Carnivorous plants

The carnivorism is a nutrition style associated to animals, to the world of heterotrophs. But it has been seen that there are plants that are also able to feed on other organisms. They are called carnivorous plants and their strategies to capture dams are very different and curious.

WHAT IS A CARNIVOROUS PLANT?

A carnivorous plants , even being autotroph, get part of their nutritional supplement by feeding on animals, especially insects.

There are three basic requirements that  carnivorous plants must comply:

• they must be able to attract, capture and kill the preys. To get their attention, they usually show reddish coloration and secrete nectar. Morphological and anatomical adaptations for retaining and killing the preys such as traps are used.
• Digestion and absorbance of the nutrients releasedby the damn .
• And finally, it has to draw significant benefit from the process.

Venus flytrap (Dionaea muscipula) (Author: Jason).

WHERE DO THEY LIVE?

Carnivorous plants are  not competitive in normal environments and tend to have a small root system, they need this specialization to allow them to grow faster. They are usually found in low mineralization soils, but with a high concentration of organic matter, sunny areas (as they still perform photosynthesis) and with  a high humidity.

Normally they are also calcifuges, i.e., they are not well adapted to alkaline soils and prefer acidic environments, where the source of calcium comes from the prey. They tend to inhabit soils with low oxygen and  saturated in water in a reducing environment. Some are aquatic and live either floating or submerged, but always near the surface.

TRAPS AND EXAMPLES

The capture system is quite diverse, but can be classified according to whether there is movement or not. We consider active strategies for those plants having mechanical or suction movements. Semi-active strategies which present mucilaginous glands and have movement and finally, passive ones, with no motion for prey capture. They can present mucilaginous glands or pitfall traps. Somes amples are given below.

ACTIVE TRAPS

Venus flytrap

In the case of this plant, the traps are mechanical and they are formed by two valves joined by a central axis. These valves are the result of non photosynthetic leave transformations. The stem acts as a petiole and performs photosynthesis, for this reason, it is thickened, increasing its surface and facilitating the process. Furthermore, the valves have nectar glands to attract preys and its perimeter is surrounded by teeth which help the capture, as when the trap is closed, the teeth overlay perfectly avoiding the animal’s escape..

But, what mechanism drives the closing? There’s a gigh number of triggers hairs inside the valves. When the dam is located on the trap and makes the trigger hairs move twice or more in less than 20 seconds, the valves close immediately.

In this vídeos From the BBC one (Youtube Channel: BBC) we can observe the whole process.

Utricularia, the bladderwort

This plant lives submerged near the surface and is known as the bladderwort, because it has bladder-like traps. The bladders are characterized for having sensitive hairs that activate the suction mechanism of the dam. Then, the bladder generates a very strong internal pressure that sucks water in, dragging the animal to the trap. It’s volume can increase up to 40% when water enters.

In the following video we can see the bladderwort trapping a tadpole of cane toad (Youtube Channel: Philip Stoddard):

SEMIACTIVE TRAPS

When I caught you, you won’t be able to escape

The presence of stalked mucilaginous glands is not unique in the carnivorous plant world, many plants use them as a defence or to prevent water loss. But, some carnivorous plants they are used to capture animals, as the sundews (Drosera) does.

The glands presents on the leaves of the sundews are formed by a stalk and an apical cell that releases mucilage. This substance attracts preys by its smell and taste. When the dam is located on the leaves, some drops of mucilage join each other to form a viscous mass that will cover all the prey, preventing its escape. We note that the glands have some mobility and move themselves to get in contact with the prey. Also, as a result, the leaf wrappes, facilitating the subsequent digestion.

The following video shows the operation of this mechanism (Youtube Channel: TheShopofHorrors):

PASSIVE TRAPS

Don’t get to sticky! 

The Drosophyllum‘s case is very similar to the previous one, but this time the stalked mucilaginous glands don’t have mobility and, therefore, the leaf doesn’t have either. The insect gets caught just because it is hooked on it’s sticky trap and cannot escape.

Insects trapped by Drosophyllum‘s stalked mucilaginous glands  (Author: incidencematrix).

Carefull not to fall!

Finally, we see the passive pitfall traps. They sometimes have a lid that protects them from an excess wàter getting in, even though it isn’t a part of the trap mechanism. The pitfall traps can be formed by the leaf itself or by an additional structure that is originated from an extension of the midrib (the tendril). The tendril lowers to ground level and then forms the trap.

