This week, a [paper] came out describing a new baby enantiornithine. Enantiornithines are early birds that are closely related to the birds we see today, but part of a separate group. All enantiornithines went extinct at the end of the Cretaceous.
An enantiornithine. By S. Abramowicz.
This paper describes a fossil from the Early Cretaceous of Spain that preserves most of the skeleton. It is a remarkable specimen because it died around the time of birth. Because of its young age, it can give us a special glimpse of how the skeletons of enantiornithines developed in their lives.
Figure 1 from the paper showing the fossil. The head is up and the face is pointing to the right.
Of all the bones in this fossil, the sternum and the tail give us the most information into enantiornithine skeletons. The sternum is the large breastbone in birds that anchor the flight muscles. Enantiornithines also have a large sternum. This fossil shows that the sternum starts to ossify (or turn into bone) later than the other bones in the skeleton. It does this in a complicated pattern that is different from what we see in other enantiornithines and modern birds.
Figure 4g from the paper showing the ossification pattern of the sternum. It starts out as cartilage (grey) and it starts to ossify in the red, blue, and yellow sections. The bone grows out from there until the whole sternum is made of bone.
The tail in birds is usually fused into a bone called the pygostyle. In young birds, the vertebrae are still separate. This fossil has more separate vertebrae than the adult enantiornithines.
Figure 4 d and e from the paper showing a tail from an adult enantiornithine on the left and the baby on the right.
Both of these characteristics are slightly different than in other enantiornithines and in modern birds. This tells us that though very similar to modern birds on the outside, enantiornithines were developing their skeletons slightly differently. Ultimately, this could shed light on the different developmental strategies that we see in modern birds (how some can walk or fly at hatching and some take weeks or years to mature fully).
Figure 7 from the paper showing a reconstruction of the baby bird. The silhouettes show how big the baby would have been compared to a cockroach of the time. By R. Martín.
Last week, an [article] was published describing an old specimen that was hidden away in a museum collection at the University of Birmingham, United Kingdom. This specimen was of a baby ichthyosaur, only 70 cm long.
Ichthyosaurs were marine reptiles that lived during the Mesozoic Era. They had torpedo-shaped bodies, similar to modern dolphins and great white sharks. They came in all sorts of sizes and shapes!
Figure 1 from the paper showing the ichthyosaur fossil.
The authors know the specimen is a baby because some of its bones are still being developed and because of the proportions of the eyes and different bones in the skull. It was not found near an adult, so it wasn’t an embryo. This is the smallest specimen of Ichthyosaurus communis ever found!
Figure 9b from the article showing the hooklets in the stomach (by the black arrows). The long grey bones are ribs.
The interesting thing, though, is what they found in the stomach. Inside the ribs, the authors found several cephalopod hooklets. Remember, cephalopods are animals like octopus, squid, and nautilis. These hooklets are found on the underside of their tentacles, exactly where you’d find the suckers on an octopus arm.
A comparison of suckers and hooks on two different cephalopods. From here and here.
This indicates that the baby ichthyosaur was eating squid as its preferred food! Other species of ichthyosaur ate mostly fish as babies and transitioned to eating cephalopods as adults. This baby specimen shows that Ichthyosaurus communis ate cephalopods as babies, giving us a more thorough view of the diets of ichthyosaurs through their lifetimes.
This post will start out a bit differently because I want you to understand how amazing titanosaurs are before getting into the news about them.
The titanosaurs were the largest land animals ever to have lived (around 100 tons). Blue whales are heavier (around 180 tons) than the titanosaurs were, but the whale’s weight is supported by the ocean they live in. Titanosaurs had to support their weight all on their own. For comparison, an African elephant (the largest land animal alive today) weight 7 tons. So a titanosaur weighs the same as 14 elephants.
They are huge.
Titanosaurs belong to the group of sauropod (long-necked) dinosaurs, which are found throughout the Mesozoic. The titanosaurs were the last group of sauropods, from 90-66 million years ago. So the largest dinosaurs were around at the very end of the Mesozoic. Stomping around and causing a big rumpus everywhere they went.
How did they get so big?? Good question! Saurischian dinosaurs, including the sauropods and theropods, developed a system of air-sacs in their body. We know this because when the air sacs were big enough, they started invading near by bone and leaving hollow spaces. These air sacs connected to the lungs and created a one-way system of respiration that is super efficient. Birds still rely on this system today.
Simple animation of how a bird breathes. Take from here.
Ok, so, titanosaurs are: 1) from the Cretaceous, 2) incredibly large, 3) can breathe really efficiently (probably true for all sauropods). A couple of other cool things about sauropods: some of them had [whip tails], some of them had [armor], some of them became dwarf-sized on [islands].
In short, titanosaurs are really amazing.
This week (April 2016), two articles were published about titanosaurs!
First, a wee baby Rapetosaurus krausei from Madagascar was [described]. This little baby shows that titanosaurs grow isometrically. Isometric growth is when your shape does not change as you get bigger. This is in contrast to allometric growth, where shape does change as you get bigger. Humans, among many examples, grow allometrically, so our baby shape is very different from our adult shape:
Our bodies change shape as we get bigger. Taken from here.
Titanosaurs are adult-shaped from when they hatch:
Figure 1A from the paper showing how the baby bones (yellow, green, blue) have the same shape as the adult bone (black). The smallest grey titanosaur is just hatched, the colored one is the size of the specimen they had for the paper.
Second, an almost complete skull of the new titanosaur (from Argentina!) Sarmientosaurus musacchioi was [described]. It was found near the town of Sarmiento, Chubut.
Look at it! It’s beautiful. (This is figure 3c from the paper.)
It’s so well preserved that the authors were able to CT scan it and create an endocast (a representation of the brain and surrounding structures).
Figure 9a from the paper – a reconstructed 3d brain (front is to the left) showing all the structures.
They were also able to use it to analyze the evolutionary relationships of titanosaurs. They ran the analysis several ways and found the same result each time: that Sarmientosaurus is an early member of the most derived titanosaurs, the Lithostrotia. The age of the rocks where Sarmientosaurus is found is older than other members of this group and makes their evolution older than what we had previously thought.
The age, evolutionary position, and great preservation of this new titanosaur helps answer many questions about the evolution of the most derived titanosaurs. It’s a spectacular discovery and addition to our knowledge of the largest land animals that ever lived.
PS: If you want to see one fully reconstructed, the American Museum of Natural History recently unveiled [one]: