… and Liaoconodon is not a mammal…

Yesterday we noted that Repenomamus was not a mammal, but nested with the stem- (pre-) mammal tritylodontids, like Pachygenelus. Today Liaoconodon hui (Meng, Wang and Li 2011; IVPP V 16051; early Cretaceous, Aptian, 120 mya), is also not a eutriconodont mammal, but nests between Probainognathus and Pachygnenelus a little deeper into the phylogeny of the Cynodontia in the large reptile tree.

Figure 1. Liaocondon skull traced and reconstructed. In the LRT it most closely resembles that of Probainognathus.

Figure 1. Liaocondon skull traced and reconstructed. In the LRT it most closely resembles that of Probainognathus. Note the enormous size of the temporal fenestrae, the downturned squamosals and postdentary bones, all shared with Probainognathus. 

Liaconodon lacks a coronoid
and the scapula has a ventral glenoid, which are traditional mammal traits. It also has a mammal-like ilium without a posterior process, like a mammal… or a pre-mammal tritylodontid, like Oligokyphus and Kayentatherium. Once again the narrow braincase of Liaconodon, like that of Repenomamus, tells us this is a pre-mammal.

Figure 2. Probainognathus skull(s) in several views along with a pectoral and pelvic girdle.

Figure 2. Probainognathus skull(s) in several views along with a pectoral and pelvic girdle. The lack of a femoral head neck is a trait shared with Liaoconodon. 

Liaconodon lacks large canines
and the lower incisors are quite enlarged. The postorbital bar does not appear to be complete, but the prefrontal, postfrontal and postorbital are still visible and unfused to other bones, as in Probaingnathus.

Figure 3. Liaoconodon in situ.

Figure 3. Liaoconodon in situ. The causals are similar in shape to those of Castrocauda. 

Jin Meng of the AMNH
made a video posted to YouTube describing how ground-breaking it was to find post dentary bones in Liaconodon, which they considered a mammal. Those post-dentary bones are indeed clear and articulated, but par for the clade in pre-mammal cynodonts.

The manus and pes are well preserved
which is something we rarely see around this node. The caudals are nearly identical to those of Castrocauda. The femora were likewise rather short.

It was a good week for finding errors.
As before, we all boggled this one. To those who are toying with the challenge I presented earlier about finding badly nested taxa in the LRT, sorry, you missed this one.

References
Meng J, Wang Y-Q and Li C-K 2011. Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont. Nature 472 (7342): 181–185.

wiki/Liaoconodon

 

Jeholodens and Spinolestes: two new tritylodontids

Revised October 4, 2016 with a shifting of Jeholodens and Spinolestes to the Tritylodontidae, which are pre-mammals arising from Pachygenelus. Tritylodontids replace their molars, something mammals do not do.

The Early Cretaceoous
included the first radiation of basal mammals. The vast majority of these, so far, have been multituberculates, small rodent-like taxa that actually nest with rodents in the large reptile tree. Traditional paleontologists nest multituberculates much more primitively, prior to the Theria (live-bearing mammals) despite their many rodent-like traits, like enlarged incisors followed by a diastema (toothless region) and flat cranial region.

With so many multituberculates
in the Cretaceous, I’m always looking for non-multituberculate mammals from the era.  Repenomamus was a tritylodont, pre-mammal. Vincelestes was a marsupial. Maotherium was an Early Cretaceous basal primate. Liaoconodon, was a pre-tritylodont.  I had high hopes that the next two Early Cretaceous mammals were, as advertised (i.e. something other than multituberculates.)

Another traditional clade of Early Cretaceous mammals
are the eutriconodonts. These include taxa with traditional tooth arcades, but lacking deep canines. Repenomamus is one traditional eutriconodont, but nests in the large reptile tree with Pachygenelus in the tritylodontids. Spinolestes (Fig. 1) and Jeholodens (Fig. 2) are also listed at eutriconodonts, but they nest together in the large reptile tree both as sisters and as derived tritylodontids.

Figure 1. Spinolestes with bones colorized in DGS and both manus and skull reconstructed.

