Gill covers vs gill slits above and below the pectoral fins

Rays, sawfish and skates have gill slits on their flat undersides. 
White and mako sharks have gill slits on their lateral sides. Sturgeons, ratfish and most bony fish, have an operculum. Lampreys have a series of lateral gill holes. Ostracoderms have a series of holes on their flat ventral surface. Moray eels and their deep sea relatives have a single lateral hole without an operculum.

Those are the observations.
What do the evolutionary patterns tell us?

Put into a phylogenetic context, 
(Fig. 1) patterns emerge, but reversals are apparent.

Figure 1. Subset of the LRT showing the pattern of gill slits and opercula in basal vertebrates.

Figure 1. Subset of the LRT showing the pattern of gill slits and opercula in basal vertebrates.

What you don’t want to do
is get caught “Pulling a Larry Martin” (= defining a clade by a short list of traits, like the type of gill openings present). Some clade members don’t follow all of ‘the rules’, but all clade members follow most of ‘the rules.’ If they don’t, they go to another clade.

What you do want to do
is let all the traits and all the taxa fight it out, out of sight, deep in the 0s and 1s of your unbiased software and see what patterns emerge.

For this situation I was curious to see
what patterns emerged, given the present cladogram. Sharp-eyed readers will note this portion has been corrected since the last time it was presented, and probably not for the last time as each new taxon sheds new light on various subsets of the LRT. It’s an ongoing project in real time. It’s never finished.

PS You’ve heard that ontogeny recapitulates phylogeny. 
Here’s a series of paddlefish larvae at weekly intervals.

and all the taxa fight it out,

Figure 2. Paddlefish larvae change as they grow. Adults have an enormous gill cover that starts off much smaller in hatchlings. Note the shark-like stage and the earlier bowfin-like stage, not so much recapitulating phylogeny, but predicting it in descendant taxa.

Note the shark-like stage
and the earlier bowfin-like stage, not so much recapitulating phylogeny, but predicting it in descendant taxa.

Happy holidays.
Thank you for your readership. Be good.

SVP abstract 20: Squamate variability within a single species

Petermann and Gauthier 2020 bring us their views on the 
“potential consequences of our inability to assess intraspecific variability in growth rates.”

From the Petermann and Gauthier abstract:
“An investigation of life-history parameters in the extant iguanian lizard Sauromalus ater (the Common Chuckwalla), a sexually dimorphic species from the SW U.S.A., revealed remarkable intraspecific variability.”

“We found expected differences in growth strategies between males and females, but also within each sex, relating to body size and the timing of sexual maturity. Males and females can grow rapidly to size-at-sexual-maturity, producing above-average adult body sizes. Or, they can grow slowly to size-at-sexual-maturity, yielding adults at or below average body sizes. Neither growth strategy influences longevity. As a result, we found that body size of similar-aged individuals varied by 53% for males and 38% for females, and maximum differences in ‘adults’ of 64% for males and 38% for females.”

Further ranging results were found here earlier in the large pterosaur tree (LPT, 251 taxa) for the lepidosaur pterosaurs, Pteranodon (Fig. 1) and Rhamphorhynchus (Fig. 2). These both became fully resolved in phylogenetic analysis.

Figure 2. The DMNH specimen is in color, nesting between the short crest KS specimen and the long crest AMNH specimen.

Figure 2. The DMNH specimen is in color, nesting between the short crest KS specimen and the long crest AMNH specimen.

Figure 2. Rhamphorhynchus specimens to scale. The Lauer Collection specimen would precede the Limhoff specimen on the second row.

Figure 2. Rhamphorhynchus specimens to scale. The Lauer Collection specimen would precede the Limhoff specimen on the second row.

Continuing from the Petermann and Gauthier abstract:
“Our results add to previous reports of intraspecific variability in extant and extinct vertebrates. High levels of intraspecific size-variability have multiple implications for vertebrate paleontology.

  1. Morphologically similar specimens from the same locality could belong to the same species even if the size difference among adult individuals exceeds 50%, which is a higher level than previously thought.
  2. Specimens that have been analyzed skeletochronologically and have been found to be similar or identical in chronological age, may not exhibit similar sizes.
  3. Variability in growth strategies may lead to mistaking males and females (especially among sexual dimorphs), or individuals using different growth strategies, as belonging to separate species.”

This is the way evolution works in all vertebrate communities, including humans, where some are taller, some are robust, some are more colorful or sexier, some are brilliant, distinct from the others. In both Rhamphorhynchus and Pteranodon, no two specimens are alike.

“We previously presented evidence that a sequence of sub-terminal skeletal suture fusions relates to maximum body size in squamates, and not to chronological age. This indicates that late-ontogenetic, suture-fusion events could be used to evaluate whether two or more specimens of similar morphology and chronological age are differently-sized conspecifics. Likewise, skeletal suture fusions may aid discerning different growth strategies within a single species, as opposed to the presence of two morphologically similar, but nonetheless separate, species in a single taphonomic assemblage.”

This follows the work of Maisano 2002, who found fusion patterns were phylogenetic in lepidosaurs. a pattern continued in pterosaurs, where fusion patterns are also phylogenetic, distinct form archosaur growth patterns.


References
Maisano JA 2002. 
Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Petermann H and Gauthier JA 2020. Intrespecific variability in an extant squamate and its implications for use in skeletochronology in extinct vertebrates. SVP abstracts 2020.

 

Sallen 2016 presents a fascinating flawed look at fish tails

Sallen 2016 reports,
“The symmetrical, flexible teleost fish ‘tail’ has been a prime example of recapitulation — evolutionary change(phylogeny) mirrored in development (ontogeny).”

Sallan’s cladogram (Fig. 1) lays out the traditional cladogram of fish. Note the position of the bichir (Polypterus), at a basal node and the sturgeon + paddlefish (Acipcenser + Polyodon) near the middle.

Figure 1. Cladogram from Sallan 2016 (above) and young fish tails (below).

Figure 1. Cladogram from Sallan 2016 (above) and young fish tails (below).

Unfortunately,
taxon exclusion mars the cladogram of Sallan 2016 according to the the large reptile tree (LRT, 1704+ taxa; Figs. 2, 5). Due to tradition Sallan has chosen the wrong outgroup. Jawless sturgeons and shark-like paddlefish should be the outgroups here, not lungfish-like bichirs (Polypterus), which are highly derived taxa close to lungfish and tetrapods.

Figure 2. Same taxa as above, but rearranged to fit the LRT tree topology.

Figure 2. Same taxa as above, but rearranged to fit the LRT tree topology. Remember, sturgeons, paddlefish and sharks are basal taxa in the LRT. Esox is a catfish related to placoderms.