Nepenthes (Author: Nico Nelson).

Dams are attracted to these traps due to nectar glands located inside. Once inside, going out is very complicated!  Walls may be viscous,  have downwardly inclined hairs that hinder to escape or present translucent spots that suggest the prey that there’s an exit, acting like windows , confusing and exhausting the prey, making it fall to the bottom, where it will drown. Other species also release substances that stun the preys, preventing them from running away.

Heliamphora (Author: Brian Gratwicke).

In some cases, large animals have fallen into these traps, though it is considered more as an effect of “bad-luck” than the plants supposed diet, though some traps measure up to 20cm long.

REFERENCES

• Notes of Environmental Plant Physiology, Degree of Environmental Biology, UAB.
• International Carnivorous Plant Society – http://www.carnivorousplants.org

Spinosaurus: the first aquatic dinosaur?

Recently, the BBC documentary series “Planet Dinosaur” has premiered on TVE2. In this series the latest paleontological discoveries concerning the biology of dinosaurs are explained. On my last entry we talked about the theropod dinosaurs, one of which is the spinosaur, one of the largest predators that have ever existed. On this entry I’m going to explain some of the facts that paleontology has revealed about the lifestyle of this creature.

TAXONOMY

The spinosaur (scientific name Spinosaurus aegyptiacus) belonged to the Spinosauridae family, a group of specialized theropods which appeared during the late Jurassic and became extinct about 93 million years ago during the late Cretaceous. This group was characterized by being relatively large theropods, with conic teeth and long snouts similar to crocodiles, and elongated neural spines through its back forming a sail-like structure (that’s where the name “Spinosauridae“ comes from, meaning spine reptiles).

Comparition of the different sizes of various spinosaurids by Scott Hartman. From right to left: Irritator challengeri, Baryonyx walkeri, Suchomimus tenerensis and Spinosaurus aegyptiacus.

Some of the more famous members on this family are, the Baryonyx from Europe, which had long curved claws on its hands to capture the fish it fed on, similar to its close relative the Suchomimus from northern Africa. Furthermore, there was the smaller Irritator of about 3 metres tall found in Brasil and finally, the Spinosaurus from northern Africa, which measuring between 12 and 18 metres long and wheighing between 7 and 20 tons, was one of the biggest predators to ever walk on land.

HABITAT AND DISTRIBUTION

The genus Spinosaurus was distributed in the zone of what is now the north of Africa. This genus lived during the Cretaceous, appearing about 112 million years ago and disappearing about 97 million years ago.

Map of the World 94 million years ago by Joshua Doubek, during the middle Cretaceous period.

During that period, the northern part of Africa was a very humid zone with high temperatures and lots of wetlands. Spinosaurs probably lived in areas with large rivers and mangrove forests next to the sea, where tidal movements flooded its habitat during certain seasons of the year. This is in accordance with the vision that spinosaurids preferred wet semiaquatic habitats with plenty of great fish to prey upon.

Reconstruction from 2010 of Spinosaurus aegyptiacus by Dmitry Bogdanov.

Currently there are two possible spinosaur species. The most famous is Spinosaurus aegyptiacus from Egypt, the species of which we have more information. A possible second species is Spinosaurus maroccanus from Morocco, which some authors consider simply as a subpopulation of Spinosaurus aegyptiacus.

FUNCTION OF NEURAL SPINES

Spinosaurs were discovered in 1912 from a fossil which included its characteristic dorsal spines. These spines grow up to a length ten times that of the vertebra from which they emerged.

The scarcity of spinosaur fossils means that the function of the spines is still a mystery for science, although there are some hypothesis. One of these is that the spines formed a “sail” along the back of the animal which was highly irrigated and helped the animal’s thermoregulation, as such a big animal probably would have had problems losing heat. Therefore its sail would have helped the spinosaur to evade overheating, orienting it towards fresh winds to cool down.

Reconstruction of the skeleton of a subadult spinosaur (Japan Museum, photo by Kabacchi).

Another hypothesis tells us that the spines held a hump-like structure similar to that of camels, which the animal would have used as a fat reserve system to store fat to withstand periods with little available feeding resources.

Lots of paleontologists think that both hypothesis could be correct and that the spinosaur used the sail both to regulate its body temperature and also to store fat to resist periods of low prey abundance. It is also possible that the sail made the spinosaur appear bigger than it actually was and that they used it during mating rituals similar to those of the modern peacock.