Figure 1. Spinolestes with bones colorized in DGS and both manus and skull reconstructed. Note the tooth pattern recovered here is different than as originally described. If your screen is 72 dpi, then this image is about half again as large as life size.

Spinolestes
has accessory neural articulations, like some shrews do. It also appears to have two sacrals and is otherwise robust overall. The entire foot is present, but scattered. I attempted a reconstruction of the lateral view of the skull based on published clues (Fig. 1).

Figure 2. Jeholodens holotype. Note the tip of the snout is missing, and so are the large anterior premaxillary teeth that characterize this clade.

Figure 2. Jeholodens holotype. Note the tip of the snout is missing, and so are the  anterior premaxillary teeth. If your screen is 72 dpi, then this image is almost twice as large as life size.

Jeholodens jenkinsi
(Ji et al. 1999) was also considered a triconodont, but the tip of the snout is missing. Not as robust as Spinolestes, Jeholodens (Fig. 2) was nevertheless a flat-bodied specimen able to slip into rock cracks. Wikipedia reports the eye was 5 cm across. The true figure is 5 mm.

Ji et al. 1999 reported, “The postcranial skeleton of this new triconodont shows a mosaic of characters, including a primitive pelvic girdle and hindlimb but a very derived pectoral girdle that is closely comparable to those of derived therians. Given the basal position of this taxon in mammalian phylogeny, its derived pectoral girdle indicates that homoplasies (similarities resulting from independent evolution among unrelated lineages) are as common in the postcranial skeleton as they are in the skull and dentition in the evolution of Mesozoic mammals.”

The present analysis indicates
that Jeholodens actually nested with pre-mammal tritylodontids. The naris and small premaxillary teeth provided in the original reconstruction are imagined because that part is broken off the matrix (Fig. 2).

Be wary when you see
the terms ‘mosaic’ and ‘modular’. As we’ve seen before, that usually means the phylogeny is off. Evolution works by a gradual accumulation of traits all over the body, not in a modular or mosaic fashion. Trityodontids look like mammals because they are the proximal outgroup taxon. Multituberculates nest with rodents, with whom they share so many traits.

Figure 3. The tarsus of Jeholodens compared to that of a cynodont, mutituberculate and Didelphis, a marsupial (metatherian).

Figure 3. The tarsus of Jeholodens compared to that of a cynodont, mutituberculate and Didelphis, a marsupial (metatherian). Note that metatarsal 5 is missing in all taxa. Metatarsal 4 becomes a dual metatarsal in Didelphis and most eutherians, but not in Vulpavus, Onychonycteris,

 

Figure 4. Rattus pes. Note distal tarsal 4 only backs up pedal digit 4 and digit 5 rides alongside.

Figure 4. Rattus pes. Note distal tarsal 4 only backs up pedal digit 4 and digit 5 rides alongside.

 

 

 

Using Didelphis for a derived tarsus is a little misleading…
From the Ji et al. 1999 paper (Fig. 3) it looks like Jeholodens has a basal tarsus because distal tarsal 4 is not wide enough to double as a distal tarsal 5, as it does in the marsupial, Didelphis. A quick peek at Rattus (Fig. 4), Vulpavus and Onychonycteris shows that these placental taxa likewise do not widen distal tarsal 4 to back up pedal digit 5. And it is not clear how the Jeholodens tarsus actually stacks up. (Fig. 5). If the tarsus was loose, as it is in bats like Onychonycteris or Pteropus, then it doesn’t necessarily mean the tarsus was primitive, like that of a cynodont. That’s why the overall scores are more important than individual character scores.

Just because something is published in Nature or Science, doesn’t mean it’s necessarily right, as we’ve seen before with Yi, Cartorhynchus, Sclerocormus, Chilesaurus, dinosaur origins. pterosaur origins and turtle origins.

Figure 5. Tarsus of Jeholodens with elements colorized as in other taxa.

Figure 5. Tarsus of Jeholodens with elements colorized as in other taxa.