Salan reports,
“Paleozoic ray-finned fishes (Actinopterygii), relatives of teleosts, exhibited ancestral scale-coveredtails curved over their caudal fins. For over 150 years, this arrangement was thought to be retained in teleost larva and overgrown, mirroring an ancestral transformation series. New ontogenetic data for the 350-million-year-old teleost relative Aetheretmon overturns this long-held hypothesis.”

By contrast,
in the LRT Aetheretmon nests with Pteronsculus (Figs. 5–7)) far from the base of all bony fish, much closer to lobefin fish and tetrapods.

The Sallan point is still made:
Many fish tails do have two parts, especially when hatchlings.

Unfortunately, Sallan does not understand
the topology of the family tree of fish due to taxon exclusion. This is something the LRT minimizes by testing a wider gamut of taxa. As readers know, we see this same taxon exclusion problem all the time in paleontology.

Figure 2. Muskie (Esox) tail ontogeny from Sallan 2016 (middle row). Top row and photo added here.

Figure 3. Muskie (Esox) tail ontogeny from Sallan 2016 (middle row). Top row (to scale) and photo (below) added here. You might remember, Esox is a derived catfish without barbels.

Salan writes,
These two tails appear at a shared developmental stage in Aetheretmon, (Fig. 4) teleosts and all living actinopterygians. Ontogeny does not recapitulate phylogeny; instead, differential outgrowth determines final morphology.”

That appears to be so, but it still needs a valid tree topology.

Figure 3. Fish tail ontogeny in extinct Aetheretmon and extant Monotrete. Note the upper and lower lobes.

Figure 4. Fish tail ontogeny in extinct Aetheretmon and extant Monotrete. Note the upper and lower lobes. In the LRT these two fish are not closely related. Aetheretmon is basal to lobefins. Monotrete is a puffer fish.

Salan speculates:
“The double tail likely reflects the ancestral state for bony fishes.”

No, the ancestral state for bony fish is the heterocercal tail documented by sturgeons and whale sharks, and this goes back to armored osteostracans according to the LRT (Fig. 5).

Figure x. Subset of the LRT, focusing on fish for July 2020.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Salan speculates,
“Many tetrapods and non-teleost actinopterygians have undergone body elongation through tail outgrowth extension, by mechanisms likely shared with distal limbs.”

Not sure what those ‘mechanisms’ would be, but basal tetrapods and stem tetrapods in the LRT have relatively short, straight tails and elongated bodies with great distances between the fore and hind limbs. Look at Panderichthys.

Figure 5. Aetheretmon is known from the oldest complete growth series for vertebrates.

Figure 6. Aetheretmon is known from the oldest complete growth series for vertebrates.

Figure 6. Pteronisculus, a sister to Aetheretmon in the LRT.

Figure 7. Pteronisculus, a Triassic sister to Early Carboniferous Aetheretmon in the LRT and it is easy to see why.

Sallan is ‘Pulling a Larry Martin’
by putting too much emphasis on one trait without testing all the traits on many more taxa. Only after a valid phylogenetic context is established can one begin to figure out if trait A came before trait B or not.

Sallan goes into great detail describing
the successive stages of growth in Aetheretmon, but this is problematic because the cladogram is invalid. “First things first” is a motto all paleontologists should ascribe to. First get the phylogeny correct. Fish workers are relying on an invalid family tree. The LRT is here to fix that.

Its worth remembering,
many fish on the other branch of bony fish (perch, anglers, etc., Fig. 5, orange right column) bring the pelvic fins beneath the pectoral fins, shortening the gut cavity and elongating the tail to extremes in some cases (oarfish). This is all distinct from the longer torso, shorter tail trend in the stem tetrapod branch of bony fishes (Fig. 5, yellow left column).


References
Sallan 2016. Fish ‘tails’ result from outgrowth and reduction of two separate ancestral
tails. Current Biology 26, R1205–R1225.
White EI 1927. The fish fauna of the Cementstones of Foulden, Berwickshire. Transactions of the Royal Society Edinburgh 55:255–287.

https://www.the-scientist.com/the-nutshell/a-tale-of-two-tails-32394

Former Gracilisuchus specimens: now closer to Trialestes

Over the last several weeks
the large reptile tree (LRT, 1660+ taxa, subset Fig. 1) was updated once again with a focus on the Crocodylomorpha. Two congeneric taxa known from a few scraps were eliminated. More insightful identification of skull bones (Figs. 1, 5) settled old issues. Over the next several posts some of the newly recovered hypothetical interrelationships will be presented for review.

We’ll start here
with a new nesting in the LRT (subset Fig. 1) for the small specimens (MCZ4116 and MCZ4118, Fig. 2) formerly assigned to Gracilisuchus (Figs. 4, 5). Now they nest either as hatchling Trialestes (Fig. 3), or, just as likely, as phylogenetically miniaturized Middle Triassic predecessors to the much larger and highly derived Late Triassic basal crocodylomorph, Trialestes. In either case, now Trialestes and its tiny doppelgänger nest together in the LRT, closer to each other than either is to any other taxon, despite a magnitude or two difference in size (Fig. 3). Gracilisuchus nests several nodes away in the next clade (Fig. 1).

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades. Images changes every 5 seconds.

Hatchling? Trialestes? (MCZ 4116, MCZ 4118, originally Gracilisuchus, Brinkman 1981; Middle Triassic; Fig. 2). These two specimens have a taller, narrow skull than Gracilisuchus (Figs. 4, 5) and a long list of other distinct traits and proportions that nest them with the very much larger Trialestes (Fig. 3) in the LRT (Fig. 1).

Figure 1. The former Gracilisuchus specimens MCZ4116 and MCZ4118 with colors added.

Figure 2. The former Gracilisuchus specimens MCZ4116 and MCZ4118 (Middle Triassic) with colors added.

Trialestes romeri (Bonaparte 1982Triassolestes (Reig, 1963/Tillyard 1918) Carnian, Late Triassic ~235 mya) is known from scattered parts here reconstructed and restored (Fig. 3). Clark, Sues and Berman (2000) redescribed the known parts and admitted the possibility that this taxon combined dinosaurian and crocodylomorph characters.

Figure 2. Trialestes reconstructed. At upper left is MCZ4116 to scale.

Figure 3. Trialestes (Late Triassic)  reconstructed. At upper left is MCZ4116 to scale.

Quadrupedal Trialestes
is indeed different than most basal bipedal crocodylomorphs (see Pseudhesperosuchus), but it has elongate proximal carpals (Fig. 3) and a long list of other croc clade traits. The elongate ilium is typical of bipedal taxa indicating a bipedal ancestry. Additional sacrals that would have filled out the sacral set between the ilia (Fig. 3) are not known, but likely were present.

Figure 4. Present reconstruction of Gracilisuchus with skull based on Romer 1971. See figure 4 for an updated on that skull.