FEEDING STRATEGIES

The Spinosaurus‘s skull shows adaptions to a piscivorous diet. The snout is longer and slender than on other theropods. Aside from this, observing the snout of Spinosaurus it has been seen that it presents a series of little holes similar to those found on crocodiles. It is thought that these structures indicate the presence of pressure receptors which helped them detect the movement of their preys underwater.

Upper jaw of Spinosaurus from the Museo di Storio Naturale di Milano, where the holes which possibly contained the pressure receptors can be seen.

While the teeth of most carnivorous theropods where curved and serrated on their posterior part to tear flesh, spinosaur teeth were conic in shape and had no serration, more similar to those of crocodiles. These teeth were more useful for catching and holding fast and slippery prey and to prevent them from escaping (for example, a fish). Also, various Spinosaurus fossils have been found to have between their theeth scales and bones of large prehistoric fish which probably populated many rivers during the Cretaceous period.

Reconstruction by Joschua Knüppe of two Mawsonia species, the rests of which have been found between the teeth of Spinosaurus.

Nevertheless, it is generally believed that the spinosaur was probably an opportunistic predator, feeding mainly on fish, also hunting small dinosaurs when it had the opportunity and stealing prey from smaller predators using its great size to intimidate them.

POSTURE AND LIFESTYLE

Spinosaurs have traditionally been represented as bipedal animals, as most similarly-sized theropods have. Eventhough most fossils are actually pretty incomplete, it is known that its forelegs were more developed than in most theropods, having long curved claws.

Traditionally it was thought that Spinosaurus hunted in a manner similar to a grey heron, roaming through zones of shallow water, sinking its long snout underwater to detect prey using the pressure receptors, and catching fish with its jaws. It then, probably used its front legs as hands to tear its prey to small pieces easy to swallow.

Reconstruction by Joschua Knüppe of Spinosaurus aegyptiacus in hunting posture.

At the end of 2014 a new Spinosaurus fossil was discovered which has changed the view we had on this animal. For the first time, scientists found a fossil which shows the structure of the hind legs of this dinosaur and they have observed a number of characteristics not found in any other theropod not even in other spinosaurids. This fossil shows that the hind legs of Spinosaurus were much more massive than those of other theropod dinosaurs, in which the bones are usually hollow to make them more agile (like present day birds). Also, in this fossil the hind legs are actually much shorter in relation to the size of the animal than in any other theropod, leading some scientists to think that Spinosaurus was actually a quadrupedal animal. This has made some paleontologist think that maybe the lifestyle of the spinosaurs was much more similar to that of a crocodile and that they spent much more time living in water than on land, making the Spinosaurus the first known aquatic dinosaur.

Reconstruction by Rodrigo Vega of Spinosaurus based on the skeleton found in 2014.

Anyway, many paleontologists argue that the biology of a species cannot be based on a single fossil and advise caution when generalizing to the whole species (the fossil could belong to an adult and a juvenile that died together or could even come from an individual which had suffered some kind of embryonic malformation that kept its legs from developing normally). Paleontology is a science in which with every new discovery we can unravel the tree of life and the evolution of the different groups of living beings. With a little of luck, future discoveries will enable us to clarify the anatomy of Spinosaurus aegyptiacus and define the lifestyle of such a unique and extraordinary reptile.

REFERENCES

The following sources have been consulted in the elaboration of this entry:

• Cover photo: Davide Bonadonna.
• http://palaeos.com/vertebrates/theropoda/spinosauridae.html
• http://www.geol.umd.edu/~tholtz/G104/lectures/104therop.html
• http://palaeo.gly.bris.ac.uk/palaeofiles/fossilgroups/dinosauria/Theropoda.html
• http://www.scielo.br/pdf/aabc/v83n1/v83n1a06.pdf

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Spinosaurus: el primer dinosaure aquàtic?

Recentment s’ha estrenat a La 2 de TVE la sèrie documental de la BBC “Planeta Dinosaure” on s’expliquen els descobriments paleontològics més recents relacionats amb la biologia dels dinosaures. En la entrada anterior vam parlar dels dinosaures teròpodes entre els qual es troba l’espinosaure, un dels depredadors més grans que ha existit mai. En aquesta entrada explicaré algunes de les coses que la paleontologia ha revelat sobre l’estil de vida d’aquest animal.

