Afrovenator

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Megalosauridae

Genus:Afrovenator

Species:Afrovenator abakensis

Introduction

Afrovenator was a large predatory dinosaur from the Early Cretaceous forests of what is now North Africa. Known from a single, nearly complete fossil skeleton, Afrovenator has been important in efforts to reconstruct the family tree for Jurassic and Cretaceous carnivores. Discovery of the dinosaur has also helped to improve theories about continental and geologic changes in the Mesozoic Era (251–65 million years ago).

In the Triassic Period, the continents were united in a single landmass known as Pangaea, which split apart during the late Jurassic and Cretaceous. This splitting gave rise to the supercontinents Laurasia and Gondwana, which contained most of today's Northern Hemisphere continents and Southern Hemisphere continents, respectively.

The presence of Afrovenator and closely related species in Africa has led to the theory that Europe and Africa were connected by a land bridge as recently as the Late Jurassic or Early Cretaceous. During that time, Afrovenator's relatives spread throughout Africa, leading to closely related species across the supercontinents.

Classification

Paleontologists use two major systems for classifying organisms. Linnaean taxonomy uses overall physical similarity to place organisms into different groups. By contrast, cladistics seeks to create groups of organisms based on evolutionary relationships; these groups are called “clades.” Cladistic analysis focuses on important key traits and attempts to trace the inheritance of a trait among descendants of a common ancestor.

In the Linnaean system, dinosaurs have traditionally been divided into two orders based on the structure of their pelvic bones: Saurischia, or “lizard-hipped,” and Ornithischia, or "bird-hipped." Although this broad division has been challenged by some researchers, it remains in wide use. Afrovenator is considered a saurischian in the suborder Theropoda, made up of bipedal carnivores with similar skull and leg anatomy. From there, Afrovenator is typically placed in the family Megalosauridae, largely because of its skull construction.

Cladistic analysis also classifies Afrovenator in the clade Theropoda, but the animal's relationships to other theropods are less clear. Paleontologists often disagree on the exact groupings of many dinosaurs, and especially theropods for which each new discovery provides new and sometimes controversial information. Generally, researchers place Afrovenator in the clade Megalosauridae, much like in the Linnaean system, and more specific groups such as Afrovenatorinae have also been proposed. Other analyses suggest that Afrovenator should be included in the tentanuran, or “stiffened-tail,” theropod group, and from there in various subclades such as Eustreptospondylinae, Torvosauridae, or Megalosaurinae. Some paleontologists have even suggested Afrovenator is more related to the older theropod Allosaurus than to other megalosaurs.

Anatomy

Afrovenator was a large carnivore, reaching a length of between eight and nine meters (26 to 30 feet) and standing about three meters (10 feet) tall. Paleontologists estimate that the animal may have weighed between 1,800 and 2,200 kilograms (3,970 and 4,800 lbs), making it one of the largest carnivores in Early Cretaceous Africa.

Afrovenator was bipedal, with long rear legs terminating in three-toed, clawed feet. The animal's forelimbs were considerably smaller, but still muscular, with three-fingered hands and small, sharp claws. Afrovenator had a long, stiff tail strengthened by bony sheaths connecting the vertebra.

Like all members of its family, Afrovenator had forward-facing eyes and a broad muzzle. Its jaws were lined with recurved, serrated teeth. Afrovenator might have had pebbled, scaled skin, similar to impressions of skin found on some dinosaur fossils. Like many modern predators, it may also have been cryptically colored to aid in predation.

Intelligence

Scientists have used encephalization quotient (EQ), based on brain and body size, to estimate animal intelligence. There have been no attempts to estimate the EQ value for Afrovenator directly, but other closely related theropods have been found to have EQ values in the range of 5.0, making them slightly less intelligent than mammalian and avian predators, but more intelligent than most other dinosaur species. Generally speaking, predatory animals tend to have higher intelligence than herbivorous animals, helping them to outsmart their intended prey.

