Friday, March 30, 2018

Archaeopteryx's lack of an ossified sternum.

In what is often described as a “missing link”, Archaeopteryx blurs the definition in what is on one hand a non-avian theropod dinosaur, and the other, modern birds.

Fossil evidence shows that bipedal theropods and birds share many attributes such as hollow bones, semi-lunate carpal (wrist) and the furcula.

Theropod Dinosaur Hollow Bone
Photo Credit: Paul Cianfaglione
However, Archaeopteryx’s most distinctive feature is its feathers, not just any feathers, but asymmetrical flight feathers on its wings and tail.

Berlin Archaeopteryx Fossil
Image Credit: Humboldt Museum, Berlin
Nevertheless, there has not always been a common acceptance that this ancient bird was an effective and dynamic flyer. The aerodynamic feathers are still at odds with many of the basic skeletal specializations that clearly identify today’s volant species. Archaeopteryx in contrast retained a long bony tail, no synsacrum, an unfused metacarpus, short and wide coracoid, lateral orientation of the glenoid, and above all, no sternum.

The lack of a sternum suggests that Archaeopteryx was most likely a poor flier, restricted to a more rudimentary flight stroke.

Because of these skeletal limitations, an arboreal Archaeopteryx, to me, has always been a tough sell.

In todays most recently published texts on avian evolution, it is assumed that in Archaeopteryx the pectoralis muscle had its origin on a small cartilaginous sternum as well as on the robust furcula. Probably having the same wing depressor function, the coracobrachialis muscle originated on the plate-like coracoid. A broad, short pectoralis muscle would have reduced the wing beat frequency and amplitude but not its muscle power (source: Wellnhofer. 2009).

Archaeopteryx Hypothetical Sternum
Image from; Archaeopteryx, The Icon of Evolution by Peter Wellnhofer (2009)
Archaeopteryx did have wings with feathers which were very similar in their form and structure to those of modern birds.

But is it at all possible to develop a cartilaginous sternum as a surface for effective flight muscles? Could muscle then attach directly to the cartilage?

My search for an answer to this question led me to a website on anatomy and physiology, with a focus on skeletal muscle movement.

*Skeletal muscles, which are the organs of the skeletal muscle system, generally act by pulling on bones to produce movement. To pull the bone, muscles need to attach to the bone, either directly or indirectly. The epimysium of a muscle can attach directly to bone or cartilage to form a direct attachment. An indirect attachment is formed when the connective tissue layers, the epimysium, perimysium, and endomysium form a complex at the end of the muscle*.

Avian Flight Muscles
Image Property of McGraw-Hill Companies
Does this type of information apply to a 150 million-year-old bird? I’m not sure. But it does lend more credence to the assumption that muscle may have inserted on a cartilaginous sternum (source: Mayr, G. 2017).

Even more proof of a visualized cartilaginous sternum can be found on our own domestic store-produced turkeys. Pictured below is the caudal end of its sternum, partially bone and cartilage.

Domestic Turkey Partially Cartilaginous Sternum
Photo Credit: Paul Cianfaglione

Friday, March 23, 2018

Palaeognathous Palate

Ratites are perhaps some of the most recognizable birds in the world. Often observed in zoos and small farms, ratites are typically large in size, long-legged and flightless. They consist of such familiar species as the emu, rheas, cassowaries and the ostrich, but they also include the smaller kiwi.

Ostrich (Struthio camelus)
Photo Credit: Paul Cianfaglione
An interesting, and often contentious discussion involves the placement of the tinamous within today’s avian phylogeny. Some studies have found tinamous to be nested somewhere within ratites, while others have suggested that they are more of a close relative. (Source and read more here)

Elegant crested tinamou (Eudromia elegans)
Photo Credit: Paul Cianfaglione
Regardless of where researchers currently place tinamous, they are both grouped together in the clade Palaeognathae. Along with Neognathae, they form today’s modern birds.

