Jurassic birds took off from the ground – SVP abstracts 2016

Everyone knows:
Ground up hypothesis – 

implies and includes flapping, always has. Birds flap, always have, at least since the elongation and locking down of the coracoid in ancestral troodontids.

Trees down hypothesis –
has always implied gliding. Gliders don’t flap, never have.

But
baby birds dropping out of trees always flap. It’s what they do. But that fact is often ignored in bird origin videos.

And, as everyone knows by now…
young birds with pre-violant wings flap them like crazy when climbing bipedally — even vertical tree trunks… also something several animated bird origin videos ignore, perhaps because of one glaring opposite extant example: the young wet hoatzin that struggles to climb with all four limbs.

With that preamble…Habib et al. 2016 provide us
a hypothesis on the origin of bird flight that appears to ignore trees and experimental work with pre-volant birds and goes straight to take-off from flat ground. Is that okay?

From the abstract:
“Many small non-avian theropods possessed well-developed feathered forelimbs, but questions remain of when powered flight evolved and whether it occured more than once within Maniraptora. Here, using a first principles modeling approach, we explore these questions and attempt to determine in which taxa takeoff and powered flight was possible. Takeoff is here defined as a combination of both the hindlimb driving the ballistic launch phase, and the wing-based propulsion (climb out). [1]

“Microraptor, Rahonavis, [2] and all avian specimens generated sufficient velocity during leaping or running for takeoff. We re-ran our analysis factoring in life history changes that can alter the flight capability in extant avians, such as egg retention and molting, to examine how these would influence take off capacity. Of the two, molting shows the most significant effects.

“When these results are coupled with work detailing the lack of arboreal features among non-avian maniraptorans and early birds, they support the hypothesis that birds achieved flight without a gliding intermediary step, something perhaps unique among volant tetrapod clades.” [3] [4] [5]

Figure 2. Cosesaurus running and flapping - slow.

Figure 1. Cosesaurus running and flapping – slow.

Notes

  1. Interesting that Habib et al. ignore the presence of trees, which are key to Dial’s hypothesis (updated in Heers et al. 2016)  and opts to go straight from ground to air. That kind of ignores key work, doesn’t it? You might recall that Dr. Habib became famous as the author of the infamous but popular forelimb quad launch hypothesis for pterosaurs.
  2.  Microraptor and Rahonavis are NOT in the lineage of birds in the LRT, but both show how widespread long feathered wings were in Theropoda. The former has elongate coracoids by convergence. The latter does not preserve coracoids, fingers or feathers, but does have the long forearm that might imply bird-like proportions for missing bones… or not.
  3. Apparently Habib et al. assume that pterosaurs and bats originated as gliders when present largely ignored evidence indicates exactly the opposite. Cosesaurus (Fig. 1) was a pterosaur precursor with elongate coracoids, unable to fly, but able to flap. Bats rarely glide, so it is unlikely that they did so primitively. Lacking coracoids, bats employ elongate clavicles to anchor flight muscles.
  4. Okay, so remember the preamble (above) about gliding and trees. When Habib et al. bring up ‘a gliding intermediary step‘, they are implying the presence of trees (high places) in competing and validated-by-experiment hypotheses for the origin of bird flight  — which they are ignoring. They also ignore the fact that baby birds don’t glide when they fall out of trees. They flap like their lives depend upon it. I find those omissions odd, but its not the first time pertinent work has been ignored in paleontology.
  5. In the LRT Xiaotingia (Fig. 2) is the most primitive bird-like troodontid to have elongate coracoids and so may have been the first flapper in the lineage.
Figure 1. Xiaotingia with new pectoral interpretation. See figure 3 for new tracing.

Figure 2. Xiaotingia with new pectoral interpretation.

References
Habib M, Dececchi A, Dufaault D and Larsson HC 2016. Up, up and away: terrestrial launching in theropods. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Heers AM, Baier DB, Jackson BE & Dial  KP 2016. 
Flapping before Flight: High Resolution, Three-Dimensional Skeletal Kinematics of Wings and Legs during Avian Development. PLoS ONE 11(4): e0153446. doi:10.1371/journal.pone.0153446
http: // journals.plos.org/plosone/article?id=10.1371/journal.pone.0153446

YouTube video showing birds running up tree trunks while flapping with nonviolent wings

ScienceNews online promo.

