Prehistoric plants

I’ve started working on a project for recreating prehistoric plants. The ultimate goal would be to generate accurate ecosystems that can be used as background scenery for prehistoric animal reconstructions.

The Bennettitales are a group of completely extinct seed plants from the Mesozoic. The leaves bear strong resemblance with those of the extant cycads thus their other name of cycadeoids. They are traditionally classified into two families, the Williamsoniaceae and the Cycadeoidaceae. The members of the first family (such as Williamsonia) are reconstructed with slender branching stems with cones at the tip of lateral branches. 

Fig 1.- Reconstruction of Williamsonia sewardiana with the leaves of the Ptilophyllum type. The genus Williamsonia is based on cones and the actual appearance of the plant remains controversial.

The members of the second family have short trunks and were widely represented with flower like structures around the trunk. The idea came from Wieland who suggested in his 1906 monograph that they have strong affinities with the angiosperms (flowering plants), interpreting the mature cones as flower like structures. However, later studies showed that the cones remained closed at maturity (Delevoryas, 1963).

Fig 2.- Alternative reconstruction of Ptilophyllum, as a Bennettitale of the Cycadeoidaceae type.

Calamites is another interesting plant from the Carboniferous and Early Permian. They look like trees with wooden trunks reaching several meters in height, but were actually related to the modern horsetails.

Fig 3.- Calamites.

References:

Delevoryas, T. 1963. Investigations of North American cycadeoids: cones of Cycadeoidea. American Journal of Botany 50: 45–52.

Watson J. and Sincock C. A. 1992. Bennettitales of the English Wealden. The Palaeontographical Society 145(588):1-228.

Wieland, G. R. 1906. American fossil cycads. Carnegie Institution of Washington, Washington, D.C., USA.

Yamada. T. 2007. Structurally preserved Zamites bayeri Kvacek from the Coniacian Kashima Formation (Yezo Group) of Hokkaido, Japan. Cretaceous Research 2009: 1-6.

Daemonosaurus chauliodus

Daemonosaurus chauliodus

The Evil Spirit lizard haunts theropod phylogeny

Meet Daemonosaurus chauliodus, a newly discovered theropod dinosaur from the Chinle Formation of the “Coelophysis Quarry” at Ghost Ranch in New Mexico. Its description by Hans-Dieter Sues, Sterling J. Nesbitt, David S.  Berman and Amy C. Henrici, has just been published in the Proceedings of the Royal Society B (Sues et al., 2011).

Fig 1.- A reconstruction of the head of Daemonosaurus. The fur is speculative.

The media has readily dubbed this little critter as the “Bucked-toothed Demon Lizard” but there is actually nothing devilish about the look of the 

animal. The intended meaning of the generic name is in fact a bit different: the authors used the Greek word daimon in its original sense of ‘evil spirit’ and allude to legends about evil spirits haunting Ghost Ranch, the place of discovery. The specific name, derived from the Greek chauliodous and which means ‘with prominent teeth’ is shared with the scientific name of the deep-sea viperfish (Chauliodus sloani). Like the viperfish, Daemonosaurus is indeed characterized by a set of much enlarged fang-like front teeth. Such teeth might be an indication of a specialized diet, but at this point, we don’t have a clue of what it was.

The prominent teeth are not the only things remarkable about this critter. Daemonosaurus is also one of the most primitive theropod which makes him all the more important as the early history of this particular group of dinosaurs is somewhat sketchy. We know that by the Late Triassic Carnian age (216.5-228 MYA) , the three principal lineages of dinosaurs, i.e. the theropods, the sauropodomorphs and the ornithischians were already well differentiated. A sample of the earliest theropods, i.e. Herrerasaurus, Staurikosaurus, Eoraptor and the recently described Eodromaeus (Martinez et al., 2011) and Sanjuansaurus (Alcober et al., 2010) were found in South America in the Ischigualasto Formation of Argentina and the Santa Maria Formation of Brazil. These primitive theropods still retained five digits on both their hands and feet (albeit greatly reduced fifth digits), while the Neotheropoda, a group that contains all the most advanced theropods including Tyrannosaurus, Velociraptor and the birds, had only three digits in their hands (with sometimes a vestigial fourth as in Coelophysis; in T. rex the 3rd digit is also vestigial), and three functional digits per feet (the fifth is vestigial and the first, is reduced to a “dew claw” on the inside or back of the foot).