Neornithines = Paleognathae + Neognathae
Image Credit:
The word itself, Palaeognathae, is derived from the ancient Greek for “old jaws” in reference to the skeletal anatomy of the palate, which is described as more primitive and reptilian than that in other birds (source; Wikipedia).

This is more properly explained below in the 2017 book, Avian Evolution; The Fossil Record of Birds and its Paleobiological Significance, by Gerald Mayr.

*Apart from differences in the proportions and relative positions of the involved bones, one of the major characteristics of the palaeognathous palate is a fusion of the pterygoids and palatines, which form a rigid unit and articulate with the braincase via well-developed basipterygoid processes. The neognathous palate, by contrast, exhibits a movable joint between the pterygoid and palatine, which allows greater mobility of the upper beak; basipterygoid processes are often reduced in neognathous birds*.

Palates of rhea, tinamou and lapwing
Image from Avian Evolution (2017), Gerald Mayr 

Greater Rhea (Rhea americana) Palate
Image Credit:
Curious, I decided to take a look at my own collection of bird skulls, seeing if I could understand exactly what was going on with these two types of palates.

I used Joel Cracraft’s 1974 list of five characteristics, which help define the Paleognathes primitive configuration.

*The vomer is large and articulates with the premaxillae and maxillopalatines anteriorly. Posteriorly the vomer fuses to the ventral surface of the pterygoid, and the palatines fuse to the ventral surface of this pterygovomer articulation.

*The pterygoid prevents the palatine from articulating medially with the basisphenoid.

*The palatine and pterygoid fuse into a rigid joint.

*The articulation on the pterygoid for the basipterygoid process of the basicranium is located near the articulation between the pterygoid and quadrate.

*The pterygoid–quadrate articulation is complex and includes the orbital process of the quadrate

My brief study of the palate involved two species, one was the Emu (Dromaius novaehollandiae), the other a Short-tailed Shearwater (Puffinus tenuirostris).

Emu (Dromaius novaehollandiae) and Short-tailed Shearwater (Puffinus tenuirostris) Skulls
Image Credit: Paul Cianfaglione

The Short-tailed Shearwater clearly exhibits a intrapterygoid joint (neognathous condition), which allows for more flexibility of the upper bill.

Neognathous Intrapterygoid Joint
Photo Credit: Paul Cianfaglione
The Emu, on the other hand, displays a more complex architecture throughout the bony palate. Observed were the vomer, quadrate and basipterygoid process. But as luck would have it, my specimen of Emu surprisingly lacked the fusion of the pterygoids and palatines. Did I really need this monkey wrench thrown into my study? Isn’t this fusion one of the major characteristics of the palaeognathous palate? How do I explain this?

Emu (Dromaius novaehollandiae) Palate
Note lack of fusion of pterygoid and palatine
Photo Credit: Paul Cianfaglione
The only logical explanation I can come up with has to do with the age of the animal. In addition to the lack of synthesis between the pterygoids and palatines, there is also a very recent fusion between the vomer and the ventral surface of the pterygoid. This Emu skull is most likely an immature bird, which brings up further questions in regards to the timing of the development of the Palaeognathous palate in general. Why is this development suspended? 

Fusion of Emu vomer and pterygoid 
Photo Credit: Paul Cianfaglione
I also considered some of the advantages, and disadvantages associated with possessing a so-called primitive palate. In tinamous for instance, the archaic structure of the palate might have had limiting factors on what it ate, as well as the way it builds its nest.

Tinamous are however surprisingly opportunistic feeders and will eat a wide range of foods. Consumed plant material includes fruit (either fallen or on the tree), seeds, green shoots, tender leavers, buds, flowers, tender stems, roots, and tubers. Much of the animal food consists of insects, including ants, termites, beetles, grasshoppers, hemiptera, and lepidopteran larvae, as well as gastropods, mollusks, worms, and small vertebrates, such as amphibians and reptiles. Larger species will eat small mammals (source: Wikipedia).