The geologically oldest Archaeopteryx (#12)

Updated November 10, 2016 with higher resolution images of the specimen. The new data moved the taxon over by one node. 

Not published yet in any academic journal,
but making the news in the popular press in Germany to promote a dinosaur museum (links below) is the geologically oldest Archaeopteryx specimen (no museum number, privately owned?). Found by a private collector in 2010, the specimen has been declared a Cultural Monument of National Significance. It is 153 million years old, several hundred thousand years older than the prior oldest Archaeopteryx. It is currently on  display at a new museum, Dinosaurier-Freiluftmuseum Altmühltal in Germany, about 10 kilometers from where the fossil was found.

Figure 1. The new oldest Archaeopteryx in situ with color tracings of bones.

Figure 1. The new oldest Archaeopteryx in situ with color tracings of bones. The ilium has been displaced to the posterior gastralia, or is absent. I cannot tell with this resolution.

Figure 1b. Archaeopteryx 12 in higher resolution.

Figure 1b. Archaeopteryx 12 in higher resolution.

So is it also the most primitive Archaeopteryx?
No. But it nests as the most primitive scansioropterygid bird. As we learned earlier, the Solnhofen birds formerly all considered members of the genus Archaeopteryx (some of been subsequently recognized by certain authors as distinct genera) include a variety of sizes, shapes and morphologies (Fig. 3) that lump and separate them on the large reptile tree. The present specimen has been tested, but will not be added to the LRT until it has a museum number or has been academically published (both seem unlikely given the private status). Given the additional publicity the specimen is now in the LRT.

The fossil is wonderfully complete and articulated
and brings the total number of Solnhofen birds to an even dozen.

This just in
Ben Creisler reports, “The fossil specimen was originally found in 2010 in fragmented condition and took great effort to prepare and piece together as it now appears.”

Figure 2. Reconstruction of the geologically oldest Archaeopteryx, now nesting at the base of the Scansoriopterygidae.   Note the large premaxillary teeth and short snout on a relatively small skull.

Figure 2. Reconstruction of the geologically oldest Archaeopteryx, now nesting at the base of the Scansoriopterygidae. Note the large premaxillary teeth and short snout on a relatively small skull.

Compared to other Archaeopteryx specimens
you can see the new one is among the smallest (Fig. 3) and has a distinct anatomy.

Figure 2. Several Archaeopteryx specimens. The geologically oldest one, (at bottom) is among the smallest and most derived, indicating an earlier radiation than the Solnhofen formation.

Figure 2. Several Archaeopteryx specimens. The geologically oldest one, (at bottom) is among the smallest and most derived, indicating an earlier radiation than the Solnhofen formation.

References
Spektakulaerer-Fund-kommt-in-Ausstellung-article
originalskelett-eines-archaeopteryx-zu-sehen.html
auf-zum-archaeopteryx

Website

Stinkbird on steroids = Gastornis!

Figure 1. Gastornis (Diatryma) was a large bird of the late Paleocene,/early Eocene. It appears to share many traits withy the living hoatzin, Opisthocomus.

Figure 1. Gastornis (Diatryma) was a large bird of the late Paleocene,/early Eocene. It appears to share many traits withy the living hoatzin, Opisthocomus. Pedal digit 1 was likely retroverted.

Adding
giant Gastornis (Diatryma) (Fig. 1) to the large reptile tree brings to mind an old Warner Bros. Tweetybird/Sylvester cartoon, nicknamed on YouTube, “Tweety on Steroids” (Fig. 1).

I could not help noticing
a long list of synapomorphies shared between the giant flightless Paleocene bird, Gastornis, with the living stink bird, more commonly known as the hoatzin, Opisthocomus hoazin. The nickname ‘stink bird’ comes from its smell, derived from the rotting vegetation of its herbivorous diet. In Gastornis, a lack of sharp talons, a lack of a hooked beak together with its heavy bones and large gut indicate an herbivorous diet as well.

Figure 1. Warner Bros. cartoon on YouTube (click to view) transforms little Tweety into a giant monster, like Gastornis.

Figure 1. Warner Bros. cartoon on YouTube (click to view) transforms little Tweety into a giant monster, like Gastornis.

A comparison to Opisthocomus 
(Fig. 2) is interesting, and will follow, but perhaps more interesting, Gastornis shares several traits with non-avian dinosaurs, evident atavisms, not visible on known sister taxa.

