Episode 562: April Fowls: Archaeopteryx. A new troodontid with a skull like a pachycephalosaur, two new prehistoric birds, the bird evolutionary tree, how birds developed the ability to fly, how we know Microraptor turned out to be a decent flier, and a mathematical rule that shapes theropod faces

News:

• A new troodontid theropod, Xenovenator espinosai, has an extremely thick skull—like a pachycephalosaur source
• Scientists have created a complete evolutionary tree of all birds (over 9,000 species) source
• There’s a new neoavian Aequornithes bird from Antarctica, Pujatopouli soberana source
• There is a new euornithean bird, Kunpengornis anhuimusei, that has gut contents! source
• How the structure of feathers in the Cretaceous tells us about their evolution source
• The specialization of a small wrist bone, the pisiform, helps birds to fly source
• A key wing muscle that helps birds fly appears to have evolved by fusing cells from multiple muscles source
• How often birds, bats, and insects flap when flying may be related to a built in constraint related to the vortex their wings generate with each flap source
• More Microraptor specimens (with soft tissues!) show it was a decent flier source
• A set of raptor dinosaur tracks indirectly shows it used its arms to help it run faster source
• Just because a theropod dinosaur had short arms and not many fingers, doesn’t mean their hands and arms were useless source
• Birds have a special organ to help them balance (which doesn’t seem to matter as much for flight) source
• Birds have been nesting in the Arctic for at least 73 million years source
• How theropod dinosaur (non-avian and bird) faces are shaped may have followed a mathematical rule source
• A study of the Chicago Archaeopteryx found that could definitely fly source
• Birds need a lot of calories to fly, and Archaeopteryx, the oldest known bird, has three features modern birds also have to eat efficiently source

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This episode is brought to you by the Colorado Northwestern Community College. Join them for two weeks digging up dinosaur bones in the field, preparing fossils in their lab, or in their new field geology program. For details go to CNCC.edu/paleo26