One must ask themselves, is there really a “disadvantage” by not possessing a intrapterygoid joint? Could there be an unseen advantage?

Even the bizarre Kiwi eats small invertebrates, seeds, grubs, and many varieties of worms. They also may eat fruit, small crayfish, eels and amphibians (source: Wikipedia).

This leaves nest building, more precisely, advanced nest building, as a possible difference maker.  

All palaeognathus nests are placed on the ground (Kiwi’s in burrows), leaving eggs (and themselves) vulnerable to predators. The evolution of the flexible upper bill has allowed neognathous birds to build a variety of interwoven nests, safely, and out-of-reach of potential predators.  

Friday, March 16, 2018

The Tarsometatarsus, an avian lower leg bone

The following text is an aid to avian bone identification.

The skeletons of birds differ from those of other vertebrates in several respects, all concerned with the adaptation for flight. Weight reduction in the skeleton is accomplished by decrease in size or number of parts.

In regards to the avian skull, most of the weight loss is due to the edentulous condition, and the paper thinness of its cranial bones.

Further weight reduction and air buoyancy is achieved by the thin walls and hollow shafts of the long bones.

Diving birds such as gulls, grebes, loons and penguins are not very pneumatized, and have skeletons reflecting a balance between the need for flight and submerged swimming. Penguins use these wings to “fly” through the water.

Today’s featured bone is the tarsometatarsus; a long bone in the lower leg formed by fusion of tarsal and metatarsal structures. The tarsometatarsus incorporates the three main bones of the foot (metatarsals 2, 3, and 4) as well as some ankle bones, the lower tarsals.

Baby Bird Partially Fused Tarsometatarsus
Photo Credit: Paul Cianfaglione
The development of the tarsometatarsus must have had significance in the evolution of the modern pattern of stance and gait, as well as in strengthening birds landing gear (Chiappe L.M. Glorified Dinosaurs; The Origin and Early Evolution of Birds. 2007).

Pleistocene Wild Turkey (Meleagris gallopavo) Tarsometatarsus with spur
Photo Credit: Paul Cianfaglione
The information provided below comes to us from the 1996 book; Avian Osteology, by Gilbert, Martin and Savage.

Tarsometatarsus Diagram
From Gilbert, Martin, Savage; 1996
Photo Credit: Paul Cianfaglione
To facilitate articulation with the convex condyles of the tibiotarsus, the cotyles at the proximal end of the tarsometatarsus are more or less concave. The mesial cotyle tends to be the larger and more concave. In most groups, it is also slightly higher (more proximal) than is the lateral cotyle.

Just posterior to the cotyles is at least a single, and often a complex group of hypotarsal ridges. These may bridge over and form tendinal canals. On the anterior surface just distal to the cotyles is a fossa containing one or more foramina. In Strigid Owls a large tendinal bridge is on the mesial side of the fossa; a small tendinal bridge in Rallidae. Often the fossa is continuous with an anterior groove.

*Blog author notes*

Observe the protective trough on the fossil Barred Owl (Strix Varia) tarsometatarsus, for the massive tendons that close the talons. Also note the supratendinal bridge, the bony bridge over a tendon.

Pleistocene Barred Owl (Strix varia) Tarsometatarsus with supratendinal bridge
Photo Credit: Paul Cianfaglione
Pleistocene Barred Owl (Strix varia) Tarsometatarsus trough
Photo Credit: Paul Cianfaglione
Distally on the shaft is an outer (lateral) extensor groove which terminates in the distal dorsoplantar foramen (in the penguins, there are two grooves and foramina, one lateral, one mesial).

*Blog author notes*

Grooves that partially separate the three metatarsals – if they are very deep, this can help identify a penguin of the genus Spheniscus.