Figure 2. The hoatzin, Opisthocomus, skeleton is quite similar to that of Gallus, the chicken. Juveniles do not have fused fingers.

Figure 2. The hoatzin, Opisthocomus, skeleton is quite similar to that of Gallus, the chicken. Juveniles do not have fused fingers.

Like non-avian dinosaurs, Gastornis has

  1. complete upper temporal arch (postorbital + squamosal)
  2. orbit not confluent with temporal fenestrae
  3. orbit taller than wide
  4. postfrontal
  5. ribs without uncinate processes
  6. lack of fused dorsal vertebrae
  7. coracoid approaching disc-like
  8. orbit shorter than postorbital skull length
  9. maxilla taller than 40% orbit height
  10. jugal with elongate qj process, short suborbital portion
  11. parietal skull table not broad, weakly constricted
  12. occiput close to quadrates
  13. ilium posterior process longer than anterior process (also as in Struthio and Hesperornis)
Figure 3. Gastornis (Diatryma) skull model with bones identified.

Figure 3. Gastornis (Diatryma) skull model with bones identified.

Like Opisthocomus, Gastornis has

  1. nasals connect medially
  2. descending jugal
  3. large gut/herbivorous diet
  4. dentary contributes to coronoid
  5. mandibular fenestra
  6. mandible ventral shape: 2 tier convex

References
Cope ED 1876. On a gigantic bird from the Eocene of New Mexico. Proceedings of the Academy of Natural Sciences of Philadelphia 28 (2): 10–11.
Matthew WD, Granger W and Stein W 1917. The skeleton of Diatryma, a gigantic bird from the Lower Eocene of Wyoming. Buletin of the American Museum of Natural History, 37(11): 307-354.
Hébert E 1855a. Note sur le tibia du Gastornis pariensis [sic] [Note on the tibia of G. parisiensis]. C. R. Hebd. Acad. Sci. Paris (in French) 40: 579–582.
Hébert E 1855b. Note sur le fémur du Gastornis parisiensis [Note on the femur of G. parisiensis]. C. R. Hebd. Acad. Sci. Paris (in French) 40: 1214–1217.
Prévost C 1855. Annonce de la découverte d’un oiseau fossile de taille gigantesque, trouvé à la partie inférieure de l’argile plastique des terrains parisiens [Announcement of the discovery of a fossil bird of gigantic size, found in the lower Argile Plastique formation of the Paris region]. C. R. Hebd. Acad. Sci. Paris (in French) 40: 554–557.
Statius Müller PL 1776. Des Ritters Carl von Linné Königlich Schwedischen Leibarztes &c. &c. vollständigen Natursystems Supplements- und Register-Band über alle sechs Theile oder Classen des Thierreichs. Mit einer ausführlichen Erklärung. Nebst drey Kupfertafeln.Nürnberg. (Raspe).

wiki/Hoatzin
wiki/Gastornis

Paleocene birds

Curious about
the distribution of Paleocene birds, I found a list online and applied it to a globe image (Fig. 1). The Chicxulub impact is added along with its projected ejecta area north to Montana.

Figure 1. The world at the K-T boundary, 65 mya and the distribution of Paleocene birds.

Figure 1. The world at the K-T boundary, 65 mya and the distribution of Paleocene birds. Click to enlarge.

I wondered if the distribution of birds in the Paleocene
reflected some kind of expansion from a refuge, perhaps at the antipodes to the asteroid impact. The answer is ‘no.’

The data shows
that Paleocene birds are found worldwide, with most specimens located in North America and Europe, close to the impact site and close to most paleontologists. How these birds survived when all others did not remains a mystery. If there was an initial refuge at the antipodes, these birds quickly spread out from that zone leaving no clue to their origin.

Figure 2. The hoatzin, Opisthocomus, skeleton is quite similar to that of Gallus, the chicken. Juveniles do not have fused fingers.

Figure 1. The hoatzin, Opisthocomus, skeleton is quite similar to that of Gallus, the chicken. Juveniles do not have fused fingers.

Figure 1. Skull of the hoatzin (Opisthocomus) with bones colorized.

Figure 2. Skull of the hoatzin (Opisthocomus) with bones colorized.

Among living birds
the hoatzin, Opisthocomus hoazin, (Müller 176) a 65cm herbivorous tropical bird from the Amazon, is often considered one of the most primitive of living birds, largely because juveniles have the atavism of individual clawed fingers that fuse upon reaching adulthood.