TAXONOMIA

L’espinosaure (de nom científic Spinosaurus aegyptiacus) pertanyia a la família Spinosauridae, un grup de teròpodes especialitzats que va aparèixer a finals del Juràssic i desaparegué fa uns 93 milions d’anys a finals del Cretàcic. Aquest grup es caracteritzava per ser teròpodes relativament grans, amb dents còniques i morros allargats semblants als dels cocodrils i espines neurals allargades recorrent l’esquena formant una estructura en forma de “vela” (d’aquí ve el nom “Spinosauridae”, rèptils amb espines).

Comparació de la mida de diferents espinosàurids per Scott Hartman. De dreta a esquerra: Irritator challengeri, Baryonyx walkeri, Suchomimus tenerensis i Spinosaurus aegyptiacus.

Els membres més coneguts d’aquesta família són el Baryonyx d’Europa, que tenia unes grans urpes corbades a les potes del davant per a capturar els peixos dels quals s’alimentava de forma semblant al seu parent proper, el Suchomimus del nord d’Àfrica. A més, tenim al petit Irritator d’uns 3 metres d’alt descobert al Brasil i finalment, a l’Spinosaurus del nord d’Àfrica, que mesurant entre 12 i 18 metres de llarg i pesant entre 7 i 20 tones, va ser un dels depredadors més grans que ha caminat mai per terra.

HÀBITAT I DISTRIBUCIÓ

El gènere Spinosaurus es trobava distribuït per la zona corresponent al que actualment és el nord d’Àfrica. Aquest gènere va viure durant el Cretàcic, apareixent fa uns 112 milions d’anys i extingint-se fa uns 97 milions d’anys.

Mapa del món fet per Joshua Doubek de fa 94 milions d'anys, a mitjans del Cretàcic.

Durant aquest període, el nord d’Àfrica era una zona humida d’altes temperatures i zones pantanoses. Segurament els espinosaures vivien en àrees amb grans rius i manglars a prop de la costa, on les marees inundaven el seu hàbitat en diferents èpoques de l’any. Això concorda amb la visió de que els espinosàurids preferien zones humides amb abundància de grans peixos dels que alimentar-se.

Reconstrucció del 2010 de Spinosaurus aegyptiacus per Dmitry Bogdanov.

Actualment hi ha dues possibles espècies d’espinosaures. La més famosa és Spinosaurus aegyptiacus de Egipte, que és l’espècie de la qual més coses sabem. Una segona espècie possible és Spinosaurus maroccanus del Marroc, que alguns consideren simplement una subpoblació de Spinosaurus aegyptiacus.

FUNCIÓ DE LES ESPINES DORSALS

Els espinosaures van ser descoberts el 1912 per un fòssil que incloïa les característiques espines dorsals. Aquestes espines arribaven a fer 10 vegades la longitud de les vèrtebres de les quals emergien.

La escassetat de fòssils d’espinosaures ha provocat que la funció de les espines sigui encara un misteri per la ciència. Tot i així, existeixen vàries hipòtesis. Una d’aquestes és que les espines formaven una “vela” al llarg de l’esquena altament irrigada amb vasos sanguinis que ajudava a l’animal en la termoregulació, ja que probablement un animal tant gran tingués problemes per a perdre calor. La vela hauria ajudat a l’animal a evitar el sobreescalfament orientat-la cap a la direcció del vent per a refrescar-se.

Reconstrucció d'esquelet d'espinosaure subadult (Museu de Japó, foto de Kabacchi).

Una altra hipòtesi diu que les espines formaven una estructura més semblant a la gepa d’un camell que l’animal utilitzava per a emmagatzemar greix per a suportar períodes d’escassetat de recursos.

Molts paleontòlegs creuen que ambdues hipòtesis podrien ser correctes i que l’espinosaure utilitzés la vela tant per a regular la seva temperatura corporal i a més que també hi emmagatzemés greix per a resistir períodes de falta d’aliment. A més, la vela segurament feia que l’espinosaure semblés encara més gran del que era i també que la fessin servir en els rituals d’aparellament de forma semblant als paons actuals.

ALIMENTACIÓ

El crani de Spinosaurus mostra adaptacions a una dieta piscívora. El musell és més allargat i prim que en altres teròpodes. Apart d’això, en observar el morro del Spinosaurus s’ha observat que presenten un seguit de petits forats semblants als que presenten els cocodrils. Es creu que aquestes estructures indiquen la presència de receptors de pressió que els permetia detectar el moviment de les seves preses a sota de l’aigua.

