VERVAIN hydrangea


The end-Permian extinction replaced the Carboniferous forests of horsetails, lycopods, and ferns with forests of gymnosperms (seed plants) that were to dominate the Mesozoic Era.A number of non-flowering plants evolved structures which are very similar to flowers such as species of the extinct group Bennettitales ( as in the image below) and the modern gymnosperm Welwitschia. As a result, insect pollination and the adaptation of anatomical structures for the attraction of pollinators and the protection of reproductive structures are not unique to angiosperms (Friis, 2006).


††††† The angiosperms (flowering plants) include 250,000 modern species, compared to 720 modern gymnosperm species.The diversity of flowering plants is often underestimated since many flowers arenít showy (such as those of this grass) and therefore arenít commonly considered as flowers.

††Early gnetophytes (a type of gymonosperm) and the earliest angiosperms had similar sizes and were living in similar habitats.  Gnetophytes are the only group of gymnosperms that can be pollinated by insects.  Two of the 3 modern gnetophytes are primarily wind pollinated but unspecialized insect pollination also occurs.  The third type lives in humid rainforests--the humid understory of rainforests is not a good environment for wind pollination.  This genus seems to depend on pollination by moths—it makes sugar droplets with odor at night on both male and female cones, and moths can get pollen on their proboscis, antennae, and legs as they search for the nectar (Kato, 1994).  Although some anatomical comparisons linked gnetophytes with flowering plants, genetic analyses suggest that gnetophytes are unrelated to flowering plants, and are instead related to conifers (Chaw, 2000; Bowe, 2000; Hajibabaei, 2006; Soltis, 2000).The type of vessel found in gnetophytes and angiosperms is also observed in an odd group of plants from the Permian called gigantopterids (whose leaves could be 4 meters long with multiple levels of venation) (Li, 1996).

††††† Although there are unusual types of pollen identified from the Triassic, there is no confirmed evidence of angiosperm fossils prior to the Cretaceous. Archaefructus is currently dated as mid-early Cretaceous (Friis, 2006). The Early Jurassic plant Schmeissneria was originally classified with ginkgoes but recent analysis suggests that it might be an angiosperm. If true, the origin of flowering plants would have occurred earlier than previously thought (Chang, 2009). One Late Cretaceous flowering plant, Archaefructus, had true fruits but they are unlike those of any modern angiosperm.A second species of Archaefructus (A. sinensis pictured below) was found which originally dated at125 million years old.It was a small plant, perhaps living in aquatic environments.It lacked sepals and petals and its stamens were paired (Sun, 1998).It is uncertain whether Chaoyangia should be classified with the gnetales or the primitive angiosperms.


††† The early branches of angiosperms whose lineages diverged from the basal angiosperms include Amborella and the families Nymphaeales, Illiciaceae, Trimeniaceae, and Austobaileyaceae. After these basal groups diverged, the magnolia lineage evolved around the time that the monocot and dicot lineages were separating. Monocots include the grasses and compose about 25% of flowering plant species (Friis, 2006; Soltis, 2000) Eudicots compose about 75% of modern plant species. The majority of eudicots are composed of the eurosids (legumes, roses, beeches, and their relatives) and asterids (asters, sunflowers, and their relatives) (Friis, 2006). Modern members of the order Magnoliales are the most primitive living angiosperms (based on a variety of characteristics such as the lack of a layer of cells in pollen grains that distinguish angiosperm pollen from that of gymnosperms).Modern magnolia flowers are depicted below.
magnolia 1 magnolia 2
One of the earliest branches of flowering plants seem to have been the lineage which led to modern water lilies.This lineage was present by the beginning of the Late Cretaceous and may have been pollinated by beetles (Gandolfo, 2004). Monocots, including the grasses, evolved from the clade of Magnolia relatives. (Soltis, 2000) The remains of grasses have been found in the coprolites of late Cretaceous sauropods from India (Prasad, 2005). Fossil pollen of monocots is known from the early Cretaceous and monocots had diversified by the late Cretaceous (Friis, 2004).By the end of the Cretaceous, flowering plants were the dominant type of plant.Members of a huge group of plants (Hamamelidae, a group which includes oaks) appear in the Early Cretaceous and diversify in the Late Cretaceous.In the oldest hamamelidaceous flowers, the stamens were transitional between modern stamens and petals in this group.† †Cretaceous genera became extinct and modern genera of this group first appear in the Tertiary.(Crepet, 1992; Humphries, 1988).The success of many herbivorous dinosaurs at the end of the Cretaceous and the decline of others may reflect changes in vegetation.Dinosaurs were probably not a major factor in the spread of angiosperms as some have suggested (Barrett, 2001).Grasses first appear in Cenozoic and spread in the Miocene due to cooling climate.


†††† Most insect groups are known since the Permian.Lepidoptera (butterflies) and Hymenoptera (ants, bees, wasps) evolved in the mid to late Cretaceous and their success was probably linked to the success of flowering plants (and vice versa). A few other groups like termites and mantises also evolved in the Mesozoic.

bee butterfly
The only insect group that appears after the Cretaceous is the fleas--they spread with the rise of mammals.


†††† Modern corals evolved in the Mid-Triassic after the Paleozoic tabulate and rugose corals completely extinct in the Permian.No corals are yet known from the lower Triassic.Corals have been the major component of reefs ever since the Triassic.Crustaceans were very successful in Mesozoic.Lobsters and crabs became major predators and this caused the extinction of many brachiopods that survived the Permian.Most mollusks that survive today can burrow to escape predators such as these.†† Since the Triassic, bivalves (mollusks such as clams, oysters, etc.) have diversified and dominate most marine habitats.Many Mesozoic groups have gone extinct.

