Lizards in Amber – A Window into a “Lost World”

Whilst much attention is focused on the Dinosauria when it comes to the fauna and flora of the Mesozoic, many scientists are busy piecing together the evolutionary relationships of a number of smaller reptiles, those creatures such as lizards that shared the world of the dinosaurs but so very little fossil evidence to indicate their existence has been preserved.  Thanks to a new study of amber from Myanmar (Burma), undertaken by researchers based in the United States and Germany, a glimpse into a “lost world” has been permitted.

Amber from Myanmar

Mid Cretaceous Amber Preserves the Lizard Remains

Affording a rare insight into small creatures of the Cretaceous.

Picture credit: Science Advances

The picture above shows some of the beautifully preserved lizard fossils in the Burmese amber (known as burmite). The fossil collection has been collated, some from American museums, many other pieces from private collections and they provide a record of the fauna and flora of a sub-tropical forest some 99 million years ago.

Key

(A) Lizard (body cavity empty, epidermis translucent)

(B) Lizard (epidermis translucent, hind leg preserved with bones)

(C) Lizard (intact specimen, with some tissue preserved)

(D) Lizard (skin and scales with some internal organs and bones)

(E)  Stem Gekkota (ancestral to modern Geckos, hind legs, pelvic area and tail base preserved

(F) Stem Gekkota (manus including bones and impressions of toe pads)

(G) Stem Gekkota (skull material and spine with disarticulated limb and pelvic bones)

(H) Agamidae (left hind leg, including epidermis)

(I) Agamidae (translucent epidermis, pelvic with elements of the left limb and pes)

(J) Lacertoidea (skeletal elements preserved as internal casts and integument)

(K) Stem Chamaeleonidae (ancestral Chameleon with most of the skeleton preserved

Scale bar 1 cm for all photographs except (F) which has a scale bar of 0.1 mm and (I) with a scale bar of 1 mm.

 Lizards Preserved in Amber

Writing in the open access journal “Science Advances” the scientists from Sam Houston State University (Texas), the American Museum of Natural History (New York), the Florida Museum of Natural History along with researchers from the California Academy of Sciences and the Bavarian State Collection of Zoology (Munich, Germany), have shed fresh light on the evolution and radiation of the Squamata.  Ancestral forms of the Chameleon and Gecko families have been identified along with other lizard specimens that relate to the agamids.

Commenting on the study, one of the researchers, Dr Edward Stanley (Florida Museum of Natural History) stated:

“The fossilised amber provides a view into a lost world, revealing that the tropics of the Mid-Cretaceous contained a diverse lizard fauna.”

Oldest Lizard Assemblage Preserved in Amber

It is rare for such small creatures to be preserved as fossils.  The specimens represent the oldest lizard assemblage preserved in amber known.  In all, the twelve fossils preserve fine details of soft tissue and bone, allowing the scientists to gain a better understanding of how unique adaptations such as the sucker-like feet of the Gecko evolved.  The fossil material was all collected from northern Myanmar (Kachin Province) and zircon crystals recovered from sediments in the Burmese amber outcrops that have been radiometrically dated indicate an age of around 99 million years.  This places the age of the amber very close to the boundary between the Early and the Late Cretaceous (Albian-Cenomanian stage boundary).

Such is the degree of preservation that the scientists were able to obtain a great deal of information from the amber nodules.

Professor Juan Daza (Sam Houston State University) explained:

“We can pretty much see how the animals looked when they were alive.  They [the fossils] provide a really nice snapshot of the past.  To me it is like going back in time and doing a lizard collecting trip when we can see what these animals looked like.”

CT Scans and High Resolution Images Reveal Remarkable Detail

Exquisite detail.

Picture credit: Science Advances

Fossilised Tree Resin

The amber (fossilised tree resin), provides a fascinating insight into some of the smaller organisms that lived alongside the dinosaurs during the Cretaceous.  Fungi, plant remains including pollen and fern spores plus many different types of invertebrate remains have been identified from burmite.

For example, last year Everything Dinosaur reported on the discovery of a remarkably well preserved Cretaceous cockroach found in amber from northern Myanmar.

To read about this discovery: Cretaceous Cockroach – Deadly Nocturnal Predator.