Mandíbula superior de Spinosaurus del Museo di Storio Naturale di Milano, on s'observen els forats que possiblement contenien els receptors de pressió.

Mentre que les dents de la majoria de teròpodes carnívors eren corbades i presentaven una serra a la part posterior per a tallar la carn, les dents de l’espinosaure eren còniques i sense serra, més semblants a les d’un cocodril. Aquestes dents eren més útils per atrapar i impedir que preses ràpides i relliscoses se’ls escapessin (com per exemple un peix). A més, en varis fòssils de Spinosaurus s’han trobat entre les seves dents restes d’escates i ossos de grans peixos prehistòrics que segurament poblaven els rius del Cretàcic.

Reconstrucció feta per Joschua Knüppe de dues espècies de Mawsonia, uns peixos dels quals s'han trobat restes entre les dents de Spinosaurus.

Tanmateix es creu que l’espinosaure devia ser un depredador oportunista, alimentant-se principalment de peixos, però caçant petits dinosaures quan podia o robant les preses a altres depredadors aprofitant-se de la seva mida.

POSTURA I ESTIL DE VIDA

Els espinosaures tradicionalment se’ls ha representat com a animals bípedes, igual que la majoria de teròpodes de mida semblant. Tot i que la majoria de fòssils trobats són bastant incomplets, es sap que les potes del davant estaven més desenvolupades que les de la majoria de teròpodes i que presentaven unes urpes llargues i corbades.

Tradicionalment es creia que Spinosaurus caçava d’una forma semblant al bernat pescaire, rondant per zones d’aigües poc profundes, enfonsant el seu llarg morro per a detectar a les preses mitjançant els receptors de pressió i capturant-la amb les mandíbules. Segurament, també utilitzava les potes del davant per a acabar de desmembrar les preses en troços més petits i menjar-se-les.

Reconstrucció feta per Joschua Knüppe de Spinosaurus aegyptiacus en postura de caça.

A finals del 2014 es va descobrir un nou fòssil de Spinosaurus que ha canviat la visió que es tenia sobre aquest animal. Per primer cop s’ha trobat un fòssil que mostra les potes del darrera d’aquest dinosaure i s’han vist un seguit de característiques que no es troben en cap altre teròpode i ni tan sols en cap altre espinosàurid. Aquest fòssil ens mostra que les potes del darrere eren molt més massisses que en altres dinosaures teròpodes, els quals solen tenir els ossos buits fent-los més lleugers (com en els ocells actuals). A més, en aquest fòssil les potes del darrere són molt més curtes en relació a la mida de l’animal que en cap altre teròpode, cosa que ens porta a pensar que Spinosaurus probablement fós un animal quadrúpede. Això ha provocat que alguns científics creguin que l’estil de vida d’aquests dinosaures era més semblant al del cocodril i que aquests passarien molt més temps vivint a l’aigua que a terra, convertint a l’espinosaure en el primer dinosaure aquàtic conegut.

Reconstrucció feta per Rodrigo Vega de Spinosaurus basant-se en el esquelet descobert el 2014.

De tota manera, molts paleontòlegs argumenten que no es pot basar la biologia d’una espècie en un únic fòssil i aconsellen precaució a l’hora de fer generalitzacions a tota l’espècie (el fòssil podria tractar-se d’una barreja d’ossos d’individus adults i juvenils o fins i tot podria ser un individu que va patir una mutació congènita que fes que les potes posteriors no es desenvolupessin correctament). La paleontologia és una ciència que amb cada nou descobriment va desentranyant l’arbre de la vida i la evolució dels diferents grups d’éssers vius. Amb una mica de sort, descobriments posteriors ens permetran aclarir l’anatomia del Spinosaurus aegyptiacus per així poder acabar definint l’estil de vida d’aquest rèptil tant únic i extraordinari.

REFERÈNCIES

S’han consultat les següents fonts per a elaborar els continguts d’aquesta entrada:

• Foto de portada: Davide Bonadonna.
• http://palaeos.com/vertebrates/theropoda/spinosauridae.html
• http://www.geol.umd.edu/~tholtz/G104/lectures/104therop.html
• http://palaeo.gly.bris.ac.uk/palaeofiles/fossilgroups/dinosauria/Theropoda.html
• http://www.scielo.br/pdf/aabc/v83n1/v83n1a06.pdf

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