In the large reptile tree, which includes only three living birds, Opisthocomus nests with Gallus, the chicken. Obviously that will change when more taxa are added, but the overall resemblance is basic.

Wikipedia reports:
“Cladistic analysis of skeletal characters, on the other hand, supports a relationship of the hoatzin to the seriema family Cariamidae, and more distantly to the turaco and cuckoo families.”

Other studies conflict
with those results. Bird phylogenetic studies often do not agree with one another. This may be due to massive convergence based on huge taxon lists.

Hoatzins are currently the only members
of the clade Opisthocomidae and the order Opisthocomiformes. Wikipedia nests them within the Passerea then within the Neoaves, not close to Gallus. Neoaves include all living birds except Paleognathae (ratites and kin) and Galloanserae (ducks, chickens and kin = Fowl).

In Opisthocomus
the feet are large, the premaxilla does not reach the frontals, the nasals are robust, the upper temporal fenestra is located laterally, below the ‘equator’ of the expanded braincase and the sternum is deep.

The other primitive living bird is
one of several tinomous. Here (Fig. 3) the tinamou, Rhynchotus, was added to the large reptile tree. It nests with Struthio (Fig. 5), but shares many traits with Gallus and Opisthocomus.

Figure 4. Rhynchotus is a genus in the basal bird family of Tinamiformes. They are related to living large flightless birds. Note the small feet. 

Figure 4. Rhynchotus is a genus in the basal bird family of Tinamiformes. They are related to living large flightless birds. Note the small feet, like Struthio, figure 5.

Figure 4. Struthio, the ostrich, is currently a sister to the tinamou, Rhynchotus.

Figure 5. Struthio, the ostrich, is currently a sister to the tinamou, Rhynchotus.

I’d be curious to know
which genera crossed the K-T boundary?

References
Statius Müller PL 1776. Des Ritters Carl von Linné Königlich Schwedischen Leibarztes &c. &c. vollständigen Natursystems Supplements- und Register-Band über alle sechs Theile oder Classen des Thierreichs. Mit einer ausführlichen Erklärung. Nebst drey Kupfertafeln.Nürnberg. (Raspe).

wiki/Hoatzin

 

 

2015 SVPCA abstract supports troodontid-bird clade

Nice to get confirmation
for a subset of the large reptile tree in a SVPCA poster (Brougham 2015).

From the Brougham results:
“The modified matrix strongly supports a Troodontidae + Avialae clade rather than a monophyletic Deinonychosauria, a topology remarkably convergent on that seen in modified Godefroit phylogeny, in which Aurornis, Eosinopteryx and the Tiaojishan paravians form a sister clade to Anchiornis and more derived avialans, the two of which in turn form a sister clade to Troodontidae.”

Figure 1. Basal theropod subset of the large reptile tree showing troodontids basal to birds and separate from dromaeosaurs.

Figure 1. Basal theropod subset of the large reptile tree showing troodontids (light red) basal to birds (red) and separate from dromaeosaurs (white).

References
Brougham T 2015. Multi-matrix analysis of new Chinese feathered dinosaurs supports troodontid-bird clade. researchgate.net/publication/280728942

The first flightless birds

Yesterday we looked at several early birds (Fig. 1). Earlier we considered the phylogenetic nesting of Balaur (Fig. 2; Csiki Z et al. 2010), which some workers (Cau et al. 2015) considered an early flightless bird.

Figure 7. Bird cladogram with the latest additions. Here the referred specimen of Yanornis nests with enantiornithes while Archaeovolans nests within the Scansoriopterygidae, not with Yanornis.

Figure 7. Bird cladogram with the latest additions. Here the referred specimen of Yanornis nests with enantiornithes while Archaeovolans nests within the Scansoriopterygidae, not with Yanornis.

When determining
the first flightless birds, one must first decide which taxon represents the first or basal bird. In the large reptile tree (subset Fig. 1) the last common ancestor of Enantiornithes and Euornithes is Archaeopteryx siemensi, represented by the Berlin and the Thermopolis specimens. Thus they represent, in this cladogram, the first or basal birds. Both the Enantiornithes and Euornithes produced specimens with a locked down coracoid and expanded sternum, anchors for powerful flight muscles attached to long feathered forelimbs.

Thus the purported first flightless bird,
Balaur, nests outside the bird clade (Fig. 1) established by the large reptile tree.