Figure 4. Present reconstruction of Gracilisuchus with skull based on Romer 1971. See figure 4 for an updated on that skull.

In Trialestes
the vertebral centra had excavated lateral surfaces, for bird-like air sacs. The radius was longer than the humerus, a character otherwise known only in dinosaurs. The long radiale was slightly shorter than the ulnare. The fingers were tiny, another indicator of a bipedal ancestry. The pelvis was semi-perforated with a well-developed supraacetabular crest, as in basal dinosaurs. The femoral head was inturned, indicating an erect posture. The ankle joint had a crocodile normal configuration and a functionally pentadactyl pes.

Figure 5. Gracilisuchus skull updated with new colors.

Figure 5. Gracilisuchus (Middle Triassic) skull updated with new colors. Compare to figure 2.

The MCZ 4116 and MCZ 4118 specimens 
are coeval with Gracilisuchus in the Middle Triassic and similar in size, but share more traits in the LRT with highly derived Late Triassic Trialestes. As we’ve seen before, new morphologies often express their genesis in phylogenetically miniaturized taxa. That may be the case with the MCZ specimens, appearing millions of years before the much larger Trialestes. More discoveries, like an adult Trialestes in the Middle Triassic, will someday settle this ontogenetic and phylogenetic issue. This blogpost is where this issue starts. If this is not a novel hypothesis of interrelationships, let me know so I can promote the older citation.

Updates have been a continuing feature
of the LRT since its origin nine years ago, along with the steady addition of taxa to the present total of 1658 taxa, plus several hundred taxa in the pterosaur and therapsid cladograms. Correcting mistakes is standard practice in every science and every correction is another rewarding moment of discovery. Holding on to outdated and invalid hypotheses has been an acknowledged problem in paleontology.


References
Bonaparte JF 1982. Classification of the Thecodontia. Geobios Mem. Spec. 6, 99-112
Brinkman D 1981. The origin of the crocodiloid tarsi and the interrelationships of thecodontian archosaurs. Breviora 464: 1–23.
Clark JM, Sues H-D and Berman DS 2000. A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs. Journal of Vertebrate Paleontology 20(4):683-704.
deFranca MAG, Bittencourt JdS and Langer MC 2013. Reavaliação taxonomica de Barberenasuchus brasiliensis (Archosauriformes), Ladiniado do Rio Grande do Sul (Zona-Assembleia de Dinodontosaurus). Palaenotogia em Destaque Edição Especial Octubro 2013: 230.
Irmis RB, Nesbitt SJ and Sues H-D 2013. Early Crocodylomorpha. Pp. 275–302 in Nesbitt, Desojo and Irmis (eds). Anatomy, phylogeny and palaeobiology of early archosaurs and their kin. The Geological Society of London. doi:10.1144/SP379.24.
Kischlat EE 2000. Tecodôncios: a aurora dos arcossáurios no Triássico. Pp. 273–316 in Holz and De Ros (eds.). Paleontologia do Rio Grande do Sul. Porto Alegre: CIGO/UFRGS.
Lecuona A, Ezcurra MD and Irmis RB 2016. Revision of the early crocodylomorph Trialestes romeri (Archosauria, Suchia) from the lower Upper Triassic Ischigualasto Formation of Argentina: one of the oldest-known crocodylomorphs. Papers in Palaeontology (advance online publication). DOI: 10.1002/spp2.1056
Reig, OA 1963. La presencia de dinosaurios saurisquios en los “Estratos de Ischigualasto” (Mesotriásico Superior) de las provincias de San Juan y La Rioja (República Argentina). Ameghiniana 3: 3-20.
Riff D et al. 2012. Crocodilomorfos: a maior diversidade de répteis fósseis do Brasil. TERRÆ 9: 12-40, 2012.
Zanno LE, Drymala S, Nesbitt SJ and Schneider VP 2015. Early Crocodylomorph increases top tier predator diversity during rise of dinosaurs. Scientific Reports 5:9276 DOI: 10.1038/srep09276.

wiki/Trialestes

Was Vellbergia really a juvenile basal lepidosaur? Let’s check…

Earlier we looked at tiny Vellbergia
(Sobral, Simoes and Schoch 2020; Middle Triassic) represented by a disarticulated tiny skull (Fig. 1). The large reptile tree (LRT) nested this hatchling with the much larger adult Prolacerta (Fig. 1). The MPT was 20263 steps for 1654 taxa.

The LRT nesting ran counter to the SuppData cladogram
of Sobral, Simoes and Schoch 2020, who nested Vellbergia among basal lepidosaurs, the closest of which are shown here (Fig. 1). Earlier I did not show the competing lepidosaur candidates. That was an oversight rectified today.

Figure 1. Vellbegia compared to the lepidosaurs it would nest with if Prolacerta and all Archosauromorpha were deleted.

Figure 1. Vellbegia compared to the lepidosaurs it would nest with if Prolacerta and all Archosauromorpha were deleted. Gray areas on Vellbergia indicate restored bone that is lost in the fossil.

To test the lepidosaur hypothesis of relationships,
I deleted all Archosauromorph taxa, including Prolacerta, from the LRT to see where among the Lepidosauromorpha Vellbergia would nest. With no loss of resolution, Vellbergia nested between Palaegama and Tjubina + Huehuecuetzpalli at the base of the Tritosauria plus Fraxinisaura + Lacertulus (Fig. 1) at the base of the Protosquamata. The resulting MPT was 20276 steps, only 13 more than the Prolacerta hypothesis of interrelationships.

That is a remarkably small number considering the great phylogenetic distance between these taxa in the LRT.

Rampant convergence
is readily visible among the competing taxa (Fig. 1). No wonder Prolacerta was named “before Lacerta“, the extant squamate. According to Wikipedia, “Due to its small size and lizard-like appearance, Parrington (1935) subsequently placed Prolacerta between basal younginids and modern lizards. In the 1970s (Gow 1975) the close link between Prolacerta and crown archosaurs was first hypothesized.” That was prior to cladistic software and suffered from massive taxon exclusion.

Allometry vs. Isometry
One of the lepidosaurs shown above, Huehuecuetzpalli (Fig. 1), is known from both an adult and juvenile. The older and younger specimens were originally (Reynoso 1998) considered identical in proportion. Such isometry is an ontogenetic trait shared with other tritosaur lepidosaur clade members, including pterosaurs. On the other hand, if Vellbergia was a hatchling of Prolacerta, some measure of typical archosauromorph allometry should be readily apparent… and it is… including incomplete ossification of the nasals, frontals and parietals along with a relatively larger orbit and shorter rostrum, giving Vellbergia a traditional ‘cute’ appearance appropriate for its clade.

Size
Sobral, Simoes and Schoch considered Vellbergia a juvenile, but it is similar in size to the adult lepidosaurs shown here (Fig. 1). On the other hand, Vellbergia is appropriately smaller than Prolacerta, in line with its hatchling status.