And while I’m thinking about it,
it may be that clades like “Triconodonta” and “Eutriconodonta” may be junior synonyms for long established taxa, as we looked at earlier here.

References
Ji Q, Luo Z and Ji S. 1999. A Chinese triconodont mammal and mosaic evolution of the mammalian skeleton. Nature 398:326-330. online.

Martin T et al. 2015. A Cretaceous eutriconodont and integument evolution of early mammals. Nature 526:380-384. online.

 

Hypsibema missouriensis – a Late Cretaceous Appalachia duckbill dinosaur

Figure 1. Model of Hypsibema missouriensis, a hadrosaurid dinosaur

Figure 1. Model of Hypsibema missouriensis, a hadrosaurid dinosaur

Hypsibema missouriensis
(Cope 1869; Gilbert and Stewart 1945; Gilbert 1945; Baird and Horner 1979; Darrough et al. 2005; Parris 2006; Campanian, 84-71 mya, Late Cretaceous) is a fairly large hadrosaurid dinosaur discovered in 1942, at what later became known as the Chronister Dinosaur Site near Glen Allen, Missouri. At present this literal pinprick in the map of Missouri is the only site that preserves dinosaur bones.

Figure 2. Where the Hypsibema maxilla chunk came from on the skull of Saurolophus.

Figure 2. Where the Hypsibema maxilla chunk (Figure 3) came from modeled on the skull of Saurolophus.

Small pieces of broken bone and associated caudals and toes
were first discovered when digging a cistern. They had been found about 8 feet (2.4 m) deep imbedded in a black plastic clay. The area is in paleokarst located along downdropped fault grabens over Ordovician carbonates.

Gilmore and Stewart 1945 described a series of Chronister caudal centra (now at the Smithsonian) as sauropod-like, reporting, “The more elongate centra of the Chronister specimen, with the possible exception of Hypsibema crassicauda Cope, and the presence of chevron facets only on the posterior end appear sufficient to show that these vertebral centra do not pertain to a member of the Hadrosauridae.”

First named Neosaurus missouriensis,
the caudals were renamed Parrosaurus missouriensis by Gilmore and Stewart 1945 because “Neosaurus” was preoccupied. The specimen was allied to Hypsibema by Baird and Horner 1979.

Figure 3. Back portion of a Hypsibema maxilla showing tooth root grooves and cheek indention close to jugal.

Figure 3. Back portion of a Hypsibema maxilla showing tooth root grooves and cheek indention close to jugal.

Back in the 1980s
I enjoyed going to the Chronister site with other members of the local fossil club, the Eastern Missouri Society for Paleontoogy. I was lucky enough to find both a maxilla fragment (Fig. 3) and a dromaeosaurid tooth. I remember the horse flies were pesky and  one morning, before the other members got there, I was met by a man with a shot gun who relaxed when I identified myself. A friend found a series of hadrosaur toe bones, each about as big as a man’s hand (sans fingers). The bone was so well preserved you could blow air through the porous surfaces.

References
Baird D and Horner JR 1979. Cretaceous dinosaurs of North Carolina. Brimleyana 2: 1-28.
Cope  ED 1869.
Remarks on Eschrichtius polyporusHypsibema crassicaudaHadrosaurus tripos, and Polydectes biturgidus“. Proceedings of the Academy of Natural Sciences of Philadelphia 21:191-192.
Darrough G; Fix M; Parris D and Granstaff B 2005.
 Journal of Vertebrate Paleontology 25 (3): 49A–50A.
Gilmore CW and Stewart DR 1945. A New Sauropod Dinosaur from the Upper Cretaceous of Missouri. Journal of Paleontology (Society for Sedimentary Geology 19(1): 23–29.
Gilmore CW 1945. Parrosaurus, N. Name, Replacing Neosaurus Gilmore, 1945. Journal of Paleontology (Society for Sedimentary Geology 19 (5): 540.
Parris D. 2006. New Information on the Cretaceous of Missouri. online

wiki/Hypsibema_missouriensis
bolinger county museum of natural history
More info and links

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

 

 

Hamipterus – a closer look at gender and ontogeny

Wang et al. 2014 introduced us
two years ago to a new collection of pterosaur parts from a monotypic population that was swept together and disarticulated by a flood event. As you may recall, five well-preserved three-dimensional eggs were recovered from the Early Cretaceous site in northwestern China. Sexual dimorphism was identified for the first time in pterosaurs with two different types of crests appeared on a variety of sizes of skulls (Figs. 1, 2). They named the new specimen, Hamipterus tianshanensis and the holotype was described as, One complete presumed female skull (IVPP V18931.1)”.

