A tiny, 120 million-year-old fossil, discovered in northeast China, is neither bird nor dinosaur but is perched on its own evolutionary branch, somewhere in between.

While the 2-centimeter-long (0.75-inch) skull of this little fella holds similarities to much larger dinosaurs like Tyrannosaurus rex, its thin and delicate body looks more like modern-day crown birds, such as sparrows or hummingbirds.

Careful CT scans and a detailed reconstruction of the fossil suggest this bizarre avian species once belonged to an extinct group of early birds called enantiornithines, or “opposite birds”.

Some other enantiornithines that have been discovered are no larger than a cockroach. This new one is slightly bigger and would have fit in the palm of your hand. Despite their diminutive size, these clawed and winged creatures were among the most abundant and diverse group of early birds living at the time.

While enantiornithines did not survive the Mesozoic mass extinction event, many of their traits still live on today and they are considered an important evolutionary step on the way to modern birds.

“Having a ‘dinosaur’ skull on a bird body certainly did not stop the enantiornithines, or other early birds, from being highly successful in places all around the world for tens of millions of years during the Cretaceous,” says paleontologist Min Wang from the Chinese Academy of Sciences.

The noggin on this early bird is particularly unique and excellently preserved. Unlike modern birds, whose upper jaws move independently from their brain case, which is known as cranial ‘kinesis’, the bones on this newly discovered skull are “locked up” and immovable.

They even show attachment points for jaw muscles, which are usually found in dinosaurs and reptiles, like lizards and alligators.

One bone in particular, known as the pterygoid, looked “exactly like that of the dromaeosaur Linheraptor”, according to Wang.

Linheraptor dinosaurs are bird-like theropods, an extinct group of dinosaurs that also includes meat-eaters like the T. rex and Velociraptor.

In fact, the back of this early bird’s skull resembles raptors more than it does living birds.

This suggests early birds could have evolved from a branch of dinosaurs that includes feathered Velociraptor and winged Microraptor.

“In combination with the ‘locked up’ temporal bones, the difference in the palate structure also points to the absence of kinesis among early birds,” says paleontologist Thomas Stidham from the Chinese Academy of Sciences.

This movement of the skull therefore must have evolved later, leading to the great diversity of skull shapes that we now see among modern crown birds.

“Despite their global conquest and success through the Cretaceous, only the crown group of birds with its derived assemblage of features, allowing for and driving cranial kinesis, survived the end Mesozoic mass extinction, and has thrived ever since,” the authors conclude.

The study was published in Nature Communications.

https://www.msn.com/en-au/news/techandscience/this-tiny-120-million-year-old-fossil-has-a-t-rex-like-skull-on-a-bird-body/ar-AALu61R?ocid=msedgntp

PermeateFree said:

A tiny, 120 million-year-old fossil, discovered in northeast China, is neither bird nor dinosaur but is perched on its own evolutionary branch, somewhere in between.

While the 2-centimeter-long (0.75-inch) skull of this little fella holds similarities to much larger dinosaurs like Tyrannosaurus rex, its thin and delicate body looks more like modern-day crown birds, such as sparrows or hummingbirds.

Careful CT scans and a detailed reconstruction of the fossil suggest this bizarre avian species once belonged to an extinct group of early birds called enantiornithines, or “opposite birds”.

Some other enantiornithines that have been discovered are no larger than a cockroach. This new one is slightly bigger and would have fit in the palm of your hand. Despite their diminutive size, these clawed and winged creatures were among the most abundant and diverse group of early birds living at the time.

While enantiornithines did not survive the Mesozoic mass extinction event, many of their traits still live on today and they are considered an important evolutionary step on the way to modern birds.

“Having a ‘dinosaur’ skull on a bird body certainly did not stop the enantiornithines, or other early birds, from being highly successful in places all around the world for tens of millions of years during the Cretaceous,” says paleontologist Min Wang from the Chinese Academy of Sciences.

The noggin on this early bird is particularly unique and excellently preserved. Unlike modern birds, whose upper jaws move independently from their brain case, which is known as cranial ‘kinesis’, the bones on this newly discovered skull are “locked up” and immovable.

They even show attachment points for jaw muscles, which are usually found in dinosaurs and reptiles, like lizards and alligators.

One bone in particular, known as the pterygoid, looked “exactly like that of the dromaeosaur Linheraptor”, according to Wang.

Linheraptor dinosaurs are bird-like theropods, an extinct group of dinosaurs that also includes meat-eaters like the T. rex and Velociraptor.

In fact, the back of this early bird’s skull resembles raptors more than it does living birds.

This suggests early birds could have evolved from a branch of dinosaurs that includes feathered Velociraptor and winged Microraptor.

“In combination with the ‘locked up’ temporal bones, the difference in the palate structure also points to the absence of kinesis among early birds,” says paleontologist Thomas Stidham from the Chinese Academy of Sciences.

