Tag Archives: morphology

Shaking dinosaur hips and messing with their heads

by Piter Kehoma Boll

This week brought astonishing news regarding the phylogeny of dinosaurus, as you perhaps have heard or read. New anatomical evidences have completely rebuilt the basis of the dinosaur family tree and I’m here to explain a little bit of what happened.

As we all know, Dinosaurs include a great variety of beasts, from the meat-eating theropods to the long-necked sauropods and from the horned ceratopsians to the armored ankylosaurs, among many others.

largestdinosaursbysuborder_scale

Silhouette of a human compared to the largest known dinosaurs of each major group. Picture by Matt Martyniuk.*

For more than a century now, dinosaurus have been divided into two groups, called Ornithischia and Saurischia. Ornithischia (“bird-hipped”) includes dinosaurus whose pelvic bones are more similar to what is found in birds, with a pubis directed backward. Saurischia (“lizard-hipped”), on the other hand, have a pubis directed forward, as in reptiles in general. This grouped the theropods and the sauropods in the same group as Saurischia while other dinosaurus were grouped as Ornithischia. But birds are actually theropods, thus being lizard-hipped dinosaurus and not bird-hipped dinosaurus! Confusing, isn’t it? So let’s take a look at their hips:

Pelvic_bones

Comparison of the hips of a crocodile (Crocodylus), a sauropod (Diplodocus), a non-avian theropod (Tyrannosaurus), a bird (Apteryx), a thyreophoran (Stegosaurus), and an ornithopod (Iguanodon). Red = pubis; Blue = ischium; Yellow = ilium. Picture by myself, Piter K. Boll.**

As you can see, the primitive state, found in crocodiles, sauropods and early theropods, is a pubis pointing forward. A backward-pointing pubis evolved at least twice independently, both in more advanced theropods (such as birds) and the ornithischian dinosaurus. But could we be so certain that Tyrannosaurus and Diplodocus are more closely related to each other (forming a clade Saurischia) just because of their hips? Afterall, this is a primitive hip, so it is very unlikely to be a synapomorphy (a shared derived character). Nevertheless, it continued to be used as a character uniting sauropods and theropods.

A new paper published by Nature this week, however, showed new evidences that point to a different relationship of the groups. After a detailed analysis of the bone anatomy, Matthew G. Baron, David B. Norman and Paul M. Barrett have found 20 characters that unite theropods with ornithischians and not with sauropods. Among those we can mention the presence of a foramen (a hole) at the anterior region of the premaxillary bone that is inside the narial fossa (the depression of the bone that surrounds the nostril’s opening) and a sharp longitudinal ridge along the maxilla.

skulls

The skulls of both ornithischians and theropods (above) show an anterior premaxillary foramen in the narial fossa (shown in yellow) and and a sharp ridge on the maxilla (shown in green), as well as other characters that are not present in sauropodomorphs and herrerasaurids (below). Composition using original pictures by Carol Abraczinskas and Paul C. Sereno (Heterodontosaurus), Wikimedia user Ghedoghedo (Eoraptor and Herrerasaurus), and flickr user philosophygeek (Plateosaurus).**

In his blog Tetrapod Zoology, Dr. Darren Naish comments the new classification and points out some problems that arise with this new view. One of them is the fact that both theropods and sauropodomorphs have pneumatic (hollow) bones, while ornithischians do not. If the new phylogeny is closer to the truth, that means that pneumacity evolved twice independently or evolved once and was lost in ornithischians.

He also mentions that both ornithischians and theropods had hair-like or quill-like structures on their skin. In theropods this eventually led to feathers. Could this be another synapomorphy uniting these groups? Maybe… but when we think that pterosaurs also had “hairs”, one could also conclude that a “hairy” integumentary structure was already presented in the common ancestor of dinosaurus. In this case, perhaps, we only had not found it yet on sauropods. Now imagine a giant Argentinosaurus covered with feathers!