Figure 1. The female holotype and male paratype from the Hamipterus population assemblage fossil. The second tracing enlarges the male skull to the same length as the female skull. The color bar overprints indicate parts that differ in length from one skull to the other and a second overlay traces tooth position shifts from one to another.

Figure 1. The female holotype and male paratype from the Hamipterus population assemblage fossil. The second tracing enlarges the male skull to the same length as the female skull. The color bar overprints indicate parts that differ in length from one skull to the other and a second overlay traces tooth position shifts from one to another. The vestigial naris appears between the nasal and jugal beneath the crest. Direct comparisons like this help reveal subtle differences that otherwise might be overlooked.

Such a sweeping together of so many individuals
provides an unprecedented insight into several areas of pterosaur biology, but the data need to be rigorously examined so as not to jump to any conclusions.

Visible differences in the two skulls

  1. Crest shape
  2. Tooth placement
  3. Ventral maxilla shape
  4. Lateral extent of the premaxilla
  5. Depth of the skull anterior to the antorbital fenestra
  6. Concave vs. straight rostral margin (sans crest)
  7. Length of the upper temporal fenestra
  8. Placement of the vestigial naris
  9. Suborbital depth of the jugal

Gender
Wang et al. report, “About 40 male and female individuals in total were recovered, but the actual number associated might be in the hundreds. All of the discovered skulls have crests, which exhibit two different morphologies in size, shape, and robustness. Although morphological variation could be interpreted as individual variation, these marked differences suggest that the skulls belong to different genders. Hamipterus tianshanensis contradicts this hypothesis, because this species indicates that morphology of the crest, rather than its presence.”

Consider what we know about gender differences in birds and lizards,
It may be too soon to generalize over gender differences in pterosaurs. While each gender could have its own signature crest, size, etc., likewise each species likely had its own signature identity/crest/color/call, plumage, etc. At present, no other pterosaurs show verifiable gender differences. That’s why the Wang et al. paper was so important. Gender differences described for both Darwinopterus and Pteranodon were shown to be phylogenetic. Darwinopterus does present a mother with an aborted egg, but the father of the egg has not been identified. Hamipterus offers the best opportunity, so far, to bring some data to the table on this topic. And what Wang et al. indicate may indeed be true.

However, not enough care, IMHO, was administered to the non-crest differences in the skull material was made. Considering just the arrangement of teeth in the jaws (Fig. 1), is it possible that two very closely related species lived near one another? Or did individual variation cover a wider gamut than we now think is reasonable? Remember, among all the Pteranodon specimens now known (to me, at least), no two are identical. The same can be said for the Rhamphorhynchus and Pterodactylus specimens. And when you give Hamipterus a rigorous study, several subtle variations arise. Some of these arise from crushing. Others do not. With given data, one wonders if these could be two Hamipterus variations could be very closely related and.or very closely nesting sister taxa. OR… with present data, gender differences could extend beyond just the crest.

It is also possible
that male pterosaurs were rare rogues and this was a colony of females only with lots of individual variation. Do male lizards help raise their young? Do females? No. But pterosaurs might have been different. Wang et al. report on 40 individuals, but not on the male/female ratio or how many skulls are known. There were three in the holotype block. I’m guessing their specimen count was based on 40 skulls.

Figure 2. Finishing up the large skull with the large crest with two smaller candidates reveals that the slightly better fit is with the female skull.

Figure 2. Finishing up the large skull with the large crest with two smaller candidates reveals that the slightly better fit is with the female skull.

