Aardonyx

Nobu Tamura (http://spinops.blogspot.com), CC BY 3.0, via Wikimedia Commons

Aardonyx means “earth” in Afrikaans and “nail, claw” in Greek.

Some incomplete fossils were found in South Africa and paleontologists stated in 2010 that the discovery had helped fill a gap in the evolution of sauropods as it showed how two legged animal started to get the features needed so sauropods could spend a life on four legs. Ardonyx filled some gaps and confirmed scientists theories which is why it was an important discovery.

The restoration picture shows how these dinosaurs were evolving from being bipedal (using two legs to walk on).

Scientists think the Aardonyx fossil discoveries were from dinosaurs that were under 10 years old. They found remains of vertebrae, dorsal and cervical ribs, gastralia, chevrons, elements of the pectoral and pelvic girdles, and bones of the fore and hind limbs It is thought Aardonyx was a powerful but slow walker.

FURTHER READING AND STUDY 

• Adam Yates et al (2009) A new transitional sauropodomorph dinosaur
• Riley Black (2009) The “Earth Claw” 
• Dr M Bonnan (2009) The Evolving Palaeontologist

Abelisaurus

Jordan Mallon, CC BY-SA 2.5, via Wikimedia Commons

Abelisaurus means “Abels lizard” and was named by Argentine paleontologists Jose Bonaparte and Fernando Novis in 1985 after Roberto Abel who discovered the specimen type.

The discovery was of a skull only which was badly damaged. It was a predatory dinosaur alive during the Late Cretaceous Period. Abelisaurus is the first dinosaur from the Abelisauridae group of carnivorous theropod dinosaurs, which mainly lived in the southern continents that we now know as Africa and South America.

It is thought the Abelisaurus had extremely small arms compared to other theropods.

Scientists have done full body reconstructions based on other dinosaurs from the Abelisauridae group which showed them it was a medium to large theropod and like many others was bipedal. Its amazing what information can be extracted from incomplete fossils.

FURTHER READING AND STUDIES

• J Bonaparte et al (1985) Abelisaurus Comahuensis
• N Longrich (2017) An Abellisaurid from the latest Cretaceous of Morocco
• R Martinez (2004) Abelisaurid remains from southern Patagonia

Achelousaurus

Nobu Tamura (http://spinops.blogspot.com), CC BY 3.0, via Wikimedia Commons

Achelousarus lived in North America during the Late Cretaceous Period and the first remains were discovered in 1987 by American paleontologist Jack Horner. The specific name refers to Horner himself and there were more discoveries made of Achelousaurus in 1989 and 1994.

Achelousarus had two horns at the top of the skull and a bony knob over its nose. The length of a fully grown Achelousarus’s skull is over 5 feet (1.6 meters) in length which would have been a very intimidating sight.

It is thought by some scientists that these dinosaurs lived in herds, this was due to bone fragments of multiple members of the ceratopsian species being found together and it was assumed in that find that they had been killed in either a flood or a drought.

FURTHER READING AND STUDY

• R Barrick et al (1996) Comparison
• A McDonald (2011) A subadult specimen 
• J Wilson et al (2021) Comparative cranial osteology  

Achillobator

Durbed, line drawing by Pilsator, CC BY-SA 3.0, via Wikimedia Commons

Achillobator was a smaller cousin to the Utahraptor, but much bigger than Velociraptor. They had extremely sharp and powerful foreclaws which were used to shred any armour that its prey might have had at speed. 

It has been illustrated that the Achillobator had a coat of feathers but this is not down to any fossil evidence, its theory is based on its evolutionary relationships with modern birds. 

The first fossil of Achillobator was found in 1989 during an exploration in South Central Mongolia. It was stored away only for it to be examined by several Palaeontologists and given its official name ten years later in 1999. 

The name means “Achilles hero” in Greek.       

FURTHER STUDY AND READING

• S Phil et al (2007) A method for distinguishing dromaeosaurid 
• P Senter et al (2012) New dromaeosaurids from Lower Cretaceous 
• R Ely et al (2019) Phylogeny of a new gigantic paravian

Acrocanthosaurus

Mariolanzas, CC BY-SA 4.0, via Wikimedia Commons

One of the most stunning dinosaurs, Acrocanthosaurus had a set of tall spikes that ran all the way down it’s spine around the neck area. Acrocanthosaurus is also believed to have had spikes on its hips and around its long upper tail. The spikes found on this dinosaur were big, but not as big as Spinosaurus’s.

Acrocanthosaurus also had quite a unique way of communicating to either attract mates or to warn off other Acrocanthosaurus during the mating season. Some scientists believe that it would stand up as high as it could taking in as much air as possible before releasing the air, making a deep noise from within its rib cage.

