Cenohadrosauria

The information here is mostly **FICTIONAL**. Do not be fooled!

## Subgroups

* Neohadrosauria
* Eucenohadrosauria
	+ Neosaurolophia
	+ Neolambeosauria
* And see text

**Cenohadrosaurs** (/sɛnəˌhædrəˈsɔːr/, from the Greek *kainos*, *hadros*, and *sauros*, meaning "new heavy lizards") are a clade of late-surviving ornithischian dinosaurs from the clade **Cenohadrosauria**. Apart from birds, they are the only other members of the clade Dinosauria to have survived the K-Pg extinction event. Over a thousand species have been named, several of which survive to the present day.

Cenohadrosaurs are traditionally divided into two types: the neolambeosaurs and the neosaurolophs, named for their convergent resemblance to the extinct lambeosaurines and saurolophines. Neolambeosaurs tended to have gracile builds and comparatively small heads, often with elaborate hollow crests; on the other hand, neosaurolophs are traditionally distinguished by their more robust musculature, relatively large heads, and solid or nonexistent crests. In recent years, other groups such as the basal Neohadrosauria and Neoaralosauria (also known as Archaeocenohadrosauria) were recognized.

Cenohadrosaurs had a variety of lifestyles. Although most members were terrestrial herbivores, the group also includes semiaquatic specialists and active predators. Several forms appear to be equivalents of mammals and other large animals in the current timeline.

## Description

Cenohadrosaurs had a wide variety of body plans. Generally, they were quadrupeds with short necks, muscular torsoes, thin forelimbs, stocky hindlimbs, and long tails.

### Size

Cenohadrosaurs had a wide range of sizes, but they were generally large. The smallest species, *Microparadoxia alatus*, was 75 centimeters (~2.5 feet) long, about the size of a medium-sized dog. The largest species, *Erythrokremnosaurus microtylos*, could reach up to 9.58 meters (~31 feet) long, making it the largest land animal of the Cenozoic, even longer than the current timeline's *Paraceratherium transouralicum*.

### Skull

Cenohadrosaur skulls are diverse, with length, crest shape, and beak shape varying greatly amongst species. The skull length is usually directly proportional to the body length, ranging from roughly 3:25 in neolambeosaurs, 2:15 in neosaurolophs, and 19:150 in more basal forms.

Like their ancestors, cenohadrosaurs had keratinous beaks and continually-replaced teeth at the backs of their jaws. Many herbivorous species kept the multi-row dental batteries that allowed hadrosaurs to conquer the world, but often reduced to at most three rows of teeth on either side of the dentary. Several species also acquired heterodont dentition with "premolariforms" and "molariforms", convergent with mammals and some extinct notosuchian crocodyliforms. Some small carnivores, like the microcenohadrosaur *Avirhynchus insolens* did not have teeth at all, only having a sharp, eagle-like beak.

Formed from expanded nasal bones, the crests of cenohadrosaurs came in a variety of forms, remarkably similar to those of the extinct euhadrosaurs. Neosaurolophs either had solid bulges or no crests at all, while neolambeosaur crests were hollowed by long nasal passages, coming in a variety of shapes including semicircular "helmets" and long, backwards-arcing tubes.

### Postcranium

Compared to euhadrosaurs, cenohadrosaur musculature was relatively reduced, creating an external appearance somewhat similar to that of the extinct non-hadrosaur hadrosauromorph *Tethyshadros*. While the neck and torso were relatively stocky, the tail was less so, creating a visible dip around the pelvic region. In general, neolambeosaurs tended to be more gracile than neosaurolophs.

Most cenohadrosaurs had muscular limbs. The forelimbs ended in a single finger, bearing its weight on a large, hoof-like claw. While the hindlimbs were digitigrade like those of earlier hadrosaurs, they also a fleshy pad extending from the ankle to the ground, creating a "pseudo-plantigrade" stance similar to that of extinct stegosaurs.

That said, there are few cursorial species that are an exception to this rule. Sacrificing strength for speed and agility, they developed reduced musculature, losing the ankle pad and acquiring a convergently theropod-like hindlimb. In terms of appearance, they are intermediate between *Tethyshadros* and an average cenohadrosaur.

### Integument

All cenohadrosaurs were covered with centimeter-wide non-overlapping scales, sometimes interspersed by larger feature scales. They can form complex color patterns that vary across different parts of the body, and in several species, no two individuals have the same exact pattern of colors.