Figure 1. Balaur compared to various dromaeosaurids and to Sapeornis, both to scale and enlarged for detail. Cau, Brougham and Naish wondered if Balaur was the first neoflightless bird, a sort of dodo of the Cretaceous.

Figure 1. Balaur compared to various dromaeosaurids and to Sapeornis, both to scale and enlarged for detail. Cau, Brougham and Naish wondered if Balaur was the first neoflightless bird, a sort of dodo of the Cretaceous.

Instead
the Scansoriopterygidae produced the first taxa in the Eurornithes with more of a dinosaur/theropod look, with Mei (Early Cretaceous) having the smallest forelimbs relative to the rest of the body in that clade. No doubt it was flightless — and with shorter coracoids and a tiny sternum, reduced its flapping. By contrast, its current sister, Archaeovolans (Fig. 3), retained a robust pectoral girdle and long forelimbs.

Figure 9. Sister taxa at the base of the scansoriopterygidae include Jeholornis, Mei and Archaeovolans, here shown to scale.

Figure 2. Sister taxa at the base of the scansoriopterygidae include Jeholornis, Mei and Archaeovolans, here shown to scale.

As everyone knows,
flightless birds have arisen several times since the Early Cretaceous with Hesperornis and Struthio as examples in the large reptile tree. In evolution everything is gradual and often enough, reversible. And behavior is best determined at the extremes of morphology. More generalized taxa probably had more generalized behavior.

In Dinosaurs of the Air
author Greg Paul Paul “argues provocatively for the idea that the ancestor-descendant relationship between the dinosaurs and birds can on occasion be reversed, and that many dinosaurs were secondarily flightless descendants of creatures we would regard as birds.” According to the large reptile tree, dromaeosaurids and basal troodontids were not birds. But birds are derived troodontids. And troodontids arise from basal dromaeosaurids.

Along these same lines Kavanau 2010 reported
“Varricchio et al. propose that troodontids and oviraptorids were pre-avian and that paternal egg care preceded the origin of birds. On the contrary, unmentioned by them is that abundant paleontological evidence has led several workers to conclude that troodontids and oviraptorids were secondary flightless birds. This evidence ranges from bird-like bodies and bone designs, adapted for climbing, perching, gliding, and ultimately flight, to relatively large, highly developed brains, poor sense of smell, and their feeding habits.” Not so, according to the large reptile tree. But, to their point, bird-like theropods have arisen about 8 times by convergence, as we looked at earlier here.

References
Cau A, Brougham T and Naish D. 2015. The Phylogenetic Affinities of the Bizarre Late Cretaceous Romanian Theropod Balaur bondoc (Dinosauria, Maniraptora): Dromaeosaurid or Flightless Bird? PeerJ. 3: E1032. DOI: dx.doi.org/10.7717/peerj.1032
Csiki Z, Vremir M, Brusatte SL, Norell MA 2010. An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania. Proceedings of the National Academy of Sciences of the United States of America 107 (35): 15357–15361.
Kavanau JL 2010. Secondarily flightless birds or Cretaceous non-avian theropods? Med Hypotheses 74(2):275-6.
Paul G 2002. Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins University Press, Baltimore, 472 pp.

wiki/Balaur_bondoc

newslink on secondarily flightless bird Epidexoptryx.

Hesperornis walking GIF

Figure 1. Hesperornis compared to a king penguin, Atenodytes. Hesperornis has larger feet and a longer tibia. Since penguins swim with their forelimbs, they have large pectoral muscle anchors. That is not the case with Hesperornis.

Figure 1. Hesperornis compared to a king penguin, Atenodytes. The patella is blue. Hesperornis has larger feet and a longer tibia. Since penguins swim with their forelimbs, they have large pectoral muscle anchors. That is not the case with Hesperornis. Click to enlarge. Marsh 1872 thought Hesperornis could stand upright. I do too. That makes only two of us.

Hesperornis regalis
(Figs. 1,2, Late Cretaceous, Campanian, Marsh 1872, 1.8m long) was a toothed, flightless marine bird with vestigial wings and asymmetrical feet. Although not related to living loons, Hesperornis is often compared to loons, which have no teeth and retain the ability to fly. Both swim with powerful hind limbs. Hesperornis can also be compared to another flightless bird clade, the penguins, with the proviso that penguins swim with powerful forelimbs and their skeletons (Fig. 1) reflect this.