One concern that appeared with this new organization is whether sauropodomorphs would still be considered dinosaurs. The term “dinosaur” was coined by Richard Owen in 1842 to refer to the remains of the three genera known at the time, Iguanodon, Hylaeosaurus and Megalosaurus, the first two being ornithischians and the latter a theropod. As a consequence, the original definition of dinosaur did not include sauropods. Similarly, the modern phylogenetic definition of dinosaur was “the least inclusive clade containing Passer domesticus (the house sparrow) and Triceratops horridus“. In order to allow Brachiosaurus and his friends to continue sitting  with the dinosaurs, Baron et al. suggested to expand the definition to include Diplodocus carnegii. So, dinosaurus would be the least inclusive clade containing P. domesticusT. horridus and D. carnegii.

In this new family tree, the name Saurischia would still be used, but to refer only to the sauropodomorphs and some primitive carnivores, the herrerasaurids. The new clade formed by uniting theropods and ornithischians was proposed to be called Ornithoscelida (“bird-legged”), a name coined in 1870 to refer to the bird-like hindlimbs of both theropods and ornithopods (the subgroup of ornithischians that includes dinosaurs such as Iguanodon and the duck-billed dinosaurs).

What can we conclude with all that? Nothing will change if you are just a dinosaur enthusiast and do not care about what’s an ornithischian and a saurischian. Now if you are a phylogeny fan, as I am, you are used to sudden changes in the branches. Most fossils of basal dinosaurs are incomplete, thus increasing the problem to know how they are related to each other. Perhaps this new view will last, perhaps new evidence will change all over again the next week.

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ResearchBlogging.orgReferences and further reading:

Baron, M., Norman, D., & Barrett, P. (2017). A new hypothesis of dinosaur relationships and early dinosaur evolution Nature, 543 (7646), 501-506 DOI: 10.1038/nature21700

Naish, D. (2017). Ornithoscelida Rises: A New Family Tree for DinosaursTetrapod Zoology.

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*Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

**Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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How are little flatworms colored? A Geoplana vaginuloides analysis

by Piter Kehoma Boll

ResearchBlogging.org As you already know, I work with land planarians, so there’s nothing more natural than seeing me talking about them. Today I’ll make a brief comment about the type species of the genus Geoplana which gives name to the family Geoplanidae (the land planarians themselves).

Geoplana vaginuloides was originally described by Charles Darwin in 1844 under the name Planaria vaginuloides. His description was based only on external morphology, which today is considered insufficient to describe correctly a land planarian. Later Stimpson (1857) moved it to his new genus Geoplana, but still only external features were used. By that time, no type species had been assigned to the genus and E. M. Froehlich (1955) decided to choose Geoplana vaginuloides (Darwin, 1844) as the type species for being the first one found by Darwin and one of the species put in the genus Geoplana by Stimpson when he described it.

It was only in 1990 that a good revision of land planarians was made by Ogren and Kawakatsu and the internal morphology, especially that of the copulatory apparatus, started to have a greater importance in describing a species correctly. Based on Geoplana vaginuloides, they defined the genus Geoplana as follows:

“Geoplanidae of elongate body form; creeping sole broader than a third of the body width; strong cutaneous longitudinal muscles; mc:h value from 4%-8%; parenchymal longitudinal musculature weak or absent, not in a ring zone; testes are dorsal; penis papilla present; female canal enters genital antrum dorsally; cephalic glandulo-muscular organs, sensory papillae and adenodactyls absent.” (Ogren & Kawakatsu, 1990).

As noticed by Riester (1938), G. vaginuloides possesses a very long penis papilla invading the female antrum, as well as other peculiar features. These aspects were important to consider a land planarian found by Marcus in 1951 as belonging to this species, even though it had external colors almost inverted when compared to the specimen described by Darwin.

Using the internal morphology to assure that all the following descriptions of land planarians belong to a single species, Geoplana vaginuloides, we can find at least 4 different external color patterns to this species:

  •  Darwin 1844:  “Ocelli numerous, placed at regular intervals on the anterior extremity; irregularly, round the edges of the foot. […] Sides of the foot coloured dirty “orpiment orange”; above, with two stripes on each side of pale “primrose-yellow,” edged externally with black; on centre of the back a stripe of glossy black; these stripes become narrow towards both extremities.”
    Locality: Rio de Janeiro, Brazil
  •  Riester, 1938: “Unterseite und Körperänder weinrot, dann zwei schmale gelbe Streifen und in der Rückenmitte ein tief Schwarz glänzendes breites Band.” (Underside and body edges wine red, then two narrow yellow stripes and in the middle of the back a deep black shiny broad band.)
    Locality: Teresópolis/Guapimirim, Rio de Janeiro, Brazil
  • Marcus, 1951: “A faixa mediana é ocre, na maior parte da extensão. Anterior e posteriormente é preta. Flanqueiam-na faixas amarelas claras, cada uma tão larga quão a mediana. As zonas dorso-laterais são pretas com pontinhos claros, que não são olhos. O ventre é claro.” (The median band is ochre in most of its length. Anteriorly and posteriorly it’s black. Light yellow bands flank it, each one as broad as the median one. The dorsolateral zones are black with white spots, which aren’t eyes. The venter is light.)
    Locality: Eldorado, São Paulo, Brazil
  • C. G. Froehlich, 1958: “The colour pattern is similar to type C of Marcus (1952, pp. 76-77, pl. 23 fig. 136) but the median reddish stripe is broader (about 1 mm. across, just in front of the pharynx), and both the black and the white stripes that follow on each side are narrower (about 0.2 to 0.3 mm broad each, in the same region). The median stripe begins at 2.5 mm from the anterior tip. The creeping sole is greyish white.”
    Locality: Itanhaém, São Paulo, Brazil

Different color patterns in Geoplana vaginuloides according do Darwin, 1844 (1), Riester, 1938 (2), Marcus, 1951 (3) and C. G. Froehlich, 1958 (4)

Location of the 4 morphotypes seen in the picture above. Image made on Google Earth.

Along with those descriptions, Prudhoe (1949), found an animal in Trinidad with the same external description given by Darwin, but its internal structure was very different from Riester (1938). So it was probably a different species.

About photographs of this species, I found only the three seen below. They all belong to specimens with a color pattern close to those described by Marcus and Froehlich. It would be interesting to find an animal with the color pattern from the original description by Darwin!

Geoplana vaginuloides (Darwin, 1844). Photo by Fernando Carbayo. Extracted from each.uspnet.usp.br/planarias/

Geoplana vaginuloides (Darwin, 1844). Photo by Fernando Carbayo. Extracted from each.uspnet.usp.br/planarias/

Geoplana vaginuloides (Darwin, 1844). Notice that this one doesn’t have the black border flanking the median orange band. Photo by Instituto Rã-Bugio. Extracted from http://www.ra-bugio.org.br

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References:

Darwin, C. 1844. Brief Description of several Terrestrial Planariae, and of some remarkable Marine Species, with an Account of their Habits. Annals and Magazine of Natural History, Annales des Sciences Naturelles, 14, 241-251

Froehlich, E. M. 1955. Sobre Espécies Brasileiras do Gênero Geoplana. Boletim da Faculdade de Filosofia, Ciências e Letras da Universidade de São Paulo, Série Zoologia, 19, 289-339

Froehlich, C. G. 1958. On a Collection of Brazilian Land Planarians. Boletim da Faculdade de Filosofia, Ciências e Letras da Universidade de São Paulo, Série Zoologia, 21, 93-121

Marcus, E. 1951. Turbellaria Brasileiros. Boletim da Faculdade de Filosofia, Ciências e Letras da Universidade de São Paulo, Série Zoologia, 16, 5-215

Ogren, R. E. & Kawakatsu, M. 1990. Index to the species of the family Geoplanidae (Turbellaria, Tricladida, Terricola) Part I: Geoplaninae. Bulletin of Fuji Women’s College, 28, 79-166

Prudhoe, S. 1949. Some roundworms and flatworms from the West Indies and Surinam. – IV. Land Planarians. Journal of the Linnean Society of London, Zoology, 41 (281), 420-433 DOI: 10.1111/j.1096-3642.1940.tb02415.x

Riester, A. 1938. Beiträge zur Geoplaniden-Fauna Brasiliens. Abhandlungen der senkenbergischen naturforschenden Gesellschaft, 441, 1-88

Stimpson, W. 1857. Prodromus descriptionis animalium evertebratorum quæ in Expeditione ad Oceanum, Pacificum Septentrionalem a Republica Federata missa, Johanne Rodgers Duce, observavit er descripsit. Pars I. Turbellaria Dendrocœla. Proceedings of the Academy of Natural Sciences of Philadelphia, 19-31

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