Some species also have scaleless skin, mostly as dewlaps or other display structures. A handful of cenohadrosaurs additionally possess superficially feather-like structures, but these appear to be highly modified scales instead of true feathers.

## History

*See also: Timeline of cenohadrosaur research*

The Cenohadrosaur timeline, as it has been named, was first discovered on May 28th, 2019 when Italian farmer Adamo Cancello inadvertently stepped through a portal in the mountains of Tuscany, Italy. He managed to bring back a carcass of a cenohadrosaur and get it scientifically proven as genuine, causing a worldwide media frenzy.

Seven months later, at exactly midnight on January 1st, 2020, the *Inter-Temporal and Inter-Universal Commission on Natural History* (IICNH), the organization that investigates the animals and plants of different times, planets, dimensions, and universes, sent a fifty-man expedition to the portal, consisting of several well-established scientists of various fields. They were sent to study the geography, climate, fauna, and natural history of the timeline, which they detailed in a series of scientific papers. The first of these is a preliminary report on the timeline, and also includes the first scientific description of a Cenozoic hadrosaur: *Cenohadros astronomicus*.

In terms of new taxa, research was initially slow, with most early papers focusing on other aspects of the timeline. In fact, the clade name Cenohadrosauria was not introduced until ten different species of Cenozoic hadrosaurs had been described. However, as time went on, interest in the creatures increased, and multiple groups of researchers, some independent of the *Commission*, began to study the Cenohadrosaur timeline. As a result, the speed of new discoveries steadily increased, including the rate of new taxa.

Initially, researchers conducted time travel trips in addition to traditional fossil excavations, in order to determine the life appearance and behaviors of studied specimens. However, a number of highly-publicized events have resulted in the timeline being significantly altered. This has led to an international boycott of time travel; however, isolated expeditions to the past continue to happen, although tightly controlled, regulated, and guided by the IICNH.

## Evolution

When first discovered, cenohadrosaurs were thought to be closely related to the ancient hadrosaur clade Kritosaurini. The following cladogram shows this hypothesis.

Later discoveries proved that this is in fact due to the convergent similarities with kritosaurins and *Cenohadros*, and that they instead evolved from a stock of basal hadrosaurids just outside Lambeosaurinae and Saurolophinae, diverging some time in the latest Cretaceous. The cladogram below illustrates this.

The oldest known cenohadrosaur, which is so far unnamed, is known from the youngest strata of the Lopez de Bertodano Formation on Seymour Island, Antarctica, which straddles the K-Pg boundary. It was closely related to the unnamed hadrosaur known from earlier in the formation (only known from a tooth), which was in turn closely related to non-euhadrosaurian hadrosaurs from South America, such as *Lapampasaurus* and *Gonkoken*.

The reason why the Antarctic ancestors of cenohadrosaurs managed to survive the K-Pg extinction lies in a combination of factors. First of all, the Antarctic hadrosaurs lived in an extremely isolated area, which spared them from the most devastating effects of the asteroid strike. They also had the ability to lower their metabolism at will in response to the dark, plant-less Antarctic winters, allowing them to survive the immediate period after the strike. By pure luck, the surviving population were also precocial hatchlings that weighed less than 25 kilograms (~55 pounds), which appeared to be threshold that determined whether an animal would survive or not. Thanks to their natural adaptability, they made it to the Cenozoic unscathed and diversified into the many forms known today.

The first major group of cenohadrosaurs to evolve was the Neoaralosauria or Archaeocenohadrosauria. Despite their basal position, they convergently resembled later neolambeosaurs and neosaurolophs, so much so that several neoaralosaurs were originally assigned to those clades. The neoaralosaurs slowly dwindled around the Paleogene-Neogene transition, being replaced by true neolambeosaurs and neosaurolophs, until they finally went extinct with the disappearance of *Neoaralosaurus maritus*, ironically the first described member of its kind, around 0.1 Ma.

The evolution of the limbs in particular has been a subject of much research, particularly due to its striking resemblance to the evolution of horses in the current timeline. Early forms resembled their close relatives such as *Eotrachodon*, *Gobihadros*, *Malefica*, and *Yamatosaurus*, being facultatively bipedal with relatively lightly muscled bodies, robust hind limbs, gracile forelimbs, and five-fingered hands with a short spiked first finger and prehensile fifth finger. The eucenohadrosaurs were more robust and their forelimbs convergently resembled those of extinct euhadrosaurs, losing the first finger and combining the second through fourth fingers into a fleshy mitten tipped by a horse-like hoof. More derived forms lost the fifth finger entirely and fused the second and fourth fingers with the third, creating a weight-bearing apparatus that was unable to faclitate bipedal locomotion.