Miocene Spheniscus Penguin Tarsometatarsus
Photo Credit: Paul Cianfaglione

In very small birds, the foramen may appear as only a pit. Distal to the foramen are the trochleae of the digits. Most groups have only three trochleae (for digits 2-4). However, others such as the woodpeckers have four trochleae, that for one extends posteriorly. In those groups with three trochleae, a facet for the first digit is present on the posterior surface of the shaft, along the mesial level of the extensor foramen.

*Blog author notes*

Northern Flicker (Colaptes auratus) photo, a woodpecker with four trochleae, zygodactyl toe arrangement.

Northern Flicker (Colaptes auratus) Tarsometatarsus
Photo Credit: Paul Cianfaglione
The photo below depicts the tarsometatarsus of a Pleistocene-aged Common Loon (Gavia immer) on the left, and the tarsometatarsus of the 50 million-year-old pseudo-toothed bird from Morocco, Dasornis emuinus. Interestingly, the loon, pseudo-toothed bird and Tundra Swan (Cygnus columbianus) all share structurally similar tarsometatarsi with similarly placed trochlea for digits.

Pleistocene Common Loon (Gavia immer) and Dasornis emuinus Tarsometatarsus
Photo Credit: Paul Cianfaglione
Do these skeletal elements of the hind limbs imply similar adaptations to habitat use. The loon and swan are both excellent “surface” swimming species. Despite its enormous wing-span and pelagic soaring behavior, did Dasornis emuinus also spend a great deal of time swimming and feeding on prey items at the water’s surface, as much as it did from the air? 

Dasornis emuinus and Pleistocene Common Loon (Gavia immer) Tarsometatarsus
Photo Credit: Paul Cianfaglione
Drag reduction is probably the most important common factor for swimming species. When birds swim it is primarily the tarsometatarsus that generates the paddle motion of the feet.

This brings up another interesting question. Osteodontornis is a more recent species of pseudo-toothed bird (20-6 million-years-ago) which evolved a tarsometatarsus that was wider and overall robust. Was Osteodontornis more of an aerial snatcher, than a surface hunter? 

Osteodontornis (left) and Dasornis emuinus tarsometatarsus comparison
Photo Credit: Paul Cianfaglione
From text, Living Dinosaurs; The Evolutionary History of Modern Birds 

Monday, March 12, 2018

China’s Feathered Dinosaurs Remembered

Sinosauropteryx prima
Generally considered one of the most important scientific exhibitions ever to be put on public display, the 120-million-year-old “feathered” animals discovered in Liaoning Province, China was held at the Yale Peabody Museum from February 13 through May 9, 1999, in their only appearance in the northeastern U.S. These finds constitute, in the words of Peabody Curator Emeritus John H. Ostrom, “the biggest event in evolutionary science since Darwin put forth his theory,” and provide compelling evidence that birds evolved from dinosaurs.

China's Feathered Dinosaurs
1999 Yale Peabody Museum Tour Program
Photo Credit: Paul Cianfaglione
Pictured above is the original program paper from the February 1999 tour of China's Feathered Dinosaurs that came to the Yale Peabody Museum. On display were Confuciusornis, Sinosauropteryx, Caudipteryx and Protarchaeopteryx. A once in a lifetime experience! 

Confuciusornis sanctus
To compliment the fossils, National Geographic Society also provided the actual models featured in their July, 1998 issue; Dinosaurs Take Wing, The Origin of Birds.

Dinosaurs Take Wing
National Geographic July, 1998
Photo Credit: Paul Cianfaglione
Dinosaurs Take Wing
National Geographic July, 1998
Photo Credit: Paul Cianfaglione

Sunday, March 11, 2018

Avian Rictal-Sensory Bristles

The actress Meryl Streep once said, “the more you are in this business, the more humbled by it you become”. I feel the same way about the business of birds. A moment doesn’t go when I think to myself, “maybe I didn't know so much about that bird as I thought I did”.

There have been lots of really exciting ornithological discoveries made over the last few years using genetic data, yet we still know little about some basic anatomical functions.