This movement of the skull therefore must have evolved later, leading to the great diversity of skull shapes that we now see among modern crown birds.

“Despite their global conquest and success through the Cretaceous, only the crown group of birds with its derived assemblage of features, allowing for and driving cranial kinesis, survived the end Mesozoic mass extinction, and has thrived ever since,” the authors conclude.

The study was published in Nature Communications.

https://www.msn.com/en-au/news/techandscience/this-tiny-120-million-year-old-fossil-has-a-t-rex-like-skull-on-a-bird-body/ar-AALu61R?ocid=msedgntp

Wow, lovely. Thank you.

> 120 million-year-old fossil

Let’s see how that fits in the timescale.
Archaeopteryx – 150.8 million
Confuciousornis – 125 to 120 million years
Hesperornis – 83.5 to 78 million years

> an extinct group of early birds called enantiornithines, or “opposite birds”. Enantiornithines did not survive the Mesozoic mass extinction event.

Genetic analysis of true modern birds gives an original divergence date for true birds in the range of 120 to 140 million years ago. Although there’s a strong tendency to lump all ancient birdlike fossils into the extinct catch-all group enantiornithines, there’s a very good chance that some of these fossils were already true birds. Someone really needs to sort this out.

> Some other enantiornithines that have been discovered are no larger than a cockroach.

I missed this!
I knew that some were as small as a sparrow. (Checks web) Gotcha.

http://www.sci-news.com/paleontology/enantiornithe-bird-fossil-05785.html

Early Cretaceous Bird Fossil Sheds New Light on Avian Evolution,
Mar 5, 2018.
The tiny fossil of a juvenile enantiornithe bird from the Early Cretaceous La Huérguina Formation of Spain is helping paleontologists understand how early birds came into the world in the age of dinosaurs.

“The 127-million-year-old fossil is a chick from a group of prehistoric birds called Enantiornithes. The specimen consists of a nearly complete skeleton; the feet, most of its hands, and the tip of the tail are the only missing parts. It measures less than 2 inches (5 cm) and would have weighed just 10 g when it was alive. It is amongst the smallest known Mesozoic avian fossils ever discovered.’

“What makes this fossil so important and unique is the fact it died not long after its birth. This is a critical stage in a bird’s skeletal formation. That means this bird’s extremely short life has given paleontologists a rare chance to analyze the species’ bone structure and development.”

Hold on. First of all, 5 cm is much larger than the cockroackes we have around here. Second, this is a newly hatched chick. A newly hatched sparrow chick is only 2.5 cm long, so this bird species is still sparrow-size, not cockroach size.

Young animals have head size large relative to body size. This one could be a young animal. Compare the head size with the skeleton of a modern baby chicken, below. Quite similar in proportion. The most obvious differences are that the fossil has a long tail and claw-like talons.

A guide to the distinction between birds and enantiornithes has been the presence or absence of a lail containing a backbone, the absense beiong called a pygostyle.

Which leaves me wondering if loss of a tail is or is not truly a reliable guide to taxonomy. For example, among the mammals, the apes, the roe deer and the Manx cat have lost their tails but that doesn’t imply that the absense of a tail is primordial to the common ancestor of apes, herbivores and carnivores.

So taillessness could have evolved multiple times in bird ancestry. But did it?

“Pygostyles probably began to evolve very early in the Cretaceous period, perhaps 140-130 million years ago. The earliest known species to have evolved a pygostyle were members of the Confuciusornithidae. There are two main types of pygostyle: one, found in Confuciusornithidae, Enantiornithes, and some other Mesozoic birds, as well as in some oviraptorosaurs like Nomingia, is long and rod- or dagger blade-like.”

“The other pygostyle type is plowshare-shaped. It is found in Ornithurae (living birds and their closest relatives), and in almost all flying species is associated with an array of well-developed rectrices used in maneuvering. The central pair of these attach directly to the pygostyle, just as in Confuciusornis. The other rectrices of Ornithurae are held in place and moved by structures called bulbi rectricium (rectricial bulbs), a complex feature of fat and muscles located on either side of the pygostyle. The oldest known species with such a pygostyle is Hongshanornis longicresta”.

Although the oviraptor Nomingia is credited with a rod-like pygostyle, it’s only the tail tip that is affected, as shown below, this is nothing like the loss of a tail seen in birds.

“Confuciusornithidae is an extinct family of pygostylian avialans known from the Early Cretaceous, found in northern China.” They first appeared 131 million years ago”. The image below has Archaeopteryx at left and Confuciornis at right.

By way of contrast, Hongshanornis is totally missing a tail, as shown below. Though I can’t say that the pygostyle looks very “plowshare shape”. “Hongshanornis is a genus of ornithuromorph birds known from early Cretaceous lake deposits of the Yixian Formation, Inner Mongolia, China. The holotype specimen, recovered in 2005, is currently held by the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. It was found in the Jianshangou fossil beds, dated to 124.6 million years ago.” Hongshanornis still had teeth.