## Classification

*See also: Phylogeny of cenohadrosaurs*

In phylogenetic taxonomy, Cenohadrosauria is defined as the most inclusive clade containing *Cenohadros astronomicus* but not *Gonkoken nanoi*, *Hadrosaurus foulkii*, *Kritosaurus navajovius*, *Lambeosaurus lambei*, *Lapampasaurus cholinoi*, or *Saurolophus osborni*.

Traditionally, cenohadrosaurs are divided into two major subclades: Neosaurolophia, with solid or no crests, and Neolambeosauria, with hollow crests. The validity of Neosaurolophia has been doubted in the past, as some scientists considered it to be a paraphyletic grade leading to Neolambeosauria, but these conclusions have been refuted. Additionally, later research has also recognized the basal Neohadrosauria and the diverse yet primitive Neoaralosauria, also known as Archaeocenohadrosauria. Neolambeosaurs and neosaurolophs were also grouped together into the Eucenohadrosauria in order to distinguish them from the Archaeocenohadrosauria.

However, despite the abundance of molecular and skeletal data, much disagreement exists about the exact internal relationships of cenohadrosaurs. This is because there is so much variation within cenohadrosaurs that even two closely related species may look completely different from each other, and widespread convergent evolution often causes distantly-related species to be more similar to each other than their relatives. The most reliable way of determining a species' phylogenetic relationships is via the "dentary bumps", a series of twenty-six small bony projections on the bottom of the dentary. These projections can appear in six different heights, and no two species have the same pattern of projections, with very few exceptions (e.g. *Neobrachylophosaurus orientorensis* and *Lentosaurus gravis*) As their patterns seem to be the only thing that remains mostly consistent across clades, phylogenetic analyses of cenohadrosaurs usually only include data from these projections.

### Taxonomy

*See also: List of cenohadrosaur genera*

The following is a simplified classification of cenohadrosaur groups based on their evolutionary relationships.

* Cenohadrosauria
	+ Neohadrosauria (basal, crestless)
	+ Neoaralosauria (diverse; several species had solid, bump-like crests convergent with Neokritosaurini; may be neolambeosaurines, neosaurolophs, or outside both groups)
	+ Neobrachylophosauridae (short, often inconspicuous crests; may or may not be neosaurolophs)
	+ Neotsintaosauridae (tall, solid crests; either neolambeosaurines, neosaurolophs, or neoaralosaurs, or a clade of their own)
	+ Riabininocenohadrosauridae (basal; may be neosaurolophs)
	+ Prothumosauridae (either neolambeosaurs, neosaurolophs, or neoaralosaurs)
	+ Eucenohadrosauria
		- Neosaurolophia (short or no crests, possibly paraphyletic)
			* Neosaurolophidae (short, spike-like crests)
			* Neoaustrokritosauridae (bump-like crests convergent with Neokritosauridae but postcranially similar to Neoedmontosauridae)
			* Neokritosauridae (solid, bump-like crests; terrestrial herbivores)
			* Neoedmontosauridae (no crests; some species semi-aquatic)
				+ Corniceninae (shoreline and riparian specialists)
				+ Neoedmontosaurinae (more aquatic than cornicenines)
		- Neolambeosauria (hollow crests)
			* Neoarenysauridae (tall, helmet-like crests)
			* Neoparasaurolophidae (arc-like crests)
			* Neolambeosauridae (often semicircular crests)
			* Microcenohadrosauria (relatively small; some species carnivorous)
				+ Ligabuehadrinae (medium-beaked; omnivorous)
				+ Coloradohadrinae (large-beaked with teeth; mostly omnivorous and piscivorous)
				+ Avirhynchia (large-beaked; carnivorous; some species toothless)

### Phylogeny

The following cladogram shows the classification of cenohadrosaurs according to the latest studies, reduced to clades only.

**1** = **Cenohadrosauria**, **2** = Eucenohadrosauria, **3** = Neosaurolophia, **4** = Neoedmontosauridae, **5** = Neolambeosauria, **6** = Neoaralosauria/Archaeocenohadrosauria, **7** = Neolambeosauridae, **8** = Microcenohadrosauria

## Biology

### Diet

Cenohadrosaurs occupied a wide range of ecological niches. While most species were herbivores like their ancestors, several were omnivorous to some degree, and others even became completely carnivorous and durophagous, the first ornithischians known to do so. Several members were also semiaquatic, with different species found in freshwater and saltwater alike.