Until recently, the later Norian and Rhaetian stages of the Late Triassic (199.6 to 216.5 MYA) have only yielded Neotheropods belonging to a single group called Coelophysoidea (some examples include Coelophysis of WWD fame, Segisaurus, Lilensternus and most probably Zupaysaurus), with the sole exception of the enigmatic Chindesaurus from Arizona which is difficult to classify due to the fragmentary nature of its remains (Nesbitt et al., 2007) but which is now generally considered a late survivor of the Herrerasaurus tribe. The evolutionary gap between the early theropods and the neotheropods started to be filled a couple of years ago with the description of a new species, Tawa hallae (Nesbitt et al., 2009), also from the Ghost Ranch locality of New Mexico and that has been shown to be intermediate between the herrerasaurs and the neotheropods. And this year, we have Daemonosaurus.

Fig 2.- Reconstructed skulls of Daemonosaurus chauliodus (top) and Tawa hallae (bottom). Based after Nesbitt et al., 2009 & Sues et al., 2010. Note the shorter snout and proportionally longer front teeth and larger orbital fenestrae of Daemonosaurus.

Daemonosaurus appears to be even more primitive than Tawa. The holotype consists of a crushed skull, vertebrae and ribs, found in the so-called Coelophysis quarry of Rhaetian age (Stewart et al., 1972). The fossil was indeed extracted from a large block containing remains of several Coelophysis bauri, and there is a chance that more postcranial remains of Daemonosaurus will turn up after completion of the preparation of the block. With its short and deep skull equipped with pointy teeth, Daemonosaurus look is surprising, unlike any of the other basal theropods. The structure of the cervical vertebrae indicates that it probably had a long neck like Tawa or Coelophysis. Like most of the other theropods of the Late Triassic, it was pretty small, measuring perhaps no more than 1.5 meters.

It now appears that the theropod fauna of the Late Triassic was far more diverse than originally thought. Due to its unusual skull shape and teeth, Daemonosaurus was however probably not a transitional form to the new theropods but an evolutionary dead-end that left no descendant.

References:

Alcober, O. A.; and Martinez, R. N. 2010. A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina. ZooKeys 63: 55–81.

Martinez, R. N., Sereno, P. C., Alcober, O. A., Colombi, C. E., Renne, P. R., Montan˜ ez, I. P. & Currie, B. S. 2011. A basal dinosaur from the dawn of the dinosaur era in southwestern Pangaea. Science 331, 206–210.

Nesbitt, S. J., Irmis, R. B. & Parker,W. G. 2007 A critical re-evaluation of the Late Triassic dinosaur taxa of North America. J. Syst. Palaeontol. 5, 209–243.

Nesbitt, S. J., Smith, N. D., Irmis, R. B., Turner, A. H., Downs, A. & Norell, M. A. 2009 A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs. Science 326, 1530–1533.

Stewart, J. H., Poole, F. G. & Wilson, R. F. 1972 Stratigraphy and origin of the Chinle Formation and related Upper Triassic strata in the Colorado Plateau region. US Geol. Surv. Prof. Pap. 690, 1–336.

Sues, H.-D.; Nesbitt, S.J.; Berman, D.S.; and Henrici, A.C. 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society B in press

Manidens condorensis

Introducing Manidens condorensis, a new Heterodontosaur from the Middle Jurassic of Patagonia...

Fig 1.- My reconstruction of Manidens condorensis.

Some critters have a mysterious appeal, which is difficult to explain. I always felt some fondness for a meter long creature named Heterodontosaurus from the Early Jurassic of South Africa. If you ignore my now lost childhood productions, it is among the first dinosaurs I’ve drawn. So I was naturally very thrilled to learn that yet another relative of Heterodontosaurus, the Patagonian Manidens condorensis has just been unearthed from the Cañadón Asfalto Formation of Middle Jurassic age. Diego Pol, Olivier W.M. Rauhut and Marcos Becerra are describing the new species in a paper about to be published in Naturwissenshaften.

Fig 2.- Old (2007) pencil sketch of Heterodontosaurus tucki in quadrupedal pose, one of the first dinosaur I’ve drawn during my adult life. Yes, I know, it was not very good, just for reference...

