Pulaosaurus

MEANING: Pulao lizard

PERIOD: Mid-Late Jurassic

CONTINENT: Asia

Pulaosuaurs is a small basal ornithischian dinosaur that is known from a very well preserved fossil specimen. Fossilized gut contents show that it ate seeds, and it also preserved a larynx, or voicebox, suggesting it probably made bird-like vocalizations. Pulaosaurus was a bipedal dinosaur that grew to about 80 cm in total body length.

Abstract from paper: The Middle and Late Jurassic Yanliao Biota is different from other contemporaneous fossil assemblages in that it lacks neornithischian dinosaurs. Here, we report a new, early-diverging neornithischian, Pulaosaurus qinglong gen. et sp. nov., from the Upper Jurassic Tiaojishan Formation of Qinglong, Hebei Province, of northern China. Diagnostic or noteworthy morphological characteristics of P. qinglong include: five premaxillary teeth; a small boss is present on the caudoventral corner of the dorsal ramus of the jugal; a nuchal crest is located along the parietal; the manus has five digits; a supra-acetabular crest is present on the ilium; the paired arytenoids are gracile and leaf-like in form; the obturator process along the ischium is located near the pubic peduncle; a notch-like shaped obturator opening is present within the pubis; a robust fibular condyle forms a dorsoventrally extending crest on the tibia; a subtriangular flange on the anterior surface of the astragalus extends dorsolaterally along three distal tarsals; three of the distal tarsals are unfused, including a small drop-shaped distal tarsal 3; distal tarsal 3 is pierced by a foramen. A phylogenetic analysis places P. qinglong as one of the earliest-diverging neornithischians yet described. Moreover, P. qinglong represents the second known dinosaur to preserve ossified laryngeal elements, thus suggesting that a bird-like vocalization evolved early in non-avian dinosaur evolution.

Pulaosaurus is from the Middle to Late Jurassic. The Middle Jurassic, spanning from approximately 174 to 163 million years ago, was a period of increasing tectonic activity and evolutionary innovation. By this time, the supercontinent Pangaea had begun to split more significantly, with Laurasia in the north and Gondwana in the south drifting apart. This movement created new coastlines, shallow seas, and rift valleys that fostered diverse ecosystems. The climate remained generally warm and humid, promoting the spread of lush vegetation, including ferns, cycads, and conifers, which blanketed much of the land and supported a wide variety of herbivorous dinosaurs.

Though less well known than the Late Jurassic, the Middle Jurassic was an important evolutionary chapter. Several major dinosaur groups began to diversify, including the stegosaurs and more derived long-necked sauropods that would later dominate the landscape. Theropods also continued to evolve, giving rise to new lineages like the megalosaurids and the early ancestors of more derived carnivores. Fossil evidence from this interval is relatively scarce compared to later stages, but what we do have paints a picture of an increasingly complex world, setting the stage for the iconic ecosystems of the Late Jurassic.

The Late Jurassic was a dynamic period, spanning from about 162 to 143 million years ago. The continents were continuing to drift apart, and the supercontinent Pangaea had fully split into Laurasia in the north and Gondwana in the south. This continental rearrangement led to the formation of large inland seas and shallow coastlines that fostered diverse ecosystems. The climate during the Late Jurassic was warm and humid, with lush forests of conifers and ferns that stretched across much of the continents, creating a rich ecosystem where dinosaurs flourished the dominant land animals.

Dinosaurs continued to diversify through the Late Jurassic, with some of the most famous species evolving in this time. Many well-known sauropods, such as Brachiosaurus and Apatosaurus roamed the land, exhibiting niche partitioning with their selectively distinct neck positions. Alongside them, stegosaurs became widespread, their plates and spikes making them one of the era's most recognizable groups. Theropods like Allosaurus and Ceratosaurus were the apex predators, evolving large, powerful bodies and sharp teeth that allowed them to hunt the gigantic herbivores. The early evolution of birds was taking place, setting the stage for the numerous species that would fill the skies in the eras to come.

Unlike the dramatic mass extinctions that marked the beginning and end of the Mesozoic, the Jurassic Period ended without a sharp boundary. As the continents continued to drift, ecosystems gradually transformed into unique habitats that supported the more specialized dinosaur species of the Cretaceous.

Pulaosaurus is a basal ornithischian. Ornithischia is one of the two major clades of dinosaurs, sister to the saurischia, which includes theropods and sauropods. Basal ornithischians were small, lightly built herbivores or omnivores and were typically bipedal, with long hind limbs and relatively short forelimbs, well-suited for swift movement. Their body plans were often simple, lacking the extreme specializations seen in later ornithischians like ceratopsians or hadrosaurs. Many had simple, triangular skulls with leaf-shaped teeth, suitable for cropping low vegetation, and some evidence suggests they may have lived in groups. Though they form the base of the ornithischian family tree, they do not belong to any of the more derived subgroups and instead exhibit a mix of ancestral traits.

Basal ornithischians are mostly known from the Jurassic. The absence of definitively known ornithischians from the Triassic has puzzled paleontologists, though some propose that certain Triassic animals, like the silesaurs, may fill this gap. However, these relationships remain debated. As the Jurassic progressed, basal forms gave rise to a wide array of more specialized ornithischians, but these early dinosaurs remain a crucial and still somewhat mysterious chapter in the evolutionary history of the group.