Detailed Preservation

The detailed preservation of the lizard fossils permits scientists to identify characteristics helping to define and reassess the phylogenetic relationships between different groups.  It has also given the researchers a surprise.  The highly sophisticated projectile tongue, a characteristic of Chameleons has been identified in one of the specimens (K).  The lizard in question, has been assigned to a basal position in the Chameleon family, the presence of the highly modified tongue suggests that this anatomical feature evolved very early on in these lizards, whereas, the absence in the fossil of those modified tree-grasping fused toes, indicates that the fused toes evolved much later.

Massive Abelisaurid from Morocco

A partial femur (thigh bone) found in Morocco has provided palaeontologists with yet more evidence of the amazing diversity of theropod dinosaurs that flourished in North Africa during the Middle Cretaceous.  The fossil, measuring around 33 centimetres in length has been identified as coming from a large abelisaurid.  Based on thigh bone comparisons with better known Abelisauridae, dinosaurs such as Carnotaurus and Ekrixinatosaurus (both from the Late Cretaceous of Argentina), scientists have estimated that this meat-eating dinosaur measured around nine metres in length and may have weighed as much as two tonnes.

A Large Abelisaurid

The Partial Femur of the New Dinosaur

Various view of a abelisaurid dinosaur femur from Morocco.

Picture credit: PeerJ.com

The picture above shows various views of the partial dinosaur thigh bone.

Key

(A) a proximal view, that portion of the femur that would articulate with the hip region.

(B) an anterior view, the view of the front side of the bone.

(C) in medial view.

(D) a posterior view, a view of the rear side of the bone.

(E) the lateral view.

(F) a distal view, the part of the thigh bone that would be furthest away from the trunk of the animal, that part of the bone closest to the lower leg bones.  Please note, the scale is different for picture (F).

The scale bar (white bar) is five centimetres.  Abbreviations gt, greater trochanter; iMie, insertion for the Musculus iliofemoralis externus (a muscle and subsequent muscle scar); fn, femoral neck; s, shallow sulcus.

From the Geological Museum in Palermo

The fossil is part of the collection at the Geological Museum in Palermo (Italy) and a paper on the femur has just been published in the on line, open access journal (PeerJ).  The scientific paper has been co-authored by PhD student Andrea Cau of Bologna University and fellow PhD student Alfio Alessandro Chiarenza (Department of Earth Science and Engineering, Imperial College London).

An Illustration of a Typical Abelisaurid Theropod Dinosaur

A scale drawing of a typical abelisaur (Rugops primus)

Picture credit: Everything Dinosaur

For models of abelisaurids and other theropods: CollectA Age of Dinosaurs Popular Models.

Stromer’s Riddle

The fossil is from the Kem Kem Formation of Morocco, that part of the deposit that has been dated to the Cenomanian faunal stage or the Cretaceous (Cenomanian faunal stage around  100 million to 93.5 million years ago approximately).  The beginning of the Cenomanian marks the start of the Late Cretaceous as defined by the International Commission on Stratigraphy.  The scientific paper concludes that the abelisaurids had indeed reached their largest body size by the “Middle Cretaceous” and that abelisaurs did co-exist with a number of other gigantic Theropods in Africa during this time.

Different Types of Meat-eating Dinosaur were Coeval

The number of different types of meat-eating dinosaur all living together in Africa during this part of the Cretaceous has posed a puzzle for palaeontologists.  The puzzle is named after Ernst Freiherr Stromer von Reichenbach, the German palaeontologist who first brought North African dinosaurs to prominence.  Spinosaurids, members of the Ceratosauria clade (Deltadromeus), Carcharodontosauridae dinosaurs and abelisaurids all seem to have been present in this part of the world.

The researchers examine this phenomenon and using comparisons with theropod lineages from South America, they deduce that these large super-predators probably did not overlap, with a number occupying different niches in the food chain, or living in different habitats.  Niche partitioning did very probably occur, however, studies of the skulls and teeth between abelisaurids and the carcharodontosaurids such as the mighty Carcharodontosaurus iguidensis indicates that these types of dinosaurs did probably compete directly for resources.

Further fossil finds and more research will need to be undertaken before a better understanding of the interactions between these theropods can be achieved.