Take sensory feathers for instance, better known as rictal bristles. Yes, those prominent hair-like feathers around the mouth of a nightjar or flycatcher, assumed forever it seems to be associated with prey capture.

Tropical Kingbird (Tyrannus meloncholicus)
Photo Credit: Paul Cianfaglione
On humans, we know them as eyelashes and ear hair; sensory hairs to protect openings that must be kept free of debris.

But on birds, there is still much debate about these feathers true function.

For flycatchers and nightjars, the use of bristles make sense. Rictal bristles on different parts of the head have a tactile function in both nocturnal and diurnal species, perhaps playing a role in capturing evading insects. 

Others have suggested sensory feathers are responsible in gathering information during flight, navigating in nest cavities and on the ground at night.

I tend to agree with all of the above; feather bristles could have certainly evolved for more than one purpose. Receptors embedded deep in the skin may be able to send information about a bird’s surroundings through sensitive muscular and nervous systems, giving it a heightened sense of feeling.  

One of the more interesting sensory feather that I have recently found has been on the underside of an owl talon.

Barred Owl (Strix varia) Talon
Photo Credit: Paul Cianfaglione
Situated near the metatarsal pad are peculiar looking, toothbrush-like bristles, which jut out from the base of a microscopic feather calamus. How these odd-looking sensory feathers had evolved is clearly centered on the hunting technique of these birds.

Great Horned Owl (Bubo virginianus) Talon Sensory Feathers
Photo Credit: Paul Cianfaglione
No bird demonstrates this technique better than the Great Gray Owl (Strix nebulosi). Hunting from a perch along the edge of a field, Great Gray Owls will often locate rodents under soft snow by sound, then plunge deep feet first to capture them. The same hunting method is applied by the Great Horned Owl (Bubo virginianus), but this time on the forest floor.

Great Gray Owl (Strix nebuloso) Hunting
Image Credit:
Located on their talons, sensory feathers are essential to an owl’s overall success, and daily survival.

Wednesday, March 7, 2018

Avian Fossilized Tracheal Rings

A fossil does not need to perfect to be special. It can be missing a skull, half its body, or could be just a few scattered bones with feathers. Every bird fossil is unique because their formation and discovery depend on chains of ecological and geological events that occur over deep time.

Unidentified Eocene Partial Bird Fossil with feathers
Green River Formation
Photo Credit: Paul Cianfaglione
My latest fossil acquisition was for that exact idea, a striking partial bird fossil, accompanied by an equally impressive extinct fish called Knightia eocaena.

Unidentified Eocene Partial Bird Fossil
Green River Formation
Photo Credit: Paul Cianfaglione
These 50 million-year-old, Eocene-Era fossils comes from one of the world's most famous Lagerstatten, the Green River Formation in Wyoming. A small portion of the bird and fish fossils from the Green River exhibits such fine preservation, including soft-tissue preservation.

Once in my hands, I took the time to carefully study the fossil under a stereo-microscope. Identified were a pair of coracoid, a furcula, partial sternum with ribs, fractional ulna and radius, and a humerus.

Unidentified Eocene Partial Bird Fossil
Green River Formation
Photo Credit: Paul Cianfaglione
But there was one other feature on this Green River plate that piqued my interest. Situated between the two clavicles (furcula) is what appeared to be fossilized tracheal rings. Is that even possible? How did I know it was a tracheal?

Fossilized Avian Tracheal Rings
Green River Formation, Eocene
Photo Credit: Paul Cianfaglione
Fortunately, there were two recent instances in which avian tracheal rings, along with the syrinx, had been brought to my attention.

First was the exciting news in 2016 regarding the discovery of the oldest fossilized syrinx found in a Cretaceous-aged bird called Vegavis iaai.

Shortly after that announcement came my own personal finding of an ossified syrinx within the skeleton of an American Crow (Corvus brachyrhynchos).