The dinosaur of the day: Archaeopteryx

• Archaeopteryx was a small feathered dinosaur that lived in the Late Jurassic (about 150 mya) in what is now Bavaria, Germany
• It’s a bird. Not the first bird, but the oldest known bird
• Some consider Anchiornis and its relatives to be birds older than Archaeopteryx, and others consider them to be troodontids
• First described in 1861 by Hermann von Meyer based on a single feather (back when the only animals known to have feathers were birds)
• Debate about what type of feather it is (especially because the calamus, or quill, is missing). One study in 2019 hypothesized it was from a different feathered dinosaur because it looked different from other Archaeopteryx feathers that were found later
• Latest studies consider the feather to be a primary covert feather (covers other feathers on the wing to help with flight)
• The first illustration (a lithograph from 1866) of Archaeopteryx was headless because no one wanted to guess what the head looked like
• In the caption it says the illustration restores it “as it may have existed in life, save for its head, which was not found with the animal’s other remains”
• 14 specimens have been found since that first feather (some found much more recently than others)
• An example of a “transitional taxon”
• Had large, feathered wings, a wishbone, and a reversed toe Also had teeth, a long bony tail, claws on its hands and small hips
• Based on Archaeopteryx and Compsognathus, Thomas Huxley suggested that birds are dinosaurs Took until John Ostrom and the Dinosaur Renaissance, with Deinonychus, to revive the idea
• Genus name Archaeopteryx means “ancient wing”
• Sometimes referred to by the German name, “Urvogel”, which means “primeval bird”
• Estimated to be about the size of a raven
• Lived on islands with shallow warm tropical seas, with lots of sharks, fish, ichthyosaurs, turtles, crustaceans, and more As well as pterosaurs and lizard-like reptiles
• WHY IMPORTANT
• Archaeopteryx discovered two years after Charles Darwin published On the Origin of Species, and seemed to confirm evolution
• DESCRIPTION
• Very bird-like dinosaur, with a beak, feathers, and wings
• Estimated to be up to 1 ft 8 in long (50 cm), with a 2 ft 4 in (70 cm) wingspan
• Estimated to weigh 18 to 35 oz (500 to 1,000 grams)
• Had similarities to dromaeosaurs (raptors), like long chevrons in the tail (bones that help with movement and anchor muscles), so had a long, bony tail
• Had sharp teeth
• Had three fingers on each hand that ended in claws
• Had sickle like claws on the second toes
• Had similarities to birds too
• Had broad wings
• Had a wishbone
• Had a partially reversed toe
• Reversed toe means it could perch Probably spent time on the ground and in trees, like pigeons and doves
• Feathers were similar to modern bird feathers
• Feathers were asymmetrical (need for flight). That’s an over-simplification, we talk about it a lot more in our 390th episode “How dinosaurs evolved flight”
• Had feathers on the legs
• No evidence of feathers on the upper neck and head, but could be how the fossils were preserved
• A 2011 study found melanosomes in the 1861 feather, and found it was likely to be black in color (doesn’t mean Archaeopteryx was all black, but had some black feathers)
• Had a hypopubic cup (feature in the hips seen in early birds, helps with spending time in trees)
• Archaeopteryx has a small premaxilla and large maxilla (tip of the jaw and upper jaw). Crown birds (includes modern birds) are the opposite
• 14 SPECIMENS
• 14 Archaeopteryx skeletons have been found, plus one feather (most specimens include feather impressions)
• All fossils were found near Solnhofen, Germany
• —The area was full of lakes which occasionally became toxic when salinity rose from the Tethys sea
• —At those times, if a dinosaur (like Archaeopteryx) died there it would get slowly buried in soft mud with nothing there to disturb it
• —That’s how the feathers of Archaeopteryx were preserved
• Rumors of more specimens
• Almost every specimen has been considered a separate taxon at some point Some specimens are fragmentary, and some poorly preserved
• Latest studies by Jingmai O’Connor and others found them all to be the genus Archaeopteryx
• Differences based on growth series (ontogeny) or individual variation Each specimen with a skull has a different arrangement of teeth
• First skeleton, the London Specimen, was found in 1861 (missing most of its head and neck, described in 1863 by Richard Owen)
• A 2004 CT scan of the London Specimen braincase found it had a good sense of hearing, balance, spatial perception, and coordination for flying
• Berlin Specimen described in 1884, and is the most complete, and the first with a complete head. Includes all the claws on the ends of the fingers/middle of the wings and a lot of detail of the feathers
• Maxberg Specimen described in 1959 (missing head and tail but rest of the skeleton mostly intact). Currently is missing. It belonged to Eduard Opitsch who loaned it to a museum until 1974. After he died in 1991, it was missing (possibly stolen or sold)