Figure 2. Click to enlarge. Hesperornis walking GIF movie. In this hypothetical scenario Hesperornis walks bipedally.

Figure 2. Click to enlarge. Hesperornis walking GIF movie. In this hypothetical scenario Hesperornis walks bipedally. Like penguins and ducks, Hesperornis does not flex its toes while walking. Nor does it take very big steps.

Wikipedia reports,
“In terms of limb length, shape of the hip bones, and position of the hip socket, Hesperornis is particularly similar to the common loon (Gavia immer), probably exhibiting a very similar manner of locomotion on land and in water. Like loons, Hesperornis were probably excellent foot-propelled divers, but ungainly on land. Like loons, the legs were probably encased inside the body wall up to the ankle, causing the feet to jut out to the sides near the tail. This would have prevented them from bringing the legs underneath the body to stand, or under the center of gravity to walk (Reynaud 2006). Instead, they likely moved on land by pushing themselves along on their bellies, like modern [loons].”

It was not difficult
to animate a bipedal Hesperornis (Fig. 2). It appears fully capable of doing so penguin-style. But the comparison to loons is indeed compelling.

Loons are ungainly
on the beach. See a YouTube video here. Yes, it does look wounded, unable to walk like a normal bird. It would probably fly if it was in a hurry. Hesperornis shares many traits by convergence with loons, but, if anything, loon hind limbs are more extreme in their proportions, including a proportionately larger projecting patella (Figs. 3, 4).

Just added after publication: The axis of the acetabulum is further foreword in Hesperornis, at the 51% mark on the torso (measured from the posterior pelvis) versus the 43% mark on the loon. That big butt makes Hesperornis less top heavy.

Figure 3. Loon skeleton with femur (yellow) and tibia/patella (green) highlighted. In this mount the center of gravity is in front of the toes, which makes this an untenable mount, unless the loon is floating on water.

Figure 3. Loon skeleton with femur (yellow) and tibia/patella (green) highlighted. In this mount the center of gravity is in front of the toes, which makes this an untenable mount, unless the loon is floating on water.

The loon femur is a little shorter and the patella is a little larger
(Figs. 3, 4) than on Hesperornis (Figs. 1,2). It’s up to our imaginations whether or not that would enable a more penguin-like locomotion in Hesperornis. Note that penguins do have a patella (knee bone) but it does not extend above the femur as it does in Hesperornis and loons.

Figure 4. Loon femur and tibia/patella. These proportions are more extreme than those found in Hesperornis.

Figure 4. Loon femur and tibia/patella. These proportions are more extreme than those found in Hesperornis. Note the right angle femoral head, as in most birds, but then look at the skeleton (Fig. 3) in which the femora are held laterally, unlike more birds and dinosaurs.

Nat Geo
and Andy Farke report on a bone growth and possible migration study (Wilson and Chin 2014) of Hesperornis here.

According to Marsh:
“The clavicles are separate, but meet on the median line, as in some very young existing birds.The coracoids are short, and much expanded where they join the sternum. The latter has no distinct manubrium, and is entirely without a keel. The wings were represented by the humerus only, which is long and slender, and without any trace of articulation at its distal end.”  

Various authors
believe the humerus would have been hidden beneath the skin and appressed to the ribs. As is typical for Kansas fossils, Hesperornis specimens are typically crushed flat. In the large reptile tree Hesperornis nests with its volant contemporary, Ichthyornis.

References
Marsh OC 1872. Discovery of a remarkable fossil bird. American Journal of Science, Series 3, 3(13): 56-57.
Marsh OC 1872. Preliminary description of Hesperornis regalis, with notices of four other new species of Cretaceous birds. American Journal of Science 3(17):360-365.
Marsh, OC 1880. Odontornithes, a Monograph on the Extinct Toothed Birds of North America. Government Printing Office, Washington DC.
Reynaud F 2006. Hind limb and pelvis proportions of Hesperornis regalis: A comparison with extant diving birds. Journal of Vertebrate Paleontology 26 (3): 115A. doi:10.1080/02724634.2006.10010069.
Wilson L. and Chin K 2014. Comparative osteohistology of Hesperornis with reference to pygoscelid penguins: the effects of climate and behaviour on avian bone microstructure. Royal Society Open Science. 1: 140245. doi: 10.1098/rsos.140245

OceansofKansas/Hesperornis

wiki/Hesperornis