American Crow (Corvus brachyrhynchos) Syrinx
Photo Credit: Paul Cianfaglione
The syrinx (Greek σύριγξ for pan pipes) is the vocal organ of birds. Located at the base of a bird's trachea, it produces sounds without the vocal folds of mammals. The sound is produced by vibrations of some or all of the membrana tympaniformis (the walls of the syrinx) and the pessulus, caused by air flowing through the syrinx. This sets up a self-oscillating system that modulates the airflow creating the sound. The muscles modulate the sound shape by changing the tension of the membranes and the bronchial openings. The syrinx enables some species of birds (such as parrots, crows, and mynas) to mimic human speech (source: Wikipedia).

The 2016 research paper titled; Fossil evidence of the avian vocal organ from the Mesozoic (Julia A. Clarke, Sankar Chatterjee, Zhiheng Li), made for some fascinating reading. It not only provided images of this remarkable fossil find, but also a host of other modern-day bird syrinx and tracheal rings.
Comparisons of the Cretaceous Vegavis and Eocene Presbyornis syrinxes to extant avian species
Image property of ResearchGate/Nature
A link to the entire paper is provided here, followed by the abstract;

From complex songs to simple honks, birds produce sounds using a unique vocal organ called the syrinx. Located close to the heart at the tracheobronchial junction, vocal folds or membranes attached to modified mineralized rings vibrate to produce sound. Syringeal components were not thought to commonly enter the fossil record, and the few reported fossilized parts of the syrinx are geologically young (from the Pleistocene and Holocene (approximately 2.5 million years ago to the present). The only known older syrinx is an Eocene specimen that was not described or illustrated. Data on the relationship between soft tissue structures and syringeal three-dimensional geometry are also exceptionally limited. Here we describe the first remains, to our knowledge, of a fossil syrinx from the Mesozoic Era, which are preserved in three dimensions in a specimen from the Late Cretaceous (approximately 66 to 69 million years ago) of Antarctica. With both cranial and postcranial remains, the new Vegavis iaai specimen is the most complete to be recovered from a part of the radiation of living birds (Aves). Enhanced-contrast X-ray computed tomography (CT) of syrinx structure in twelve extant non-passerine birds, as well as CT imaging of the Vegavis and Eocene syrinxes, informs both the reconstruction of ancestral states in birds and properties of the vocal organ in the extinct species. Fused rings in Vegavis form a well-mineralized pessulus, a derived neognath bird feature, proposed to anchor enlarged vocal folds or labia. Left-right bronchial asymmetry, as seen in Vegavis, is only known in extant birds with two sets of vocal fold sound sources. The new data show the fossilization potential of the avian vocal organ and beg the question why these remains have not been found in other dinosaurs. The lack of other Mesozoic tracheobronchial remains, and the poorly mineralized condition in archosaurian taxa without a syrinx, may indicate that a complex syrinx was a late arising feature in the evolution of birds, well after the origin of flight and respiratory innovations.

Placed under a microscope, the Green River bird fossil distinctly shows the ossified tracheal rings, which was confirmed to me by a paleornithologists. It was also pointed out that these structures are not all-too uncommon in Eocene birds. What would be “uncommon”, is the occurrence of a syrinx.

Fossilized Avian Tracheal Rings
Green River Formation, Eocene
Photo Credit: Paul Cianfaglione
Preliminary photographs of the tracheal did not provide clear evidence of an actual vocal organ. But a more detailed look at the base of the structure did finally reveal bronchial half rings, which according to the 2016 research paper is consistent with the existence of the medial tympaniform membrane that contributes to sound production, or a probable simple syrinx.

Fossilized Avian Bronchial Half Rings
Green River Formation, Eocene
Photo Credit: Paul Cianfaglione
I also considered the bones of this 50-million-year-old fossil bird. Although I was told that the specimen was simply too fragmentary for a well-based ad-hoc identification, I thought it was worth the effort to try and locate structurally similar bones.