• The Haarlem Specimen was described in 1857 as a Pterodactylus, then reclassified in 1970 by John Ostrom (found in 1855, so was the first specimen found, but was incorrectly classified). Mostly limb bones, some neck bones, and ribs. In 2017 it was renamed Ostromia (after John Ostrom who first noticed it was a dinosaur). Talked about this in our second episode of I Know Paleo, about Quetzalcoatlus and in ep 159, titled Lufengosaurus
• The Eichstätt Specimen was described in 1974, and is the smallest known specimen (has the second best skull)
• The Solnhofen Specimen was described in 1988 (originally thought to be Compsognathus). Largest one known, missing parts of the neck, tail, backbone, and head. Considered to be the genus Wellnhoferia (which may be a synonym)
• The Munich Specimen was described in 1993 (only the front of the face is missing)
• The Daiting Specimen was found in 1990
• A study of the 8th specimen in 2018 (Daiting specimen) found it was a basal bird Comes from the Mörnsheim Formation and younger than the other Archaeopteryx species Named it Archaeopteryx albersdoerferi Had a lighter skeleton and fewer teeth
• The Bürgermeister-Müller (“chicken wing”) Specimen, a fragmentary fossil of a single wing
• The Thermopolis Specimen, found in Bavaria and described in 2005 (best preserved head and feet)
• The eleventh specimen was described in 2014, missing the skull and one arm (privately owned, no nickname yet)
• A twelfth specimen described in 2018, with a complete, mostly articulated skeleton with a skull (no feathers)
• Talked about in episode 171, titled Bactrosaurus
• Includes a well preserved skull, claws, wings, tail, everything in between, and is older than the previously found Archaeopteryx specimens, by about a million years. Had different number of teeth and other slight differences in the skull from the other specimens
• A thirteenth specimen was described in 2025 (right arm, shoulder, fragments of other limbs)
• Talked about it in our last April Fowls episode, ep 533: The Shady Dinosaur and April Fowls
• Fossils found in 2019 (specified in the paper, May 31) Found in nine limestone slabs, with brittle, flaky surfaces Lots of changes from fossilization, but the wishbone and other bones show it’s Archaeopteryx
• The Chicago Specimen was acquired by the Field Museum in 2022 and went on display in 2024 (talked about in episode 495, titled “Why Dinosaurs? Plus the first dinosaur bones from South America”
• Found sometime before 1990 by a private fossil collector, and has been in private collections since 1990 A group of people helped the Field Museum get it, and it got to the museum in August 2022 Museum had to prepare it In the x-ray, saw in the slab it was nearly complete
• Multiple species have been named
• A 2007 study reviewed all the specimens and found there are two species: A. lithographica and A. siemensii (differences in the foot claws)
• FLIGHT
• Had feathers and wings
• Lots of debate about how well it could fly (powered flight or gliding)
• The latest: able to flap its wings and fly
• But first…
• From ep 366: T. rex skull strength, tooth arrangement, and running speed
• There are four factors: bone strength, feather shape, wing anatomy, and flapping power to consider
• Habib and Pittman at an SVP talk studied the Munich Archaeopteryx and found it could launch no problem, it’s possible it could climb, it didn’t have much muscle so sustained flight/flying steadily was a maybe
• (like I said though, the latest studies found it could fly)
• The brain
• From ep 360: The Welsh “chief dragon”
• Angela Milner reconstructed Archaeopteryx’s brain, and showed it had evolved brain regions for flight control and better vision
• Wing bones and skeleton
• Didn’t have a bony breastbone, where the flight muscles attached, so had small flight muscles, and may not be a strong flier
• From ep 173: Kosmoceratops
• Talked about a study that investigated Archaeopteryx flying ability, by using the European Synchrotron to look inside the bones of three specimens
• Found it was similar to modern flying birds, especially those that use “short-distance flapping”
• From ep 232: Indosuchus
• Talked about a study that examined Archaeopteryx under UV and found it had a very light skeleton (highly pneumatic)
• Likely had air sacs and bird-like respiration
• And had several vertebrae between the shoulder and hips that were reinforced for extra strength. May have evolved to deal with additional forces from flapping wings
• Feathers
• (Quick plug, if you want to hear all about feathers listen to our episode 458, titled Beyond Bones: Feathers)
• Had relatively large wings
• Had “hind wings”
• Had broad tail feathers (long tail covered in feathers likely made it too difficult to fly long distances)
• From ep 388: The largest megaraptorid ever?