Time
Remember also that Vellbergia is from the Middle Triassic. Prolacerta is from the Early Triassic. They were not found together and some differences are to be expected just from the millions of years separating them.

For comparison: another juvenile Prolacerta,
this time from Early Triassic Antarctica (Spiekman 2018; AMNH 9520), is much larger than Vellbergia from Middle Triassic Germany (Fig. 2), but just as cute. Note the relatively larger orbit and shorter rostrum compared to the adult Prolacerta (Fig. 1), traits likewise found in Vellbergia.

Figure 2. Small Prolacerta specimen AMNH 9520 from Spiekman 2018 compared to scale with Vellbergia.

Figure 2. Small Prolacerta specimen AMNH 9520 from Spiekman 2018 compared to scale with Vellbergia. Sclerotic rings (SCL) identified by Spiekman 2018 are re-identified as pterygoids here.

Generally
crushed, disarticulated and incomplete juvenile specimens of allometric taxa are difficult to compare with adults. Even so, what is left of hatchling Vellbergia tends to resemble the larger juvenile and adult specimens of Prolacerta more than hatchling Vellbergia resembles the similarly-sized adult lepidosaurs it nests with in the absence of Prolacerta from the taxon list.

Phylogenetic analysis is an inexact science.
Nevertheless no other known method breaks down and rebuilds thousands of taxa more precisely. Only taxon exclusion appears to trip up workers at present.


References
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Parrington FR 1935. On Prolacerta broomi gen. et sp. nov. and the origin of lizards. Annals and Magazine of Natural History 16, 197–205.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.
Sobral G, Simoes TR and Schoch RR 2020. A tiny new Middle Triassic stem-lepidosauromorph from Germany: implications fro the early evolution of lepidosauromorphs and the Vellberg fauna. Nature.com Scientific Reports 10, Article number: 2273.
Spiekman SNF 2018. A new specimen of Prolacerta broomi from the lower Fremouw Formation (Early Triassic) of Antarctica, its biogeographical implications and a taxonomic revision. Nature.com/scientificreports (2018)8:17996

wiki/Prolacerta

A baby paddlefish enters the LRT looking like a baby shark

Earlier the primitive paddlefish
(Polyodonentered the large reptile tree (LRT, 1634+ taxa) as the basalmost bony fish, distinct from and not related to traditional chondrostean relatives like the sturgeon (Psuedoschaphorhynchus), the bichir (Polypterus), and the extinct ‘chondrostean’ Chondrosteus.

Figure 4. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.

Figure 4. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.

Today, a baby paddlefish,
lacking a long paddle bill (Fig. 2), enters the LRT. Why? Because the paddle bill of the adult stands out as an autapomorphic trait in the cladogram, and I’m looking for plesiomorphic transitional taxa that link clades together.  The short-snouted baby paddlefish (Fig. 2), looking just like a baby shark, but with an operculum, had the potential to do exactly that.

Figure 2. A shark-like juvenile paddlefish (Polyodon) has teeth and lacks a paddle-snout. Compare to the adult in figure 1.

Figure 2. A shark-like juvenile paddlefish (Polyodon) has teeth and lacks a paddle-snout. Compare to the adult in figure 1. Legnth = 2.9cm. or slightly longer than one inch. Images from Grande and Bemis 1991, The pterygoid appears here for the first time.

Despite the lack of an elongate rostrum
and the score changes that brings, the baby and adult Polyodon nest together in the LRT.

Figure 2. Falcatus traced with DGS methods with reconstructed freehand image applied from xxx.

Figure 3. Falcatus nests at the base of the shark clade, not far from baby Polyodon. Note the same underslung jaw loosely connected to the cranium + rostrum.

If ontogeny recapitulates phylogeny
in Polyodon, then the baby provides insight into the plesiomorphic morphology of a basalmost bony fish taxon, not far from a basalmost and transitional shark-clade taxa. That dichotomy likely extends back to the Late Silurian or Early Devonian. Thus, this long-sought and previously elusive mystery taxon might be best represented by a baby paddlefish. That means it was  under our nose all along!

BTW
in the ‘old’ days, Polyodon used to be called the ‘paddle-bill catfish.’ Not sure when the common name change took place.


References
Grande L and Bemis WE 1991. Osteology and phylogenetic relationships of fossil and Recent paddlefishes (Polyodontidae) with comments on the interrelationships of Acipenseriformes. Society of Vertebrate Paleontology Memoir 1. Journal of Vertebrate Paleontology 11, Supplement to Number 1. 121pp.
Walbaum J 1792. Petri Artedi renovati. Part 3. Petri Artedi sueci genera Piscium in quibus systema totum ichthyologiae proponitur cum classibus, ordinibus, generum characteribus, specierum diffentiis, observationibus plumiris. Redactis Speciebus 2. Ichthyologiae, III: 723.

wiki/Polyodon

Flugsaurier 2018: ‘Young istiodactylid’ nests with tall pterodactylids in the LPT

Flugsaurier 2018 opens today, August 10,
and the abstract booklet is out. So it’s time to take a look at some of the news coming out of that Los Angeles pterosaur symposium. Since the purpose of the symposium is increase understanding of pterosaurs, I hope this small contribution helps.

Figure 1. The Erlianhaote specimen attributed by Hone and Xu 2018 to istiodactylidae nests in the LPT with the large derived pterodactylids.

Figure 1. The Erlianhaote specimen attributed by Hone and Xu 2018 to the clade Istiodactylidae (within Ornithocheiridae) nests in the LPT with the large derived pterodactylids. Note the un-warped deltopectoral crest and lack of a deep cristospine, along with the long legs and short wings.

Hone and Xu at Flugsaurier 2018
describe, “An unusual and nearly complete young istiodactylid from the Yixian Formation, China (Fig. 1). The specimen shows the characteristic istiodactylid cranial features of tooth shape and enlarged nasoantorbital fenestra. However, it has proportionally large hindlimbs and wing proportions that are similar to those of azhdarchids. This has led to suggestion that the specimen may be a composite and that only the cranial material is istiodactylid. Preparation work around some key parts revealed no inconsistencies in the matrix or evidence of glue. The specimen is held in the Erlianhaote Dinosaur Museum, Erlianhote, China.”

Figure 2. The Erlianhaote specimen nests with these pterodactylids in the LPT, not with Istiodactylus (Fig. 3). Compare to valid istiodactylids in figures 4–6/

Figure 2. The Erlianhaote specimen nests with these pterodactylids in the LPT, not with Istiodactylus (Fig. 3). Compare to valid istiodactylids in figures 4–6/

Reconstructed as is
(Fig. 2) and added to the large pterosaur tree (LPT, 233 taxa, not yet updated due to no museum number nor genus name) the young ‘istiodactylid’ nests as a large derived pterodactylid. 13 steps separate this taxon from the Istiodactylus clade.