FURTHER READING AND STUDY

• P Currie et al (2000) A new specimen of Acrocanthosaurus
• J Harris (1998) A reanalysis of Acrocanthosaurus 
• J Stovall (1950) Acrocanthosaurus atokensis

Aegyptosaurus

Levi bernardo, CC BY-SA 3.0, via Wikimedia Commons

Aegyptosaurus is Greek for “Egypts lizard” and this dinosaur lived in Africa during the Late Cretaceous Period. Its actually a close relative to the ginormous sauropod Argentinosaurus that lived in South America but it was a smaller relative as you will see when you compare the two.

Aegyptosaurus was given its name by a German palaeontologist named Ernist Stomer in 1932 as its fossils were found in Egypt and the Sahara desert. 

Unfortunately during World War 2 the fossils were destroyed in an allied bombing raid as the fossils were kept in a museum in Munich. Only fragments survived.

Its possible Aegyptosaurus was hunted by Carcharodontosaurus as fossil remains have been found in similar locations but there is no evidence of this. 

FURTHER READING AND STUDY

• J Smith et al (2001) A giant sauropod dinosaur 
• H Atfy et al (2019) Repeated occurrence 
• N Ibrahim et al (2016) Evidence of a derived titanosaurian 

Afrovenator

PaleoEquii, CC BY-SA 4.0, via Wikimedia Commons

Afrovenator, the “African hunter’s” fossils were first discovered in Niger, Africa in 1993. Its named using the Latin afer meaning “African” and venator meaning “hunter”.

The skeleton found meant Afrovenator was the most complete predatory dinosaur from the Cretaceous period discovered in Africa. 

It is thought that Afrovenator was a cousin to Allosaurus, that lived in North America, and reconstructions have shown that it was a predator built for speed. A sauropod that was from the same time was Jobaria, and while no scientific proof has been discovered its possible that Afrovenator hunted it. 

FURTHER READING AND STUDY

• P Sereno et al (1994) Early Cretaceous dinosaurs from the Sahara
• R Allain (2002) Discovery of megalosaur
• P Sereno et al (2004) New dinosaurs link southern landmasses

Agilisaurus

Danny Cicchetti, CC BY-SA 4.0, via Wikimedia Commons

Agilisaurus was discovered in Asia and it was a bipedal runner (it ran on two feet) that was thought to be really fast. This was due to the dinosaur having no armour which meant it was exposed to predators and so its defence was speed and agility. Agilisaurus was a herbivourous and used its beak like structure jaw to help it consume plants. 

It had a long tail which was used for balance and studies completed think that Agilisaurus was an active dinosaur in the daytime and rested at night.

Interestingly the only complete skeleton was only discovered in the reconstruction of the Zigong Dinosaur Museum in China in 1984 and was named in 1990 by  Chinese palaeontologist Peng Guangzhou. The skeleton came from Dashanpu Quarry which is one of the richest quarry’s in dinosaur fossils ever discovered.  

FURTHER READING AND STUDY

• G Peng (1992) Jurassic ornithopod Agilisaurus
• P Barrett et al (2005) Small-bodied ornithischian dinosaurs 
• F Knoll et al (2008) Gongbusaurus and the early phylogeny

Alamosaurus

Петр Меньшиков, CC BY-SA 4.0, via Wikimedia Commons

You can tell by looking at the measurements that Alamosaurus was an enormous dinosaur. Some scientists estimated it could have been up to 30 meters (98ft) in length as most of the fossils were either of juvenile or small adult specimens. This  suggests it could have been in comparable size to other sauropods such as Argentinosaurus.

It lived in what is now the southern part of North America and scientists believe it was amongst the last surviving non-avian dinosaur species. 

There is a restored Alamosaurus skeleton mounted at the Perot Museum in Dallas. It was discovered when a member of an excavation team was working at a nearby fossil site. The member had to go around the other side of the hill they were working on as he had to “answer natures call”. A remarkable story and the restoration is impressive.       

FURTHER READING AND STUDY 

•  T Lehman et al (2002) A juvenile specimen of the sauropod dinosaur 
• S Lucas et al (1989) Alamosaurus and the sauropod hiatus 
• R Tyoski et al (2017) An articulated cervical series of Alamosaurus 

Albertaceratops

Nobu Tamura (http://spinops.blogspot.com), CC BY 3.0, via Wikimedia Commons

Albertaceratops name means “horned face”, and as the name and picture shows this dinosaur had very prominent horns above its eyes, that curved out to the sides.  There is only one ever finding of Albertaceratops and all is known from a single complete skull that was discovered in August 2001 in Canada.