Ontogeny
Wang et al. report, “Ontogenetic variation is reflected mainly in the [lateral] expansion of the [spoon-shaped in dorsal view] rostrum.” Wang et al. reinforce what we know from other pterosaurs that they developed isometrically. Note the similarity between the crests of the smaller and larger ‘male’ specimens (Fig. 2). We’ve seen that before with Tupuxuara juveniles (Fig. 3).

Figure 1. Ontogenetic skull and crest development in Tupuxuara. Note the eyes are small and the rostrum is long in juveniles. Only the crest expands and only posteriorly.

Figure 3. Presumed ontogenetic skull and crest development in Tupuxuara. Note the eyes are small and the rostrum is long in juveniles. Only the crest expands and only posteriorly. Are are these two different sized but otherwise related species? With that longer rostrum, the smaller specimen may be distinct phylogenetically. No small crest Tupuxuara specimens are known.

Sedimentology
Wang et al. report, “Tempestite interlayers where nearly all of the pterosaur fossils are found suggest that large storms caused the mass mortality, event deposits, and lagersta¨ tte of the pterosaur population.”

Phylogenetically
Wang et al. discussed what Hamipterus is not. Their analysis nested it at the base of the Ornithocheiridae with complete lack of resolution. The large pterosaur tree nests Hamipterus with complete resolution between Boreopterus and Zhenyuanopterus.

Eggs
Wang et al. report, “A total of five eggs were recovered from the same site. The outer surface is smooth and exhibits no ‘papilla-like ornamentation,’ as was reported of the first pterosaur egg found in China.” Well that was a giant anurognathid egg, for which finding the parent will be big news. I’d be more interested to see comparisons to the second pterosaur egg found in China, the JZMP egg/embryo, which belonged to a rather closely related [to Hamipterus] ornithocheirid.

Wang et al. report, “Due to the close proximity to Hamipterus tianshanensis, the sole taxon found at the site, all of the eggs are referred to this species. Compared with other reptiles, the Hamipterus eggs show more similarities with some squamates,” I love it when every bit of data supports the theory that pterosaurs are lepidosaurs.

Wang et al. report, a 60µm calcareous eggshell followed by a thin 11µm inner membrane. They compared that to a snake egg of similar dimensions with a 60µm calcareous membrane followed by a much thicker 200µm inner membrane. Then they speculate wildly with this imaginative statement, “It is possible that Hamipterus also had a much thicker membrane, which was not completely preserved. We propose that such an eggshell structure, similar to that of some snakes, may well explain the preservation of the outer surface observed in pterosaur eggs.” IMHO, paleontologists go too far when they try to explain away data, rather than dealing with it directly. Elgin, Hone and Frey (2011) did this with their infamous wing membranes which they speculated suffered from imagined “shrinkage” in order to protect their verifiably false deep chord wing membrane hypothesis.

Wang et al report, “The [egg] size differences might also reflect different stages of development, since mass and dimensions differ between recently laid eggs and more developed ones.” There’s another possibility. Since we know that half-sized female pterosaurs were of breeding age (Chinsamy et al. 2008) they could have laid smaller eggs, producing smaller young, one source of rapid phylogenetic miniaturization.

Wang et al. report, “The combination of many pterosaurs and eggs indicates the presence of a nesting site nearby and suggests that this species developed gregarious behavior. Hamipterus likely made its nesting grounds on the shores of freshwater lakes or rivers and buried its eggs in sand along the shore, preventing them from being desiccated.” There’s another possibility. Since pterosaurs are lepidosaurs, they could have retained the eggs in utero until the young were ready to hatch. That also prevents them from desiccation. Since the flood tore the bones apart, any in utero eggs would have been torn away from the mother as well.