Ornithocheirids,
like Istiodactylus (Figs. 3, 4) and the SMNL PAL 1136 specimen (Fig. 5), share a very large wing finger, a short metacarpus, a warped deltopectoral crest, small free fingers and deeply keeled sternal complex not found in the Erlianhote specimen.

Figure 3. Istiodactylus has a shorter neck, longer wing finger and deep cristospine, among other traits not found in the new Erlianhaote specimen.

Figure 3. Istiodactylus has a shorter neck, longer wing finger and deep cristospine, among other traits not found in the new Erlianhaote specimen.

Figure 4. Istiodactylus sinensis is an istiodactylid from China sharing few traits with the new Erlianhaote specimen. Note the warped deltopectoral crest not warped in the new specimen.

Figure 4. Istiodactylus sinensis is an istiodactylid from China sharing few traits with the new Erlianhaote specimen. Note the warped deltopectoral crest not warped in the new specimen. Manual 4.1 is shorter than in other well-known istiodactylids.

The largest ornithocheirid

Figure 5. The unnamed largest ornithocheirid, SMNK PAL 1136, nests with Istiodactylus.

Figure 6. The Erlianhaote pterodactylid reconstructed in several views.

Figure 6. The Erlianhaote pterodactylid reconstructed in several views. The imagined (gray) areas of the skull here were imagined as an istiodactylid, but the better restoration is shown in figure 2.

It’s better not to eyeball certain specimens.
Sometimes you have to run them through a phylogenetic analysis to find out what they are. That’s what the LPT is for. It minimizes taxon exclusion and handles convergence.

Pterosaurs are still lepidosaurs.
So they follow lepidosaur fusion patterns, which follow phylogeny. Hone and Xu made the mistake of imagining pterosaurs might have archosaur fusion patterns that follow ontogeny.

Why am I not at Flugsaurier 2018?
In addition to about a dozen reasons that I can list later, or your can guess now, I can be more helpful and timely here.

References
Andres B and Ji Q 2006. A new species of Istiodactylus (Pterosauria, Pterodactyloidea) from the Lower Cretaceous of Liaoning, China. Journal of Vertebrate Paleontology, 26: 70-78.
Bowerbank JS 1846. On a new species of pterodactyl found in the Upper Chalk of Kent P. giganteus). Quarterly Journal of the Geological Society 2: 7–9.
Bowerbank JS 1851. On the pterodactyles of the Chalk Formation. Proceedings of the Zoological Society, London, pp. 14–20 and Annals of the Magazine of Natural History (2) 10: 372–378.
Bowerbank JS 1852. On the pterodactyles of the Chalk Formation. Reports from the British Association for the Advancement of Science (1851): 55.
Hone DWE and Xu 2018. An unusual and nearly complete young istiodactylid from the Yixian Formation, China. Flugsaurier 2018: the 6th International Symposium on Pterosaurs. Los Angeles, USA. Abstracts: 53–56.
Hooley RW 1913. On the skeleton of Ornithodesmus latidens. An ornithosaur from the Wealden shales of Atherfield (Isle of Wight)”, Quarterly Journal of the Geological Society, 69: 372-421
Howse SCB, Milner AR and Martill DM 2001. Pterosaurs. Pp. 324-335 in: Martill, D. M. and Naish, D., eds. Dinosaurs of the Isle of Wight, The Palaeontological Association
Wang X, Rodrigues T, Jiang S, Cheng X and Kellner AWA 2014. An Early Cretaceous pterosaur with an unusual mandibular crest from China and a potential novel feeding strategy. Scientific Reports 4 : 6329, pp. 1-9. | DOI: 10.1038/srep06329
Witton MP 2012. New Insights into the Skull of Istiodactylus latidens (Ornithocheiroidea, Pterodactyloidea). PLoS ONE 7(3): e33170. doi:10.1371/journal.pone.0033170

wiki/Istiodactylus

The origin and evolution of bats part 4: distance vs. accuracy

Earlier
we looked at bat origins here, here and here from several perspectives. Some of these are now invalid given the following scenario.

Today we’ll take a fresh look at
the behavior and traits of the closest bat relatives in the large reptile tree (LRT, 1233 taxa, subset Fig. 1) and see what they can tell us about bat origins. This is called ‘phylogenetic bracketing‘. In such a thought experiment we can put forth an educated guess regarding an unknown behavior or trait for a unknown taxa (e.g. pre-bats) if all related specimens share similar behaviors and traits inherited from a known or unknown last common ancestor.

We start off with a cladogram
focusing on bat relationships (Fig. 1) and take things one logical step at a time.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

One. Living sister taxa.
The closest tested sister taxa to bats here (Fig. 1) are pangolins and colugos (flying lemurs) in order of increasing distance. The origin of bats and pangolins has remained a traditional enigma. Like the origin of pterosaurs and Longisquama, the surprise is, they are most closely related to each other, despite their current differences.

Two. Ancestral taxa
Th bat/colugo/pangolin clade had its genesis near the original dichotomy of placental mammals, when Carnivora split off from all others. At the next dichotomy the bat/colugo/pangolin clade split off from all others. So this clade is not far from an ancestral clades with living genera. Monodelphis, the short-tailed opossum today restricted to South America, nests just outside of all mammals with a placenta. Nandinia, the African palm civet, is a basal member of the Carnivora, somewhat larger than its Mesozoic forebearers.

Three. Timing for clade origins
The bat/colugo/pangolin clade had its origin in the Early Jurassic based on the more primitive egg-layers, Megazostrodon, Brasilitherium and Kuehneotherium in the Late Triassic and the much more derived arboreal multituberculate/rodent, Megaconus, in the Middle Jurassic. As you can see, Jurassic mammals remain extremely rare, currently represented only by the likes of Megaconus. Others will, no doubt, be discovered in time.

Four. Arboreality (tree niche)
Some bats, colugos and pangolins live in trees, and so do their last common ancestors, short-tailed opossums and African palm civets.

Five. Climbing trees
Bats no longer have to climb trees because they can fly. Colugos and pangolins both climb trees in a series of symmetrical short hops/extended reaches (colugo video, pangolin video), distinct from palm civets and short-tailed opossums, which put forth one hand at a time, like primates do.

Six. Descending trees.
Bats fly between trees. Colugos glide between trees. Pangolins use their prehensile tail to ease themselves down. The African palm civet drops out of trees in play. It also descends tree trunks like a squirrel, head first.

Seven. Nocturnal
Most bats, colugos, pangolins, palm civets and short-tailed opossums prefer to be active at night.