The bones that I felt held the most promise for a possible comparative study were the coracoid, furcula, sternum and humerus.

My search eventually led me to a specimen of stem-roller named Primobucco mcgrewi, and a free online paper titled; PRIMOBUCCO MCGREWI (AVES: CORACII) FROM THE EOCENE GREEN RIVER FORMATION: NEW ANATOMICAL DATA FROM THE EARLIEST CONSTRAINED RECORD OF STEM ROLLERS (Ksepka and Clark. 2010).

Primobucco is the smallest-bodied and most widespread taxon of stem-roller. P. mcgrewi in particular is now represented by at least 15 individuals from multiple localities. This species is now recognized as one of the most common components of the Green River avifauna.

Primobucco mcgrewi fossil
Image Property of Ksepka and Clark
Below is a short list of Primobucco features from the paper that display similarities with the fossil presented here.

Eocene Partial Bird Fossil
Green River Formation
Photo Credit: Paul Cianfaglione
* The furcula is U-shaped. The rami are medio laterally flattened at the omal ends and become more cylindrical near the symphysis. At the symphysis there is a slight thickening, but a hypocleidium is absent.

* Five ribs articulate with the sternum in FMNH PA 724, as in Coraciidae and the fossil Eocoracias brachyptera.

* In all specimens of Primobucco mcgrewi preserving the complete sternum (FMNH PA 346, FMNH PA 724, FMNH PA 738, FMNH PA 758), posteriorly, the slender medial (lateral?) trabeculae show a slight expansion.

*The coracoid; the processus procoracoideus is large and slightly hooked. The coracoid has a proximodistally short procoracoid process. The medial margin is smooth, with a minute notch located at approximately the same level as the tip of the lateral process. The lateral process is well projected and oriented anterolaterally.

*The humerus; The head of the humerus is situated dorsally of the shaft due to the large crista bicipitalis. The crista deltopectoralis is short.

Thursday, March 1, 2018

A Possible Fossilized Limpkin Egg

Most birds have fragile, hollow-bones, generally smaller skeletons which are rare in the fossil record. Fossilized eggs are even rarer, almost inconceivable considering their delicate nature.

The egg that I’m about to introduce to you today is quite phenomenal. It was discovered in the White River Formation of Nebraska, which is home to some of the best-known fossil mammals from North America.
Possible Fossilized Limpkin Egg
Photo credit: Paul Cianfaglione
At an age of 33 million-years-old, the bird egg is nearly complete, with part of it collapsed in on one side. The shell from the missing area is still attached and pushed inside. Along the side, you can see that the egg still retains its “egg” shape.

Possible Fossilized Limpkin Egg
Photo Credit: Paul Cianfaglione
This specimen was professionally prepared and shows a beautiful egg texture across its surface. It was hinted to me that the field collector had tentatively identified the egg as belonging to a species of duck.

However, since my acquisition, I have discovered information that has almost completely contradicted those claims.

The first break in my investigation came from a website called; The Fossil Forum. Here I found images, and a brief discussion on nearly the identical looking egg. The website also featured a link to the only known scientific account of these fossils.

The paper, THE FIRST RECORD OF BIRD EGGS FROM THE EARLY OLIGOCENE (ORELLAN) OF NORTH AMERICA by Chandler and Wall (2001), depicts the eggs as being closely compared to the living Limpkin, Aramus guarauna.

The abstract begins; Three bird eggs from the Scenic Member of the Brule Formation, Badlands National Park, Shannon County, South Dakota are the first published record of eggs from the early Oligocene (Orellan) of North America.  The fossil eggs compare closest to gruiform birds: cranes, rails, limpkins, and their relatives (Aves: Gruiformes) in size, shape, and eggshell porosity. Our understanding of the Paleogene paleo-avifauna is based on fossil skeletons from a limited number of well-known Eocene and fewer Oligocene localities.  Eocene and Oligocene gruiform bird species are known; one of which is the earliest record of a limpkin, Badistornis aramus (Wetmore), from Shannon County, South Dakota.

