Bird, pterosaur, dinosaur simplified chronology

Following the earlier post on non-arboreal post K-T boundary birds…

…this one pretty much speaks for itself.
Here (Fig. 1) is a chronology, very much simplified, of birds, pterosaurs and dinosaurs according to the LRT.

Figure 1. Mesozoic chronology of bird, dinosaur and pterosaur clades.

Figure 1. Mesozoic chronology of bird, dinosaur and pterosaur clades based on taxa in the LRT.

If you’re curious about any of the taxa,
in the chronology, simply use Keywords to locate them.

Early Cretaceous stem chameleon/horned lizard

Unnamed stem chameleon (Daza et al. 2016; Early Cretaceous, 1.2cm in length; JZC Bu154; Fig. 1) is a tiny neonate preserved in amber. It also nests basal to horned lizards like Phrynosoma, in the large reptile tree (LRT, 1089 taxa). Note the long, straight hyoid forming the base of the shooting tongue. The split fingers and toes of extant chameleons had not yet developed in this taxon. Found in amber, this newborn lived in a coniferous forest.

Figure 1. The Early Cretaceous stem chameleon/horned lizard found amber. Snout to vent length is less than 11 mm. Much smaller than a human thumbnail.

Figure 1. The Early Cretaceous stem chameleon/horned lizard found amber. Snout to vent length is less than 11 mm. Much smaller than a human thumbnail. Insitu fossil from Daza et al. 2016,  colorized and reconstructed here. At a standard 72 dpi screen resolution, this specimen is shown 10x actual size.

This specimen further cements
the interrelationship of arboreal chameleons and their terrestrial sisters, the horned lizard we looked at earlier with Trioceros and Phyrnosoma in blue of this cladogram (Fig. 2) subset of the LRT.

Figure 3. Subset of the LRT focusing on the neonate stem chameleon/horned lizard.

Figure 2. Subset of the LRT focusing on the neonate stem chameleon/horned lizard.

Figure 6. Phyronosoma, the horned lizard of North America.

Figure 3. Phyronosoma, the horned lizard of North America.

Figure 2. Trioceros jacksonii overall. Size is 12 inches (30 cm) from tip to tip.

Figure 4. Trioceros jacksonii overall. Size is 12 inches (30 cm) from tip to tip.

References
Daza JD et al. 2016. Mid-Cretaceous amber fossils illuminate the past diversity of tropical lizards. Sci. Adv. 2016; 2 : e1501080 4 March 2016

New flightless and giant nyctosaurs: Alcione and Barbaridactylus

Scale bar problems
and a lack of reconstructions in the original paper are issues here.

Longrich, Martill and Andres 2018
bring us news of “a diverse pterosaur assemblage from the late Maastrichtian of Morocco that includes not only Azhdarchidae but the youngest known Pteranodontidae and Nyctosauridae. [This] dramatically increases the diversity of Maastrichtian pterosaurs. At least 3 families —Pteranodontidae, Nyctosauridae, and Azhdarchidae — persisted into the late Maastrichtian. These patterns suggest an abrupt mass extinction of pterosaurs at the K-Pg boundary.”

The authors summary starts off with an invalid statement:
“Pterosaurs were winged cousins of the dinosaurs.”  That was invalidated by Peters 2000, 2007 and ignored every since. We looked at that problem earlier here, here and here in a 3-part series testing all candidates. It’s time to realize that no one will ever find pterosaur kin among the dinos. They’ve already been clearly identified among the lepidosaurs.

The authors failed to include the Maastrictian tupuxuarid
found in southern Texas (Fig. 1; TMM 42489-2) and did not consider the Maastrichtian footprints discovered in 1954 and reexamined in 2018 that include two ctenochasmatids we will look at tomorrow.

TMM 42489-2, the tall crested Latest Cretaceous large rostrum and mandible. It's a close match to that of Tupuxuara, otherwise known only from Early Cretaceous South American strata.

Figure 1. TMM 42489-2, the tall crested Latest Cretaceous large rostrum and mandible. It’s a close match to that of Tupuxuara, otherwise known only from Early Cretaceous South American strata.

Alcione elainus gen. et sp. nov.
The new 1.5x larger nyctosaurid, Alcione elainus, known from disassociated bones including a shorter radius + ulna, a shorter metacarpal 4, a larger femur, and a tiny sternal complex (identified as a ‘sternum’ in the text) only 40 percent the size of a standard nyctosaur sternal complex (if the scale bars are correct). When placed on a reconstruction of a more complete Nyctosaurus (UNSM 93000; Fig. 2), scaled to the humerus, the result produces a likely flightless nyctosaur. Strangely, the authors called this a “small nyctosaur” even though it is half again larger than UNSM 93000. The authors mislabeled the shorter, straighter scapula as a coracoid, and vice versa.