Reproduction and Population

Paleontologists believe that most dinosaurs were oviparous, or “egg-laying” animals, like modern birds and many reptiles. No nests or eggs have been found for Afrovenator, but nests of other theropods indicate that the animals often laid two eggs at a time, and laid multiple times in a single nest. Afrovenator probably laid its eggs in nests built up from soil and vegetative material.

Paleontologists are unsure about the population size of Afrovenator or about how widespread the species was within its range. Paleontologists have found few predatory dinosaurs among fossil beds in Northern Africa and Afrovenator was one of the largest, though there was at least one larger theropod sharing its environment. As Afrovenator is known only from a single specimen, paleontologists have not determined whether there was any morphological difference between males and females of the species.

Diet

Afrovenator was most likely an opportunist, preying on a variety of dinosaurs and other animals in its environment. Because Afrovenator was large, it may have been able to prey on large herbivorous dinosaurs in North Africa, like Lurdusaurus, a member of the group known as the Iguanodontids (from the family iguanodontidae). There were also a variety of sauropods, long-necked herbivores that were among the largest of the dinosaurs, living in Early Cretaceous Africa.

Some paleontologists believe that large theropods, like Afrovenator and its North American relative Tyrannosaurus, would have been inefficient hunters and most likely obtained at least part of their diet by scavenging carcasses. Investigations of large theropod skulls indicate that the animals had enlarged olfactory bulbs in their brains, which may have evolved as an adaptation to help them find carcasses or wounded animals.

Behavior

As Afrovenator is known from only a single specimen, paleontologists have no evidence to suggest whether the species displayed any social behavior. Afrovenator and the other large theropods in North Africa were large enough to hunt and kill dinosaurs on their own but may have gathered into chaotic groups around large prey, like sauropods, competing to strip meat from a carcass.

Whereas dinosaurs were once thought of as sluggish, slow-moving animals whose weight made it difficult for them to move quickly, modern theories equate dinosaurs more closely with living birds, suggesting that dinosaurs were capable of fast movement. Theropods were the dinosaurs most closely related to birds and may therefore have shared a variety of behavioral patterns with living birds.

Habitat and Other Life Forms

During the Early Cretaceous period, the part of Gondwana that contained modern-day India and Madagascar was splitting from the portion of the continent that would become mainland Africa. Northern Africa had more moisture than in the modern era, and was covered in a variety of forest and woodland habitats.

Gymnosperms such as conifers and cycads were the dominant type of vegetation in the Early Cretaceous, along with ferns and other spore-bearing plants. The first angiosperms also appeared and spread during this time. A variety of reptiles, amphibians, and small mammals lived in Cretaceous Africa, many of which closely resembled modern species. Flying reptiles called pterosaurs were the dominant flying animals, though the first birds had already appeared during the Late Jurassic.

Afrovenator was medium-sized compared to other African theropods, living alongside the larger Carcharodontosaurus, a large theropod discovered in 2007 that rivals North America's Tyrannosaurus in size. There was also Deltadromeus, a swift theropod similar in size to Afrovenator that probably fed on similar prey.

Herbivorous dinosaurs in North Africa included a few varieties of sauropods, including the small Malawisaurus and the long-necked Nigersaurus. Africa also had a number of unique species, like the “sail-backed” dinosaur Ouranosaurus, which shared many characteristics with iguanodons and duck-billed hadrosaurs in North America but had an extended crest on its back.

Research

Paleontologist Paul Sereno, from the University of Chicago, discovered a skeleton of Afrovenator from a fossil bed in the Sahara Desert portion of Niger in 1993. Since 1993, evaluations of Afrovenator have helped to refine the relationships between theropods and other carnivores of the Early Cretaceous. A species of theropod similar to Allosaurus, found in 1925 in the Sahara formations, may have been an ancestor of Afrovenator, indicating that the species may be related to the Jurassic allosaurids. In the absence of further findings, most research continues to focus on refining classification, and theropods in general have seen considerable debate within the paleontology community.

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