Question 1

How do you say Chevron?

Accepted Answer

Chevron is pronounced SHEV-ron, with the stress on the first syllable. The first part rhymes with 'rev' as in revving an engine, and the second part is just 'ron' like the name. Say it fast: SHEV-ron. You might recognize the word from the gas station brand or from military rank stripes, and it is pronounced exactly the same way in paleontology.

Question 2

What is a chevron bone in a dinosaur?

Accepted Answer

A chevron bone is a small V-shaped or arch-shaped bone that hangs beneath the tail vertebrae of many dinosaurs. It sits on the underside of the tail, attached between pairs of vertebrae, forming a protective canal around the major blood vessels running through the tail. Chevrons also served as anchor points for powerful tail muscles. They are separate from the vertebrae themselves and vary widely in size and shape depending on the species.

Question 3

Did all dinosaurs have chevron bones?

Accepted Answer

Most dinosaurs had chevron bones, but not all tail vertebrae in every species had one. Chevrons are typically present along much of the tail but may be absent or reduced near the very tip. Some heavily armored dinosaurs like ankylosaurs had quite small chevrons, while long-tailed sauropods and large theropods had well-developed ones. The presence, size, and shape of chevrons varied enormously across different dinosaur groups and species.

Question 4

What did chevron bones do for dinosaurs?

Accepted Answer

Chevrons had at least two main jobs. First, they formed a bony protective arch around the caudal artery and vein, the major blood vessels running beneath the tail, preventing those vessels from being crushed when the tail bent and flexed. Second, they provided attachment points for large tail muscles, including the powerful caudofemoralis muscle in theropods, which connected the tail to the hind leg and was crucial for walking and running. Some researchers also think chevrons may have supported additional soft tissue structures.

Question 5

Do any animals alive today have chevron bones?

Accepted Answer

Yes, chevron bones exist in many living animals. Crocodilians, which are the closest living relatives of dinosaurs among reptiles, have well-developed chevrons in their tails. Many lizards also have them. Some mammals including opossums and kangaroos retain chevron-like bones in their tails, showing that this is a very ancient vertebrate structure. Even whales have remnants of similar structures, a clue to their evolutionary history as land mammals that returned to the sea.

Question 6

How big were chevron bones in sauropod dinosaurs?

Accepted Answer

In large sauropods like Diplodocus and Apatosaurus, chevron bones could be quite substantial relative to the vertebrae they attached to, sometimes reaching lengths of 15 to 25 centimeters or more in the largest individuals. Some sauropod chevrons were also bifurcated, meaning they split into two prongs toward their lower end, creating a forked shape that gave extra surface area for muscle attachment. Diplodocus had more than 80 tail vertebrae, and a large proportion of them carried chevron bones underneath.

Question 7

Can scientists tell a dinosaur's gender from its chevron bones?

Accepted Answer

Scientists have tried to use chevron shape to determine the sex of dinosaur fossils, but the results are still debated. In living crocodilians, the first chevron behind the pelvis is shaped differently in males and females because of differences in reproductive anatomy. Some researchers have applied this same reasoning to dinosaur fossils, looking for similar variation. However, because individual variation and growth stages also affect chevron shape, most paleontologists consider sex determination from chevrons alone to be unreliable without additional evidence.

Question 8

Why do scientists care so much about such tiny bones like chevrons?

Accepted Answer

Even though chevrons are small, they carry a lot of information. Their shape, size, and angle can help scientists identify a species, estimate muscle mass, reconstruct how the tail moved, and even make inferences about behavior and locomotion. In some cases a single chevron is enough to identify which group of dinosaurs a specimen belongs to. Paleontologists say that in the fossil record, no bone is too small to be informative, and chevrons are a perfect example of why that is true.

Question 9

Could Diplodocus really crack its tail like a whip using its chevrons?

Accepted Answer

This is a genuinely exciting scientific question. In 1997, researchers Nathan Myhrvold and Philip Currie proposed that the long tapering tails of sauropods like Apatosaurus could be swung fast enough to create a sonic boom, similar to cracking a bullwhip. Their work relied on analyzing the structure of the tail vertebrae and the flexibility allowed by the chevrons. While some scientists accept the basic idea and others remain skeptical, the debate highlighted just how much information about dinosaur behavior can be extracted from studying tail anatomy including the chevrons.

Question 10

What is the difference between a chevron and a haemal arch?

Accepted Answer

Chevron and haemal arch refer to the same bone. Chevron is the more informal and widely used term, named for the V-shape of the bone. Haemal arch is the more technical anatomical term, coming from the Greek word for blood, and it highlights the bone's function of forming an arch around the blood vessels beneath the tail. You will see both terms in books and scientific papers, and they are completely interchangeable. Some scientists prefer haemal arch in formal writing while chevron is more common in popular science and museum contexts.

Question 11

Where exactly is a chevron located on a dinosaur skeleton?

Accepted Answer

Chevrons are located on the ventral side of the tail, meaning the underside or belly side. They attach between adjacent caudal vertebrae, hanging below the main column of tail bones. If you picture the tail vertebrae as a horizontal row of discs or spools, the chevrons are the downward-pointing structures beneath those discs. In a mounted dinosaur skeleton at a museum, you can often spot them by looking at the underside of the tail, where you will see a series of small arched or V-shaped bones running along its length.

Question 12

Are chevrons the same as spines or plates on a dinosaur's back?

Accepted Answer

No, chevrons are completely different from dorsal spines or plates. Plates and spines on a dinosaur's back, like those on Stegosaurus, grow from the top surface of vertebrae and point upward or outward. Chevrons grow from the bottom of the tail vertebrae and point downward. They serve different purposes and are found in different locations on the body. The plates of Stegosaurus are called osteoderms or dermal bones, while chevrons are part of the core skeleton of the tail itself.

Question 13

Did T. rex have chevron bones?

Accepted Answer

Yes, Tyrannosaurus rex had well-developed chevron bones in its tail. The chevrons near the base of the tail were especially important because that region was packed with the caudofemoralis muscle, one of the largest and most powerful muscles in the T. rex body. This muscle ran from the tail vertebrae and chevrons down to the femur, or upper leg bone, and it was the main driver of T. rex's walking and running stride. Scientists studying T. rex locomotion pay close attention to the chevron anatomy because it helps them estimate how large and powerful those tail muscles really were.

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