Notable by its absence
is any report of embryo bones inside the eggshells. I presume none were found or they would have been reported. That’s a shame, too, because eggs are nice little containers for complete skeletons, something lacking at the Hamipterus site. Some of the eggs appear to be evacuated, as if they were empty when buried. Or maybe all the juices were squeezed out during the rush and tumble of flood waters. If there was an embryo inside one of the Hamipterus eggs, and that is likely as the egg shell is applied just before egg laying, the embryo might have looked something like this (Fig. 3) based on the other pterosaur embryos inside their own two-dimensional eggs and the appearance of more complete sister taxa. During taphonomy the embryo inside would have been shaken AND stirred (but note some skulls are preserved complete without destruction!). The three dimensional egg contents would not accumulate on the randomly chosen longitudinal saw cut.

Figure 3. Wang et al. sliced one of the eggs lengthwise (yellow). if there is an embryo inside, it might have looked something like this. Since the egg has not been crushed to two dimensions, all the bones would not be now located in the plane of the slice, which was a random cut, not recognizing any embryo inside.

Figure 3. Wang et al. sliced one of the eggs lengthwise (yellow). if there is an embryo inside, it might have looked something like this. Since the egg has not been crushed to two dimensions, all the bones would not be now located in the plane of the slice, which was a random cut, not recognizing any embryo inside. Other embryos are typically in this pose.

Pterosaur hatchlings
of this size were precocial, able to fly shortly after hatching and large enough not to suffer from desiccation caused by so much surface area compared to volume.

References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Elgin RA, Hone DWE, and Frey E. 2011.
The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111 doi:10.4202/app.2009.0145 online pdf
Wang X et al.*, 2014.
 Sexually Dimorphic Tridimensionally Preserved Pterosaurs and Their Eggs from China, Current Biology. http://dx.doi.org/10.1016/j.cub.2014.04.054

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

Is this the missing skull of the basal bird, Archaeornithura?

Updated March 16, 2016 with new images. The beak, if present, is ephemeral, questionable. Only two scores changed.

The spectacular plate and counter plate
of the basal ornithouromorph bird, Archaeornithura (Figs. 1-3, Early Cretaceous, Wang et al. 2015) appear to present every aspect of this specimen in full detail, but only the back of the skull (the occipital plate) appears to be readily preserved on the split surfaces.

Figure 2. That little patch by the shoulder could be the beak, eye and cranium of Archaeornithura.

Figure 2. That little patch by the shoulder could be the beak, eye and cranium of Archaeornithura.

Where is the rest of the skull? 
It might be here (Fig. 2). At least part of it, the beak tip, scleral ring and cranial bones (frontal and parietal) give the impression of being there. I can’t be sure working from photos alone, but when you put the parts on a reconstruction of the rest of the body (Fig. 3), the parts fit both morphologically and phylogenetically.

Figure 3. Reconstruction of the basal ornithuromorph bird, Archaeornithura with skull added. Feathers and ribs omitted. The length of the tail is hard to determine.

Figure 3. Reconstruction of the basal ornithuromorph bird, Archaeornithura with skull added. Feathers and ribs omitted. The length of the tail is hard to determine.

Despite the rather short arms, 
the long wing feathers (Fig. 1) made the wings large enough for flapping flight. The robust and long coracoids attest to the ability to flap with great vigor. The sternum is not flat, but more deeply keeled than in more primitive birds. The large pelvis anchors strong leg muscles. The fragile pubes framed larger air sacs. Despite robust sacral vertebrae that broadened the hips, the tail was reduced and without a robust parson’s nose-type pygostyle, which developed by convergence in other birds clades and in more derived ornithuromorphs. The perching toe was not so well developed and all pedal unguals were rather small, similar to those of wading pterosaurs like Ctenochasma.

Hedging paragraph:
I don’t think there is no way to tell how long the beak of Archaeornithura was given the present data. Currently I have the beak tip not very separated from the occiput giving it a rather short skull. Alternatively the length of the skull might be measured from the in situ beak tip to the in situ occiput. Then this bird would have had a longer rostrum, more like that of its beach combing analog among pterosaurs, Ctenochasma. Perhaps other specimens will help fill in the data gap here.

References
Wang M et al. (7 other authors) 2015. The oldest record of ornithuromorpha from the early cretaceous of China. 6:6987 DOI: 10.1038/ncomms7987

wiiki/Archaeornithura