FLORISSANT FOSSIL INSECTS: PATTERNS OF TAXONOMIC DIVERSITY

The fossil insects known from the lacustrine shales of the Florissant Formation comprise nearly 1500 species.  Exhumed primarily over a fifty-year period from the 1870’s to the 1920’s, most species were described a century or more ago, when paleoentomology was in its infancy.  Recently, a comprehensive summary of the Florissant fossil insect fauna was completed by compiling all species descriptions from the scattered original publications, documenting the existence and location of type specimens, and updating the higher taxonomy (subfamily and above) of the 806 genera into which the Florissant species have been placed.  This paper analyzes the diversity of the Florissant fossil insect fauna in the context of modern insect systematics and taxonomy.  There are 199 insect families representing 18 orders in the Florissant fossil fauna. Ranked by number of species, the top ten orders found in the Florissant shales differ intriguingly from the sequence of orders ranked by total species in North America today.  The two rankings are given in the table below (based on 31 extant insect orders), along with the percentage of total species for each data set.  Anomalies, such as the disparate abundance rankings in Lepidoptera and Dermaptera, and congruencies, such as the similarity of relative species richness in Coleoptera, Hymenoptera, and Orthoptera, will be addressed in this presentation. Other patterns to be considered include the taxonomic distribution of the considerable number of extinct genera described from Florissant fossil insect material, the significance of specimens considered incertae sedis, and the effect of taphonomy on taxonomic representation in the fossil record of the Florissant insect fauna.

 

ORDER	FLORISSANT  FOSSIL INSECT FAUNA		LIVING INSECT FAUNA OF NORTH AMERICA
	RANK	% of species	% of species	RANK
Coleoptera	1	39.5%	38.1%	1
Hymenoptera	2	19.9%	19.5%	3
Diptera	3	15.9%	20.7%	2
Hemiptera	4	10.3%	4.1%	6
Homoptera	5	4.4%	7.2%	5
Trichoptera	6	2.1%	1.4%	7
Lepidoptera	7	1.4%	12.8%	4
Odonata	8	1.3%	0.5%	14
Orthoptera	9	1.2%	1.2%	8
Dermaptera	10	0.8%	<0.1%	24