Eight. Omnivorous diet
Some bats eat insects, others prefer nectar or hanging fruit. Colugos prefer leaves, shoots, flowers, sap, and fruit. Pangolins eat ants. Palm civets and short-tailed opossums are omnivorous. African palm civets feed by holding their prey in their hand-like front paws, biting it repeatedly and then once dead, swallowing it whole.

Nine. Extradermal membranes
Colugos and bats both have extradermal membranes to their unguals that extend their glides in the former and enable flapping flying in the latter. Such membranes are lost in living pangolins, but the Early Cretaceous pangolin, Zhangheotherium appears to have scale-lined membranes between the elbows and knees. These were overlooked in the original description. The gliding membrane in colugos is fur-covered and camouflaged dorsally, naked underneath. In bats the flying membrane is naked, translucent and never camouflaged.

Ten. Mobile clavicle, interclavicle and scapula
The basal pangolin, Zhangheotherium, has a mobile clavicle-interclavicle and the large scapula rises above the  dorsal vertebrae, as in bats, but not colugos.

11. Sprawling femora
Zhangeotherium and bats share sprawling hind limbs, distinct from the more erect hind limbs of most limbed mammals.

12. Silent vs. noisy
African palm civets are noisy. Colugos and pangolins are largely silent. Bats are constantly chirping to one another and (micro-bats only) as part of their sonar attack system.

13. Enemies
All current enemies of bats (e.g. birds, snakes) evolved during or after the Late Cretaceous. Jurassic trees might have been a refuge for small early climbing mammals, like colugo, bat and pangolin ancestors. However…the minimally feathered, small theropod dinosaur, Sinosauropteryx, contained the jaws of Zhangheotherium, perhaps caught after descending from the trees or plucked out of lower branches. Certain pterosaurs (e.g. giant anurognathids) might have preyed on arboreal  mammals in the Jurassic, but no evidence of this is yet known.

FIgure x. Calcaneal spur in Zhangheotherium. Not venomous, but perhaps to anchor a uropatagium.

FIgure 2. Calcaneal spur in Zhangheotherium. Not venomous, but perhaps to anchor a uropatagium as in bats.

14. Calcaneal spurs
Hurum et al. 2006 originally considered the small spurs found on the calcaneum of Zhangheotherium (Fig. 2) similar to venom spurs found on the platypus, Ornithorhynchus. Phylogenetic bracketing indicates the closer homolog is with the basal bat, Onychonycteris, which has longer calcaneal spurs framing a trailing uropatagium.

Figure x. Monodelphis babies in an open pouch. This is how placentals began, slowly evolving from the less open pouch.

Figure 3 Monodelphis babies in an open pouch. This is how placentals began, slowly evolving from the less open pouch.

15. Newborns and mothers
All basal placental mammals give birth to helpless newborns that ride with the mother until mature enough to go out on its own. Monodelphis demonstrates a primitive version of this, protecting its ten young with lateral flaps of skin (Fig. 3). Carnivore mothers make nests for newborns (2-4 for African palm civets), but colugo, bat and pangolin mothers take their one or two babies everywhere they go, like marsupial mothers do. Zhangheotherium might have been fossilized with several newborns. (Fig. 4) and extradermal membranes between elbows and knees, as in bats and colugos. As we know from colugos, these extradermal membranes in basal pangolins (and Chriacus?) likely formed a playpen or nursery for developing young riding beneath their mother during the earliest stages of development.

Figure x. Zhangheotherium showing possible extradermal membranes (green) with keratinous scales (red) and several newborns scattered in the abdominal area, similar to Monodelphis in figure x.

Figure 4. Zhangheotherium showing possible extradermal membranes (light blue and green) with keratinous scales (red) and several newborns scattered in the abdominal area, similar to Monodelphis in figure x. These amorphous blobs with tiny tail bones need further inspection. Some may just be stains and shapes.

16. Curling (flexing the spine)
Mother opossums, palm civets, colugos, bats and pangolins are able to curl their spines so much that the mother’s mouth is able to assist wiggling newborns climb to the abdominal nipples. This curling ability is co-opted by pangolins as they defend themselves by rolling into a tight ball and by bats that catch prey in their tail before curling up to bite the victim as it is brought close to the jaws. Higher mammals lose the ability to curl ventrally in this manner. Humans and other primates have a limited ability to do this. Instead they use their hands. More derived mammals with stiffer backs have more developed newborns.

17. Upside-down vs. right-side up nursery for the young
Colugos may rest right-side up (preferring to hang from below a slightly leaning tree trunk) or upside down hanging by all fours beneath a horizontal branch. When doing so the mother’s extradermal membranes form walls making a protective nursery for the young ones.

By contrast, bats rest up-side down, sometimes hanging by only one locked foot. To fly bats simply release this foot lock, then plummet and start flapping. Bat membranes also provide a protective nursery for their young as they cling to their mothers’ chest and her wings fold over them.

Nowadays pangolins roll into a ball while nursing their young. Later in life, babies ride on the mother’s back and tail when able to do so. Zhangheotherium (Fig. 4) appears to have provided a colugo-like, but scale-lined membrane nursery for several growing babies. The late-surviving pre-bat, Chriacus (Fig. 5), likely did the same, based on phylogenetic bracketing.

18. Claws
Short-tailed opossums and African palm civets use their claws to climb trees and grab prey and fruit, bringing it to the mouth. So do basal primates. Colugos, bats and pangolins use their larger, curved claws principally to hang from trees, though living pangolins have co-opted their large claws to dig out ant and termite nests from trees and underground.

19. Distance vs. accuracy
Colugos leap and turn away from their tree trunk base in order to launch themselves into a glide. Can they do this while hanging beneath a branch? I don’t know. With their long limbs, colugos can just leap (without gliding) across gaps of 5m or more. With limbs extended, they can glide for 136m at 10m/second. Gliding is good for a quick escape from predators, and access to patches of food that are otherwise inaccessible. It does not save them energy to glide, let along climb back to a gliding height.

Bats drop from trees, then fly wherever they please, typically landing upside down on another high branch or cavern roof. The origin of bat flight enabled by flapping hyper-elongated webbed fingers is the key question here, and it is answered by combining all of the above numbered traits.

Before bats could fly Jurassic pre-bats had to climb trees, probably like colugos and pangolins do (see #5 above), before standing bipedally, but upside-down, on a horizontal branch. Why would they do that? To prepare to dive bomb insects on and in the leaf litter below. Here is where sonar became valuable, detecting insects in the leaf litter at night. Here is where the leaf litter became valuable, cushioning the early awkward landings of small dive-bombing pre-bats. Here is where flapping, even with small hands around colugo-like dermal membranes became valuable, at first in panic, then in gradually learning how to better direct the fall to cover the prey below.  (By analogy birds flap their wings vigorously while dropping to slow their descent.)

