Newly discovered dinosaurs fill in evolutionary gap spanning 70 million years

Newly discovered dinosaurs fill in evolutionary gap spanning 70 million years
This illustration shows where two newly discovered dinosaur species fit in the lineage of alvarezsaurs (from left): Haplocheirus, Xiyunykus, Bannykus and Shuvuuia. The species show lengthening of the jaws, reduction of the teeth and changes in the hand and arm over time. Credit: Viktor Radermacher

Two newly discovered dinosaurs may be missing links in an unusual lineage of predators that lived between 160 million and 90 million years ago, new research suggests.

The two species, Xiyunykus and Bannykus, were theropods—a group of bipedal, largely . Some theropods eventually gave rise to birds, while another branch, the alvarezsauroids, evolved into strange-looking insectivores with short arms and hands with an enlarged finger for digging into nests.

But until now, little was understood about how this change happened because of the 70-million-year evolutionary gap separating the insect-eating alvarezsauroids from the earliest known member of the group, Haplocheirus.

"The significance of Xiyunykus and Bannykus is that they fall within that gap and shed light on patterns of evolution within Alvarezsauroidea," explained Corwin Sullivan, a University of Alberta paleontologist who participated in the international study.

"These specimens greatly improve the scientific community's understanding of the early stages of alvarezsauroid evolution and give us a better idea of what early alvarezsauroids were like."

Sullivan noted the new specimens reveal clues about how the creatures' diet shifted from meat to insects.

"The forelimbs show some adaptations for digging, which would later become more exaggerated, and some features of their skulls also resemble those of insectivorous alvarezsauroids. The hindlimbs are less modified, suggesting the arms and head of alvarezsauroids underwent significant change before the legs did.

"There's still a lot to learn about the early of alvarezsauroids," added Sullivan, who is also curator of the Philip J. Currie Dinosaur Museum.

"Xiyunykus and Bannykus are currently represented by one incomplete specimen apiece. Those specimens provide a good deal of intriguing information, but we'll need many more fossils before we can be confident that we have a clear understanding of how alvarezsauroids, to put it bluntly, got so weird."

The paper, "Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution," was published in Current Biology.


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More information: Xing Xu et al. Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution, Current Biology (2018). DOI: 10.1016/j.cub.2018.07.057
Journal information: Current Biology

Citation: Newly discovered dinosaurs fill in evolutionary gap spanning 70 million years (2018, September 3) retrieved 25 June 2019 from https://phys.org/news/2018-09-newly-dinosaurs-evolutionary-gap-spanning.html
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Sep 03, 2018
What exactly was found? Typically what is usually found is a small piece of bone and then an artist has complete reign to raw whatever he/she wants.

Why is it that billions of fully formed fossils are found but only a very small number of questionable "transition" fossils? Over millions of years there should be many, if not a very large quantity, of "transition fossils". But, no. Only fully formed easily recognizable ones.

Charles Darwin had a huge problem. He couldn't name any transitional forms in his Origin of Species (1859). Instead he devoted a whole chapter "The Imperfection of the Geological Record", in which he wrote:

"Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory. The explanation lies, as I believe, in the extreme imperfection of the geological record."

Sep 03, 2018
What exactly was found? Typically what is usually found is a small piece of bone and then an artist has complete reign to raw whatever he/she wants.


Stupid comment. Why didn't you just read the linked paper?


Sep 03, 2018
What exactly was found? Typically what is usually found is a small piece of bone and then an artist has complete reign to raw whatever he/she wants.


Stupid comment. Why didn't you just read the linked paper?



If only everyone did.

Sep 04, 2018
TS, I'm trying to understand your proposed "Theory".

Kinda difficult to have an opinion about it, unless you actually articulate your speculative ideas!

Also, I thought this was an article claiming to have newly discovered data showing the presently available evidence for the different stages of evolution within this clade of insectivores.

What does that have to do with the geological record? Well of course it's imperfect. Reality is a chaotic mess of "imperfectly" available information.

And what billions of perfectly formed fossils have you examined? Can you specifically point out your verified evidence for claiming that there are errors in the generally accepted fossil record?

Not just disparage other peoples work because you disagree with their methodology. What specific improvements would you make to improve the reliability of the Scientific Method?

Charles Darwin was one of the last of the Philosophers of Science. Lacking all our modern tech and data.

Sep 10, 2018

BLA, bla, "transition" fossils? Only fully formed easily recognizable ones.

Charles Darwin had a huge problem.


Unfortunately, ALL fossils are transitional forms. 100% of them mate. You guys are too obsessed with concepts that you have pulled out of your own sleeve, which invalidades any argument from your part as you aren't even discussing the same matters as the rest. It's as if somebody where criticizing the color of Noah's Ark, to put it into a terrain more familiar to you than science.

Sure, Darwin had a huge problem: He lived in the XIX Century.

;)


Sep 11, 2018
Charles Darwin had a huge problem. He couldn't name any transitional forms in his Origin of Species (1859).


That is history albeit leaving out that Wallace observed the same process, and notably the basic process of biology was recognized within years of both publications. Further on the phylogenetic methods that are used by him and the paper here show the transitional forms, despite that the fossil record - as also noted in the article - is still fragmentary and always will be.

TL;DR: Buffoon comment born out of ignorance based - if US comment - in religion and not the world as we know it; basic biology changes is the best tested process we have in all of science. Using religion to discuss the world is like using homeopathy to cure diseases.

Sep 11, 2018
Unfortunately, ALL fossils are transitional forms. 100% of them mate
I cant rate on this phone but THAT is a very good point.

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