The Brule Formation incidentally was deposited between 34 and 30 million years ago, roughly the Rupelian. It occurs as a subunit of the White River Formation in Nebraska, Colorado, North Dakota, South Dakota, and Wyoming.

Brule Formation; Badlands, Nebraska
Image Credit:
Badistornis aramus Wetmore (1940) is the earliest record for a limpkin in North America (Brodkorb, 1967). In his Remarks section, Wetmore states, the close general resemblance of the fossil specimen to the metatarsus of the living Aramus scolopaceus [A. guarauna] is such as to leave no doubt almost at glance that it is a species of the family Aramidae.   The tarsometatarsus of Badistornis aramus is slightly longer than that of the Limpkin: holotype = 155mm vs. A. guarauna = 113-123mm (n=6, Gilbert, et al., 1981:234).  However, osteologically the characteristics of the holotype are that of a limpkin.

The fossil eggs themselves are pictured below with the papers description to follow.

Fossil and modern day Limpkin Eggs
From Chandler and Wall paper
GCVP 3610 (Fig. 1A) is in the best state of preservation of the three eggs, with little or no distortion and only slight cracking.  Its overall geometry (elongation average, bicone average, asymmetry; as defined by AOU, 1962:13; Preston, 1953:166; Preston, 1968) is elliptical in profile and equal to that of the Aramidae (Preston, 1969:248, Table 1).  The porous nature of the eggshell is preserved and compares well with that of Limpkin eggs (Fig. 2).

GCVP 3682 is slightly more distorted by compression than GCVP 3610 with many more cracks (Fig. 1B).  Although not as well preserved, the elliptical geometry and the porous nature of the eggshell is still apparent.

GCVP 3958 is in the poorest state of preservation with numerous cracks and flattening. However, the elliptical geometry and porous nature of the eggshell is preserved (Fig. 1C).

Measurements: GCVP 3610 = length 58.11mm x width 44.13mm; GCVP 3682 = [54.56]mm x [46.12]mm; GCVP 3958 = [55.46]mm x [39.08]mm; Limpkin (Aramus guarauna) 55-64mm x 41-47mm (Walters, 1994:82).

*The fossil egg presented in this posting measures length = 54 mm x width 42 mm*


In overall geometry (elongation average, bicone average, asymmetry) and eggshell porosity, and texture GCVP 3610 compares closest to the egg of the Limpkin, Aramus guarauna.  GCVP 3682 and 3958 both compare very closely to GCVP 3610.  An extinct limpkin, Badistornis aramus Wetmore, has been described from essentially the same locality (using identical stratigraphic, lithologic, and age criteria).  Although B. aramus did have slightly longer tarsometatarsi than A. guarauna, overall the birds would be of very similar body size and weight.  It can be surmised that these two closely related species of North American limpkins would have had eggs of similar size and shape.  There are other extinct birds represented in the fossil record during the early Oligocene such as a guan and a quail (Galliformes: Cracidae, Phasianidae, respectively), a hawk (Falconiformes: Accipitridae), and an extinct relative of the modern seriema (Bathornithidae), but all of these living birds have eggs of a very different shape and/or size.

The Chandler and Wall (2001) paper was undoubtedly a major help with the identification of this unique fossil, however, I did take one exception with the description of the eggshells porosity and texture, touted as being similar to that of a modern-day Limpkin.

Possible Fossilized Limpkin Egg
Photo Credit: Paul Cianfaglione
How the researchers came to that conclusion is a little confusing, since the Limpkin egg is smooth, with little or no gloss (Source: Birds of North America online edition). The fossil eggshell in contrast shows a granular-pebbly surface to it when viewed under a stereo-microscope.

Possible Fossilized Limpkin Egg
Photo Credit: Paul Cianfaglione
Could this fossil bird egg represent an interesting mixture of primitive and advanced traits?