††††† Many of the older groups of sharks died out in the end-Permian and end-Triassic extinctions.Hybodontoid sharks were a diverse group throughout entire Mesozoic which dwindled towards the end of the Cretaceous and survived only shortly after the end-Cretaceous extinctions.All modern sharks share a common ancestor from the second great shark radiation in the Early Jurassic.All modern shark groups evolved in Jurassic and Cretaceous and achieved their greatest diversity in the Cretaceous.

†††††† Teleost fish are the major group of actinopterygians today, representing 99% of all living fish.There are 20,000 genera of teleosts, which is half the number of vertebrate genera.They first evolved in Triassic and greatly diversified in the Cretaceous.They possess a jaw mechanism that allows the jaw to protrude and suck food rather than bite it.††† They are unique in having 2 supramaxillary bones and cartilaginous uroneurals in tail.Bony elements of the skull are reduced so that they can stretch more.Most have a gas-filled swim bladder for buoyancy; as a result, fins are no longer needed to thrust upward.Changes in the position of their fins allow for better steering.



††††† A large number of diverse reptile groups adapted to aquatic and marine environments.

ichthyosaur utatasaurus
††††† Ichthyosaurs were the most specialized marine reptiles.The first bones of ichthyosaurs were found in 1705 and were interpreted to be Pre-Flood monsters. Cranial anatomy suggest that the ichthyosaurs evolved from non-diapsid reptiles.Although they do possess a temporal fenestra, it seems to have evolved separately from those of diapsids.A number of amphibian and reptile groups have evolved different fenestrations of the skull (Maisch, 1998a). They first appeared in the Early Triassic, were most numerous in Jurassic, and died out before the Early Cretaceous.The earliest forms (such as Chensaurus and Utatsusaurus) were long, slender, and probably swam with an eel-like motion.These Late Triassic forms had both primitive characteristics and traits of later ichthyosaurs (Montani, 1996).


ichthyosaur limbs
The basal ichthyosaur Choahusaurus was more derived than Utatsusaurus but possessed a more primitive fin in which the radius and ulna were longer and not fused to each other, unlike the condition of later forms.The ichthyosaurs which survived to the Jurassic lacked digit I and others lacked digit II as well.Additional digits evolved in some, such as Ichthyosaurus (Montani, 1999).Early ichthyosaurs possess a tarsal bone (the centrale) which is lost in later ichthyosaurs (Brinkman, 1992).
†††† Later ichthyosaurs resembled dolphins in body shape, possessed a large orbit, and swam differently due to a stiffened vertebral column.Some specimens show young in utero or in the process of being born.They declined in the late Mesozoic, perhaps because sharks were becoming dominant.Shonisaurus approached 50 feet in length, had a skull of 3 m, and weighed 30 tons.One 9 meter ichthyosaur appeared to have fed on large quantities of small marine life, as do many modern whales (Grady, 2001).
In the middle Triassic, the primitive ichthyosaur family Mixosauridae was widespread.The largest known mixosaurids are estimated to have reached 5 meters in length.This group possessed a sagittal crest formed by the nasal, frontal, and parietal bones (Maisch. 2001).


Ichthyosaur skulls became more specialized over time.


The primtive marine reptile Nanchangosaurus may be a relative of the group which gave rise to ichthyosaurs.


†† ††Sauropterygians were a group of marine reptiles that include nothosaurs and plesiosaurs.


claudisaurus pachypleurosaurus



††††† Plesiosaurs were large reptiles whose long necks possessed up to 76 vertebrae.Plesiosaurs seem to have evolved from nothosaur-like ancestors.Plesiopterys was a small plesiosaur with fewer than 40 neck vertebrae and which retained a number of primitive characteristics not found in more advanced plesiosaurs (OíKeefe, 2004).

Elasmosaurs possessed up to 70 neck vertebrae and were capable of significant lateral movement, although their necks were probably not oriented in a swanlike “S” shape (Zammit, 2008).

†††† A second group, the pliosaurs, had larger skulls and shorter necks.Liopleurodon was the largest predator that has ever lived.Its skull could reach 5 meters in length and its body 25 meters, approaching the size of the largest modern whales.It might have weighed about 150 tons.

Internal development of fetuses occurred in at least three groups of marine reptiles: ichthyosaurs, mosasaurs, and pachypleurosaurs (Carter, 2008).





††††††† Many marine groups were decimated by the end Cretaceous extinction.Of the microscopic planktonic diatoms, only 15-16 species survived to give rise to all Cenozoic species.Many sponges became extinct, and they have been in decline since, serving as only a minor component of modern reefs.Only coiled ammonoids (squid-like nautiloids) survived of all the diverse ammonoid groups.Sand dollars were very diverse in Mesozoic but were reduced in this extinction.Many groups were affected by the global cooling that occured in the Eocene-Oligocene including radiolarins, diatoms, many bivalves, and sand dollars (sand dollars never recovered from this epoch and have been a minor group since).

 By the early Jurassic, a shallow Liassic sea covered much of Europe and extended into the developing rift between North America and Africa as far south as Virginia. A shallow sea covered Northwest Canada and the Northwestern U.S. as far south as New Mexico. It was about the size of the modern Gulf of Mexico and at times became saltier than the ocean. This sea drained in the Mid Jurassic. In the Early Cretaceous, another inland sea formed in central North America which allowed flow between shallow Artic waters and the Gulf of Mexico (Russell, 1989).