Heterodontosaurus and Manidens belong to a small group of ornithischian (bird-hipped) dinosaurs called heterodontosauridae. In the world dominated by giants, these critters were comparatively very tiny. The largest representative, Lycorhinus angustidens, also from the Early Jurassic of South Africa and mainly known from dentaries, had an estimated length of only 2 meters, while Fruitadens haagarorum from the Upper Jurassic of Colorado, with an estimated length of 65-75 cm has been dubbed the smallest known ornithischian at the time of its discovery.

Heterodontosaurs are also characterized by their highly differentiated teeth, thus the meaning of their name (“different-toothed lizards”). They have a pair of well-developed tusk-like canines on the lower jaw that are accommodated by a gap (diastema) in the upper jaw when the mouth is closed. They also have highly derived cheek teeth that are, in the most derived forms, columnar in shape with almost no space in between, reminiscent of the mammalian molars. The toothless tip of the upper jaw may also have supported a beak. All in their teeth cry for a preferential vegetarian diet. What did they look like? Before Tianyulong (see below), representations of heterodontosaurs were based on the only complete skeleton known for the group, i.e the Heterodontosaurus tucki specimen SAFM K1332 housed in the South African Museum (Santa Luca, 1980). They were lightly built and had a very long tail. The arms were quite long for a dinosaur with hands having all five digits. The leg proportions tibia/femur show adaptation for speed, indicating they were probably agile bipedal runners.

Fig 3.- Cast of the Heterodontosaurus tucki specimen SAFM K1332. By Flickr user kyknood uploaded on Wikipedia by user Funkmonk under a Creative Common License.

Heterodontosaurs are a rare find and little was known of their affinities until quite recently. This is due not only to the scarcity of their remains but also to the large gaps in the fossil record of early ornithischians (there were simply not many other critters to compare to). Before Y2K, only three species were known with high degree of confidence, Heterodontosaurus tucki, Abrictosaurus consors and Lycorhinus angustidens, all from the Early Jurassic of Southern Africa, with in addition some dubious taxa, Lanasaurus, Geranosaurus both from South Africa and the enigmatic Echinodon becklesii from the Early Cretaceous of England known from a jaw fragment with teeth, which might or might not be an heterodontosaur (Norman & Barrett, 2002). Recent studies all place Echinodon outside the heterodontosaur clade.

Fig 4.- Illustration of Heterodontosaurus tucki, adult and juveniles indicating a probable omnivorous diet, made for the press release following the publication of Butler et al., 2008b.

However things changed quickly and quite dramatically in the last few years. All the previous indubitable heterodontosaurs were from the Early Jurassic of South Africa. Discoveries from the new millennium have considerably extended the temporal and geographical range for the group, covering the Late Triassic of South America (Báez & Marsicano, 2001), the Early Cretaceous of China (Zheng et al., 2009) and the Upper Jurassic of North America (Butler et al., 2010).

As for their systematic affinities, scientists in the past have variously placed them as an early but highly specialized sister taxon to the marginocephalians (ceratopsians and pachycephalosaurs) or as the most basal members of ornithopods. Recent phylogenetic analyses indicate that they actually represent an early offshoot of basal ornithischians (Butler et al., 2008a) and this seems to be comfortably confirmed by subsequent studies (Butler et al., 2010, Zheng et al., 2009, Pol et al., 2011). The presence of the canine-like teeth in a juvenile specimen of Heterodontosaurus also questioned the previous assertions that these tusks were a mark of sexual dimorphism and primarily used for sexual display (Butler et al., 2008a). Not so sure, what to do with the tusk less specimen of Abrictosaurus, now... but it is also true that there is a need to revise the South African materials (What a perfect paleontology PhD subject, any taker?) Finally, heterodontosaurs experienced a drastic change of look after the discovery of a remarkably well-preserved specimen from the Liaoning province of China (Zheng et al., 2009). Indeed, the fossil of Tianyulong confuciusi has clear impressions of filamentous integuments covering the body like a fur. They may be analogous to the proto-feathers found in theropods and the quills found on the basal ceratopsian Psittacosaurus. Well, no more scaly and skinny heterodontosaur, time for fuzzy Mesozoic furry balls…

Fig 5.- Complete view of Manidens condorensis.