Figure 2. GIF movie of Nyctosaurus and Alcione showing a likely flightless nyctosaur based on the parts preserved.

Figure 2. GIF movie of Nyctosaurus and Alcione showing a likely flightless nyctosaur based on the parts preserved. Three frames change every 5 seconds. The sternum is tiny (assuming the scale bars are correct), the metacarpus and antebrachium are short and the femur is long.

They did not mention the possibility of flightlessness.
They did report, “The abbreviated distal wing elements in Alcione indicate a specialized flight style. The short, robust proportions suggest reduced wingspan and increased wing loading, implying distinct flight mechanics and an ecological shift. Short wings would increase lift-induced drag at low speeds, but reduced wing areas would decrease parasite drag at high speeds, suggesting that Alcione may have been adapted for relatively fast flapping flight compared to other nyctosaurids. Alternatively, reductions in wingspan might represent an adaptation to underwater feeding, i.e., plunge diving of the sort practiced by gannets, tropicbirds, and kingfishers, where smaller wings would reduce drag underwater.”

Not sure why they mentioned
‘distal wing elements’ here. They did not list or discuss distal wing elements elsewhere. Perhaps they meant proximal.

The reconstructed mandible of Alcione
is narrower than the rostrum in UNSM 93000.

Based on the vestigial fingers of UNSM 93000
and the short metacarpus of the new specimen, Alcione might have been the first pterosaur to walk on metacarpal 4, albeit at the very end of the reign of pterosaurs.

Other flightless pterosaurs include:
the basal azhdarchid form the Solnhofen, Jme-Sos 2428 and the Late Jurassic anurognathid PIN 2585/4 from the Sordes slab. They demonstrate that the distal wing elements reduce first. Thus the reconstruction, based on nyctosaur patterns restores a wing that was not volant.

Longrich, Martill and Andres did find a giant nyctosaur
which they named Barbaridactylus grandis based on a large humerus (Fig. 3). The humerus of the more complete UNSM 93000 specimen is 9.5 cm. By comparison the humerus in Barbaridactylus is 22.5 cm. I’m going to trust the text comment that the ulna + radius are 1.3x longer than the humerus. The scale bars indicate about half that length. Similar problem possible in the scapula/coracoid, according to the nyctosaur bauplan.

Figure 3. Barbaridactylus, a giant nyctosaurid. If the wing was like UNSM 93000, then it could fly. If the wing was like Alcione, then it could not. The scale bars did not match the text description on the ulna + radius, so both sizes are shown.

Figure 3. Barbaridactylus, a giant nyctosaurid. If the wing was like UNSM 93000, then it could fly. If the wing was like Alcione, then it could not. The scale bars did not match the text description on the ulna + radius, so both sizes are shown. Sometimes you have to be prepared for the occasional mistake in a published paper.

Other giant nyctosaurs
Earlier and here we noted giant nyctosaurs were flying over the Niobrara Sea (midwest North America) based on a large wing finger with unfused extensor tendon process (YPM 2501) and a large nyctosaur pelvis (KUVP 993; misinterpreted by Bennett (1991, 1992) as belonging to a female Pteranodon). 

No reconstructions were provided
by Longrich, Martill and Andres 2018. Reconstructions and a nyctosaur blueprint might have helped these paleontologists with firsthand access to the specimens discover the issues they missed.

It’s good to know
more pterosaurs made it to the latest Cretaceous.

References
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992.
 Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Longrich NR, Martill DM, Andres B 2018.
Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary. PLoS Biol 16(3): e2001663. https://doi.org/10.1371/journal.pbio.2001663
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2007. 
The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.

Press coverage
Smithsonian
Newswise
PhysOrg

Parrot mimic from the Early Cretaceous

This fossil can be found
(Figs. 1, 2) in the Jeholornis Wikipedia page, labeled Shenzhouraptor. It’s interesting because the rostrum of this Early Cretaceous bird (with impressed feathers) has a downturned tip unlike that of any local taxon. Of course the dentary turns down anteriorly to fit it, as in the convergent parrot, Ara (Fig. 3). I don’t know what the museum number is, nor do I have any reference works that name the genus and species.

Figure 1. What is the museum number and latest generic label for this specimen?

Figure 1. What is the museum number and latest generic label for this specimen?

Here
(subset Fig. 3) it nests with the larger Jeholornis in the large reptile tree (LRT, 1068 taxa). Both are scansoriopterygids.

Figure 2. The Hong Kong specimen attributed to Shenzhouraptor reconstructed from a low-rez image.

Figure 2. The Hong Kong specimen attributed to Shenzhouraptor reconstructed from a low-rez image. If higher resolution is available, please send it along. There is much I am guessing at here. Not sure how to interpret the rostrum based on the presently crappy data. The scale bar is inaccurate.