Upon landing the extended pre-bat nursery membranes ‘put a lid’ on the prey. Then, curling the tooth-line jaws toward the tail and the tail toward the jaws (see #16 above) spelled doom for the captured food item. Over time, larger fingers made better flapping parachutes. Ultimately flapping bats  learned how to hover before diving bombing their prey, like owls do. Later, after further development, bats gained the power and morphology to enable flight, slowly at first, then better and better to escape ground-dwelling predators and avoid having to climb a tree for the next attack. Only later did bats learn to use their sonar and flying skills on flying insects.

So what began as a small pouch, then a larger nursery membrane for bat and colugo infants became a killing zone for bat prey on the ground, another example of co-opting an old trait for a new behavior in derived taxa. Distinct from birds and pterosaurs, which used their nascent flapping behavior to ascend tree trunks to escape predators, create threat displays and slow their descents from branches, bats used their nascent flapping ability only to slow and direct their descent from branches. Distinct from colugos, which glided for distance, bats dropped for accuracy. Distance came later, after flight developed.

Remember the fall need not be far at first. Conifers can have very low branches and leaf litter can be a soft cushion for a mouse-sized mammal. Graduating slowly to higher branches provides bats a wider ‘field-of-view’ for their slowly developing sonar, and more time to develop flapping. Bat hind limbs are not long or heavily muscled. They are not good at leaping, like colugos.

Fruit eating bats could not have developed until flowering and fruit-bearing trees developed, later in the Cretaceous. The LRT and the fossil record indicates that fruit-eating bats are derived relative to smaller insect-eating bats. So sonar-emitting apparently was lost in fruit-eating bats, rather than never a part of their lineage. The great variation now seen in sonar-emitting bat morphology was likely developed during and after the Cretaceous, based on the current fossil record. I think we’ll find fully volant fossil bats in the Cretaceous someday.

I happened upon this idea while watching a pigeon descend from a roofline to a balcony beneath it and wondered if accuracy was more important for bats, while distance was more important for colugos. That distinction seems to be the key driver in both clades. In any case, it is important that any proposed scenario be viable at every point during the gradual evolution of new traits and behaviors. In this case, developing flapping forelimbs had to originate with a bipedal configuration, even it inverted. Developing sonar had to originate from simply listening to nocturnal insects and other small prey rustling in the leaf litter, not far below, gradually getting better in those families that randomly had slightly better skills once dive-bombing and trapping became the method for predation.

20. Bat ontogeny
Recapitulates this phylogenetic scenario. The fingers elongate last. 

21. Solitary vs. communal
Colugos and pangolins are solitary. So are African palm civets except when food is plentiful. Bats are communal, whether nesting in trees or caves. According to Kerth 2008, “Variable dispersal patterns, complex olfactory and acoustic communication, flexible context-related interactions, striking cooperative behaviors, and cryptic colony structures in the form of fission-fusion systems have been documented. tropical bats often form groups year-round, whereas sociality in temperate-zone species is sometimes restricted to certain times of the year. In most species, females form so-called maternity colonies to rear their young communally, whereas males are solitary, form groups of their own, or join female groups. In only a few species are both sexes solitary, meeting only to mate.”

Kerth concludes, “None of the three factors that I identify as important for the evolution of sociality in bats (ecological constraints, physiological demands, and demographic traits) can fully explain the frequency and diversity of group living in bats.”

Figure 1. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins.

Figure 5. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins..

22. Soles of the feet oriented opposite to those of most mammals
Distinct from most mammals, the knees of bats are splayed laterally, which should extend the toes laterally. However, the ankle is rotated another 90º producing a foot in which the soles are ventral during flight and while hanging. In the case of long-legged fish-eating bats, the feet help bring captured fish back to the mouth.

FIgure 1. Wondering if Chriacus had an inverted stance and dermopteran membranes? Comparisons to Onychonycteris and Pteropus.

FIgure 6. Wondering if Chriacus had an inverted stance and dermopteran membranes? Comparisons to Onychonycteris and Pteropus are shown. Yes, the knees are straight in derived fruit bats, bent in Onychonycteris and micro bats. The uropatagia are spread while inverted and while flying. Chriacus appears to be a much larger and much later-surviving version of much smaller Jurassic pre-bats. The membranes are conjectural and may have been lost in this large specimen, but it illustrates the possibility of a dive bombing taxon that covered prey like a casserole lid.

Why do bats hang upside down?
Without a phylogenetic or deep-time perspective, the following video is the best answer current bat workers can provide:

Bats are not using their wings to cool off.
A recent heat wave killed many fruit bats. They fell dead out of the trees (see below). None were creating a cooling breeze with their wings or extending their wings in a cooling fashion, like elephants sometimes do. Microbats that live in caves never have this problem.

Bat wings notes:

  1. Finger flexibility during flight varies greatly in bats.
  2. The flight stroke is otherwise bird-like with elbows raised above the back, nearly meeting at the midline, for maximum power at low airspeed, or less so for cruising at higher airspeeds.
  3. The large fingers do nothing else but push air for thrust and lift. They are not extended to cool the bat, nor do they extend or flash during courtship.
  4. Bat fingers hyper flex at the wrist to tuck away the flight membrane and reduce its surface area when not in use, as in pterosaurs and birds. When flexed they do little but envelope the bat and its clinging young.

Miscellaneous notes:

  1. Zhangheotherium was originally considered a symmetrodont mammal, but its teeth seems to converge with archaeocete whales in this regard. The reappearance of a more primitive symmetrodont molar shape is here considered an atavism in the evolution of toothlessness in both certain odontocetes and pangolins by convergence.
  2. The uncoiled cochlea of highly derived Zhangheotherium and multituberculates, has been traditionally considered a trait that nests these taxa in more basal branches of the mammal family tree. Here, in the LRT, these traits appear to be neotonous or atavistic developments that, taken alone, tend to confuse systematics. No traits should ever be taken alone to determine systematics. That would be ‘pulling a Larry Martin.’
  3. The initial splitting up of Pangaea in the Early Jurassic gave the previously dry climate a more lush, subtropical parade of cycads, conifers, ginkgoes and tree ferns. So there were plenty of standing and fallen trees for early mammals to gambol upon, learning how to climb and leap. The forest floor was likely cushioned with a carpet of leaves and fronds to absorb accidental falls and hunger-driven dive bombs mediated by fluttering pre-wings and large membranes co-opted for eventual flight.

Addendum
Video showing a bat descending on a mouse in leaf litter appears here.

References
Byrnes, Libby, Lim & Spence. 2011. Gliding saves time but not energy in Malayan colugos. Journal of Experimental Biology http://dx.doi.org/10.1242/jeb.052993
Hurum JH, Luo Z-X and Kielan-Jaworowska Z 2006. Were mammals originally venomous? Acta Palaeontologica Polonica 51(1): 1–11.
Kerth G 2008. Causes and Consequences of Sociality in Bats. BioScience, Volume 58, Issue 8, 1 September 2008, Pages 737–746, https://doi.org/10.1641/B580810
Online here.

