck sloping down), but rather with neck angled upwards and head held a little higher than its back
- Could quickly rotate around the hips, and keep the tail pointed at the predator (though a fast predator could still get to the tail base, which wouldn’t have hurt as much when it swung its tail, and then attack the unprotected neck and upper body (but to kill a Kentrosaurus may have required hunting in packs)
- Had a flexible neck, and could look over its back
- Could possibly throw its head back to keep looking at attacker
- If it was a herding animal, working together with tails would have kept them safe from predators
- An early interpretation of how Kentrosaurus defended itself was to charge through attackers with its spines, similar to modern porcupines
- When walking, Kentrosaurus had an upright posture, but sprawled in defense
- May have sprawled when defending itself
- Short forelimbs and long hindlimbs
- Kentrosaurus showed sexual dimorphism (seems there were more females than males)
- Type types of thighbones, so one (female) had larger, more stout thighbones than the other
- Females probably had the thicker thigh bones
- Herbivore, mostly swallowed food in large chunks
- Beak that bit off plant material
- Considered to be a low browser for food (but could rear up)
- On all fours, could eat food up to 5ft 7 in or 1.7m high, could also rear up on hindlegs to reach higher vegetation; because of its long tail, it’s center of mass was close to its hind limbs, so it could potentially support itself in a stand up position (tail would have either been fully lifted or used as a third leg, though Bob Bakker said he thinks the tail wasn’t stiff enough to be a third leg); standing up, it could have reached food as high as 11 ft or 3.3 m
- Can see a composite skeletal mount in the Natural History Museum in Berlin, Germany
- The mount in Berlin comprised of a nearly complete tail, hip, dorsal vertebrae and parts of limbs from one individual (mount dismantled in 2006-7 and remounted with an improved pose. Braincase and spine and other parts thought to be lost in WWII, but then were later found in a drawer of a basement cupboard
museum of the Institute for Geosciences of theEberhard-Karls-University Tübingen has composite mount, with about 50% original bones - Belongs to the group Threophora (also called Enoplosauria), a group of dinosaurs with dermal armor (includes stegosaurs and ankylosaurs)
- Stegosauridae is a family of thyreophoran dinosaurs
- Includes stegosaurs more closely related to Stegosaurus than Huayangosaurus
- Lived into the late Cretaceous
- Had rows or osteoderms along their neck, trunk, and tail (plates and spikes, used for display, thermoregulation, and defense)
- Had front legs shorter than rear legs, (powerful but slow)
- Could shear small branches
- Skulls are shallower than early stegosaurs
- Two subfamilies: Dacentrurinae and Stegosaurinae
- Stegosaurinae are larger
- Fun Fact: According to the Nature article titled “Sauropod dinosaur osteoderms from the Late Cretaceous of Madagascar” the biggest known animals ever to have osteoderms were titanosaurs. Specifically they describe a single osteoderm found in Madagascar about the size of an American football (with an estimated volume of about 10 L) which is the most massive osteoderm ever discovered.