Figure 3. Scansoriopterygidae includes two Solnhofen birds traditionally labeled Archaeopteryx, but clearly distinct genera. Note, none of these taxa have a styliform bone, as originally figured in Yi qi.

Figure 3. Scansoriopterygidae includes two Solnhofen birds traditionally labeled Archaeopteryx, but clearly distinct genera. Note, none of these taxa have a styliform bone, as originally figured in Yi qi.

By convergence,
The parrot, Ara (below), has features similar to those first appearing in the Hong Kong specimen. Note the deep robust mandible and the ascending jugal, separating the orbit from the conjoined temporal fenestra, making the skull stronger for cracking seeds.

Figure 4. Skull of Ara macao with bones colored.

Figure 4. Skull of Ara macao with bones colored.

References
Looking for them now.

https://en.wikipedia.org/wiki/Jeholornis

Basal mammals: Guess what they evolved to become.

Can you guess
(or do you know) which of these taxa evolved to become a human? a killer whale? a rabbit? a giraffe? a bat? a pangolin?

Figure 1. Can you guess which of these taxa evolved to become a human? a killer whale? a rabbit? a giraffe?

Figure 1. Can you guess which of these taxa evolved to become a human? a killer whale? a rabbit? a giraffe?

H. Onychodectes – basal to all large herbivorous mammals, including giraffes.

G. Maelestes – basal to tenrecs and toothed whales.

F. Tupaia – basal to the gnawing clade including rodents and rabbits.

E. Ptilocercus – basal to Primates, including humans (but note the loss of all premaxillary teeth in this extant taxon).

D. Palaechthon – basal to flying lemurs, bats and pangolins.

C. Monodelphis – basal to all placental mammals.

B. Asioryctes – basal to Monodelphis and all placental mammals.

A. Eomaia – basal to all therian mammals (placentals + marsupials).

These are the basalmost taxa
in various clades of Eutherian (placental) mammals. Not a lot of difference to start (which makes scoring difficult). So much potential at the end. Eomaia goes back to the Early Cretaceous, so it’s not difficult to imagine the radiation of these taxa throughout the Cretaceous.

This falls in line with
the splitting of the African golden mole (Chrysochloris) from its South American sister, Necrolestes, a diversification, migration and split that had to happen before Africa split from South American in the Early Cretaceous.

Sharp-eyed readers
will note the re-identification of bones and teeth in Palaechthon, Ptilocercus and Tupaia. It’s been a long weekend trying to figure out long-standing problems in this portion of the LRT. Some of these taxa were some of the first studied and my naiveté was the source of the earlier disinformation, now corrected. If you see any errors here, please advise and, if valid, repairs will be made.

… and Liaoconodon is not a mammal…

Updated September 22, 2018
with a re-nesting of Liaoconodon with Repenomamus.

Yesterday we noted that Repenomamus was not a mammal, but nested with the stem- (pre-) mammal trithelodontids, like Pachygenelus. Likewise, today Liaoconodon hui (Meng, Wang and Li 2011; IVPP V 16051; early Cretaceous, Aptian, 120 mya; Figs. 1, 3), nests between Gobiconodon and Repenomamus in the large reptile tree (subset in Fig. 2).

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.

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

Liaconodon has a dentary-squamosal jaw joint
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. The narrow braincase of Liaconodon, like that of Repenomamus, tells us this is a pre-mammal. More importantly, phylogenetic analysis nests Liaoconodon outside the last common ancestor of all living mammals: Megazostrodon (Fig. 2). Thus, the dentary-squamosal joint appeared by convergence in Liaoconodon and mammals.

Figure 1. Subset of the LRT focusing on the Kynodontia and Mammalia. Non-eutherian taxa in red were tested in the LRT but not included because they reduce resolution. Eutherian taxa in red include a basal pangolin and derived xenarthran, clades that extend beyond the bottom of this graphic. The pink clade proximal to mammals was considered mammalian by Lautenschlager et al. due to a convergent mammalian-type jaw joint.

Figure 2. Subset of the LRT focusing on the Kynodontia and Mammalia. Non-eutherian taxa in red were tested in the LRT but not included because they reduce resolution. Eutherian taxa in red include a basal pangolin and derived xenarthran, clades that extend beyond the bottom of this graphic. The pink clade proximal to mammals was considered mammalian by Lautenschlager et al. due to a convergent mammalian-type jaw joint.

Liaconodon lacks large canines
and the lower incisors are enlarged. The postorbital bar is not complete.

Figure 3. Liaoconodon in situ.

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

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 are typical for 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 Castorocauda and Repenomamus. 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 tritylodont. Liaoconodon was also a 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 mammal, 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. Note the ear pinna is preserved here on this pre-mammal.

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 nests 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