There was further fossils found in the river bed in Montana but these were later ruled out to be a different dinosaur. 

The skull of Albertaceratops is on display in the Phillip J. Currie Dinosaur Museum in Canada and it was formally named in 2007 by Michael Ryan after he did  genetic analysis of the skull. Later family members of the group would develop considerably reduced brow horns.  

Albertaceratops was a herbivore and its full species name of Albertaceratops A. nesmoi is based on a rancher named Cecil Nesmo who has aided fossil hunters in the past. 

FURTHER READING AND STUDY 

• K Chiba et al (2016) Re-evaluation of Medusaceratops
• M Ryan et al (2010) A new chasmosaurine ceratopsid 
• S Sampson et al (2013) A remarkable short-snouted horned dinosaur

Albertosaurus

Nobu Tamura email:nobu.tamura@yahoo.com http://spinops.blogspot.com/ http://paleoexhibit.blogspot.com/, CC BY-SA 4.0, via Wikimedia Commons

Albertosaurus was a much smaller tyrannosaurid relative of the Tyrannosaurus rex, but was a bipedal (two-legged) predator in its own right that lived in the western North America but fossils of an indeterminate species have also been discovered in Mexico. 

It was discovered in 1884 and named in 1905 and since the first discovery over 30 fossils of Albertosaurus have been discovered.

26 were found at one sight which meant scientists say that was evidence of pack behaviour. 1,128 fossil bones of Albertosaurus have been discovered, and is the largest number of any theropod  bones from the Cretaceous Period. In fact scientists have been able to see the effects of diseases and parasites that were found on some individuals. This group found were aged between 2 years old and 23 years old and the oldest specimen that has been found was 28 years old.

Albertosaurus has been described to reach walking speeds of 14 – 21km/hour (8-13 mph) with running speeds a lot higher. 

FURTHER READING AND STUDY 

• F Therrien et al (2021) Mandibular force profiles and tooth morphology
• L Buckley et al (2010) Quantifying tooth variation
• R Bell et al (2010) Palaeopathological changes in Albertosaurus

Alectrosaurus

Conty, CC BY-SA 4.0, via Wikimedia Commons

Alectrosaurus was a tyrannosauroid theropod dinosaur that lived in Asia and was thought to be a very fast predator that was able to hunt down his prey with devastating efficiency. 

If we had a third description of the type of dinosaur then Alectrosaurus would have been a Medium sized theropod as it was not as big as Tyrannosaurs rex but was not small either. 

Alectrosaurus was discovered in 1923 by an expedition of the American Museum of Natural History that was searching for dinosaur fossils in Mongolia. During this expedition two discoveries were made 30 meters apart from each other by an assistant palaeontologist George Olsen. These fossil specimens were only named in 1933 by American palaeontologist Charles Gilmore. 

The name Alectrosaurus means “alone lizard” and the specific name Alectrosaurus olseni was in recognition of George Olsen who discovered them.   

Its believed Alectrosaurus lived alongside theropods such as Achillobator, Garudimimus or Stegnosaurus. 

FURTHER READING AND STUDY 

• B Mader et al (1989) A redescription and revised diagnosis
• N Kramarenko et al Joint Soviet- Mongolian Paleontological expedition
• J Hurum et al (2003) Skull structure and evolution in tyannosaurid dinosaurs

Alioramus

Fred Wierum, CC BY 3.0, via Wikimedia Commons

Alioramus was a bipedal (two-legged) theropod dinosaur that lived in Asia and was discovered in the early 1970’s by a joint Soviet-Mongolian expedition and was named in 1976 by Russian palaeontologist Sergei Kurzanov.

Since it was first discovered there was a lot of consideration that Alioramus was in fact a juvenile of the larger Tarbosaurus due to the small amount of fossils obtained. But when the second species was discovered in 2009 they found more evidence to keep Alioramus in its own separate genus as it had more teeth and a series of five crests on the top of its snout.

The name Alioramus translates as “different branch” and was named this as Alioramus’s head and body was different to other tyrannosauroids. Its estimated size is also an area of contention because without fossils from a fully grown Alioramus its very hard to be certain the estimates are correct.       

FURTHER READING AND STUDY 

• G Bever et al (2011) Variation, Variability, and the origin
• M Gold et al (2013) The cranial pneumatic sinuses of the tyrannosaurid 
• S Brusatte et al (2009) A long-snouted, multihorned tyrannosaurid 

Alvarezsaurus

User:Karkemish, CC BY 3.0, via Wikimedia Commons