### Reproduction and life history

Cenohadrosaur reproduction is very much like that of their ancestors. All species laid eggs which could be buried in soft sediment or laid in carefully-constructed nests. Several herd-dwelling species also forming nesting colonies after the breeding season, where tens of nests could be formed in relatively small areas. Because most species of cenohadrosaurs are too heavy to sit on their nests like birds, eggs were instead incubated by covering them with warm, rotting vegetation.

Babies are hatched with weakly developed limbs, so parents would bring food back to their nests. They grow relatively fast during the earliest stages of their life, and most species are ready to leave the nest and become independent at less than one year of age.

The first years of their life so happens to be the most dangerous, which means that most species spent these times in forests and other places where they can easily find cover. As they grow older, they gradually move towards more open areas, where they seek out conspecifics that they can form herds or mate with. Sexual maturity is achieved long before skeletal maturity.

Many species observe mating seasons, which vary among species. Similar to earlier hadrosaurs, cenohadrosaurs had complex display and mating rituals, often involving visual and auditory displays using the crests and other structures. Males of various species also engage in brutal fights for the right to mate.

## References

Note: These sources are a mix of fictional and real publications. Fictional ones will be marked with an asterisk.

1. ↑ 1.0 1.1 1.2 1.3 \*Aguilar (date unknown). "A new Cenozoic hadrosaur and the recognition of a new clade of Cenozoic hadrosaurs." *Annals of the Inter-Temporal and Inter-Universal Commission on Natural History.*
2. ↑ \*Author unknown (Date unknown). "The smallest known cenohadrosaur."
3. ↑ \*Author unknown (Date unknown). "A large cenohadrosaur adapted for montane environments."
4. ↑ Larramendi, A. (2016). "Shoulder height, body mass and shape of proboscideans." *Acta Palaeontologica Polonica*.
5. ↑ \*Author unknown (Date unknown). "Patterns in the head-to-body proportions of cenohadrosaurs (Cenohadrosauria): a mathematical analysis."
6. ↑ O'Connor *et al.* (2010). "The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana." *Nature*.
7. ↑ \*Author unknown (Date unknown). "A small raptorial cenohadrosaur (Cenohadrosauria: Microcenohadrosauria) with a toothless beak."
8. ↑ \*Matthews, D. (date unknown). "The unusual hindlimbs of *Neoedmontosaurus aquaticus*, a late-surviving non-avian dinosaur." *Annals of the Inter-Temporal and Inter-Universal Commission on Natural History*.
9. ↑ \*Author unknown (Date unknown)."Determining the origins of the feather-like structures in *Pennahadros apateios* (Cenohadrosauria: Neolambeosaurinae)."
10. ↑ 10.0 10.1 10.2 \*Cancello *et al.* (Date unknown). "Preliminary background of the 'Cenohadrosaur timeline' with the description of a late-surviving non-avian dinosaur." *Annals of the Inter-Temporal and Inter-Universal Commission on Natural History.*
11. ↑ \*Author unknown (Date unknown). "A Private Team Has Just Organized an Expedition to a Different Dimension. Should We Be Worried?" *The Washington Post*.
12. ↑ \*Author unknown (Date unknown). "History Might Have Just Been Altered. Worry. *The Washington Post*.
13. ↑ Olivero *et al.* (2007). "Depositional settings of the basal Lopez de Bertodano Formation, Maastrichtian, Antarctica." *Revista de la Asociación Geológica Argentina*.
14. ↑ \*Author unknown (Date unknown). "Getting to the origins of cenohadrosaurs: an improbable tale of survival." *Annals of the Inter-Temporal and Inter-Universal Commission on Natural History.*
15. ↑ \*Author unknown (Date unknown). "66 million years of evolution, documented by the forelimbs of cenohadrosaurs."
16. ↑ \*Author unknown (Date unknown). "A complete phylogenetic analysis of cenohadrosaurs."
17. ↑ \*Author unknown (Date unknown). "An unusual ancient cenohadrosaur and convergent evolution of dentary bumps".
18. ↑ Dodson *et al.* (1994). *The Age of Dinosaurs*.
19. ↑ Woodward *et al.* (2015). "*Maiasaura*, a model organism for extinct vertebrate population biology: A large sample statistical assessment of growth dynamics and survivorship". *Paleobiology.*