The holotype of Manidens condorensis is a partial associated skeleton including most of the skull, the anterior part of the vertebral column, pelvic girdles, left scapula and coracoids. Referred materials include a set of teeth. The phylogenetic analysis conducted by Pol et al., indicates that it is more derived than Tianyulong and Fruitadens but slightly less than the South African genera. The teeth of Manidens are also quite interesting. Whereas the more derived members of the heterodontosaurs such as Heterodontosaurus show clear adaptation for an herbivorous diet (closely packed teeth, high tooth crowns, and extensive wear facets on the maxillary and dentary teeth), the basal members lack those, pointing to a more omnivorous diet. But Manidens is in an intermediate stage with high tooth crowns but no wear facets. Basal members of heterodontosaurs were probably ecological generalists that fed on miscellaneous diet including plants but also small animals such as invertebrates.
Manidens was extremely small for a dinosaur, Pol et al., give it a size comparable to Fruitadens, but I believe it might have been a bit smaller if I trust the scales indicated in the figures of their respective articles. The examination of the holotype skeleton of Manidens indicates that it is from an old adult, despite its small size and comparatively large eye socket, while the material from Fruitadens are based on juveniles.

Fig 6.- Comparison of the skulls (only known parts are represented) of different heterodontosaurs, drawn to scale. a) Fruitadens haagarorum [modified from Butler et al., 2010], b) Tianyulong confuciusi [modified from Zheng et al., 2010], c) Abrictosaurus consors [modified from...(forgot the ref)] note the lack of tusks, this was interpreted as belonging to a female, d) Manidens condorensis [modified from Pol et al., 2010], e) Heterodontosaurus tucki [modified from Butler et al, 2008b]

There are still a lot of mysteries surrounding these critters due to the large gap in their fossil record. For instance, the most derived members from South Africa all date from the Early Jurassic, while the most primitive and less specialized member, Tianyulong, is from the Early Cretaceous. Did the more derived strictly herbivorous members went extinct out-competed by new groups of hungry ornithischians, while the more primitive unspecialized and opportunistic members survived because they could do a meal from almost anything? Who knows? It was also originally thought that the group originated in the Gondwana where the most primitive and earliest ornithischian, Pisanosaurus mercki, has been found but with the discovery of Tianyulong from China and Fruitadens from North America, all the cards are reshuffled. Looking forward to the next big heterodontosaurian discovery…

Fig 7.- Phylogeny of heterodontosaurs [adapted from Pol et al., 2011].

References:
Báez A.M., Marsicano C.A. 2001. “A heterodontosaurid ornithischian dinosaur from the Upper Triassic of Patagonia”. Ameghiniana 38:271–279.

Butler, R. J., Upchurch, P. & Norman, D. B. 2008a “The phylogeny of the ornithischian dinosaurs”. J. Syst. Palaeontol. 6, 1–40.

Butler R.J., Porro L.B., Norman D.B. 2008b. “A juvenile skull of the heterodontosaurid dinosaur Heterodontosaurus tucki from the ‘Stormberg’ of southern Africa”. J Vert Paleont 28:702–711.

Butler R.J., Galton P.M., Porro L.B., Chiappe L.M., Henderson D.M., Erickson G.M. 2010. “Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America”. Proc R Soc B 277:375–381.

Norman, D. B. & Barrett, P. M. 2002. “Ornithischian dinosaurs from the Lower Cretaceous (Berriasian) of England”. Spec. Papers Palaeontol. 68, 161–189.

Pol, D.; Rauhut, O.W.M.; and Becerra, M. 2011. "A Middle Jurassic heterodontosaurid dinosaur from Patagonia and the evolution of heterodontosaurids". Naturwissenschaften in press.

Santa Luca, A. P. 1980. “The postcranial skeleton of Heterodontosaurus tucki (Reptilia, Ornithischia) from the Stormberg of South Africa”. Ann. South Afr. Mus. 79, 159–211.

Thulborn, R. A. 1970. “The systematic position of the Triassic ornithischian dinosaur Lycorhinus angustidens”. Zoo. J. Linn. Soc. 49, 235–245.

Zheng, X.-T., You, H.-L., Xu, X. & Dong, Z.-M. 2009. “An Early Cretaceous heterodontosaurid dinosaur with integumentary structures”. Nature 458, 333–336.