• In 2012, Nicholas Longrich and others analyzed wing feather arrangement in Archaeopteryx and Anchiornis, and found they had multiple rows of feathers
• From ep 311: T. rex walking speed and bite force
• A 2020 study found Archaeopteryx may have molted (based on missing feathers)
• Modern birds molt to get rid of feathers that impede flying, though the earliest birds with feathers probably didn’t fly so molting would have evolved without pressure to fly
• Archaeopteryx appears to have a center-out molting pattern (strategy to maintain flight performance)
• Now on to the most recent studies!
• “Chicago Archaeopteryx informs on the early evolution of the avian bauplan” Jingmai O’Connor and others Nature
• A study of the Chicago Archaeopteryx found that could definitely fly
• The Chicago Specimen (pigeon sized, and the smallest Archaeopteryx specimen) has lots of soft tissue and more details in the skeleton than previously known
• Used CT scans and UV light
• Had a layer of feathers called tertials (innermost flight feathers that cover the space between the body and the wings, and wings need them to generate lift) that hadn’t been found in Archaeopteryx before Along with asymmetric feathers, means it could fly
• Earliest known dinosaur able to use its feathers to fly (though not as well as modern birds)
• Had a long upper arm bone, so the tertials are very important (don’t want a gap between the feathers of the wing and the rest of the body) In non-avian dinosaurs that are closely related to birds, wing feathers stop at the elbow (tells us they couldn’t fly)
• Also found…
• Had a large pisiform in the wrist (talked about the pisiform earlier in the episode)
• Had scales on the bottom of the toes, so likely spent lots of time on the ground Goes well with the short reversed hallux (first toe) Could move easily on the ground and in trees, similar to pigeons and doves
• Had soft tissue on its hands (means the third finger could move independently), was free and able to move Had bones in the roof of its mouth (help show the evolution of cranial kinesis, feature in modern birds that let the beak move independently from the braincase, and is hypothesized to be what allowed birds to evolve specialized skulls to fit different niches and evolve into more than 11,000 species)
• Had a longer tail than previously known and a less rigid skull Had 24 tail bones (before only 22 found preserved) Had 14 back bones and 9 neck bones
• Lack of fusion in bones may mean its not fully mature
• And last, but not least…more evidence that Archaeopteryx could fly
• “Avian features of Archaeopteryx feeding apparatus reflect elevated demands of flight” Jingmai O’Connor and others The Innovation
• Birds need a lot of calories to fly, and Archaeopteryx, the oldest known bird, has three features modern birds also have to eat efficiently
• Of all the ways animals move, flight takes the most energy Archaeopteryx, the oldest known bird, has three structures also found in modern birds that help with efficient feeding (don’t see these features in flightless non-avian dinosaurs) Shows these features evolved in early birds to help them get enough calories to fly
• Modern birds have a very efficient digestive system to get all the calories they need to fly. Includes: the crop (to hold food in a pouch in the esophagus so they can quickly swallow lots of food and digest later or regurgitate for their young), bidirectional peristalsis (muscular contractions that move food in two directions from the mouth to the gizzard), stomach divided into two specialized chambers, and ceca (two pouches where the small and large intestines join for helping digest food)
• Examined FMNH PA 830 Used UV light and CT scans Found: Tip of the upper jaw has a small area with no teeth (edentulous) with an opening in front of the first tooth Also an opening at the tip of the lower jaw These are neurovascular openings, and there was probably a soft tissue structure (in the same location as the BTO of birds) BTO (bill-tip organ), a specialized structure at the tip of the beak that lets birds detect vibrations and pressure changes in mud, water, soil, to find food Could be non-avian theropods facial sensitivity were the precursor to these structures
• Also found Archaeopteryx has a basihyal bone, which means it had a highly mobile tongue Basihyal bone helps support the tongue and helps with swallowing (one found in Microraptor) Has also been found in a couple Early Cretaceous birds The one in Archaeopteryx is similar to the one in the fruit eating Longipteryx (bird from the Early Cretaceous) Longer and more narrow, which may mean it could move it more
• Last, Archaeopteryx had oral papillae Oral papillae, small bumps that cover the tongue to help grip food Works well with the mobile tongue
• Being in Archaeopteryx shows these structures co-evolved or appeared shortly after tongues became more mobile
• To sum up, Archaeopteryx is the oldest known bird and it could fly!

Fun Fact:

Birds just like to dance

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