Massospondylus embryo joins the LRT

…and guess where it nests?

Figure 1. Massospondylus embryo from Reisz et al. 2010.

Figure 1. Massospondylus embryo from Reisz et al. 2010.

This should be easy:
The embryo nests with the adult Massospondylus in the large reptile tree (LRT, 1212 taxa), despite the many proportional and a few osteological changes that attend ontogeny in this basal sauropodomorpth from the Early Jurassic.

Figure 2. Massospondylus adult and several sub adult and juvenile skulls to scale.

Figure 2. Massospondylus adult and several sub adult and juvenile skulls to scale. Note the bipedal pose based on hind and fore limb disparity… distinct from the quadrupedal embryo.

These embryos are the oldest known
dinosaur embryos and apparently they were just days from hatching.

Massospondylus kaalae was a short-snouted basal sauropodomorph from the Early Jurassic closely related to Efraasia and SaturnaliaMassospondylus had a short round snout and long blunt fangs. Another species, Massospondylus carinatus, had a relatively longer skull as an adult.

The embryo Massospondylus
includes a taller antorbital fenestra, a premaxilla lacking a posterior narial process, a naris closer to the jaw line, a straight (not descending) jaw joint, a smaller coronoid process, a lack of teeth, relatively shorter neck, larger fore limbs, a shorter ventral pelvis, distally broader chevrons and smaller feet.

Figure 3. Embryo Massospondylus compared to hatchling Scipionyx.

Figure 3. Embryo Massospondylus compared to hatchling Scipionyx. The predator babies were larger than the bite-sized and more numerous prey babies. 

References
Barrett PM 2009. A new basal sauropodomorph dinosaur from the upper Elliot formation (Lower Jurassic) of South Africa. Journal of Vertebrate Paleontology 29(4):1032-1045.
Morris J 1843. A Catalogue of British Fossils. British Museum, London, 222 pp
Reisz RR, Scott D; Sues H-D, Evans DC and Raath MA 2005. Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance. Science. 309(5735): 761–764.
Reisz RR, Evans DC, Roberts EM, Sues H-D and Yates AM 2012. “Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus. Proceedings of the National Academy of Sciences of the United States of America. 109(7): 2428–2433.
Riley H and Stutchbury S 1836. A description of various fossil remains of three distinct saurian animals discovered in the autumn of 1834, in the Magnesian Conglomerate on Durdham Down, near Bristol. Proceedings of the Geological Society of London 2:397-399.

wiki/Massospondylus

Proconsul, Pan and Homo: face changes

Just some musings today
over chimps and humans (Fig. 1) and some other higher primate skulls (Figs. 2, 3). Chimps have not yet made it into the large reptile tree (LRT, 1068 taxa), but they will someday.

The tradition is
to consider chimps (genus: Pan) the starting point in human (genus: Homo) evolution and to make comparisons between the two. Once again, taxon exclusion becomes a problem.

The actual starting point
is closer to an extinct ancestor of both, Proconsul (aka: Dryopithecus; Hopwood 1933; 18–14mya; Figs. 2, 3) a genus that resembled a chimp, but did not knuckle-walk (Fig. 3) and lacked brow ridges, both traits retained by Homo.

Figure 1. Chimp baby and human baby compared to chimp adult and human adult. See text for details.

Figure 1. Chimp baby and human baby compared to chimp adult and human adult. Pupils are aligned. Everything else morphs. See text for details.

 

Question #1 today is…
What changes can we see in the face of a human compared to a chimpanzee?

  1. Forehead present (housing more cerebral frontal matter)
  2. Longer and protruding nose with ventral nostrils (better for underwater)
  3. Shorter nose-to-lip distance with philtrum (medial furrow)
  4. Chin boss (deeper in adults)
  5. Internal lip tissue externalized
  6. Shorter muzzle
  7. Thicker, less patchy and eternally growing cranial hair (+ beard on males)
  8. The rest of the face (and most of the body) hairless
  9. Smaller iris vs. sclera (whites of the eyes)
  10. Smaller ears
  11. Fewer wrinkles on breeding adults and babies
  12. Brow ridges absent, replaced by decorative eyebrows
  13. Maturity does not include a change of face color
  14. Not visible: smaller canines
  15. Lower cheekbones (jugal, zygomatic arch) relative to tooth row

It looks like the ears are lower in humans, but relative to the eyes and nose, they are not.

Figure 2. The skulls of Pan (the chimp), Proconsul and Homo (the human) for comparison.

Figure 2. The skulls of Pan (the chimp), Proconsul and Homo (the human) for comparison.

Question #2 today is…
What changes can we see in the face of a chimp (Pan) compared to Proconsul?

  1. Loss of forehead in Pan compared to Proconsul
  2. Nose unknown in Pronsul, but bones are shorter and flatter in Pan
  3. Longer nose-to-lip distance in Pan
  4. Chin, absent, as in Proconsul
  5. Internal lip tissue unknown in Proconsul
  6. Muzzle the same in Pan, less above, but more below the nose
  7. Hair unknown in Pan
  8. Skin unknown in Pan
  9. Eyes unknown in Proconsul, but note their relatively higher placement in Pan
  10. Ears unknown in Proconsul
  11. Wrinkles unknown in Proconsul
  12. Brow ridges present in Pan, absent in Pronsul
  13. Skin color unknown in Proconsul
  14. Canines slightly larger in Pan
  15. Higher jugal relative relative to tooth row (= taller premaxilla and maxilla) and coronoid process of mandible
Figure 3. Proconsul displays primitive traits for chimps and humans. It did not walk on its knuckles.

Figure 3. Proconsul displays primitive traits for chimps and humans. It did not walk on its knuckles

And then there’s one more transitional taxon
Ardipithecus (Fig. 4) nesting somewhere between Proconsul and Homo

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo.

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo.

In Ardipithecus,
compared to Proconsul, we find larger eyes, a larger, lower nose, smaller canines, and an overall shorter/wider face… and a pelvis more appropriate for an upright stance, freeing the long arms to do something else, like carrying everything from infants to water to weapons to belongings. This is where we lost our hair, became long distance runners, developed sweat glands, and became wanderers.

Figure 5. Ardipithecus in lateral view compared to Australopithecus and Homo (ghosted out).

Figure 5. Ardipithecus in lateral view compared to Australopithecus and Homo (ghosted out).

 

 

References
Hopwood AT 1933a. Miocene primates from British East Africa. Annals and Magazine of Natural History (Series 10), 11, 96-98.
Hopwood AT 1933b. Miocene primates from Kenya. Journal of the Linnean Society of London. Zoology 38:437–464.

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